Playing around with a 10 m trailer cruiser

[marshmat]

It seems when I'm not designing things for school or for work, I somehow end up designing things just because....

I've been thinking lately about what to build when my Bolger-designed runabout, Sunset Chaser, now in her seventh season, starts to feel a bit too small. I'm looking at least five years down the road here, and all of this is of course hypothetical, but it's fun to dream.

The mission is an efficient, comfortable boat for use on inland lakes, rivers and canals, with inshore ocean cruising in fair weather being within reach. Extended cruising for two and long weekends for 4 should be comfortable, with the capability to host as many as 10 on day cruises. The ability to gunkhole around in log-strewn and rocky bays is essential, as is the ability to be towed cross-country on a standard licence, ideally with nothing larger than a 250-series pickup. A 25-knot cruise should be possible with a reasonable load, but the ability to maintain a smooth, level, stable and efficient attitude right through the 'hump speed' phase is more important.

I'm currently on the seventh loop around the design spiral with this one and I suspect it'll take at least another forty before I'm happy with it. (Version 6 is shown below.) But at this point I think the concept is ready for my friends on here to take a look at. I haven't done anything on the pilothouse, deck, interior, etc. yet, right now it's just hull concepts and a preliminary weight and balance estimate (~3500 kg in running trim, full tanks).

So what we have here is a shallow V low-speed planing hull, slightly soft chines at the transom smoothing to rounded chines as we move forward. The running surface is nearly monohedral at around 10 degrees for the first 3.5 metres forward of the transom, sharpening to a fine 30-40 degrees where the entry point would be when planing. No rocker or hook in the aft parts of the running surface, and I'm trying to keep the bow sections just a little bit convex. Construction would be in wood/epoxy strip plank. At present the concept is being drawn with a single waterjet drive in mind; it seems so far that hull resistance at 25 knots should be no more than 7-8 kilonewtons.

Suggestions, comments and recommendations of other vessels to take inspiration from are welcome (I've already taken inspiration from about 20 other vessels already mentioned on the forum, esp. in the "option one" project). Commentary on the probable running habits of the hull or experience with similar shapes is especially so. Keep in mind that this is just a concept at present and if it does ever take to the water, that's at least five years off. The linesplan below shows more or less what I have in mind for the hull, awaiting scrutiny and review. (Delftship/Freeship is being used for the preliminary sketching.) GIF format for now so everyone can see, if there's requests for different formats I'll post them.

[FAST FRED]

Looks good but don't boats of that style usually have some sort of chine to keep she spray at speed under control?

"A 25-knot cruise should be possible with a reasonable load, but the ability to maintain a smooth, level, stable and efficient attitude right through the 'hump speed' phase is more important.".

Estimated mpg?

FF

[marshmat]

Good point Fred.... perhaps a spray rail will be added. I very much like the ride and motion of a soft-chine hull though.
I haven't got around to calculating fuel consumption estimates just yet; I find it preferable at first to work towards minimizing hull resistance, and then look at powering. Right now I'm thinking of a lightweight marine diesel with a waterjet drive, but I'm not far enough along yet to know for sure.

[marshmat]

Round seven....
I figure a slightly flatter bottom with a bit more planing area wouldn't hurt, given the conditions this boat would see. The bottom's been widened a bit in the aft sections, with the chines being somewhat more square. Transom deadrise at the keel is still 10 degrees but that shallow angle is now maintained over a somewhat wider planing surface with a little bit more surface area. I figure this should improve planing lift in the aft sections and stiffen the at-rest motion a bit, at the expense of a slightly harsher ride in bad chop.
The spray rail's coming soon, just trying to think of how to get it to flow nicely with the hull lines.....
I'm thinking that one of the lighter 150-200 hp marine diesels spinning a Hamilton HJ 241 or 274 waterjet would be a good match. It looks so far that no more than 8 kN of thrust at 25 kts would be necessary but I haven't gone into too much detail on that yet. I know waterjets are usually best at higher speeds but I think if I were to build this one that I'd prefer the minimal draft and the absence of "sterndrive headache", at the expense of a bit of low-speed efficiency.

[Guillermo]

Nice project and nice lines, Matt.
To my taste I rather prefer #6 ones, just making the stern wider as to bring sides almost parallel all the way back to stern. I think for speeds in the range of 20-25 knots, the more warped half rear body lines of #6 look to me more adequate than the #7 ones, and the softer bilge radius will be easier to build in strip planking. Spray rails will also proof useful, in my opinion.
As per a very, very rough estimative, I think it will need close to 200 HP to get a 22 kn cruise speed for the stated 3500 kg disp with a jet, so perhaps a higher rated engine will be required....?

Cheers.

[marshmat]

Thanks for the comments, Guillermo; much appreciated. More drawings will certainly follow....
Good point about the sharper chine making it harder to do a strip-plank build. It would seem to me though that widening the stern much more would encourage it to stuff the bow down when in a following sea, an irritating trait of my current boat that I'd like to avoid.
I haven't actually drawn in the wheelhouse yet (working on a few different styles but aiming for sort of a Downeast lobster-boat shape) but preliminary estimates of the size and location of the remaining bits seem to put the fully loaded weight (full fuel/water, 4-6 crew, plenty of supplies) right around the 3500 kg design displacement. I've been told that for a low-speed planing hull the centre of gravity should be around 1/3 of LOA forward of the transom; this is about the balance this one has now. Does this sound about right?
As to power. At 24-25 knots, which is the highest speed I'd expect this boat to be able to sustain for any period of time, 8 kN of hull drag translates to approximately 100 kW of total losses. (That 8 kN is still just an estimate, I have yet to finish comparing the results of different resistance calculations.) Bottom loading on plane is around 200 kg/m2 fully laden. Let's say the inefficiencies in the jet are around 30% as the jet makers often claim, that translates to 145 kW or 190 hp at the driveshaft. Factor in a bit of gearbox and drivetrain loss and something like the 220 hp Yanmar 6BY220 or similar would appear to be sufficient (220 hp peak, 170 hp continuous, burns around 32 L/hour at 3600 rpm), yielding 63 hp/tonne. This seems to match well with HamiltonJet's average performance curves for a single-jet boat of this size and weight. Rough guess would thus be around 1.3 litres per nautical mile or about three nautical miles to the gallon at the 25-knot maximum cruising speed. A less aggressive cruise speed in the high teens would hopefully get closer to 5 nmpg, perhaps a bit better under light load. Sound reasonable?

[Guillermo]

I think it makes sense. Perhaps power would need to be a little bit higher, in my opinion, but maybe I'm wrong.
Cheers.

[marshmat]

I think I'm closing in on something I like here :)

I've been playing around with a few planing resistance methods the last few days, especially a couple of the Savitsky-based spreadsheets posted on here (Dingo's is especially good, in my opinion). The results have convinced me she needs a bit more lift in the stern; I've brought the transom deadrise down to a hair under 8 degrees and widened the aft planing surface a touch. The midships sections are more or less unchanged while the entry is a tad sharper. The chines have been softened a bit and the sides are closer to vertical at the stern. Perhaps she'd look a bit classier with the transom raked back 5 deg. or so, I'll see how that looks in the next version.

It looks like my preliminary resistance estimates were somewhat high. Now that there's actually a hull to work from, it looks like drag in loaded condition will actually be closer to 5-6 kN at 12.5 m/s (25 kts), or about 65-75 kW of total hull losses at maximum cruise. It seems Savitsky's method isn't quite meant for soft-chine hulls but with some simplifying approximations to the geometry I figure it's close enough. And although this is probably wrong in every sense of the word, I also ran it through Michlet (with appropriate guesses for trim and -ve sinkage, aka lift.) That yielded drag estimates that, while somewhat different in shape, were on the whole roughly comparable. I'm thinking of trying a run in Fluent, but that program gives me enough of a headache in plain air, let alone a two-phase flow with a free surface.

Based on what I have now, it looks like a diesel peaking at no more than 200-220 hp would be more than sufficient for what I want; remember this isn't a fast boat, there's no need for it to do much more than 25 knots. She'll probably trim about one degree down by the bow at rest, and likely never more than 4 deg up throughout the transition speed range.

The hullform will probably continue to evolve little by little; I'm going to start working on the structure and interior in more detail soon. I'm thinking of putting a model together to pull beside the current boat for some tests, perhaps that will shed some more light on it.

[Guillermo]

Nice forms, Matt. I like them.
Savitsky should be good enough at this stage.....
Cheers.

[lazeyjack]

Matt, my comment, this boat will be wet, the spray will lift up the topsides in a plume and if the wind blows, will soak the boat,

I like this sort of boat they always run quiet,
I could help more with the trailer, I had a die cut, 130x75x8 6061T6 ally. I used to make these for all my trailer boats to 4 tonnes
the beams were bolted in naturally because you never weld across a girdar(chassis rail) never had a failure in all those years For larger boats used air over hydraulics, where air was avilable, and override sometimes, on boats to 1.5 tonnes

[marshmat]

Just a few more quick-n-dirty pics of it here, version 10....
I finally found a line I think I like for the spray rail (it protrudes a good 2" from the hull, more than double the size of the fairly effective rail on my current, smaller boat). A parabolic-entry nacelle pod for the jet intake has been added (she doesn't have enough draft for a pump to prime well in a conventional keel-cutaway installation). All the drives being considered transmit their thrust through the intake plate so there's gotta be room in the nacelle pod for some beefy stringer tie-ins as well. Superstructure is in work and will be posted when I'm satisfied it isn't completely butt-ugly :D

[Guillermo]

You have to take into account the jet intake is placed at the more charged area when planning, and that diminishes the lifting force. That will go against performance, increasing the power needed.
I think the position of the spray rail is somewhat high.
Cheers.

[marshmat]

You have to take into account the jet intake is placed at the more charged area when planning, and that diminishes the lifting force. Good point.... I'm trying to figure out just how big this effect will be, none of the jet makers seem to offer any numbers on the loss of lift due to the intake. Suggestions?
Most pumps that would be suitable have intakes from 80x40 to 100x45 cm, or a bit less than 0.5 m^2 out of a hull with a planing area of 13 to 16 m^2 (depending on speed/load). That's around 3-4% of the lifting surface that's lost to the intake, albeit right at the transom. Seeing as the water in that area is actually being diverted upwards into the boat, it would seem the actual reduction in lift has to be slightly higher than 3-4%, but by how much? (I'm figuring the jet nozzle would angle down by the standard 5 deg, ie. normal to the transom, which should partly offset the loss of lift from the intake.....)

Some might be wondering why I'm so insistent on jet drive for this design, given that jets are usually thought to be inferior to propellers below around 20-25 knots. There are a few reasons. First is that if I were ever to build this one, I want to be able to run with 8-10 crew and full tanks, as well as being able to run with 2 crew and no gear, and anything in between. There's more than a 30% weight difference between loaded and empty cases and the efficiency of a jet does not depend on weight nearly so much as a prop does, nor can a jet overload the diesel if the boat's too heavy. I'm fairly convinced from the data and spec sheets I've found that it is indeed possible to select and tune a waterjet to come close to prop efficiency in the speed range I'm considering, if the focus is shifted away from top-end and in favour of balanced mid-range performance. Also, I'm sick of outboards and their many ills, as well as sterndrives and their maintenance headaches- a jet seems much simpler. Finally, I like to know that I'm not going to be crippled mid-lake if I run over a piece of submerged driftwood.

