expandable foam drain??

Hey all. New here and I am in the process of rebuilding a small 12' power boat. I have found the stringers and all other wood in the boat to be rotten. I plan on filling the voids around the stringers below with flooring with 2 part expandable foam for flotation and maybe to add a little strength in the spans between the stringers. I know even closed cell foam over long periods of time can start to absorb water so my question is this........do I seal the hell out of the voids where the foam will be to keep water out or do i somehow make for a way that it can drain out if it gets wet. If I seal it and water does get in there then it will likely stay in there. If I leave a way for the foam to drain then water will be able to get to the foam through the drain. What to do? thanks in advance

 

After my first boat which was built with fibreglass covered wood I vowed never to use wood again. Instead I made beams from fibreglass using cigrette boxes, milk cartons... anything suitable.

My current boat I've used a closed cell foam that doesn't absorb water - not even in the long run. It's a polly foam, UV resist, rot resist and of course expensive. Unfortunately it's not available as a pour foam, I would have loved if they could fill the boat up and I just cut route mill the cavities I want out and glass the rest. You can have a look at www.sondor.co.za - I'm sure you should find a similar product. One of the first reasons for using this foam is flotation (SS Unsinkable ), it's easy to work with, cut saw mill route file sand, and you can even bend it into odd shapes if required. Stunning product.

One advantage you have now that you have to redo/replace the interior, you can organize it the way you like... I wouldn't attempt to salvage the old stuff, it won't last, add it to the compost heap.

 

I will be using either nidacore or coosa board to replace all wood so rot should no longer be a problem. I am also looking for the foam to serve as a little strength between the stringers and against the inside surface of the hull.

 

I have used a 20mm foam (sheets) and it is very strong with a couple of fibreglass layers. The fibreglass also bonds very well to the foam.

Once you've rid the rig from the wood and have your foam glassed in you'll have something that should last a lifetime if done well. It's a lot of work, but you have to start with the end in mind.

 

From sad experience if you use foam use it only where water cannot get under it ie SEAL it and everything around it. If it's applied to wood remember if the wood gets wet the water will move through the wood thence under the foam. Therefore you must seal everything else too.

I did about the same thing you propose thinking the foam would stick to the wood, which it did, but as above the wet wood wicked water under the foam. Had lots of rot (and old foam) to dig away, about half the keelson and lower centerbord well. It was a mess. Foam is OK for totally dry holes maybe but not for a wet sailboat.

For floataion I therefore prefer loose foam blocks.

 

the 2 part foam is said that if it gets wet it looses its floatation ability and needs to be replaced. and if you keep it off the hull by a little, and keep a place in the middle for drainage it should be o.k. .

 

Just a thought - everyone is talking fibreglass over wood, but are we talking EPOXY or Resin as the 'hard bits'

There is supposed to be a product called CPES ins the USA that can be applied to really rotten wood, and make it totally structurally sound and rot proof.
If the orginal fibreglass coating was plain GRP resin, that would cause a lot of problems. Using Resin with fibreglass after proper treatment would save a lot of heavy foam.

 

It seems you should treat your wood before you epoxy or glass it with the CPES. I've never used epoxy, only fibreglass.

If you use foam it has to be one that does not absorb water. Any foam that will absorb water will in time add a lot of weight which is not acceptable.

 

Yes, - fix the wood, then Epoxy over it.
Resin makes all the difference to wooden boats - it gets applied like GRP, but excludes water much better.
Foam is surprisingly heavy in small boats, especially expanding foam.

 

CPES is Epoxy

My understanding is that CPES is the same as the "clear" low viscosity epoxy hardners such as West 105/207.

Is there anyone with a background in chemistry that knows the difference? I've always used West System clear epoxy to seal wood with excellent results.

 

I bet it would be similar, but CPES seems to have made a speciality of it. I dont see West Systems advertising that they can stabilize even rotten wood like CPES do, or quote satisfied results.
Let me know about comparitive costs if you get that far. The West Systems only low viscosity hardner 207, costs more than the Epoxy itself in my part of the world.

 

100 years ago i helped my uncle do some major repairs to his wooden 65 novi. he fished for sardines, and we sprayed some (freaky) stuff in his holds and it was to stop the rotting and to keep it from starting again. i cant remember the name, or if i even knew it heh but if ya search for wooden boat dudes they prob know the stuff

 

CPES .vs. West

I've had great results with West 207 on teak, and teak & holly soles, it gives "the look" of depth/wetness that everyone strives for. It is not cheap relative to other epoxies, that's for sure. Does a great job of filling cracks, dings, scrapes, and other wear marks.

I've read that mixing in walnut shells makes it less slippery on floors, going to try that trick on the aft cabin floor next spring.

U.S. Composites sells a clear epoxy that I've never tried. Anyone have experience with it?

The only real fix for rotted wood is to replace it, so I've never tried CPES -- when I first started on the current project I tried all the fixes, injecting resin under the laminate, antifreeze, drill holes and put in git rot -- these approaches worked in a few places, mostly horizontal areas, in the walls they didn't work at all.