Repairing floor stringers

[seagull369]

Evening everyone. I just signed up to the site after reading some impressive posts here, and was hoping a few of you wouldnt mind taking the time to read about a problem I have of my own and some solutions I've thought up.

I've just finished ripping out the rotted floor/ wet foam/ and rotted stringers out a my 19' mid 80's Bayliner Cuddy. I plan on keeping this boat a long time so I'd like whatever I material I use to rebuild them to be as bulletproof as I can get them. FOr me, this pretty much excludes using wood of any kind, or foam core even.

Stringers:
There are channels (of sorts) left by the wood I've removed from the stringers. I thought about using a polyesther reinforced filler (bondo-glass or bondo-hair, for example) to fill them in and level off with the surrounding areas. The wood that was originally in there only measured about 3/4" X 3/4" in most sections, so the amount of filler I'd need isnt tremendous (they sell the stuff in gallon cans too). I tested out a cured piece of this stuff in the above dimensions and, though I found it to be pretty darn stiff, I don't know enough if I'm asking for trouble by using it. (I should mention there are 6 stringers althogether in the boat: 4 that ran the entire length and 2 shorter ones that run about half the length).

Floor supports:
As for the floor supports, I've thought of using cellular pvc trimboard. This stuff is similar to wood, very light and will not rot, but on the downside it's not meant to be load bearing. In an attempt to make it that way, I thought about encapsulating it in fiberglass material (cloth/ matt, roving or bi-ax) and resin (epoxy or polyesther). I've already tested a small piece of the pvc with a mixed batch of polyester resin and the pvc help up well. Another good thing about Cellular pvc is it can be screwed into just like plywood, so I could easily secure whatever floor that will go above it without too much of a concern. .

Floor:
As for the floor itself, I could use pvc again (I can get it in 4'X10'X3/8" sheets) and laminate it again with one of the cloths/ resins. Or,,,, I thought I could just skip the pvc and make it all fiberglass-- (throwing a plastic liner over a plywood template, then start laying on top, for example).

So that's about it. Does this all sound crazy or does it actually have a chance? I've tried to talk to some local marinas in the area about this (or even the standard way to make these repairs) and frankly no one really seems knowlegeable enough to tell me much of anything. I'd be eternally grateful as to any help you could provide.

Thanks for reading,.

[the1much]

first off,,, you dont want to fill your stringers with bondo.,,,wood or foam is BEST,,remember, even tho its a stringer, it still needs to FLEX. and it will or your boat will do it AROUND your stringer====not good.the "filler,,wood/foam" is there to fill the empty space and give a little rigidity,,but still flexible.
pvc stuff?,, couldnt tell ya nothing about it,,, sounds like plastic wood,,,,, which is useless when glassing. fiberglass wont stick to it,,,, ya i know you can get a piece of glass to KINDA stick to plastic,, but the very first flex of your boat will change your mind on that.
and theres NOTHING wrong with wood floors,, as long as you encapsulate them in resin (epoxy),, then glass over. and as long as you dont put no "sissy-momma" rug in it ,,hehe ;)

[mongo75]

Yeah what Jim said, minus the 50 commas LOL. I've rebuilt 3 boats and I'm never scared to use wood, because as long as it's properly encapsulated, it'll last a LONG time. On my last boat, a 25' 1974 Bayliner Saratoga Express, I had to rebuild the entire cockpit (about 7x8') and used plywood exclusively because never had any actual stringers, just a plywood grid from the factory??? But it worked great, and she held up fine (unintentionally) jumping 3-4 waves on the ocean. On my current boat, a 25' 1968 Luhrs (can you tell my buget by the year of my boat hehe) I ripped out the flimsy 3/4" ply stringers, and replaced them with 15' of double plied 3/4" ply held togetherwith epoxy and matt. I then tabbed that to the hull with 6" glass tape, and then covered the whole mess with roving on the sides, 6" tape over the top, and then finally one layer of 8oz cloth, and the damn things are SOLID. Good luck!

