Deck Rot but boat has NO STRINGERS? I searched!

[jrotten]

I have an 80 Monark trihull that has a rotted deck. I took the rotted deck out and it resembled mulch and good topsoil. The boat has NO stringers and the fiberglass of the hull is very thin. The original floor system was very rotten, and it was comprised of small pieces of rectangular wood that formed the "bottom" of the boat and that was overlaid with a pretty thin layer of chopped strand to keep it waterproof and then carpet. When I took the stuff up it came out in sections of small wood blocks with what appeared to be a burlap type backing. I have it down to bare fiberglass hull now.

Now I have to give the boat some strength, either by glassing/epoxying in non PT exterior plywood directly in contact with the paper thin thin fiberglass hull, or glassing in non PT exterior plywood and adding stringers. I'm pretty confused as to where the hull strength for this boat came from to begin with. Does the boat even need stringers if it was designed without them? Is the hull designed to flex? Confused.

Thanks! John

 

[Cadwelder]

Re: Deck Rot but boat has NO STRINGERS? I searched!

Sounds like a balsa core construction, got any pictures?

 

[ajgraz]

Re: Deck Rot but boat has NO STRINGERS? I searched!

Was there foam? What held up the deck?

Might this be someone else's crappo deck replacement job? Do you see any evidence of the previous existence of stringers?

 

[jrotten]

Re: Deck Rot but boat has NO STRINGERS? I searched!

After a little more reading regarding the balsa core construction as suggested above I believe that's what it used to have. I tried to replace this deck in the late 90's with 2 layers of 1/4" AC overlaid with poly resin. I did not encase the 1/4" just tried to seal it using resin but no cloth. I must have missed a leak somewhere because once it came into contact with water it delaminated after 3 years. So the pics attached are what I have now - bare glass hull. I read a lot last night and even watched some good vids on youtube on stringer replacement. I am thinking about adding glass to give the hull some added thickness, (4) dimensional lumber stringers bedded to the hull and encased, poured foam in between, and a 3/4" treated plywood deck on top. This is a fishing boat and looks are not nearly as important to me as safety, function and ultimate cost.

Some may suggest 3/4" encased plywood for the deck, but I am a bit leary of that notion since I have already tried 2 layers of bonded 1/4" and it failed. Not sure if stringers would have prevented that failure or not. Any input is greatly appreciated - don't want to do this a 3rd time lol.

 

[oops!]

Re: Deck Rot but boat has NO STRINGERS? I searched!

the reason that the deck most likely rotted was because the foam was saturated.

you say you have the boat down to the bare hull?....

please post pics of the structure.

cheers
oops

 

[jrotten]

Re: Deck Rot but boat has NO STRINGERS? I searched!

Well I am finally working on this project some more after LOTS of reading on this and other forums. My hull was in fact a balsa parquette hull before it turned to mush. Since the boat has no stringers and adding some would make a shallow boat impractical, I have been thinking about using something like Divinycell between layers of CSM and Biax mat and preserving the basic construction type but using modern and non-rotting materials. I am not sure if this technique would be stiff and strong enough though. The hull on this boat is SCARY thin, like 1/8" of chopper gun mat. I am definitely going to add thickness and strength by laminating in alternating CSM and Biax layers before I install any kind of core be it Nidacore or balsa or even 1/2" marine plywood. I probably have to use unwaxed poly resin due to cost constraints. Thoughts? Has anybody used Nidacore for a laminate hull? Would I be better off just thickening the hull and adding stringers and filling foam in between the stringers?

 

[jbcurt00]

Re: Deck Rot but boat has NO STRINGERS? I searched!

You say you have the boat down to the bare hull?....please post pics of the structure.
cheers. oops

You'd get better response, from iboat members w/ more experience (enough to be of great assistance, Yacht Dr,oops, WoodOnGlass and others) if you'll post some pix of what you are working w/ now, the bare hull, and possibly pix that don't go a tad blurry when enlarged. Designing a new deck system &/or strengthening the existing thin hull, adding (or not) expanding flotation foam & stringers, are all important to maintaining the structural integrity of your boat and it's handling characteristics.

Use photobucket account & you can post pix directly into your threads text & description of the pix:

You'll want to upload pix to your photobucket acct, and look for the IMG code tag under each pix. It looks like this:
{IMG]http://i1246.photobucket.com/albums/%20people%20boats%20or%20pix%20info/twiggy.jpg[/IMG}

Just highlight & copy that text & paste it into your thread...

Makes it easier to follow, and advise you when you don't have to bounce back & forth between small attachment pix

 

[jrotten]

Re: Deck Rot but boat has NO STRINGERS? I searched!

 

[jrotten]

Re: Deck Rot but boat has NO STRINGERS? I searched!

 

[jrotten]

Re: Deck Rot but boat has NO STRINGERS? I searched!

 

[jrotten]

Re: Deck Rot but boat has NO STRINGERS? I searched!

Hopefully these pics can be seen better. Any input is greatly appreciated?

 

[jbcurt00]

Re: Deck Rot but boat has NO STRINGERS? I searched!

Now your cooking w/ gas. This 1's a great shot. Even cell pix can be pretty good. You might try to re-shoot those 1st 2pix you just posted, they lose a lot of detail in the blur.

