Steve Sanford
Well-known member
Good morning, Josh~
I don't want to hijack this thread, but thought I'd respond to your concern about plywood and rot.
Boats like Devlins are fundamentally different from "traditional" plywood vessels. Devlin's (and many others') employ the methodology known a epoxy encapsulation - or Wood Epoxy Saturation Technique - hence the W.E.S.T. system developed by the Gougeon Brothers. It relies on encapsulating all surfaces of the wood to preclude entry of moisture into the wood. This is fundamentally different from traditional plank-on-frame boat building where the wood of the hull is intended to become swollen with water during the boating season. Traditional plywood construction is somewhere in between. Although not requiring swelling to become watertight, the plywood is expected to get wet during use. The key is that it be allowed to dry out - and so prevent rot (so-called dry-rot requires sufficient moisture within the wood to support fungi and other decay microorganisms).
I have very little experience with the W.E.S.T. or encapsulation building methods - but remain a fan of plywood for many applications on boats. Instead of encapsulating it - i.e., maintaining a moisture-proof skin on all surfaces at all times - I try to apply a watertight skin on the outer surfaces only - usually in conjunction with 'glass to provide a tough physical barrier to abrasion and wear.
Most traditional plywood boats use/used Fir (typically Douglasfir - not a "true fir" technically speaking) in the laminations. Marine plywood is superior to exterior grade Fir plywood in that all of the laminations should be free of defects - each ply having defects replaced with the "footballs" so that there are no voids within the sheet of plywood - hence the higher cost. Fir is strong and naturally decay-resistant and has a long history in wooden boats.
Nevertheless, Fir is notoriously difficult to keep paint on. Its surface checks invite intrusion by moisture and so failure of paint. Thus, most plywood boats are skinned with resin + 'glass cloth. Epoxy resin is both inherently more "water-proof" in this regard - AND it adheres the cloth to the wood more strongly. Trouble begins, though, when the plywood is 'glassed on both sides. Unless that encapsulation is maintained perfectly, moisture/water that enters any break in the seal with stay in and migrate within the wood because it is trapped there. Rot will ensue. Most earlier 'glass hulls have been built with wood transoms and stringers that failed over time because the wood was encapsulated in 'glass and resin. The resin was typically polyester resin - which allows moisture to penetrate, even when intact. This is why most modern 'glass boats use structural foam and other plastic components for their framing and other reinforcements. - and not wood. (It's also why polyester resin is still the best resin to use for structures that are all-plastic.)
An approach that works is to skin only the outside with epoxy + 'glass cloth (or mat, etc). The interior surfaces can be painted or - better yet - treated with a wood preservative. For many decades, Cuprinol was the go-to choice. I still use such copper-based rot preventers on the interior surfaces of the hull. Depending upon its location, I might topcoat it with an oil-based paint. Such paints allow moisture to move through them and so do not trap moisture as completely as does epoxy resin.
All this is my long way of saying I would not 'glass (or seal with epoxy) the interior of a plywood boat UNLESS it were a true W.E.S.T. system vessel - like Devlin's boats. I would generally rely upon a combination of wood preservative, paint and the opportunity for air to circulate and dry the hull and any confined spaces within, especially when stored in the off-season.
So, don't give up on plywood boats altogether!
Hope this is helpful - and not too confusing....
SJS
I don't want to hijack this thread, but thought I'd respond to your concern about plywood and rot.
Boats like Devlins are fundamentally different from "traditional" plywood vessels. Devlin's (and many others') employ the methodology known a epoxy encapsulation - or Wood Epoxy Saturation Technique - hence the W.E.S.T. system developed by the Gougeon Brothers. It relies on encapsulating all surfaces of the wood to preclude entry of moisture into the wood. This is fundamentally different from traditional plank-on-frame boat building where the wood of the hull is intended to become swollen with water during the boating season. Traditional plywood construction is somewhere in between. Although not requiring swelling to become watertight, the plywood is expected to get wet during use. The key is that it be allowed to dry out - and so prevent rot (so-called dry-rot requires sufficient moisture within the wood to support fungi and other decay microorganisms).
I have very little experience with the W.E.S.T. or encapsulation building methods - but remain a fan of plywood for many applications on boats. Instead of encapsulating it - i.e., maintaining a moisture-proof skin on all surfaces at all times - I try to apply a watertight skin on the outer surfaces only - usually in conjunction with 'glass to provide a tough physical barrier to abrasion and wear.
Most traditional plywood boats use/used Fir (typically Douglasfir - not a "true fir" technically speaking) in the laminations. Marine plywood is superior to exterior grade Fir plywood in that all of the laminations should be free of defects - each ply having defects replaced with the "footballs" so that there are no voids within the sheet of plywood - hence the higher cost. Fir is strong and naturally decay-resistant and has a long history in wooden boats.
Nevertheless, Fir is notoriously difficult to keep paint on. Its surface checks invite intrusion by moisture and so failure of paint. Thus, most plywood boats are skinned with resin + 'glass cloth. Epoxy resin is both inherently more "water-proof" in this regard - AND it adheres the cloth to the wood more strongly. Trouble begins, though, when the plywood is 'glassed on both sides. Unless that encapsulation is maintained perfectly, moisture/water that enters any break in the seal with stay in and migrate within the wood because it is trapped there. Rot will ensue. Most earlier 'glass hulls have been built with wood transoms and stringers that failed over time because the wood was encapsulated in 'glass and resin. The resin was typically polyester resin - which allows moisture to penetrate, even when intact. This is why most modern 'glass boats use structural foam and other plastic components for their framing and other reinforcements. - and not wood. (It's also why polyester resin is still the best resin to use for structures that are all-plastic.)
An approach that works is to skin only the outside with epoxy + 'glass cloth (or mat, etc). The interior surfaces can be painted or - better yet - treated with a wood preservative. For many decades, Cuprinol was the go-to choice. I still use such copper-based rot preventers on the interior surfaces of the hull. Depending upon its location, I might topcoat it with an oil-based paint. Such paints allow moisture to move through them and so do not trap moisture as completely as does epoxy resin.
All this is my long way of saying I would not 'glass (or seal with epoxy) the interior of a plywood boat UNLESS it were a true W.E.S.T. system vessel - like Devlin's boats. I would generally rely upon a combination of wood preservative, paint and the opportunity for air to circulate and dry the hull and any confined spaces within, especially when stored in the off-season.
So, don't give up on plywood boats altogether!
Hope this is helpful - and not too confusing....
SJS
