what makes you think it's not epoxy? West system has been around since the early 70's, and if it's a custom boat it was probably built in a small shop that favored the less-toxic nature of epoxy over the polyesters and vinylesters that were available at the time.
First and foremost, s&g plywood is an excellent construction system. boats that DO come apart all suffer the same ailment... delamination of the plys. wether or not this happens depends entirely upon the quality of the plywood and the adhesive used to manufacture it. the seams are generally the strongest part of the boat.
short answer: yes, plywood can rot in salt or fresh water, but delamination is the greater evil.
saltwater won't rot wood? well, not exactly. constantly-soaked wood generally won't rot (reason why 100yr old wooden boats exist) but wood that cycles between wet and dry (salt or freshwater is irrelevant) WILL rot. in the case of your boat, however, this is moot, because it's a composite construction. once the wood gets wet, it expands and the 'glass skin delaminates and you've got a real mess because the rot spreads dramatically and the structure has been weakened.
most boatbuilders have a love/hate relationship with 3M 5200. does it seal today's leak? you betcha. does it make life HELL the next time you need to work on that piece? YOU BETCHA!!!. Yes, properly bedding deck hardware is important, but when it comes to sealing fastener penetrations, reliance upon 5200 is somewhat irresponsible. when bedded with 5200, by the time you see water insude the cabin it's too late. it's already soaked into the plywood core. ALL hull and deck penetrations should be sealed by precoating the exposed edgegrain with epoxy. This way when the bedding compound fails and you see water inside the cabin, you have a much better chance of catching the leak before it soaks the plywood core. Besides... critical deck hardware should be unbedded every 5 years or so anyway just to check for cracks or corrosion. 5 years is well within the service life of the less intense bedding compounds.
as a sidenote.... if this guy is bedding things with 5200 and STILL getting regular leaks, he's doing something very very wrong.
yeah, okay, the 5200 thing a pet peeve. sue me. It sounds like the sellor was pretty passionate about his upkeep, if somewhat misguided.
1983 40' custom tri..... who's the designer? Marples? she's 20 years old, how's the rig? how's the engine?