[seagull369]

Thanks guys for replying. Guess I was under the assumption that sturdier the stringers were, the better she'd hold up. Good to know that isnt always the case.

As far as the cellular PVC stuff I mentioned, yea, it is plastic but I did fing -glass adhesion to be pretty good, AS LONG as the stuff was seriously scuffed up prior (I used 60 grit on a belt sander). Whether it holds up under the rough and tumble of a marine environment is certainly something to think about and I'll definitely be testing it out more rigourously before I decide to go with it.

One other material I found online (on this site and elsewhere) is this Nida-Core stuff. I'm sure most of you have heard of it. Supposedly good for stringers, floor and bulkheads as long as it's glassed up properly. I'm still gathering info. on it if it'll meet my needs, tho. An interesting idea concerning the stringers was to use regular old PVC plumbing pipe in there- specifically cutting the pipe in half lengthwise, throwing one of the halves in the stringer channel halfmoon side down, then glassing over with fiberglass.

I know some of you are probably thinking all these 'alternatives' are the wrong way to go about this (and I hate to sound like a sourpuss by passing it up), but I've just had my fill of dealing with wood and the rot that always seems to come with it.

[the1much]

the ONLY way for wood to get wet in a stringer,, is if you didnt glass right ;)

[BHOFM]

Forget the PVC stuff, it is for plumbing, not serious boat
repair. Even scuffed, when it moves the glass will release
after a time.

Keeping the inside clean and dry as possible will be the
trick to make sure your repair lasts a long time!

Is it a trailer or slip kept boat?

[seagull369]

Hi, I keep the boat on a trailer.

[the1much]

ya if the stuff is plastic it will never bond right,, it flex's at a different # of force and BEFORE the glass will. ( dont ask how i know ;) ) it will feel like it does,,but,, take a 2x2 sheet of that stuff and a 2x2 sheet of glass, overlap say 6" , when you resin,, resin the whole piece of glass. after its cured, put 1 end of the plastic in a vise,,now grab the other end of the glass, and bend. WEAR GLASSES.. there is NO application that i have ever heard of that will bond glass to plastic. ( talking bout that, i owe 1 of my old bosses a plastic "coleman" canoe,,,WOW what a ride down those rapids hehe :D )

[PAR]

Yep, everyone's right on the bondo or other type of surfacing filler in the stringers. Replace with a structural element, such as closed cell, high density foam, good wood, honeycomb core, or other "core" material.

As you mentioned in your original posting, those PVC planks are not load bearing and there's a reason why. They break, deflect dramatically under load, can't even support their own weight in longer lengths and generally are unsuitable for structural pieces.

PVC will shed anything other then PVC that's been "welded" to it. It doesn't like paint, chemicals, heat, cold, UV, all of the common adhesives, is brittle, doesn't hold fasteners and the list is extensive.

[naturewaterboy]

You may want to see if Bayliner will tell you if the wood is even necessary. I cut open the stringers on my Silverton and went spent a lot of time and money before I thought to email Silverton. They emailed back that the wood was totally unnecessary to replace. It was only used as a form to lay the glass up on.

[the1much]

You may want to see if Bayliner will tell you if the wood is even necessary. I cut open the stringers on my Silverton and went spent a lot of time and money before I thought to email Silverton. They emailed back that the wood was totally unnecessary to replace. It was only used as a form to lay the glass up on.

their FULL of sh!t ,,,, and dont ask bayliner nothing,,, they cant even build a boat right,, why would someone ask their opinion?

[missinginaction]

Naturewaterboy is right. You don't have to take a manufacturers word for it, read Dave Gerrs book "The Elements of Boat Strength".