[Guillermo]

I'd say around a 5%, but I'd consult with OTTO RANCHI, who has a good deal of experience with jets. PM him.

[Willallison]

Matt - I reckon that almost 1/2 the people on these boards are or have at one stage, played with something very similar. I've been at it on and off for a few years!

I'd concur that this has the potential to be a wet boat. Also that your spray rail is too high. It really needs to be at the turn of the bilge to be really effective. I'd add at least one more lower down too.
I disagree that your looking at running trim no more than 4 degrees. The soft chine will add about 1 degree and the 66% lwl location of your cb/cg is too far aft, so will probably add another degree at lower speeds. Add this to the loss of lift around the jet intake and I reckon your looking at at least 6 degrees at lower speeds. For a boat design to run well at 'hump' speeds you really want the cb to be around 58% lwl.

If this is to be a trailer boat, then most of the perceived maintenance drama's involved with sterndrives can be avoided. I agree that at 3500kg it's getting too big for outboards, but I'm yet to see a waterjet propelled boat that performs well at low planing speeds. Not that they won't do it, just that they use an extraordinary amount of fuel.

The soft chines will make it easier to build strip plank, but will have a negative effect on performance. You have to weigh up which is going to be more important. I like the lack of a hard chine fwd - primarily because it eliminates chine slap whilst at anchor.

I attach an image of a 40 footer I designed with similar lines to yours. I'll also post a few of version 20 of my trailerable version soon too. It suffers from a few of the problems I've mentioned to you, but more of that later....

[marshmat]

Thanks for the tips Will :)
Beautiful boat you've got there.... are we likely to see the real thing on the water soon?

Been playing around with the hydrostatics and balance some more, with the result being Version 14 (below). The shallow-deadrise planing surface is a bit wider at the transom now, and is carried farther forward, for an effective bottom area about 10% higher than before (thus correspondingly lower bottom loading). There's also a bit more width in the bow, but the overall beam has been trimmed 2% (with gunwale rails, she was just a tad too wide to trailer before!).
Now that I have some rough layout plans (not going to post them just yet, they're still pretty rough and blocky), a more detailed weight balance is putting the CG at around 40-45% of LWL forward from the transom (ie, 55-60% of LWL aft of the entry). CB in level trim is about 10-15 cm aft of this, so she'd trim very slightly down by the bow at rest. Still looking at 3500 kg loaded, around 2500 kg empty.
Spray rails should follow the turn of the bilge, eh? I'll try to work this into the next one. Makes a lot of sense now that you point it out, Will.
Is it considered somehow improper to bring the aft end of the spray rail right to the transom below the waterline, thus making it transition from a spray rail up front to a bit of extra planing surface at the transom?
Somehow I'm convinced that a jet doesn't have to be inefficient at low speed, they just tend to be that way when you optimize them based on top end alone (as virtually all common installations are). I suspect I'll have to coax more data out of the jet makers to see if this is actually the case though. My understanding of the reason for the crappy low-speed performance of most jets is that when you optimize for a 30-50 knot top end, you end up with an impeller that can't absorb anywhere near as much power as the engine is producing at 10-20 knots, thus the cavitation, poor thrust and inefficiency. Sizing the drive and impeller for a 15-25 knot cruise, not worrying about higher top speeds, should be possible.

[RANCHI OTTO]

My opinion is that with 3500 kg, the speed of 25 knots will be reached with 250 hp abt. not less.

The waterjet intake openings at bottom doesn't reduce the lift in this area because the water in the duct produces a vertical lift and for this reason normally no deduction on lift is foreseen.

[Willallison]

Unlikely to see this one one the water any time soon Matt. It's one that I did for one of my Westlawn lessons. I did do it originally in the hope that I'd build it, but I'd need to make a few changes to the hull shape 1st. The shape of the 'chines' is similar to yours in that they are radiussed all the way to the transom. I've refined the shape somewhat now so that they become hard from about station 6 to the back. This should lower trim and power requirements somewhat.
I'm also considering a more contemporary look. Currently though, as I said before, I'm working on a trailerable boat. 9m LOA with a target displacement of 2800kg. This one I've used all developable surfaces for, to simplify construction, so unfortunately I'll have to put up with the chine slap if it ever gets built (or rather, the complaints from the 1st mate that she can't sleep!;) ). It's still early days for that one, so I'm not nailed down on the chine setup yet. I'll post some images as soon as I get a chance...

Which brings me to the question of your boats weight - how do you come up with 3500kg - it seems pretty heavy. Apart from the additional power required, you have to consider that by the time you sit it on a trailer, the total mass will be approaching 4500kg, which will require something bigger than your average 4wd to tow....

[marshmat]

Which brings me to the question of your boats weight - how do you come up with 3500kg - it seems pretty heavy.
The standard weights-and-moments spreadsheet method, summing the estimated weight of every individual component. (Using some aggregate guesses here, too, since the structure's not designed yet.) The 3500 kg is at maximum load, it's more like 2500 kg dry, and I think many of my weight estimates are rather on the conservative side (ie, she could very well end up somewhat lighter when all is said and done, but probably no heavier).

[marshmat]

For those of you who have yet to realize that I'm probably a hopeless cause when it comes to things marine.....
Hull #16!
In the interests of getting a bit more lift in the stern to keep her level in the lower speed ranges, the chines have been sharpened up aft. Still a soft chine hull for the most part but after playing with control point weights for a while I've elected to take the advice of those more knowledgeable than I and flatten out the chines at the stern. It's more or less identical to the last version but with varying point weightings along the chine.
Spray rail and gunwales are in place now, too.... (this is about the 20th, maybe 25th attempt at getting a spray rail that would both work and look OK on this shape). Opinions welcome, as always :)
(I should probably point out, BTW, that my naval architecture training is absolutely nil.... what I know I got from books, from studying the boats I see and use, and from paying attention to those who really do know what they're doing; I'm just a senior engphys undergrad student with a love of boats and a tendency to read far too much :D )

[longliner45]

hey marshmatt,,I see your love of boats,,,,and you put much effort into it.do you want 10 meter trailorboat?because of its size? maybe could put more technology into the trailor itself?,,,,,that is what im doing ,,32 ft,sailboat standart keel, 4ft11inchs ,10.500 lbs ,,,great lakes(3hrs) or chesepeke bay(12hrs) or gulf of mexico(14hrs),from enon ohio....,longliner

[marshmat]

Thanks longliner :) Sounds like an interesting and very practical boat you've got going there.

As far as trailers go, I like them solid and reliable.... no monkey business, just good quality metal, good axles and brakes, a wiring system that doesn't short out.... (if such a thing exists?)

Why a trailer boat? With my current (trailerable) runabout, I can get to all sorts of neat inland lakes that marina queens can't reach. I can get to neat, remote cruising grounds, and be back in time for class/work. I want to keep that ability.
Why this size? It's light enough to tow with a normal pickup (or in my case probably a pickup with a homebuilt diesel-electric drive) on a normal licence, but large enough to take a decent size group of friends out for a day, or to comfortably live aboard for a week or two.

[Willallison]

Now we're getting there!:D
I see just a hint on concavity in the bottom fwd sections. Ideaaly you would want convex, or failing that straight sections throughout. It lessens the tendency to bow steer and softens the ride. Post a shot of the waterlines - again, they should be convex as they approach the bow....

"Chine" rail looks good.....

Wish I'd had a chance to grab an image of mine - you'll be surprised at how similar they look!

[Guillermo]

Matt,
In my opinion you'll find 8º deadrise at the transom is somewhat low for a jet installation, making for some tendency to broach with a following sea, as I have found with one of our clients' boat. You'll probably need to add a couple of fins, very much in the way of Tad's. See http://www.boatdesign.net/forums/showpost.php?p=107409&postcount=179
Other possibility is to increase deadrise at transom.
I tend to agree with Otto about the power needed. I also think it's going to rather be in the region of 250 HP.
On the lifting thing, I would appreciate very much Otto referring me to some good book on waterjets where to study what he states. I understand the change in direction of the water flow through the jet duct provides some upwards lift, but I'm surprised about this being of the same amount as the loss of lift due to the intake.
Cheers.

[lazeyjack]

Matt,
In my opinion you'll find 8º deadrise at the transom is somewhat low for a jet installation, making for some tendency to broach with a following sea, as I have found with one of our clients' boat. You'll probably need to add a couple of fins, very much in the way of Tad's. See http://www.boatdesign.net/forums/showpost.php?p=107409&postcount=179
Other possibility is to increase deadrise at transom.
I tend to agree with Otto about the power needed. I also think it's going to rather be in the region of 250 HP.
On the lifting thing, I would appreciate very much Otto referring me to some good book on waterjets where to study what he states. I understand the change in direction of the water flow through the jet duct provides some upwards lift, but I'm surprised about this being of the same amount as the loss of lift due to the intake.
Cheers.
i agree on the jets I have done, the owners put on autopilots, even with twins, the bloody things wander all over the place, you have a constant deadrise which is correct

[Willallison]

Hmm - Hinckley's much acclaimed picnic boat has a transom deadrise of about 15 degrees, so the boys might be onto something there...
The problem is that as you are aiming for low speed efficiency, low trim angle and no discernable hump, the lower deadrise would generally be considered better. But with nothing in the water to give directional stability.....

see here for more on the Hinckley: http://www.boatdesign.net/forums/showthread.php?t=112&highlight=hinckley

[lazeyjack]

Hmm - Hinckley's much acclaimed picnic boat has a transom deadrise of about 15 degrees, so the boys might be onto something there...
The problem is that as you are aiming for low speed efficiency, low trim angle and no discernable hump, the lower deadrise would generally be considered better. But with nothing in the water to give directional stability.....

see here for more on the Hinckley: http://www.boatdesign.net/forums/showthread.php?t=112&highlight=hinckley

I built one with quite a long box keel, twins, and it still wandered, they are a NIGHTMARE, unless being used on rivers, whcih is what they were designed for

[lazeyjack]

I posted abt the trailer which you ignored I posted abt the jets which you ignored , well this is me a long time ago before you even heard word jet
Lots of theory in this place, bugger all hands on

[marshmat]

The Hinckley's one of the boats I took inspiration from in this shape.... it's a beautiful boat, unfortunately it's also just a tad on the pricey side for my tastes!
The lack of any lateral area on the jet drive to keep the hull tracking straight could be a concern. I think I'd rather use fins to correct this, though, rather than a sharper deadrise which would compromise the low-speed lift.

Regarding the bow sections on this boat- I'll post more images later today when I'm not at work. I've been trying to keep a slight convexity overall but I may have missed something.

lazeyjack- don't worry, I'm not ignoring you at all, I very much appreciate what you've said so far. IMHO, experience beats theory any day, and you seem to have plenty of the former.

