Epoxy vs Polyester resin

[imported_Daniel]

I might be looking at a boat this weekend. The owner built it and it is mahogany ply over sawn LLYP frames. He seemed like a nice old fellow and has built a few boats in his time. I am not familiar at all with the polyester resin though. Is there anything specific I should look for regarding the polyester? Here is the copy for the ad:

Custom 20 Sedan Cruiser 1999
Mercury 135, 162 hours, two batteries. Sleeps two. Complete galley, electronic cooler, enclosed head, fitted cushions, generous storage, AM/FM radio, full instrumentation, basic running gear. Hull, mahogany plywood. All exterior fiberglassed. 2002 survey. Trailer bunk and roller, surge brakes, electric winch, spare tire.

Thanks all, I will post pics if I go down to see it. I must admit, I am excited!!

edited to add: The owner designed the boat himself, and he has been cruising Georgian Bay with it since he built it.

[ 04-22-2005, 07:57 PM: Message edited by: Daniel ]

[Tom Lathrop]

Daniel,

I do not see in the ad where the builder says that he used polyester resin for anything. It would make a determining difference in my opinion whether he used polyester or epoxy in sheathing the hull with fiberglass.

[imported_Daniel]

Tom, I spoke with him on the phone and he told me he used polyester resin for sheathing the hull with 6oz fiberglass. Is this a problem?

[ssor]

Polyester resin is more water permeable than is epoxy. But after six years if the wood hasn't let go of the glass it is probably well sealed. As added protection epoxy barrier coats are available but they are opaque.
Has this boat spent its summers in the water or has it been trailered?
162 Hrs on engine or the whole rig?

[Bob Smalser]

I've restored two 1960's-era plywood boats slathered with polyester inside and out. I don't think the "water absorption" property goes both ways like it does with epoxy...it absorbs water, all right, but it doesn't let it out.

The only problem I encountered was rot where Bondo was used as a filleting agent. That thick layer of polyester absorbed water and rotted the wood next to it, probably because the thick polyester paint applied on top of it didn't breath well.

Other than that it was a problem free, hard finish that's a pain in the butt to remove. I use epoxy primer and plain old alkyd oil paint atop it successfully.

[Frank Wentzel]

Daniel

My boat is polyester-fiberglassed plywood. It was built in 1968. By 1980 the glass deck and the plywood underneath were no longer a laminate but only "close together". The glass had not cracked, so there was no rot or water damage, but I was able to peel it off by hand in 18" wide strips. Needless to say the replacement glass was put on with epoxy. As has been said many times before; the only thing to which polyester will bond with certainty is uncured polyester. That is not to say that there are not polyester-glass-plywood hulls out there that have performed perfectly. It is just that there are many more boats in which the bond has failed or is about to fail. "You pays your nickel and you takes your chances."

Good luck

/// Frank ///

[imported_Daniel]

Thanks for the input folks. I think the 162 hrs is on the engine, but I am not 100% sure. I will find out if and when I go to see it. It is freezing rain here today, not good for driving.

[Tom Lathrop]

Others may have differing views and experience but I would not want a lot of money in a boat sheathed with polyester resin. I did use polyester resin and glass in the fifties but changed to epoxy when it became available for the reasons mentioned above.

[imported_Daniel]

Thanks for your replies. I wont be buying this boat, looks like I will still be building one though, hopefully next year...sigh. :(