I just posted a couple of photos in the post right before this one "bulkhead connection - cored construction". FWIW, you can see what I did there. I'm doing my first restoration, but I did my homework before I started. I don't pretend to know nearly as much as some of the pro's here. That said, the stringers that I made up are extremely strong due to the fiberglass, not the foam core. The core of a stringer that is covered in a properly thick fiberglass laminate (there are formulas in Mr. Gerrs book that will show you how thick your laminate should be for various engine sizes) carries NONE of the loads. As Mr. Gerr states in his book, you could (and some manufacturers have) laid up stringers over foam cores and then dissolved the foam leaving a hollow core. The fiberglass does all the load carrying. That is why it's so important to learn how to laminate properly and radius your corners to spread loads, etc...

Regards,

MIA

[the1much]

Naturewaterboy is right. You don't have to take a manufacturers word for it, read Dave Gerrs book "The Elements of Boat Strength".

I just posted a couple of photos in the post right before this one "bulkhead connection - cored construction". FWIW, you can see what I did there. I'm doing my first restoration, but I did my homework before I started. I don't pretend to know nearly as much as some of the pro's here. That said, the stringers that I made up are extremely strong due to the fiberglass, not the foam core. The core of a stringer that is covered in a properly thick fiberglass laminate (there are formulas in Mr. Gerrs book that will show you how thick your laminate should be for various engine sizes) carries NONE of the loads. As Mr. Gerr states in his book, you could (and some manufacturers have) laid up stringers over foam cores and then dissolved the foam leaving a hollow core. The fiberglass does all the load carrying. That is why it's so important to learn how to laminate properly and radius your corners to spread loads, etc...

Regards,

MIA

ANYONE that says its o.k. to dissolve the foam inside a stringer should be shot!
O.k. regulars,,,,,here comes the soda can!!!
take a freakin soda can, empty it,,,,now step on the damned thing,, what happens????? now take an empty can, fill it with sand, all tha way,,,,now step onit,,,what happened????
a hollow stringer is like having a freakin boat made of paper! end of story!

[missinginaction]

Shooting someone seems a little extreme don't you think? (I couldn't resist)

If the soda can analogy is true........consider this.....

How can the wing of a 747 hold up hundreds of tons?

FWIW, Gerr didn't recommend dissolving the stringer cores, he just mentioned that it had been done. He didn't recommend it because if the stringer developed a pin hole (in the laminate) water would enter and you'd end up with long water tanks in the bottom of your boat. This could cause problems, especially in cold climates. Should the water freeze and expand....well, it wouldn't be good. Nevertheless the skin carries the load.

Now where's my flack vest?

MIA

[the1much]

even SUGGESTING it is a "shootable" offense. and i know people that have built boats that floated for about a month,,,so if they did it should i put it in my book? people have done ALOT of things,,, doesnt mean its right. and how does that wing stay up? IT HAS "STUDS" IN IT,,,IE: SOLID STRINGERS.and a wing of a plane doesnt keep the plane together like stringers do in a boat.
what about your motor mounts to that hallow stringer?,, that should last about a week.
and theres way bigger problems with hallow stringers then it becoming a water tank.
:D;)

[Butch .H]

Have you seen the componants that are used for a 747 wing:D

[BHOFM]

How can the wing of a 747 hold up hundreds of tons?

Because the wing is full of structure! Ribs and spars!

[naturewaterboy]

Jim,
A soda can is pretty damn thin... especially these days! I remember, back in the day, when Coors were the only thin cans - all other cans were way heavier. Nowadays I had to change my exercise routine - 12 oz. curls - have do do more reps now... :D

I did put plywood back in my stringers, not for bending loads, but for just what you mentioned - if you want to bolt something to the stringer, like an engine maybe, it needs to be filled - and not with some whimpy foam.

[the1much]

i got some old STEEL beer cans,,,,talk bout a work out hehe :D;)
and its all common sense,, if the wood or foam was just for something to "lay up" on,, then they could just make a mold of a stringer, lay that up,, take from mold and stick it in the boat,,,,,but NOBODY does that,,,wonder why? ;)

[seagull369]

Thank you everyone for keeping this thread alive. Every post gets me 1 step closer to getting this project headed in the right direction (beer cans included :cool: ).