[Willallison]

Finally got a chance to grab a couple of images of one of the hulls I've been working on. The images themselves aren't much chop, but they give you the general idea.

This is from a 12 x 3.8m vessel - so a bit bigger than the one we're talking about here, but the same general principal applies. You can see that the hard portion of the chine extends further fwd - probably a bit too far at the moment - and there's considerable convexity in the fwd section - again, possible a bit too much. It's still early days as far as the hull shape goes really.
As I usually do, I've put a knuckle part way up the topsides. This will get rid of any persistent spray that the chine spray rail (not shown) doesn't separate from the hull. It also helps to make the boat look a little sleeker I think....
I anticipate a single sterndrive as propulsion for this one - 350hp. Top speed should be about 25 knots

[marshmat]

Very nice, Will! Your craft is somewhat larger than mine and from the shape of the V I imagine it's meant for rougher water, but we do seem to be thinking along similar lines :)
****
Right now I'm pretty much beat, things are insanely intense at the shop right now.... if I'm more awake later tonight I'll get a few more pics up here.

[Willallison]

Actually, Stu brings up a very good point. People spend way too little time considering the setup of their trailers.... worthy of its own thread me thinks.... will do so shortly....

[marshmat]

Having spent the last two years driving the solar car's trailer across the province.... I have to agree. Not nearly enough thought goes into the construction of these rigs. People will spend $70k on a decked-out F350 to haul their precious new toy, and then trust the rig to a set of $200 surge brakes. Amazing, really. I'm lucky to have good brakes, good electrics, good bearings and a solid frame on the one I've been hauling lately..... I see an awful lot who aren't so fortunate.

[longliner45]

yes the trailor is very important ,,your investment rides on it ,,,boats dont like to feel thier wieght...im modifieing my trailor with tractoro trailor air ride..dual wheels ,,2 one ton tractor axils,,hydrolic breaks ,,keel is 4ft 11 inchs ,,lowering the boat 3 more ft ,,reason is ,I like lake erie,but it freezes,,I like chesepeke bay and the gulf ,,but it is hard to be there all the time..you gotta be realistic ..hitting a pothole at 45 mph,,,,is no good ,,and you just cant avoid them all,, all the time,,plus I got to keep her under 13 and a half ft ,,,,,,,Ill sneek buy with the 10.5 beam ,,but not on the hieght,,,,,,longliner

[marshmat]

Another update....
(Work's been getting in the way of boating again- haven't been able to play with this one much lately!)
Thanks to all who have commented on the hull bottom.... latest drawings below; I've smoothed everything out and made sure there's no concavity where there shouldn't be, etc. (Stations and waterlines in the bow area read as convex outward except for the first couple of inches at the stem, where they tend to be pretty much linear to very, very slightly concave.) I think I'm getting more or less happy with it, but if I get time this summer I'd like to build a model to pull around just to be sure....
Got some suspension bits for the solarcar back recently, all done up in gorgeous glossy coloured anodizing.... thinking of the type of beefy bolted-aluminum construction lazeyjack mentioned a few days back, maybe have the beams anodized up and clearcoated- it's gotta look good on the ramp, right? :)

[Willallison]

looking good!:)
I don't have much experience with jet installations, but I do know that they are pretty fussy about the waterflow around the intake. You might want to ask one of the myriad of knowledgeable chaps around these parts about the 'pad' that you have on the bottom....
I still remain unconvinced about how well you can make a jet perform at intermediate speeds. I know you have some concerns about maintenance, but a sterndrive would probably be simpler, cheaper, more economical and avoid any of the wandering issues that others have mentioned....

Now - when are we going to see some profile and arrangement pics - just rough sketches will do....c'mon, I'm getting excited about this 'little' project!!:D

[lazeyjack]

looking good!:)
I don't have much experience with jet installations, but I do know that they are pretty fussy about the waterflow around the intake. You might want to ask one of the myriad of knowledgeable chaps around these parts about the 'pad' that you have on the bottom....
I still remain unconvinced about how well you can make a jet perform at intermediate speeds. I know you have some concerns about maintenance, but a sterndrive would probably be simpler, cheaper, more economical and avoid any of the wandering issues that others have mentioned....

Now - when are we going to see some profile and arrangement pics - just rough sketches will do....c'mon, I'm getting excited about this 'little' project!!:D

quite simply put, a screw gets aa grip on the water a jet does not, jets are maintanence free, sterndrives are quite the opposite, but maintained well can last for years I have several worked 6000 hrs
jets often cost more than the engine, see HAMILTON JET, ask for Trever and tell him Stu said so!!:))

[Willallison]

Stu - yes, that's what I was getting at...I too have had sterndrives. I spent at most $1000 AUD per year servicing my last one (on a boat kept in the water btw, which always increases maintenance on s/drives) and never had a problem. In the scheme of things, it wasn't really a significant factor for me. From an efficiency and overall cost point of view, I think they're hard to beat for a midsize boat.

I've started a trailer thread. Would welcome all comments....
http://www.boatdesign.net/forums/showthread.php?p=145581#post145581

[lazeyjack]

Stu - yes, that's what I was getting at...I too have had sterndrives. I spent at most $1000 AUD per year servicing my last one (on a boat kept in the water btw, which always increases maintenance on s/drives) and never had a problem. In the scheme of things, it wasn't really a significant factor for me. From an efficiency and overall cost point of view, I think they're hard to beat for a midsize boat.

I've started a trailer thread. Would welcome all comments....
http://www.boatdesign.net/forums/showthread.php?p=145581#post145581

true, I,m off to NZ to fit one of the bigger Volvo ones , on 20th, has the 310hp diesel 5.7, never seen this one, but then I,m only picking up again after 6 years, give you a bell sometime!! ciao

[Willallison]

That would be the D6 I presume. The 40 foorter that I posted was designed to have the 350hp version of the same engine. Meant to be very good. But bloody pricey - 85 grand (AUD) including the DP leg!

Have agood trip - make sure you take some pics and we look fwd to your report....

[marshmat]

Will,
The drive nacelle was based on a paper published by Ultradynamics, which proposed it as a well-tested and proven means of getting better jet immersion than the more traditional cutaway in the keel. I'm going to run both it and the drivetrain proposal by the folks at Hamilton to determine whether my proposed jet drive is, in fact, possible. If they say it can't be done efficiently, the Volvo DPH sterndrive with one of their D4 motors (or a Yanmar) would be the other option. Probably from the rebuilt market because I would not be thrilled about dropping eighty large on a driveline.
Layout, arrangement and deck/superstructure drawings are on the way, but I'll have to keep you waiting until next week- I'm moving halfway across the province this week and so time is in short supply.
Enjoy your trip, Stu :)

[marshmat]

Got some news today from Ian Gillon at HamiltonJet (they seem to be both incredibly quick and incredibly helpful!)
Now, I know that as a jet maker, their main interest will be in selling their products, so one would expect a report that strongly pushes their own unit as being the absolute best. But that's not what I got back from them. Ian sent a couple of neat and concise summary calculation pages, an explanation of how to interpret them, and some comments on how the jet options stack up against both claimed and actual propulsive coefficients for prop drive options (lower than sterndrive makers usually claim, but when the calculations are done on the same mathematical basis the jet has about the same overall propulsive coefficient- around 50% give or take a few points). The math makes sense and the numbers work out, albeit somewhat differently from what conventional wisdom about high-speed jet drives would indicate.
Based on the thrust curves HamiltonJet gave me for the Yanmar 180 hp 4cyl and 220 hp 6cyl engines with an HJ274 pump and appropriate gearing, here's what it looks like the boat would do (speeds given as cruise/max, knots)
_______Empty (2.5 t)___Full (3.5 t)
180 hp____23/27________18/23
220 hp____26/30________22/27
I would tend to leave the exact engine choice open for now, suffice it to say that I'm convinced a marine diesel in the 180-220 peak hp range (not necessarily a Yanmar of course) would suffice to get the performance I desire with a jet. The key seems to be to use a large diameter, low RPM impeller compared to the diameter and RPM you'd have in a normal high-speed jetpump or propeller in a similar application.
Ian also explained that the stern lift Ranchi Otto mentioned earlier is real, but only at speeds well above 25 knots; it's apparently the result of high boat speeds forcing more water past the intake than the jet can accept, thus the water flow over the intake actually has a positive pressure at the trailing lip of the intake. Apparently it's not an issue in the speed range I'm considering.

[fcfc]

I am just curious about your layout.

Because the propulsion will be around 5' len, 2.5' wide and 2.5' heigh (HJ274 + yanmar 6BY220). This raw engine dimension. Need to add some more space for floors and side tickness, sound proofing, engine move on silentblocks, mechanical accessibility etc ...

I do not think this can be hidden under a floor.

[marshmat]

Layout / general arrangement plans are coming. I have my hands rather full with fibreglass mould-making at work until tonight, plus moving. I'll post some sketches very soon.
The jetpump itself will be hidden under the cockpit deck; I'm trying to find creative uses for the top of the engine box which will have to occupy a fair bit of the cockpit and will protrude slightly into the saloon.

[Willallison]

Whenever I'm stuck with an engine-box, I tend to have the fwd 1/2 as part of the saloon dinette seating and the aft 1/2 as aft-facing cockpit seating. It seems to work pretty well.

[marshmat]

We do seem to think alike, Will... the sketches I was playing with earlier this afternoon have the motor box as a sunpad/bench in the cockpit and front-end belt/fittings access through one of the dinette benches. Sketches below are VERY rough (like, 4 minute rough) so please don't laugh....

[fcfc]

I am just comparing the layout sketches with the last dimensionnned drawing you posted ( http://www.boatdesign.net/forums/showthread.php?p=144731#post144731 ).

You intend to have a headroom of about 1500 mm (5' ) in the forecabin and head, and about 1800 mm (6' ) in the saloon ?

IMHO the head look small, around 600 mm (2' ) wide and limited headroom for a boat that will cost over 100 000$ (200 hp + jet drive). Looks much more of a locker than a head.

Why do not us use a pivoting back seat. You put the back seat in rear position, you sit in facing front and make pilot bench. When you put the back seat in front position, you sit in facing back and make dinette bench.
This would allow to widen the head space and give more knee/feet space. ( I am sorry for the english description. I reach the limits of my english skills).


BTW, is a inside steering position really needed ? You will have to match field of vision requirements if you do so. ( http://www.boatdesign.net/forums/showthread.php?p=109013#post109013 )


As a side note, the width of the forward double berth do not match. From the dimensionned drawing, the width at station 3 at the heigth of the berth is around 1000 mmm (3' 4" ) Very very narrow for a double berth.

[marshmat]

The rough sketches I just posted are not really to scale, just concepts....
Interesting idea of using a pivoting bench for the helm, fcfc- our VIA Rail trains use similar pivoting seats to switch between 2- and 4-person groupings. Very quick and easy to do with their mechanism.
I definitely want the helm to be inside the wheelhouse. I've been thinking about a semi-convertible top on the house, much like Ellings and some new Hinckleys have- weathertight when it's cold and wet out, open to the sky on nice days.