Hopefully, you'll get some experienced glass gurus thru here now that they have some details

 

[Coho Ghost]

Re: Deck Rot but boat has NO STRINGERS? I searched!

jr,

If you use divinycell foam I think you will have to use epoxy resin not poly. I think poly eats up divinycell foam. Some of the experts correct me here if this info is incorrect.

FWIW
Coho Ghost

 

[jbcurt00]

Re: Deck Rot but boat has NO STRINGERS? I searched!

Hopefully these pics can be seen better. Any input is greatly appreciated?

If you read thru some of the glass resto threads, you'll get an idea of who's on iboats regularly, well experienced & most importantly helpful... If you can reshoot those 1st 2pix, if you don't get a response in the next 12-24hrs you can just type a quick reply that says "Bump"- That way your thread goes back to the top of the threads list in the Resto forum. Of course, it's July & boating season, so many of the resto's have been splashed & people are out using their boats. And those that do lots of glass work can make extra $ by getting repairs done quickly so the damaged boats owner can get their's back in the water. It may take longer then usual to get some helpful insight & assistance.....

 

[Scott Danforth]

Re: Deck Rot but boat has NO STRINGERS? I searched!

hard to tell from the photos, is the the bottom of the hull, or is that simply the underside of the sole?

 

[jrotten]

Re: Deck Rot but boat has NO STRINGERS? I searched!

Scott,

Thanks for replying! That first pic is the actual bottom of the hull near the transom. It was a balsa core hull from the factory. The balsa turned to mulch. I'd rather not put rot prone balsa back in, hence my inquiry about Divinycell. Would the same construction principal work though? ie, glass-Divinycell-glass?

 

[Scott Danforth]

Re: Deck Rot but boat has NO STRINGERS? I searched!

if the balsa turned to mulch, there was a leak for a really long time. many boats are balsa cored. end grained balsa is extremely strong, even when wet. It lasted 32 years.

if you put balsa back in, seal up the leaks, it would last another 32 years.

I can not comment on Divinycell as I have no working knowledge.

 

[Georgesalmon]

Re: Deck Rot but boat has NO STRINGERS? I searched!

Divinycell will work with polyester, as will other PVC cores. Kinda expensive though and comes in many different densities. The original balsa was something like 8 lbs/sq/foot density. Give or take because its not manufactured and GOD grew it in a tree. You almost need to vacuum bag the foam or use a resin infusion process to get a good bond with PVC foams. If you use enough layers of fiberglass to get the same stiffness in the hull you will be way to heavy. The original reason for the balsa was to get stiffness without the weight.

IMHO This a is a difficult fix and will require some fiberglass layers and maybe something like a low beer crate stringer arrangement, and some higher density flotation foam to boot.

 

[jrotten]

Re: Deck Rot but boat has NO STRINGERS? I searched!

I found sheet balsa at Eastern Burlap & Trading, Inc. for $33 per 2'X4'X 3/4" sheet so I think that will be the way to go as long as I am certain that I nailed all the leaks when I add my extra glass. I also found Contourcore at Defender.com for $60 per 2'X4'X3/4". I believe that the Contourcore is much more like the rotten parquettes that I removed, lotsa little rectangles held together with a fiberglass skrim as opposed to a 2X4 sheet. Contourcore is supposedly "chemically enhanced and pre-coated, and pre-wetting is not required". If the Contourcore does not require pre-wetting then the greater cost is not even a consideration because I will use less resin. I gotta use unwaxed poly resin though or vinylester though, I cannot afford epoxy unfortunately.

I am leaning toward adding a low 1708 reinforced marine plywood beer crate stringer system or a 1708 reinforced foam stringer system to supplement it though since delamination is a big concern. I gotta hand lay this stuff. The choice of stingers is a whole another topic of course but the foam stuff looks pretty neat. Only problem is foam stringers would not tab into the transom, just bond to the hull.

So I am thinkin', add 1/8"+/- CSM/Biax/CSM glass to the bare hull for strength and leak repair, 4 low prefab foam stingers, Contourcore between the new stringers, and top coat the whole thing with more CSM/Biax/CSM to knit it all together.

Thoughts?

 

[Georgesalmon]

Re: Deck Rot but boat has NO STRINGERS? I searched!

You got the right idea. Just make sure that you bed the balsa into a couple of resin rich layers of 1 1/2oz CSM. Use one layer of the CSM you were putting over the 1708 for this plus another one if you do it that way. Roll the balsa down with a roller and nice even pressure, don't push on with your hands to much on small spots. Let it cure, than a CSM and 1708 over the top. Cores are supposed to be in the center of the laminate. Same thickness of skin on both sides. Your not building a rocket ship though so it doesn't have to be perfect. If it were me I would just put two layers of 1 1/2oz mat down on the hull just as it is (skip the 1708 under the balsa)and bed the balsa. Then CSM and 1708 over the top and call it a day. Don't know why you keep wishing for epoxy, I don't know any boat builders making new boats out of epoxy. Even the ones using vinylester are only doing a skin coat below the water line for blister resistance. Some are even using DCPD poly's for print through protection and that is really crap (very low elongation). If you do it right with polyester it will certainly last longer that you will.