boat rot...wet foam prevention.
Standard Poly resins used to construct most of the older boats has 2 major draw backs:
1, Poly resins will not prevent water entry in the long term, so the 20 year
re work will not away as long as this resin is in use.
2. Poly resin will not stick to timber in the long term, this allows some
movement and results in cracks that allow moisture into the timber and it
rots.
The other common problem is the type of foam used, many will take up moisture and retain it, when little or no air will flow through or around it, in some cases it turns into a wet pulp mess.
We need a well sealed timber cover that will not allow water to pass and will not crack when the hull is pounded or otherwise stressed; we also need a foam that will not allow moisture to enter it.
Leaking deck fixtures like seat stems and deck fixing screws also contribute to moisture entering the area below the deck.
If possible, foam should not be replaced as it causes or contributes to the problem, however this is not always possible due to structural and legal requirements; but if you can avoid it by some re engineering or design changes it can be an advantage.
Starting at deck level:
All ply decks should be treated with an epoxy resin to prevent moisture ingress.
The deck to gunwales joint should be a coving of Micro fibres and epoxy resin to provide a smooth rounded well sealed joint ready for glassing.
This means cutting and shaping then applying at least 3 layers of epoxy resin. The first coat can be thinned with 30% Methylated Spirits by volume to get better penetration, particularly around the edges and end grain areas.
All deck securing screws that pass through into timber stringers should be drilled out oversize and over depth, then filled with Micro-fibres and epoxy resin, then re drilled to screw shank size only and countersunk where possible.
Any bolt holes must be treated as above but the final drill out size will be the same as the thread size; this also applies to any transom fittings.
Stringers:
Should be stripped, a coving of Micro fibres placed at the base to provide a rounded gusset for the glass, then coated with epoxy resin and cloth (no CSM) and roving's added after each 2 to 3 layers of cloth. Finishing with a roving will ensure no strands of the cloth are close to exposure on the surface; when all glass has been placed, add at least 3 coats of resin, wet on tacky will avoid sanding between coats.
Drainage:
Limber holes should be located to ensure no water is trapped regardless of point of entry, this includes fore and aft as well as athwart (side to side) ship. so may have to drill the outer stringers, drill the holes oversize, cut a length of conduit or other tubing and fix in place with epoxy resin and Micro-fibres, this ensures water will not enter the timber via the limber holes.
Foam:
If foam must be installed, use a closed cell foam and save yourself any worry about ever having to do all this again. Closed cell foam can be applied in layers cut from sheets that come in a variety of thicknesses.
Each layer should be secured when placed to prevent any movement that may cause wear; Epoxy resin and Micro fibres form a very strong glue a daub about every 6 inches on a grid pattern should be ample, just keep it away from limber holes and build layer on layer till you reach the under deck level.
I hope you find this of some help.
Avagoodweekend......
(Ducks for cover)