[Willallison]

Yes - it's difficult to get a double berth in the bows as you've shown it, without having it located so far aft that it becomes impractical. I'f you're not hell-bent on being able to walk (stoop;) ) around it, then a vee-berth is often a better solution - except when the bloody pillow falls off the end of the bed!

[fcfc]

I have tried to sketch something similar of your proposal time ago in the O1 thread. Euro trailerable , so sligthly smaller than US trailerable. Really smaller engine. I have found cutting the speed by 2 cut the engine power by 5.

But I have miserabily failed to sketch something realistic and usable. My current impression is that the layout is a very complex and crucial stage of the design and drive all (for cruising boats of course,for racing a bit different:P ).

For informations, in the last stages of my delirium, before complete madness, was to design some kind of box garboard / box keel / hull bossing to lower a bit the engine. and to put some raised dinette al la deck saloon sailboat above the engine. ( http://www.sirius-werft.de/Bilder/32DS/32DS_Daten.jpg ). But the problem is that the dinette has to extend well past the centerline of the boat to cover the full width engine protrusion and the remaing passage between the dinette and the galley is rather very narrow and is the only place where you have standing headroom.

[fcfc]

...
I definitely want the helm to be inside the wheelhouse. I've been thinking about a semi-convertible top on the house, much like Ellings and some new Hinckleys have- weathertight when it's cold and wet out, open to the sky on nice days.

That is perfectly possible. But the helm inside will practicaly kill the headroom in the head. There was a thread about head up or down in the O1 forum. Steering from inside mandates you to head down, in the forecabin. And you will have very hard time to achieve standing headroom there. If you put head up in the saloon,where headroom is easy, it will mask rear field of vision.

One of the cheating is to have two steering stations. One outside, declared as primary, with the required field of vision. And one inside, declared as secondary. With placards specifying the limited rear field of vision. Beyond the increased cost of dual stations, it also eat precious space both in the cockpit and in the wheelhouse.
The other cheating is to have of big windows in the front and rear bulkheads of the head, protected with curtains when in use. That prevent any mirror or cabinet fixed on the bulkheads. Either in the head or in the saloon.

[Willallison]

fcfc - is complying with ISO 11591 - the field of vision standard to which you refer - a requirement for ALL vessels built or used in Europe? If it is then there's an awful lot of boats that don't comply. Many with the fwd vision, let alone when looking aft.....

The relevant part of the standard, when considering head up/down is this:

5 Field of horizontal vision — astern
5.1 Craft without permanent cabin or other superstructure aft of the main helm position
obstructing vision astern
A field of vision astern to the horizon shall be provided throughout a horizontal arc of 135° equally divided on either
side of a longitudinal axis directly astern from the helm. Vision astern shall be provided without leaving the helm or
controls, i.e. not more than 0,5 m to either side form a seated position or 1 m to either side from a standing position
in craft intended to be operated from a standing position.
5.2 Craft with permanent cabins or other permanent superstructure aft of the helm obstructing
vision astern
NOTE Readily removable obstructions to vision, such as convertible or camper tops, aft and side cockpit curtains, are not
considered as permanent superstructures. It is assumed that, during inclement weather when these items are in place, caution
in operation will be exercised and a lookout will be maintained.
Other means such as mirrors shall be provided to meet the requirements for vision astern specified in 5.1, without
leaving the helm or controls.
On craft fitted with autopilots, the helmsman may leave the helm position briefly to meet the requirements for
visibility in 5.1.

This suggests to me that, for a boat that meets the std, you are't necessarily confined to the head down arrangement. Just that there is a further complication to consider. The problem with locating the head down is - as you've alluded to - in order to get sufficient headroom, the overall height of the vessel must be increased significantly, increasing the weight, raising the CG etc. The upside, however, is that you gain a far more open feel to the main cabin / cockpit area(s)

[marshmat]

My interpretation of the standard is that if the view aft from the helm is obstructed (ie, by the head), you simply have to add mirrors and/or CCTV monitors to ensure you can see what's behind you. To be honest I see very few vessels, anywhere, that fully comply with the standard at all helm stations.

[Willallison]

You wouldn't be required to comply with it in the States anyway would you Matt?

[marshmat]

Canada, and no, I wouldn't be required to follow an EU standard.... but having studied ergonomics extensively while on the solar car team, I intend to do a much better job with visibility and comfort than was possible on that project. I'm pretty sure this one will meet the standard in most if not all respects.
More drawings coming tonight (hopefully) now that moving is more or less done.

[Willallison]

Canada, and no.....

Oops, of course, sorry...;)

[marshmat]

As promised, a general arrangement and a profile.
Still very very rough of course but you get the idea....

[Mat-C]

'nother thought. As you've shown it, the cockpit doesn't appear to be self draining...?

[Willallison]

hmmm - got me a little confused. Does this mean that the head will have a raised section where the engine box protrudes in? If so, what will be above it? I guess the basin could go there.
You could lower the overall height by lifting the step at the helm. This means there is no longer standing headroom there, but allows the helmsman to poke his head out a hatch directly above for improved visibility or comunication with deck crew etc

[marshmat]

As you've shown it, the cockpit doesn't appear to be self draining...? She only draws about 30-35 cm at rest- the cockpit sole is 40 cm above the keel, so with appropriate one-way flaps on the scuppers it could self-drain.
Does this mean that the head will have a raised section where the engine box protrudes in? If so, what will be above it? I guess the basin could go there. Yep; basin above motor would seem to make sense, unless there's something else that goes in the head that needs to be elevated. I was thinking just a basic head and a small basin. The idea is that this is a fairly large, but uncomplicated, trailer cruiser- if it ain't there I don't have to shell out cash when it breaks.
Should a boat this size have porcelain tile, bidet and a 28-jet Jacuzzi? ;) (OK, the Jacuzzi can stay on shore....)
I think I'd rather have standing headroom at the helm and more window area; she is only 2.5 m (8 ft) overall height which I don't think is excessive. Thinking of how to get that retractable-hardtop thing going, sort of like an Elling E3 has.

[Willallison]

Of course it should have a jacuzzi! - as long as you cruise in warm waters, just redirect the jet so it fills a watertight cockpit, add a venturi type system so it aerates the water being fed to the jet - and hey presto, instant bubble bath:D

No I agree, the overall height is still not that high, but the ability to poke your head out is a real bonus - particularly if you're finding your way into an anchorage at night. The retractable hardtop idea is cool - though the Elling version sounds a bit on the expensive side and doesn't really go with your "if it aint there I don't have to fix it" mantra. It might be difficult to achieve whilst maintaining the trad looks too. Why not just go for simple canvas lid? Light, simple, inexpensive...

[fcfc]

Probably what Willallison is speaking of http://www.nimbus.se/modelPageCoupe.aspx?pageid=437

And this one http://www.rangertugs.com/r/r-25.cfm has a similar layout to marshmat. But as they have the same weigth and beam limit, they have choosen to shorten the boat and have it deeper. So they could hide the engine under the cockpit sole. They have also used small yanmar engine, ones with the lower heigh (under 65 cm for the 125 hp). They also made bossings in the hull for the engine. http://www.c-brats.com/modules.php?set_albumName=Seaboldski&id=Engine_room_1&op=modload&name=gallery&file=index&include=view_photo.php

[Guillermo]

Matt,
have you considered the 200 HP JetPac engine? If so, what's the reason not to adopt it?
http://www.swordmarine.com/Products/200hpdsl.htm

[Willallison]

Yes - Nimbus make some of my favourite production boats, though as always, there's some things I'd do a little differently!;) Even boats that enjoy the best of visibility from their internal helms can't match the vision that's available from an appropriate outside steering station. The ability to poke your head out the roof provides both.

On the surface, the Ranger tug is a quite different beast to the one that Mat is proposing - though at 2600kg it's actually lighter, which I found surprising. I doubt that with the standard jet installation you would have sufficient room to install the engine entirely under the cockpit sole - at least not without shortening the cabin significantly.
You would then step down into the cabin, so have to consider how to deal with that in terms of cockpit overhang.

[marshmat]

Nimbus - Gorgeous boats, I like them :) A lot of similarities to what I'm thinking of, but they are wider, substantially heavier, and far more luxurious than this project.
Ranger - A clever and efficient little thing with some features I'm likely to copy. Overall it's a similar concept done in a very different style. It's three-quarters of the length of mine (7.5 m versus 10 m); I wouldn't call it super-light for its size but it's far from being heavy either. Theirs is a semidisplacement hull, and it has twice the draught of my concept (66 cm versus 30-35 cm). It looks like they put the engine completely under the sole- making the cockpit fairly high. I'm leaning more towards having the engine box protrude into the cockpit, but as a seating/sunpad area.
JetPac - I can see it being a really good option for something a bit faster than this. But taking 300 kg out of the hull at 1.5 m forward, then adding that weight back on at 0.5 m behind the transom, seems to make it hard to keep the LCG of this boat far enough forward to plane at low speeds. I'd probably have it high on the list for a slightly smaller, faster boat though.
I don't think an opening in the hardtop has to be expensive or complex. Electro-pneumatic actuation isn't on the must-have list; I'd be quite content with a big panel that just unclips and slides aft by hand on minivan-style roller rails. Canvas would work, of course, but where's the engineering fun in snapping on a piece of cloth? ;)
The Hamilton HJ274 is the drive of choice for design purposes at present; I haven't ruled out similar jets from other makers of course. A Duoprop or Bravo-3 is of course also possible, although I'd rather have the jet.

[Willallison]

In terms of large overhead hatches, many of the manufacturers make off-the-shelf items now. Lewmar, Taylor and others spring to mind

[Willallison]

Canvas would work, of course, but where's the engineering fun in snapping on a piece of cloth?


That in itself is the engineering challenge - to come up with a better system. Just coz it's canvas, doesn't mean it has to be awkward and crappy.
Beneteau had quite a good system for their Ombrine range. The canopy folded down forwards, into a recess in front of the screen. When it was lifted it slotted into something on the screen top and then tensioned aft.

[fcfc]

On the surface, the Ranger tug is a quite different beast to the one that Mat is proposing - though at 2600kg it's actually lighter, which I found surprising.

From what I understood, Mat project is 2500 kg on the trailer, 3500 kg in running trim, full tanks.
For the R-25, the only figure quoted is 2600 kg. But given what they put inside, I assumed it was empty/trailer weigth.

[fcfc]

Nimbus - Gorgeous boats, I like them :) A lot of similarities to what I'm thinking of, but they are wider, substantially heavier, and far more luxurious than this project.

The nimbus 280 coupe I have put the link is 3000 kg, beam 2.85 m. OK wider and heavier, but not that much. But it is no longer in production.

[fcfc]

As promised, a general arrangement and a profile.
Still very very rough of course but you get the idea....

I know that critics is easy, and art difficult. And I also know I failed my own attempt.

What I would say on that design is that berths are narrow, if they are double. I would expect the converted dinette to expand up to the hull planking to provide adequate width when used as berth. I would use kind of removable back seat along cabin side. With back seat, seat width up to cabin side. Without, berth width up to hull side.
IMHO, U shaped dinette are only useful if you need the space under the central bench (the bottom of the U). Otherwise, it makes a very small table and do not provide much seating space (no places for foots/legs). Face to face dinnette provide more space.
The galley is on the narrow side. I guess the galley counter will be around the heigh of the catwalks. So the usable depth of the galley counter will be limited by cabin side. It provide a very narrow space for a stove/burners. There is a safety issue if the burners are too near the cabin side.

