Epoxy vs Vinyl vs Polly

[RichardM]

I am boat shopping and I'm fairly new to boating and I'm confused by the different types of resins and methods being employed. Everyone seems to agree vacuum bag wet-out and epoxy resin apears to be the superior method of hull construction. Lighter, stronger, more stiff, better bonding, lower water transmitence and overall most cost effective.
If it were simply a matter of economics, i.e. epoxy cost more than vinyl and vilyl more than polly I could understand why manufacturers choose different methods, but I am finding sport fish boats fabricated with epoxy construction competitively priced to their polly and vinyl counterparts.
Am I missing something? Why don't all builders use epoxy?

[gonzo]

Polyester resin costs about 1/4 of epoxy. It is also easier to use. It wets faster and the mix ratio is not as critical. For medium performance applications, where minimum weight is not necessary, epoxy is a waste. On the other hand, the cost of the hull is maybe 10% of the total boat. That means that using epoxy increases the total cost by 15-20%.

[Deering]

Epoxy is clearly superior in most respects. If I could buy the same boat, for the same price, in either epoxy or polyester, epoxy wins hands down, regardless of the usage. Different boats, different prices... now you need to consider other factors as well.

Did that help? No? Sorry... welcome to boating.

[John ilett]

Poly or Viynelester boats can all use gelcoats to get the nice durable and glossy moulded finish whereas epoxy gelcoats do not really exist. For a moulded epoxy hull a poly gel can be applied with extra tie coats or needs to be painted which is not so durable.

[RichardM]

Thanks John. I thought urethanes were taking the place of gelcoats o0n epoxy hulls.

[Raggi_Thor]

I think polyurethan paints can last as long as polyester gelcoat and look better without any waxing.

[John ilett]

Gelcoats may need polishing in the longer term but are harder, thicker and more durable (abrasion durability) than paints. Your paints are generally thin and when scratched will cut through to your undercoat or primer to often show another colour. Sure paints look good when new but but may look pretty average 5 years down the track. I feel when restoring older boats the gelcoat finish should be kept and maintained as long as possible.

[JR-Shine]

I think polyurethan paints can last as long as polyester gelcoat and look better without any waxing.


I second this opinion - Gel coats may be harder, but they are also much more brittle - they crack. paint will not crack as easy.

Unless you need it to build something in a mold - I cant think of any other application where I would prefer it over paint.

[John ilett]

The gel only cracks where a laminate is too flexible, usually solid laminate boats without sandwich construction.

[JR-Shine]

Please explain cracks in gelcoat around mounted hardware (hinges, bowrails, consoles, etc....)

[John ilett]

These are points where the laminate is flexed I imagine.

[JR-Shine]

I disagree, the gelcoat can crack due to its being brittle alone - the laminate under it does not need to move.

You are right also, it the laminate moves - then the gelcoat will most likely crack.

[yokebutt]

But, but, but, John, how can that be, all the old salts I've talked to insist that solid laminates are much stronger....

Yoke.

[John ilett]

A solid laminate boat is more robust and fail safe like, but that does not stop them flexing. The laminate will flex (not fail) and the gel coat being brittle cracks.

Sandwich boats are typically much thicker/stiffer and do not flex.

[FAST FRED]

"all the old salts I've talked to insist that solid laminates are much stronger..."

What has fooled the "old salts" is that at high load spots the solid laminate is usually stiffer than cored material with poor (quick) construction for the high load.

Cracks in gelcoat at stress points is a SURE sign of broken laminate and the need for a robust repair..

Most glass is strong enough , but getting it stiff enough to not come unglued over the years is always the hard design part.

Basically if its stiff enough to never flex , it may weigh a bit more , but will last almost forever.

The old glass boats , that were built to what would be insane scantlings today , dont flex and will live till sunk, or burned.

FAST FRED

[zerogara]

A solid laminate at stress points may flex and not fail, go through elastic deformation and return to its original form. It's gel coat may crack through this transition or a repetition.
A sandwich will most likely not flex if it is built sufficiently but when it does it will most likely fail (it is less elastic) and delaminate. Usually between the FRP layer and core, or if bonded really well the core itself might fail. At that point you may be screwed and not even know it until a winch or a shroud plate comes off with part of the deck or hull. I had seen a really well made trimaran loose its whole roof of sandwich together with the 10' traveler in a strong gust.
Not a pretty picture of that "convertible".

A boat/hull that doesn't flex is over designed or under utilized. If you don't hear squicky noises inside a sailboat you are not pushing it hard enough. When you do it is flexing! Why is wiring and tubing through a boat installed properly to be loose and allow movement and prevent chaffe from that movement?

:idea:

[Robjl]

RichardM,
Polyester is the oldest... cheapest...has poorest adhesion to other materials, even to itself when cured...it is not suitable to use with modern stiched fabrics that enable thinner (lighter) construction unless chopped strand matt (CSM) is laid between the layers of fabric and that defeats the purpose a bit. And most important, polyester laminates absorb water!!!
Epoxy is the most expensive...but less is used if stiched fabrics are used (no CSM needed) Excellent adhesion to itself and other materials...doesn't absorb water. Also has higher strength.
Vinyl-ester is somewhere in the middle.
So... if you are trying to compare apples to oranges it won't work.
An epoxy boat is likely more expensive but the hull should be either lighter or stronger or both. And of course osmosis is not the problem it is in poly laminates.
I only regard the osmosis as a problem if the boat is permanently in the water. If you are looking at trailer boats it's not an issue.

Cheers
Rob