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Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

Epoxy or Polyester resin

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Tomas Kruska
Admiral

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Czech Republic
522 Posts

Initially Posted - 09/07/2010 : 06:59:55

Do you know if any of early C25s' were made from epoxy resin instead of polyester resin?

I think that back in the days (<1980) the epoxy resin was cheaper then today.

The epoxy resin has the advantage that its resistive to the osmosis.

10Q (this is from Malaysia collegue as they use this for Thank You

)

Dalpol Phobos 21, 2013, Sole Mio, hull #27, current adventures - We sail Phobos 21

PO of Catalina C25, 1978, High Anxiety, hull #701, SR, FK, L-dinette, inboard diesel Volvo Penta MD2010C w/saildrive - more info

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Steve Milby
Past Commodore

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USA
5851 Posts

Response Posted - 09/07/2010 : 07:54:56

As I understand it, in the past, most fiberglass boats were built of epoxy resin, but, in the early 1980's, for some reason, boat hulls began to develop osmotic blisters. This was not unique to one or two boat manufacturers, but was common to most builders. The problem continued until the late 1980s, when boat builders changed from epoxy resins to vinylester resins, which were found to be more resistant to moisture. In the meanwhile, the industry was able to develop barrier paints, which sealed the older hulls from moisture. If boats were ever commercially built of polyester resin, I'm not aware of it.

My 1981 C25 only had 1-2 tiny blisters during the 23 years that I owned it, and I only barrier-coated it about 2 years before I sold it. I wouldn't be afraid of an older, well-maintained boat, especially if it was barrier-coated. If it's 25-30 years old and still has a clean bottom, I wouldn't worry about it, unless it's a cored hull. So far as I know, Catalina didn't build any cored hulls.

Edited by - Steve Milby on 09/07/2010 08:43:33

Dave5041
Former Mainsheet Editor

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USA
3754 Posts

Response Posted - 09/07/2010 : 19:26:29

I don't think production boats were ever built with epoxy resins. Even through the seventies when I was building some one-off car parts, epoxy was much more expensive than polyester. I did several internet searches and could only find references to custom and custom racers being built up with epoxy currently and back to the early eighties. Vinylesters are generally only used on the outer skin of the laminate below the waterline because they are much more expensive than epoxies which are much more expensive than polyesters. Epoxy was used briefly during the osmotic blister period in that role on some high end brands, but development of the much effective vinylesters displaced it. Polyesters are an ongoing chemical science, and polyesters today are dramatically different and superior to those of a decade or two ago.

Edited by - Dave5041 on 09/07/2010 19:30:41

Stinkpotter
Master Marine Consultant

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Djibouti
9016 Posts

Response Posted - 09/07/2010 : 20:41:10

There are a few builders making hulls with epoxy on composite fibers like Kevlar and carbon--the new C&C models, for example. Epoxy provides greater strength with less weight at a higher cost. Most everything else used to be polyester and is now vinyl ester, which is supposed to make stiffer laminations than even epoxy. Epoxy is the least water-permeable--that's why it's used as a barrier coat--but the new vinyl esters are close enough to not be an issue. If the builder applies each lamination properly, with the correct timing, blisters and delamination are things of the past.

I doubt that there are any epoxy C-25s--I suspect they're mostly polyester, and maybe vinyl ester in the later years.

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Tomas Kruska
Admiral

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Czech Republic
522 Posts

Response Posted - 09/08/2010 : 00:27:56

I know about the boats that were made using epoxy resin till 1977 in Germany called Neptun like this one http://www.jachting104.cz/galerieNeptun/index.htm.
The hull and deck is to stiff you can screw the equipment just to the deck without nuts on the other side :)

Interesting fact about vinylester resin http://en.wikipedia.org/wiki/Vinyl_ester that its based on epoxy.

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Dave5041
Former Mainsheet Editor

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USA
3754 Posts

Response Posted - 09/08/2010 : 13:26:47

"Epoxy-based vinyl esters were invented by Interplastic Corporation thirty years ago and their remarkable corrosion resistance and physical properties make these resins hallmarks of today's resin industry.

How it Works
A marine vinylester decreases the amount of water getting into the laminate via osmotic pressure and it provides an inert barrier. <font color="blue">By laying down a skin coat of vinyl ester behind the gel coat</font id="blue">, or by completely replacing the regular resin used in the laminate with the Interplastic vinyl ester, the laminate is too corrosion resistant to be attacked."

This is the cost effective approach used in moderately priced production boats like ours. Epoxy may resist degradation by absorbed water, but vinyl esters are the best barriers. It wouldn't make sense to use an inferior product that costs twice as much as epoxy as a barrier. There is little doubt that in the total picture epoxy outperforms anything except possibly the very newest vinylesters

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