About the corner in head, where you suggested to put a basin. If you put a basin there, you would like to be in front of it to use it. That mandate the trone to be in the front startboard corner of the head.
I would put a locker of shelfes instead. I would put the trone aft, between engine box and side, and basin in the corner side / front bulkhead.

BTW, http://www.roughwater.com/content/images/29/brochure/29_RW_Family_Cruise.jpg another idea for a boat (empty 2800 kg, loaded 3600kg). They removed the inside helm, but put a two level roof to have a enclosed helm station above the engine.

[Willallison]

About the corner in head, where you suggested to put a basin. If you put a basin there, you would like to be in front of it to use it. That mandate the trone to be in the front startboard corner of the head.
I would put a locker of shelfes instead. I would put the trone aft, between engine box and side, and basin in the corner side / front bulkhead.


I'd put the basin over the box, and the throne next to it, in the aft stbd corner.

Yes - I agree that the cruising weight of Mat's boat and the R-25 are going to be quite similar, though the boats are 5ft different in length. I'm still not convinced though that Mat's boat needs to be that heavy, given the KISS principle that he's adopting.

BTW - Mat - when are you going to give this boat a name, so we can stop calling it "Mat's Boat"?

[marshmat]

From what I understood, Mat project is 2500 kg on the trailer, 3500 kg in running trim, full tanks. That's the current estimate, yes- 2.5 t dry, 3.5 t in full-load condition. Since I don't have the actual scantlings yet the structural weight (1500 kg) is still plus or minus about 30% but based on 15-20mm thick strip plank hull with appropriate frame/stringer structure that's what I estimate at present.
I'm still not convinced though that Mat's boat needs to be that heavy, given the KISS principle that he's adopting. I agree with you; of course, my approach to design is to assume the worst, and then be thrilled if it comes out better- rather than assume an ideal case from the start and have to make it heavier later. Nothing wrong with being a bit conservative on the initial estimates.
I would use kind of removable back seat along cabin side. With back seat, seat width up to cabin side. Without, berth width up to hull side.
IMHO, U shaped dinette are only useful if you need the space under the central bench (the bottom of the U). Otherwise, it makes a very small table and do not provide much seating space (no places for foots/legs). Face to face dinnette provide more space.
Interesting thoughts. I've experienced the U-shaped dinette in camping trailers of similar interior dimensions and I don't mind it that much, but your idea of nesting the 'berth mode' partway under the catwalks would be a much more efficient use of space than my earlier sketches.
I'm not sure I'd even bother putting a stove in the galley. I've done long stints without using one before and don't really miss it, so long as I can grill a steak or burger somewhere else now and then. For a day or weekend trip a fridge, sink and microwave would seem to be sufficient; any longer trips would definitely include some shore time.

BTW - Mat - when are you going to give this boat a name, so we can stop calling it "Mat's Boat"? All in good time, my friend, all in good time... ;)

[Willallison]

That's the current estimate, yes- 2.5 t dry, 3.5 t in full-load condition. Since I don't have the actual scantlings yet the structural weight (1500 kg) is still plus or minus about 30% but based on 15-20mm thick strip plank hull with appropriate frame/stringer structure that's what I estimate at present.


One of the best things about strip planking is that you don't need much in the way of framing. Obviously the engine has to be bolted to something so there's a couple of stringers to consider, but other than that, bulkheads and bonded in place interior fixtures should be sufficient.
BTW - what 'rules' are you using to calculate your scantlings?

[marshmat]

BTW - what 'rules' are you using to calculate your scantlings? That decision has not yet been made; I haven't designed the final structure yet (the estimates I have are based on what I've seen in similar boats and on some simple first-principles engineering calcs, not on actual scantling rules). I am looking for an appropriate rule/guide for strip-plank planing hull structures (suggestions welcome).

[Willallison]

That decision has not yet been made; I haven't designed the final structure yet (the estimates I have are based on what I've seen in similar boats and on some simple first-principles engineering calcs, not on actual scantling rules). I am looking for an appropriate rule/guide for strip-plank planing hull structures (suggestions welcome).

Well, without doubt, the simplest would be Dave Gerr's Elements of Boat Strength. He also includes a development of Lindsay Lords rules, which are considered to be some of the lightest.
In genreal Dave's are considered pretty conservative, but I guess at the end of the day you'll wind up with a structure that you can be confident in. A recent edition of Proboat had an articles comparing his rules for foam cored hulls to the ABS rules and there was stuff all between them.

Apart from 1st principles, I'm not aware of any others.... but like you, I'm always open to suggestions

[marshmat]

Just a little update here, now that moving's all done and I've got a bit of time to work on this project again. I'm starting work on a tow-test model, around 1/5 or 1/6 scale, to check out how this hull shape actually runs. Proper tank tests are out of the question, of course, but I'm working on a rig to tow it alongside Sunset Chaser which I think will give pretty decent results provided the lake is fairly calm. I'll keep you guys posted on how it goes.

[Willallison]

There have been a couple of good articles on tow model set ups in Proboat if you have access to them. Tom Lathrop (Tom28571) also has some good info on his website about the setup he used.

[longliner45]

hey marshmat ,,in novembers sailing mag ,there is a 40 ft trailor sailer ,made by scott minclintock of az ,,he says he launches it at the ramp,sorry I cant post a pic ,but maybe someone can,,,longliner

[marshmat]

Thanks for the tips guys :)
I've read Tom Lathrop's article and I will probably use a similar bridle configuration to the one he designed for the Bluejacket tests. It does seem substantially more realistic than towing from the bow, although probably not as good as a true yacht dynamometer (waaaay too pricey for this!).
The test model is being built at 1/6 scale, making it 1.667 m long. No, this is not an arbitrary decision; mathematical simulations were done to confirm that the relevant dimensionless groups will be reasonably well matched over the entire speed range under study. Matching Froude number between model and prototype, the main concern in the speed range I am considering is that significant laminar flow may occur on the bow sections of the model (Re=5E5 occurs at around 21 cm aft of entry on the model at 10 knots scale speed). Suggestions on how best to account for laminar flow effects on the model (since there is virtually no laminar flow on the real boat) are welcome. I'm looking into mathematical ways of correcting for it; roughening the surface is an option albeit probably not a desirable one.
Some snapshots of the model under construction are below. Nothing's fixed in place yet but I couldn't resist the temptation to just slide a few bulkheads onto the strongback to see how it looked..... more snaps coming soon with bulkheads fixed in and keel mounted.

[Willallison]

Glad you cleaned your workshop up 1st, Matt!;)

[SAQuestor]

Glad you cleaned your workshop up 1st, Matt!;)
I know all y'all go back a long ways together and all, but boy, I am sure glad I wasn't the only one to notice that spiffy workbench. ;)

[marshmat]

When a workbench is in such condition, it is easier to simply call it "storage space" than to endure the futile battle to maintain order :D

[lazeyjack]

my last trailer boat

[SAQuestor]

When a workbench is in such condition, it is easier to simply call it "storage space" than to endure the futile battle to maintain order :D

Good advice that I'll remember when SWMBO says something about my "workbench" :D

[fcfc]

my last trailer boat

This one is also trailerable. (it is the same boat, shown on different trailers at different stage of the construction).

http://www.bymnews.com/photos/albums/Megayachts/Ocea_DSCN0742.jpg
http://www.ocea-yacht.fr/images/bateauyachtsfleet/photo13_1.jpg

It just depends on what trailerable mean for you.

[Willallison]

Bloody lovely boat, that.

I like a person who adhears strictly to the less is more principal!

[marshmat]

How long did you have that one, lazeyjack? Looks like a good, solid build and practical design... what the working fishermen across from the yacht clubs call a "real boat". Got any more pix on ya?
It just depends on what trailerable mean for you. Gotta love those pics fcfc :D The 14-axle boat trailer... what will they think of next?
*****
Update on the project- my towing test model is coming along well, just trying to track down some appropriate strips of wood for the outer skin (it's darn near impossible to get anything smaller than a 1x2 in the normal lumberyards, so I'm hunting down other local suppliers for the 1/8" strips I need). Hoping to get some numbers before the end of the summer. In the meantime, the ongoing repair/upgrade work on the existing runabout takes priority of course- rule of thumb, the highest priority is always to keep the boat that actually works in top condition ;) The model's being slotted into whatever time is left.

[lazeyjack]

built it for a farmer, he never touched it in 10 yrs so I,m putting the engine in, doing the interior, there are some pics in will trailer thread, but will post here too
she is very deep fine entry, huge girdars 400mm deep run full length, carries 550l fuel, but the disp will be higher now as he bought the D6 Volvo, weighs 750 kg with leg

[lazeyjack]

you can see the wide chines, pretty essential for getting the boat planing and holding the plane at lower speeds and getting the tracking right downweather, I dont put on strakes , as they make the ride hard,
i,m trying to get the design from Rhino and Solid into freeship, but no luck yet, and takers to advise

[marshmat]

Hi all,
I know it's been a while since the last update.... things have been a bit busy here.
Got a chance recently to do a few more sketches on this one. Layout concepts and a few more profile sketches (yes, that's a Duoprop on the top one). Sorry about the lousy scan quality; image scanning for the moment consists of putting the drawing on the floor and pointing the digital camera at it, then bumping the contrast way up.
The first profile sketch is a more open design and matches with the general arrangement sketch shown. A canvas enclosure would be put up in bad weather. The layout drawn has the head down under the helm (there's good sitting headroom but no standing up in there); the two side benches would fold out into a transverse double berth at anchor. There's no dinette in this one; since this boat would usually see shore stops several times a day, perhaps the extra space would be better left open (the boat will also be expected to ferry lots of gear and crew around now and then). Small folding tables like those on a passenger train could be added to the bench ends.
Another profile idea (at bottom) is with a fully enclosed deckhouse, with the retractable hardtop (a la Mercedes SLK, right? ;) ) and a raised deck over the forward cabin to improve headroom there.
On a semi-related note, I'm working through Dave Gerr's scantling guide (in Elements of Boat Strength) as a starting point for the structure.
Finding wood and time to finish planking the tow model is taking a while, so I'm not sure that'll happen this season. There's still plenty of time, of course, since the keel wouldn't be laid for some years yet.

[Willallison]

Hi all,
Sorry about the lousy scan quality; image scanning for the moment consists of putting the drawing on the floor and pointing the digital camera at it, then bumping the contrast way up.


Digital !! - Oh you techno nerd!!;)

I've been wondering how you were getting on.....
Couple of thoughts:
1. If you can move the windscreen fwd a touch, you might be able to squeeze standing headroom in the "lobby" of your fwd cabin area, by leaving it open above.
2. Have you checked against your waterlines to make sure that the sole extends as far outboard as you've shown it? It looks too wide to me at a glance- particularly up towards the berth. Also, I doubt you'll need 3 steps from saloon down to cabin - probably only 1.

