lamination shear strength

[powerabout]

Does anyone know where I can find the shear strength of a solid lamination re pulling bolts through it in shear.
I would prefer not to include data for kevlar and carbon so woven biax etc

[TollyWally]

I see from your various posts it looks like you are puzzling over how big a load through bolts can handle before ripping through a hull skin. Perhaps rigging loads etc.

Just thinking out loud, perhaps you could laminate a chunk of metal within your laminate schedule. A strap captured within then drilled along with the usual precautions might take a pretty big load.

[powerabout]

TW
I will repair my boat with the same stuff as it was when new as they dont have a problem. ( it rotted)
My interest is how did the designers come up with the ubiquitious chain plate that any structual engineer would tell you is very poor design.
The boat structual designers must have also known how much strength they expected in the plywood which not being a homogonous material would vary tremendously.
Or are they relying on the lamination?
The more I ask and the more there is silence is no surprise in the yacht industry (guesswork)

[PAR]

Your question seems simple enough, but there isn't a quick and easy answer for you. Calculating panel, laminate, scantling or hard point loading can get quite involved. What boat do you have (make, model, year)? This would go a long way toward helping address you concerns, as it's likely one of us will have scantling and other design information in a data base, possibly with other related information, such as common flaws, design alterations and corrections, model run changes to address issues, etc.

The questions you pose about sheer and pullout strength are covered in several engineering texts and is included in many software packages.

Engineers, NA's and designers make mistakes, just like everyone else, though lives can possibly be at stake, so careful checking and rechecking is usually preformed. When issues arise (they always do) then updates and alterations are incorporated into the spec's of a particular project. Plywood is a homogonous material as is cured resin. Plywood is also stronger then steel, pound for pound.

So, if you provided the boat type, it's likely we could tell you if it was an issue, what was done about it and how well these "fixes" addressed the problem.

[powerabout]

Par
it a J24

[TeddyDiver]

http://www.jboats.com/j24/j24dimensions.htm This one?

[Manie B]

Please post pics of the "rotted" area

i am very surprised at this thread - seeing that it is a J24 of all boats from a big builder

[powerabout]

Its made in the 80's and with slack production plenty of them from this era have rotted bulkheads and decks
Large fleet has nothing to do with quality build that is just marketing and almost every large fleet is the same.

[PAR]

Considering the large family and focus available for these boats, I'm surprised you haven't found a "group" that have addressed these issues before. I'm familiar with the issues and location you're having problems with, but most just reinforce the laminate, either with more plywood or other material, then increase the laminate schedule in the general area.

Delaminating bulkheads, rotten decks, pulled chain plates are typical, especially on a boat that likely had the first half of it's life strained hard on the race course. This is a pretty normal affair in a 20+ year old racer.

[mongo75]

In an attempt to keep it simple, why not just laminate the bigest piece of 1/4" aluminum you can fit under the bolt? Yeah that might be more than necessary, but it'll take any questions of structural integrity out of the loop.

[powerabout]

mongo75
yes that would work if the sheet of aluminium was also bolted to the bulkhead in enough places to exceed the chain plate holding force.

[PAR]

I don't understand the problem. Grind a healthy taper, use plywood (better bond then aluminum with epoxy) to span the void, well bedded in thickened epoxy (silica and milled fibers), then use multiple layers of biax to tie the repair into the surround area. The high modulus fabric and the epoxy will over come the short falls of the polyester resin and mat originally used. The area will be stronger and less prone to rot or moisture ingress.

[powerabout]

what I wanted to know was where do I find the data on a various solid laminations and their shear strength with various bolt sizes.
I have this data for plywood but not laminates.
Are all the boat builders just guessing when they design chain plates?

[fcfc]

what I wanted to know was where do I find the data on a various solid laminations and their shear strength with various bolt sizes.
I have this data for plywood but not laminates.
Are all the boat builders just guessing when they design chain plates?

You can find some data there : ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19880005638_1988005638.pdf

You can probably find standard values strength in compression, tension and shear for marine composite in ABS ORY.

You are probably right that before this publication, boat builders were just guessing. Most serious one were simply trying various bolting patterns and layup, and selected the one that did not fail. Without understanding why some failed, and others not.

The next step, now you have a way to transmit your force from metal chainplate to the entry point of a composite structure, is now to compute the strength of your composite structure up to the canceling force (probably ballast counteracting). This is also wild wild guess.

I fear only recently and only very big names rely on composite Finite Element Analysis to rationaly compute things.

[mongo75]

I looked through that document, and now the smoke alarms are going off, from the smoke coming out of my ears. uuuuhhhhh........ LOL

[powerabout]

We know they are all guessing as when a new system comes along like a canting keel they fall off..why coz all back yard engineering is guess work.