Just to clarify, the cellular pvc trimboard I've been talking about for the floor is somewhat of a different animal than the pvc like in plastic pipes and fences that some of you might have in mind. AZEK a popular brand of the stuff. It doesnt crack (at least under normal temps) but rather sags, much like TREX can when not supported underneath in sufficient intervals. I don't dismiss, however, what you've all said about glass not adhering to it well and frankly, considering the $115 cost of a sheet of 4'X8', I doubt I'll be taking the risk to find out.

I noticed PAR saying honeycomb (such as nidacore, I'm assuming?) or other "core" material would be sufficent to use in the stringer channels there. If I dont end up using honeycomb, do you think the pvc plumbing pipe idea I mentioned earlier would make a decent core material? The other posts that suggested I could use foam (covered in bi-ax) and/or it's the -glass on top of the core that really does the work, make me think the pipe would be all right. In case you're wondering, I compared an equivalent size piece (both that would fit in my boat's stringer channel) of PVC to one made of wood- which was originally in my boat- and did find PVC (schedule 40) to be limp-ier/ not as rigid as the other, esp. in longer sections. ABS pipe has also crossed my mind.

Sorry I keep picking your brains on this stuff, but your answers really are helping me tremendously.

[the1much]

whatever you use as your stringer "core" the glass NEEDS to bond to it,, or you'll have air pockets, even using wood you should scratch up the wood, and radius all your corners,, inside corners, and outside ones,, just so you dont get those air pockets. plastic has alot of uses on a bot, like,,,ummmm,,,,,, cup holders, and,,,,ummmm,,,,,ya SOME uses,,,none of them structural. IMO

[PAR]

The whole point is a that a core needs to withstand compression loads, some flexural loading and to be a successful core material it has to remain attached to the laminate.

I was speaking about the cellular PVC, now being marketed as "wood replacement" material for a number of tasks, mostly decking and siding on houses. It's very intolerant of heat or cold, becoming brittle or deforming, plus all the other stuff I mentioned.

ABS, the more rigid PVC's, HDPE, UHDPE and most of the "new" plastics can satisfy some of the core material requirements, but not all. If it can do all of the job it's asked, it will fail.

It's your call . . .

[mongo75]

I would use nothing but wood (for the costs alone) but fom "does" work seeing as how alot of the big boys use the stuff. As far as using half a piece of pvc tube for a FORM, I've seen it done alot of small pieces like hatches, to support the underneath. I would suppose the same could hold true for adding strength to a hull, however I would never use it as a replacement for a true stringer.

I'm getting a chair and popcorn for the rest of this forum LOL

[seagull369]

Ahh, ok, it's the bonding part that's important... I understand. As far as wood, will the glass adhere well enough to a pressure treated type in the stringer or would it be best to use non-PT?

[mongo75]

I'd use non-pt. IIRC, isn't PT wood infused withsome kinda chemical as well? I'd just use good old plywood (or solid timber if you're just making engine beds) and coat it with epoxy so it soaks in good, then glass it over and be done.

[the1much]

theres no sense in using marine grade,, just plain ole ply., it will (SHOULD) be totally encapsulated in glass so there should be NO need for anything "better"

[PAR]

Marine grades of lumber are constructed better, have more veneer layers, fewer if any voids, far fewer defects and are reliably stronger. Construction grades are cheaper, but you don't know what you've got inside (if anything), they're weaker, don't bend well, can fail suddenly if stressed, etc.

In a perfect world, you could coat anything with epoxy and it should keep out the wet stuff. In reality, the epoxy will get chipped, banged, gashed or other wise breached, which will let in the moisture. Knowing this it's usually cheaper in the picture, to install the good stuff, so in the event of a coating failure or breach, the wood can tolerate extended periods getting wet, without issue, before proper repairs can be made.

In the 17' daysailor I'm just finishing up, I used nothing but 1088 Okoume. It cost about 60% more then cheaper 6566 meranti, but the hull is 20% lighter and measurably stronger as a result. This means when I met another boat of similar configuration, they kick it's butt.