The Open version is the prettier of the two OMHO. You could probably achieve a more closed in 'saloon' by doing something along the lines of the MJM 34Z ( http://zurnyachts.com/ )
with roll-down clears.

Though they're often frowned upon by many 'real' designers, I see no problem with using Gerr's rules for scantlings. Granted, they are somewhat on the conservative side, but they are well proven, based on sound engineering, and (provided they are applied correctly) should give a long-lasting and solid boat. I know of quite a number of well known, practising designers who use them for almost all their work.

What timber are you going to use for the model?

[fcfc]

Something like this ?

http://www.boatdesign.net/gallery/showphoto.php/photo/1674/size/big/cat/500/ppuser/2043
http://www.tantonyachts.com/977ga.jpg

Seems to have a hinged top above what looks like a shower.

[marshmat]

Tanton's "Search" does have some similarities to what I'm thinking of, albeit in a somewhat different style. It looks to be meant for longer self-sufficient periods than mine is, but he's got some neat features sketched in there.
The Zurn 29 and 34 mentioned by Will are a neat design that I might look at in more detail. I think I prefer real glass over plastic film for the house sides, especially in the cooler parts of the Canadian boating season.
Now, the sketches I posted yesterday were done in the back of a van a good 300 km from my computer, so no I have not mapped the actual hull shape onto them- these are just to toss around layout concepts, with the details to be refined later. I'm not sure how far forward I can extend the windshield without making it look like a houseboat-barge, but there might be a way to improve headroom up front while keeping the look I want.... we'll see after a few more sketches.
I've heard from a few people now that Gerr's rules are quite conservative; this is exactly what I want. The boat would be expected to survive for quite a few decades, weather the occasional bout of terrible weather, and live on a trailer- light scantlings just don't jibe with the requirements of this design. I've spent enough time working on ultra-lightweight carbon structures for solarcars in the last few years; for this boat I'd prefer solid and reliable.

[Willallison]

Something like this ?

http://www.boatdesign.net/gallery/showphoto.php/photo/1674/size/big/cat/500/ppuser/2043
http://www.tantonyachts.com/977ga.jpg

Seems to have a hinged top above what looks like a shower.

Well, no, that's not really what I was suggesting. Just that if the space at the base of the companionway step(s) is open to the saloon and windscreen above, then you'd have full headroom there.
Search is an interesting boat - not too sure about the complete lack of bench space in the 'galley', or the height of the wardrobe that's imediately in front of the helmsman though....

[marshmat]

In case anyone wondered where this one went, no it has not died. It's just constantly getting bumped by higher-priority projects. Getting rid of me ain't so easy..... ;)
Another teaser here, of what might be coming soon. Been playing around with profile shapes; here's a slightly more protected version of the "open" profile from August. Yes it is just a wireframe superstructure, and yes the 3D is coming. It's faster to play around with wireframe for now though, since I don't have Rhino4 yet with its nifty linking of surfaces and the curves they came from. I figured I'd spare you guys the eye strain of another one of my digicam-scanned sketches.
I think I've settled on roughly the hardtop coverage shown in this one. Any more hardtop and you start to lose the open feel, but I want to keep decent and comfortable protection from rain and spray when the weather's less than pleasant.
There would be no physical barrier between the cockpit and the area covered by the hardtop; canvas sides and tonneau could be installed over the cockpit in bad weather.

[Willallison]

How's the model coming along Mat?

[marshmat]

Slowly. It's fully framed up but I have yet to buy and slice up the 1/8" veneer from which the planking strips will come. That'll get 1 mm of fibreglass overtop before being faired smooth. A loose approximation of the construction method of the real thing. It shouldn't take that long but other, higher priority projects keep displacing it..... I'm sure everyone's familiar with that feeling.

[rwatson]

I've considered waterjets for all the same reasons, right up until the price kicks in. I dont know why the costs are so high (around 6-10k) for that kind of propulsion.
My project is smaller, under 30ft to fit in a container - so I wondered if a waterski setup could be incorporated.
I had a 26ft macgregor that did 18 knots on a 50 hp, so this project seems very feasible. But I would like to keep the sailing ability also, but with an interior steering station for non sailing weather.
The lines on this project are very interesting to me.

[marshmat]

I've considered waterjets for all the same reasons, right up until the price kicks in. I dont know why the costs are so high (around 6-10k) for that kind of propulsion.
It doesn't make much sense to me either, why they're so expensive. There are cheaper ones, too- an Aggressor "Junior" series is worth around three grand- but that's a high-RPM, lightweight-boat pump for 50 mph plus. Those options will be considered as well on this project, in due time. And I haven't ruled out a Duoprop or Bravo-3.

Sailing ability will not be a factor on this boat- I'm trying to optimize for an efficient shape at low planing speeds under minimal power (in the end, the power will likely trace back to either biodiesel or cellulosic ethanol, both of which will be widely supported by the time she's launched). I do wish there were more boats with the combined power/sail ability of the Macgregor; they seem to have some interesting performance traits that should be further developed by a bit of healthy competition.

This link http://www.woodenboat-digital.com/woodenboat/20070910/ was posted on another thread recently, it's an excellent description of an adaptation of a jet-ski drivetrain to a "real" boat. I have not ruled out using one or two of these units here, but I have yet to do the research on the feasible propulsive coefficients and thrust curves with such a setup.

As for the model testing- finally getting back on track with its construction; today I started laminating the sheets of birch veneer to plank the tow test model with. Time for this is of course a bit scarce but I'm figuring on having the model, towing rig, measurement systems, etc. suspended off the gunwales of Sunset Chaser for the start of boating season '08.

By the way, the scantlings (as of this time) will be more or less based on the method outlined in Gerr's Elements for wood-epoxy strip plank (leaning more towards the epoxy-sheathed strip-plank-on-frame types than the strip-plank-cored-composite types in this case), with a scantling number of 1.26. Those calculations, plus proper engineering analysis where I deem it fit, are in progress.

[marshmat]

Just in case anyone thought this concept was gone.... it is not. At last, there is a 1/6 scale fibreglass model sitting in the basement. Still needs a deck and a bit (ok, a lot) of fairing mud, but should be ready for next boating season....

Parallel development is progressing, now, on a second, smaller vessel based on the same parent hull. This would be more of a day boat, or a weekender for two, than the 10 m version (which, as you may recall, is intended to be a weekender for 4 or a cruiser for two). Targets for this version are a length of around eight, maybe eight point five metres overall, displacing no more than 1500 kg at the dock (2100 kg with crew and cargo). (I'm working on bringing the vessel weight down below 1200 kg when on the trailer, which would put towing comfortably within reach of vehicles such as minivans, that do not have thirsty 300 hp diesel engines.) Power of between 100 to 150 hp would be fitted to achieve calm-water speeds approaching those of the big boat (which is intended for 25 knots at WOT with typical loads). Although the smaller version will sacrifice some rough-water capability, its bottom loading would be around 20% less than that of the 10 m craft, which should translate to a slight improvement in planing ability in the 10-20 knot range where it would spend most of its time.

I'll be back with more soon.... (and by soon, as I'm sure some of you have noticed, I likely mean within a few weeks ;) )

[Willallison]

Boat's looking great... but I note you still haven't tidy'd the workshop...;-)

[EStaggs]

Mat, what kept you from going the double wedge route instead of the warped plane with a v aft? I like the concept of the boat very much, but am curious what kept you away from the lobster boat shape and the extra efficiency of a dead flat at the transom.

Looks good!

E

[marshmat]

E,

I'm glad you like the concept :) I am hoping that something will eventually come out of it....

Why doesn't she have a lobster boat style shape at the stern? Well, to be honest, I did consider flatter-bottomed hull forms, and forms with an upward-sloping run, in the earlier stages of the concept (before this thread). From what I've seen and read (and I haven't spent any time on lobster boats), these vessels are extremely efficient for what they do. Their hulls are optimized for inshore running in ocean waters, at semi-displacement and low planing speeds with significant loads (I have heard of a 4-tonne, 9-metre boat of this style that broke 20 knots with a 200 hp diesel).

The inland lakes and canals this boat would be intended for (plus the coastlines of the Great Lakes) tend not to have the relatively big, rolling wave systems found over the Grand Banks. We tend to have short, confused chop coming from all angles, at a shorter wavelength and smaller amplitude than would be expected for a given wind condition. So the ability to maintain a steady slow plane in this kind of sea is substantially more important in this design than is the ability to keep a comfortable motion in big waves, as is paramount in an inshore working boat. Both the 10 and 8 metre versions of this craft are intended to be very light boats (for both efficiency and trailering/launching reasons), with very low D/L ratio and relatively low bottom loading. They're too light, it seemed, for the lobster boat forms to be able to maintain their proportions at this scale while retaining their advantages over the shallow-V. (I should note that while the maximum 3500 kg displacement at full load remains for the 10-metre, I am trying to lighten things up considerably in the unloaded condition.) Add to that, the minimal-draught requirement, the desire for both jet and prop possibilities, and the desire to maintain relatively even trim with little discernable 'hump'- hence the high-lift, low-bottom-loading shallow-V form which is currently being studied (but which, I should note, is not necessarily the final form of the boat!) Given the slightly higher speeds at which this boat would run, and its somewhat lighter weight, I am keeping a bit of deadrise in there (although with each successive iteration, the deadrise does seem to decrease a bit).

So in short, as much as I love lobster boats (and am taking styling and functional cues from them in many cases), the capabilities required here don't seem, from my perspective, to mesh with the design intent of a craft designed for what is, in the end, a rather different type of service than this one will see.

(A further note - the powering calculations done on the 10 m version so far indicate that with the jet drive at a propulsive coefficient of between 0.5 to 0.55, we would be seeing at 3500 kg displacement, a cruise of 19 knots drawing a hair over 130 hp, and a top speed of 24 knots at 175 hp- I think this compares reasonably well with the 4-tonne lobster boats I've compared the design against, typ. 16-17 kts @120-150 hp and 20-22 kts @ 200 hp. Or put another way, this one might need about 1.95 hp/tonne/kt at 19 knots cruise with the jet drive, roughly comparable to those lobster-style boats' 1.8 to 2.2 hp/tonne/kt at their typical cruise speeds. I suspect the added drag of the long keel/skeg seen in most such craft compensates for the relatively greater efficiency of the large, straight-shaft props.)

(ps- nice blog, E, btw! dangerously addictive reading.....;))

[EStaggs]

Thanks for the kind words on the blog. I needed a creative outlet for my somewhat disjointed thought process, so why not entertain people at the same time, right?

So I can understand the additional beam aft, keeping her more in the warped plane territory than the double wedge. It seems to be not only more efficient, but might allow more accomodation per square foot of boat. My boat, during the sea trials for example, had alarmingly higher performance for her given design. The hull is warped to a 0 degree transom, and she gets along at about a 12 mph advantage over her intended speed (a 40% improvement with 20 additional horsepower). This has an unintended consequence of pounding at speed, which the V would seem to mitigate a bit id imagine.