[powerabout]

Its all guess work coz when something new comes along like canting keels that all fail as its all guess work.
There are no standards because there has been no testing so....
standard operating procedure in the yacht industry..
sell your experiments to a sucker and then after you have done that enough times you will be the expert and several years on the lecture circuit universites will have a course and then finally some standard association will say 'we have the standards'

[PAR]

I just spent over 100 hours doing structural calculations for the schedules on a new yacht, so you can kiss my ass for it being guess work. The builders don't figure out the laminate schedule, though they often fool around with it, in ways they shouldn't, usually in an effort to save some materials or labor.

I've never seen such a clueless response "it's all guess work". Bite me.

When designing a cutting edge racer, all bets are off. The engineering team shaves all the weight off the boat with very small margins. Then the crews take them out, do crash jibes in 40 knot winds and wonder why their high tech rig is lying on the deck. Have you ever been on a big boat during race? Seen what kind of loads the crews and skippers impose, before relenting and tucking in a reef (even though they'd actually go faster).

Sure some real pieces of shit have been designed over the years, but the vast majority have been over engineered, not under (unless it's a British sports car). And yes, every damned boat ever built has or will have some design issue(s) that may need addressing.

But for you to whine and carry on about so generic an issue as the J-24's chain plates, a problem that has been addressed many times over, by nearly every older 24 owner I know is plan lazy.

Get a life, join a J-24 group and bitch about the under engineered (your guess work there) laminate schedule, to the people that have already fixed the problem and are used to the crying.

A friend of mine has an old J-24 and he's fixed his chain plates. He'll get another 20 years out of it if he's as hard on it as he is my boat.

Again, the laminate sheer strengths and other information you desire is easy to find, but you do have to be quite specific about what you want. For example, what resin system is used, the layup (assumed chemical bond), structural considerations: is the layup a flat plane, curved (compound or single axis) angled, radiused, does it have adjoining elements, etc., etc., etc. Without an understanding of the engineering involved, the information is useless. For example (again) if your resin is ortho, it's about 9,400 PSI in tensile and elongates about 1.8% before cracking, but what good is this information, especially if you don't know the modulus of the fabrics used. You could upgrade to iso and gain more elongation or vinylester (about 11,600 PSI and twice as much elongation as iso).

[powerabout]

Par
Nice to know someone is doing the right thing.
I sailed both kinds of boats, the ones where stuff failed and in the same conditions the ones that survived.
I guess their's my answer, some well engineered and some not.

I was not trying to re engineer my J I was just interested to know how designeers designed/calculated the construction required to keep the rig up.
I always wondered why the rig goes loose on the leward side when all mast builders say it should never happen and it doesn't on serious boats.

I just had an email exchange with Dave Gerr and he suggested that there is much better designs than a piece of stainless strip with bolts all in the same plane as per his lecture notes from Westlawn.
He suggested a reading list which I am working through.

I do think the newer design (last 10-15 years )of making the rigging pickup point on the deck to hull join much better as there are no bolts and stainless strip/fllatbar inside..and no wood.

( My J also has a main bulkhead thinner than the current spec! I dont know if the spec has ever been upgraded but it is now 3/4 ply. Mine has had repairs before possibly if it was 3/4 it might not of ever needed a repair but the are so many variables they must of been built with a lot of margin.)

Re swinging keel, there was a long thread on Sailing Anarchy when a few fell off and designers posting what the specs should be if you use ABS standards ( not knocking them in isolation) which are clearly inadequate.
The question everyone is asking is how did they determine the specification as where did they get the forces the bulb will be subjected to?
I'd like to know when they sailed a boat fully canted off a big wave and the boat dropped into the trough then the hull resists with a few 'G' and that chunk of lead is out on an arm at maximum leverage?
I wonder if the ones that have had no problems were over engineered or just carefully built to spec?

Re Race boats, what happens in the future when a boat designed to one job is sold on and becomes a recreational punters race boat who may or may not know what it was designed for?
How does the industry limit is liability on this issue?
There are more and more EX race boats out there now and some of the issues are just coming to the surface.
1st gen TP 52's are safe offshore but the new ones no way, and they haven't been designed to either, we know that but what about the average punter in a few years time?
Will designers include a capability document with vessels i.e not for winds exceeding *** not for waves over *** size and speed etc?
I am scared to go down below on the new GP42's except when it at the dock, we know we will have a new one next year...what happens down the road when it no longer has a professional crew and budget and kept out of the water?
I feel the yacht industry has a few issues to cover as it plays in the high tech one make race today throw away tomorrow like race cars etc BUT know-one will buy a old F1 except to do what it was designed to do knowing the risks or the cars are scrapped.
This doesn't seem to happen in the yacht industry and the volume of one season race boats is increasing dramatically.
I would not want to be a designer or builder in the not to distant future as I can see some big court cases?

I would be interested in your view on ( old) race boats should that be your area?
Have you had had to look at a canter yet and were happy with the industry criteria?

Regards

Powerabout