The other question thats really rattling around on me right now is the rooting issues. These warped plane boats have a nagging tendency to root and broach in a following sea at speed. Long, lean boats with a lean forefoot, lots of lateral plane, and a little speed tend to come around unexpectedly, and most will add a skeg of significant size to protect against this. Mine is no different, as im sure you've seen in the blog. Is this going to be a consideration? It definitely throws a wrench in the works for the pump. Im wondering if you are thinking of something along the lines of strakes, bilge keels, or if the V allows enough stability to prevent or reduce the tendency.

Im definitely seeking an efficient design in the 8m range, one that can fish, and be a coaster for my wife and I in the Inside Passage. This has the right personality. Is this something along the cabin profile?:

http://www.bateau.com/images/boatpics/DE25_Cockpit_rear_350.jpg


http://www.bateau.com/images/boatpics/DE25_cockpit_inside_350.jpg

Jacques Mertens, www.bateau.com ,penned this boat. It really has some pop, but I prefer a forward tilted workboat windshield, and at 6'3, enough headroom to stand.

Always enjoy watching designs unfold! Now, back to work (2 heart attacks, a stroke, 2 car wrecks, and 5 other various calls so far today).

E

[marshmat]

The other question thats really rattling around on me right now is the rooting issues. These warped plane boats have a nagging tendency to root and broach in a following sea at speed. Long, lean boats with a lean forefoot, lots of lateral plane, and a little speed tend to come around unexpectedly, and most will add a skeg of significant size to protect against this..... Im wondering if you are thinking of something along the lines of strakes, bilge keels, or if the V allows enough stability to prevent or reduce the tendency.
I'm hoping to get some answers to these questions from the model tests this spring and summer, E. At 1/5 or 1/6 scale, it should be possible to duplicate such a tendency should it exist.

It seems a lot of jetboats, especially those of this general form, do have at least a slight tendency for the stern to kick out sideways in a following sea. If this is the case here, there are a few possibilities- twin small pumps and a centre skeg, single pump and bilge keels/strakes, jet intake nacelle, a counter-rotating sterndrive.... I'll wait until I have some test results to figure this out from.

My current boat (based on Phil Bolger design #432- "Diablo") has a two foot wide flat pad as the centre of the bottom, with a deadrise of about 26 degrees for a foot and a half either side of that. Amazing boat, fast as a bat outta hell, but you need a substantial load to prevent her from pounding in a short chop. Given that the new boat has roughly comparable bottom loading and displacement/length ratio, I think a slight bit of V is necessary to reduce the pounding effect. Transitioning to a flatter deadrise at the stern might be possible with a sterndrive or inboard variant, but goes against everything the jet suppliers say is best for their units.

The Mertens design mentioned above (the Down East 25, if I'm not mistaken, http://www.bateau.com/proddetail.php?prod=DE25Cockpit ) is a beauty indeed- she does share some similarities to this boat, both in possible layouts and general style (the hull is of similar type, although it appears optimized for higher speeds than mine). It is marginally faster and a bit smaller than both the 8- and 10-metre versions of my current project; still, a boat worth investigating further.

[EStaggs]

From the research I have been doing on pumps, Id definitely go with the Ultra-style nacelles. That seems to be the ideal way to feed the pump, minimizing air introduction and offering a little extra lateral plane aft where it needs to be (though its pretty tiny). In the PNW, so many jet boats exist that are specific to whitewater that pumps seem to have taken a bad rap. Huge horsepower on heavy alu boats, bad fuel economy, and the stigma left behind by the go-fast big block jet boats of the 70s have eclipsed the efficiencies available with pumps. Im excited to see that progress as well.

Is the pump there for efficiency? Draft? If not for skinny water work, would a set of small skegs, possibly something at the sides of the nacelle, be the ticket? I know that its a trick of the fast boats to add small fins to the sides of the intake grate, and this would be an opportunity to add intake pressure as well as providing a bit of stability in what may be an inherent "personality" to the boat.

This shift is getting long....

E

[marshmat]

Is the pump there for efficiency? Draft? If not for skinny water work, would a set of small skegs, possibly something at the sides of the nacelle, be the ticket? I know that its a trick of the fast boats to add small fins to the sides of the intake grate, and this would be an opportunity to add intake pressure as well as providing a bit of stability in what may be an inherent "personality" to the boat.
In my case, the motivation for considering a jet is:
- Reduced vulnerability to damage (during high-water season, the amount of submerged semi-floating driftwood in some of these lakes is phenomenal- a prop repairman's dream)
- Reduced draught (beaching, for one, but also for the shallow and often uncharted rivers/canals I like)
- Reduced maintenance headaches (the relative simplicity and durability of a proper jet pump when compared to something like a Bravo-3)

In the jet configurations, I actually did end up playing around with the idea of small fins to either side of the intake after last night's discussions, as well as a few other forms of fin out near the chines. I'm not really putting much time into this aspect of it now, though, until I have a better idea of the true directional stability of the thing from the model tests.

This shift is getting long.... One of those days, eh? Although I suppose in your line of work, E, a long boring shift means things are going pretty well in your town :)

[Pericles]

Just a couple other thoughts to confuse the issue.:D

Looking back in this very interesting thread, I see that the Roughwater 29 and Lazeyjack's vessel on the trailer both have superb 360 visibility with the raised helm position, This can be sited over the engine box. A full height shower and head could then be accommodated in the cabin area to starboard alongside the helm, with access to engine from the portside passageway to the cockpit.

Guillermo's suggestion about the 200 hp Jetpac could still work as the unit supports much of its weight when immersed. Its dry weight is 422 kg or 930 lbs and Guillermo can advise you of the transom load in salt water. Watch the videos.

http://www.swordmarine.com/

The Tolman Jumbo can take 500 lbs on the transom and the Suzuki 140 seems to be the power of choice. The group has posted many examples of their work in building these Alaskan skiffs.

http://www.fishyfish.com/

Apologies if I have trodden on anyone's toes.

Regards,

Pericles

[marshmat]

Sword Marine's JetPac certainly has the distinct advantage of not fouling up the cockpit with a massive honkin' motor box. It also has the advantage of being essentially plug-n'-play, almost like a large outboard, without the wire-by-wire rigging of an inboard. I will be researching this unit further.
What I'm worried about, in this case, is what adding around 200-300 kg (the weight that remains cantilevered after deducting the thing's own buoyancy) well aft of the transom will do to the trim at low planing speeds- even with the inboard it's proving tricky to keep the weight far enough forward. One of the goals for this hull shape is to reduce or nearly eliminate the "hump" and bow rise / stern squat when coming to plane, and to be able to cruise in that speed range if necessary. I have yet to reach a decision on whether to consider or reject the JetPac; that will depend mainly on how things look when I plug the unit into the boat's weights & moments spreadsheet.

[Guillermo]

The JetPac diesel can be rated 100, 150 and 200 HP, on the same basic engine. The higher the power the lighter the duty, of course.

Soon we'll mount in Vigo a 200 HP unit at the transom of a devotedly designed aluminim rib-like craft, for demo purposes (boat almost complete now). I'll post images soon.

Cheers.

[marshmat]

Soon we'll mount in Vigo a 200 HP unit at the transom of a devotedly designed aluminim rib-like craft, for demo purposes (boat almost complete now). I'll post images soon. Looking forward to seeing that in action, Guillermo!

*****

Below, some teasers of topside styling on the 8.5 metre version..... the cockpit sole, at 10 cm above load waterline, remains self-bailing and the engine cover forms a cockpit seat or table. Looks like 1500-1700 kg sitting at the pier and about 2370 kg at design load, for the current weights and moments table on this version. Those side windows on the wheelhouse would slide back completely over the fixed (opaque) segment to open up the cabin in good weather.

[Pericles]

Matt,

The Tolman discussion group to which I belong is currently discussing the use of both the Armstrong bracket and 200 hp

outboards.http://www.armstrongnautical.com/repower.htm


----- Original Message -----
From: John
To: tolmanskiff@yahoogroups.com
Sent: Monday, December 31, 2007 12:18 AM
Subject: [tolmanskiff] Re: Outboard Motor Bracket


Neal,

We changed our plans in mid-stream. Before we glassed the bottom we
found out more information about the Armstrong type brackets and
decided then that is what we wanted. At about the same time we bought
a 200 HP Mercury for our power.

Ok, how do we go about adding an Armstrong bracket? I thought of
cutting into the transom next to the existing stringers so we could
sandwich the extensions about four feet. I worked all of the logistics
out in my mind and was about ready to do it......

But then I changed my mind again and decided to make the bracket out
of aluminum. Will start laying bracket and internal gussets and
brackets out in two to three weeks. The bracket will have flotation,
it will also have the hydraulic lift.

I don't know where to place the fuel tank, so the plan is to finish
cabins, flooring on the outside of the stringers, mount and set up
motor. Make a temporary floor between the stringers so it will hold
weight equivalent to a tank full of fuel (gearbox)for experimenting. I
will test boat with the weight distributed at different locations aft
and forward till I find the location for the center of the tank.

John

--- In tolmanskiff@yahoogroups.com, "skiffkits" <neal@...> wrote:
>
> John,
>
> Thanks for posting the bracket link.
>
> After reading the articles, a hot setup for a J24+ would be, build a
> 16-18" bracket built off extended stringers, (easily done, lt. wt.
> and strong) this would allow for added floatation between the
> stringers and a half or full width swim step and full ht. tranny,
> with walk-thru door(s) :-), if desired. Then use a 6" setback jack
> plate (preferably hyd.). This setup should be considerably cheaper
> than an Armstrong or other factory built full width bracket,
> especially when built into a new hull, it should give the same or
> even better performance results, as you'd have motor ht. adjustment
> on the fly for fine tuning and running shallows. If more forward
> tilt space for larger motors is needed you could use a 8"-10" set
> back JP instead of the 6", or build the bracket longer. Most
> brackets I've measured are 28-30" long to allow for full tilt range
> on the big motors (200hp plus). The Suzuki 140 can use a 24"
> bracket, transom angle must be taken into account too. With motors
> having to be mounted higher when a bracket is used the JP makes it
> easy to find the "sweet spot" and return to it, and with using a 25"
> shaft motor this keeps the power head higher for less chance of
> dunking.
>
> Careful consideration regarding wt. placement (fuel/water tanks
> etc.) would need to be allowed for during construction.
>
> I'm seriuosly considering going this route on my next build, which
> may start soon. :-)
>
> Neal
> Skiffkits LLC
>
>
>
> --- In tolmanskiff@yahoogroups.com, "davewright112002"
> <usuallywright@> wrote:
> >
> > --- In tolmanskiff@yahoogroups.com, "John" <jklistof@> wrote:
> > >
> > > http://continuouswave.com/whaler/reference/engineBrackets.html
> > >
> > > We are going to add an Armstrong type bracket to our boat.
> > > http://www.thegearboxguys.com/boat.htm
> > >
> >
> >
> > Interesting article John, thanks for posting. It will be nice to
> see
> > how your boat works out with the bracket.
> >
> > To my particular prejudice, and it's only worth 2 cents, the
> molded
> > in bracket of the article made the most sense, i.e., you lengthen
> the
> > hull to whatever you desire in the first place, and shape the aft
> > section with step, or whatever other features you might want,
> > achieving everything a bracket may provide in an integrated "non
> add
> > on" fashion.
> >
> > But if you don't or can't plan for this ahead of time, then
> perhaps
> > the bracket is attractive.
> >
> > I liked the article's consideration of the downsides of brackets
> as
> > well as the upsides. The author seems to favor long extended
> > brackets, but I'm not sure that an objective weighing of the
> pluses
> > and minuses that he details would necessarily lead to his
> favorable
> > conclusion.
> >
> > In any case, you'll get a longer boat and the bracket will
> probably
> > meet all of your expectations and more.
> >
> > Best wishes to you for a successful installation and a heck of a
> nice
> > boat.
> >
> > Dave Wright
> >
>
---- Original Message -----
From: davewright112002
To: tolmanskiff@yahoogroups.com
Sent: Monday, December 31, 2007 3:01 AM
Subject: [tolmanskiff] Re: Outboard Motor Bracket


--- In tolmanskiff@yahoogroups.com, "nordski61" <enstad@...> wrote:
>
>....I have 60 gallons up against the #6 bulkhead and it's not too far
>forward. I don't have a big cabin so I can sure tell a difference when
>the tank is low on fuel. I had just 10 gallons in
> it the other day and really had to trim the engine in to get the
>proper boat trim......

Good info Aaron! I suspected this might be the case, but you're the
first Jumbo builder I've noticed mentioning it. I suspect that the
shorter the Tolman, the greater the bow up trim, and I notice it on my
18 footer.. I'm planning on adding a wedge to my motor mount this
spring to get more engine "in" trim for running up wind on breezy days.

This business is not unusual, and there're a number of boats that have
water ballast up forward for trim.

Dave Wright

------------------------------------------------------------------------

Matt,

The length of the Jetpac is only 50" on a 10 metre design and the longest Tolman Jumbo is about 25' 6", The Bateau DE 25 can be fitted with an Armstrong bracket as well. The videos at Sword Marine show RIBs jumping waves.:cool: :cool:

http://www.swordmarine.com/WatchItWork.asp

Addendum. From FAQs at website: The engine and water jet are both enclosed in a fiberglass shell, designed with enough buoyancy to fully support the weight of the complete unit, that attaches to the transom of a boat, like an outboard.

Elsewhere on this forum there have been discussions about powering boats onto trailers. I have a DVD showing the Jetpac boat doing just that, but without scouring the ramp bottom or damaging a lower unit.:D :D

Water ballast and judiciously placed diesel fuel tanks should take care of the hump, bearing in mind the good holeshot capabilities of water jets. I have purchased the Bateau plans for both the DE 25 and the LB 26. Whichever I build will have Jetpac power, especially as the LB 26 is an inboard.

http://www.bateau.com/studyplans/LB26_study.htm?prod=LB26

Good luck,

Pericles

[marshmat]

Just to prove that this thing hasn't died :)

The test model now has a deck and its first coat of fairing mud. It will take a few more weeks before it's all faired up and looking pretty. Towing brackets still need to be mounted- there will be one on each side (directly above the at-rest CB and with several tow points so that the towing force can be made effectively parallel to the thrust of the real drive unit) and one at the bow.

The towing rig will project out from the port side of my current runabout, keeping the model out beyond the tow boat's bow wave. I'm trying to figure out how to include a camera mount on it to get a video record of the tests. A scale factor of 0.167 means that the 2500 kg displacement of the 10 m prototype will translate to 11.6 kg in the model, which will use sandbags or other movable weights so that trim and displacement can be adjusted.

Since I don't have (or want to pay for) a digital speed log that is accurate in the 2-8 knot range in which the model will be towed, target speed will be approximated with the tow boat's speedometer and determined accurately by stopwatch over a measured distance (likely a floating line of known length stretched between two buoys).

I am not currently planning to use the model to evaluate hull resistance, although I may implement such a setup later. The model will be used primarily to evaluate trim, directional stability, ride quality and wake properties.

The tests will consist of back-to-back runs in opposite directions, at Froude numbers of 0.1 to 2.0. (Fr=2.0 equals 26 knots in the 10 metre LOA (9 m LWL) boat.)

Suggestions are welcome, as always! :)

[Willallison]

Nice to see you're still progressing Matt.
Why not get hold of a hand-held GPS to measure your speed. It will be infinitely more accurate than your speedo, which in my experience are shockingly inaccurate at lower speeds. Your speeds will be over-the-ground as opposed to thru the water, but that is usually averaged over 2-way runs, and the effects minimised by selecting your test site carefully...

[marshmat]

Dammit Will, now you've given me an excuse to buy another gadget. The electronics must be breeding or something; I'm already up to 11 digital displays of some form or another in this room alone.

I'm doing another fairing coat on the model tomorrow (yes, I know this is dragging out forever) and am starting on a towing harness. More to follow.
There's also a few mods to make to the tow boat... jacking the outboard up a bit (been meaning to do this for a couple of seasons but just finished fabricating the parts recently, and now have to take it to a welder) and some painting, among other things.
This is the great thing about small boats- all the fun of fixing up something big, without the rapid exodus of cash from one's wallet.

[Guillermo]

Congs for the improvements, Matt.
I had promised some images from the demo boat with the JetPac. Well, here it is at the Vigo Boat Show in March. Unit is a D200 HP and although the aluminium working boat is rather heavy for its lay-out and length (1200 kg w/o engine, 5.7 m open hull), we got 32 mph with 150 lts of fuel and four people aboard. I'll post more images of her in the water in another thread at the propulsion forums.

Cheers.

[marshmat]

Looks like a good, solidly built craft, Guillermo. The photo really illustrates the advantages of the Jetpac over an outboard- nothing cluttering up the full, no-cutaway transom and nothing sticking down below to get caught on buoy chains, rocks, etc. I'll keep an eye on the propulsion forum for your sea trials :)

[marshmat]

Here's version 23 of the 8.5 metre variant. I'm trying here for more of an open feel while keeping the weather protection afforded by a full pilothouse. The wheelhouse in this one is down to just three panes of glass, but they're enormous- the single piece windshield is nearly 1.6 square metres. (Would probably be of acrylic or polycarbonate, as curved glass that size would be darned heavy and darned expensive.) The back of the wheelhouse has been opened up (canvas could, of course, be used over the cockpit in bad weather). Gunwale and spray rails have been changed to 2" aluminum extrusions after a closer look at some of the local docks.
Note that this version is laid out for a single sterndrive setup. Using the Volvo 4.3/DPS, it looks like it would come in a hair under two tonnes with full fuel and water (still working on cutting that down) and trim within a degree of where it should be at rest. (The boat itself is currently reading a bit under 950 kg, the engine/drive 420 kg, and the rest being tankage, batteries, gear, a grossly oversized anchor/rode, etc.)

[marshmat]

The 1/6 scale tow test model hit the water today. Not quite ready for action but it's getting close. Now that most of the pre-season work on the tow boat Sunset Chaser is done, I can focus on this again; I'm hoping to get some runs with it in June.

The model is 1.67 m LOA and currently weighs in at 13.20 kg dry. Each of the bricks currently in the engine bay is 2.30 kg. The model is slightly heavier than it should be when empty, and I am going to drill out some bulkheads up front to lighten it. With the ballast bricks in the stern, it sits pretty much level on its design waterline in the pool. (The nominal 3500 kg loaded displacement of the 10 m parent hull translates to 16.2 kg in this scale; with the ballast shown, the model is 17.8 kg, so it sits just a hair deeper than it should.)

The towing rig attaches to those brackets sticking out the side, which are roughly in line with the aftmost possible at-rest CB. This is similar to the setup Tom Lathrop came up with for testing his "Bluejacket". Tom's accounts indicate that towing from this point gives more realistic results than towing from the bow, especially when studying directional stability issues; my own calculations suggest he is correct.

(I should note, for the benefit of anyone else trying the backyard non-CNC way of doing this, that the glass-over-wood method used to construct this model is probably not ideal- the model is a bit heavier than it should have been, mostly because of the extra fairing that was needed with this construction method. For the next model I'm likely going with carved foam and a single-layer glass skin.)

[Willallison]

Ok - I'm happy to be the bunny to ask the obvious question..... what's with the tennis ball?

And while I'm at it... how come everyone paints their tow models yellow?

Good work btw:p

[marshmat]

Ok - I'm happy to be the bunny to ask the obvious question..... what's with the tennis ball?
The steel towing bracket and the vinyl pool liner are not the best of friends. Tennis ball serves to keep the disagreement from turning violent.
And while I'm at it... how come everyone paints their tow models yellow?
Good work btw:p
Thanks :)
As for yellow.... good question. Maybe to make it easier to find when it breaks loose? More likely (and the actual reason in my case) is to provide good contrast with the wake for photo/video shooting.

[Chuck Losness]

Nice looking boat. I read your post and all the replies. The hull shape looks very slippry and easy to propel thru the water I would think that it would not burn too much fuel. I look forward to reading about your test results.
I would like something similar for my next boat. Similar size, 34' LOA 9.5' beam, but optimized for 8 to 10 knots. About 10000 lbs displacement. Just a dream on my part. But your work is an inspiration to me
Thanks,
Chuck

[marshmat]

Thanks for the kind words, Chuck. I'll keep everyone posted on how things come with this one. If you want to see inspiring work, though, go ask Tom Lathrop (he actually followed through on something that started as a concept like this, and has been cruising on the result for a few years). Or Phil Bolger, or that Willallison guy who's been hanging around this thread ;) . There's some seriously dedicated designers for you....

[Chuck Losness]

I'm retired and on a very limited income. I also live aboard full time and that adds some complications. Although I live very simply, you still have to have a full galley and head, decent sleeping accomodations and a place to lounge around down below. My biggest stopping point is that I would have to build out of wood (no problem skill wise) and the finished product no matter how beautifully it was built and how famous the designer is would not be worth even the cost of the materials and may only be saleable at a fraction of the cost of materials. But I still may do it. Atkin's Dancing Feather design looks to be close with a different cabin layout. It's designed for the speed range that I want. There other designs out there that would also probably work well.
I looked at tom Lathrop's blue jacket boats and they are too small. I also don't want to go that fast. Beautiful boats though. 8 to 10 knots is just fine and in my primary cruising grounds of the Sea of Cortez, you can't even go that fast when a norther is blowing and you are bashing into the 3' to 6' square chop that passes as waves. Imagine the wind chop on a lake and then increase the size to 6'.
I like what Tad has to say and some of his designs, but a custom design is out of my budget.
Well keep up the good work and I look forward to your furture posts.
Chuck

[marshmat]

Well, we had the towing rig and model out on the lake today for some preliminary testing. And it works!

Around the dock, the 3-point harness is a bit of a handful to control. Once there's a bit of drag on the model it works beautifully. We ended up cleating off the bow line and hand-holding the side lines; this enabled the person up front to not only steer the model but also to try inducing directional instability. Took a bit to get used to, but it is working quite well. The towing rig, of course, need