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Old 18-11-2007, 02:59   #1
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Epoxy

Why are so few catamarans built with epoxy resin?

I'm no boat building expert, my only experience in composites is with sailboards. But that's a pretty demanding use and epoxy is the only game in town. Older poly construction was heavier and less durable, cracking easily under impact, less rigid, worse in every way.

Catamarans seem to have a lot of the same design constraints, where rigidity, toughness and weight are at a particularly great premium relative to monohulls. Furthermore being in the water 24/7 you have to worry about osmosis. Not to mention, in the middle of the Atlantic in a storm I'd like to know that my boat is built from the strongest materials available. Yet just a handful of series production catamarans being built with epoxy nowadays:

1) African Cats
2) Gunboat
3) Chris White Atlantic cats
4) ...any others?

Is this just a cost issue or is there some other advantage of polyester/vinylester resins? I can't imagine that the cost difference is such a big deal compared to the cost of fabrics and labor -- maybe a few grand in a half million dollar boat.

Martin
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Old 18-11-2007, 04:06   #2
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Originally Posted by Sparohok View Post
Why are so few catamarans built with epoxy resin?
You're right, it's a price issue. I've often wondered the same thing.
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Old 18-11-2007, 04:53   #3
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A hull built with epoxy resin could end up costing up to twice that of one built with polyester resin.
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Old 18-11-2007, 10:22   #4
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It is a cost issue, but it reflects the quality of most modern charter cats. Epoxy is FAR superior.
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Old 18-11-2007, 10:34   #5
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To give you the facts in actual pricing,
a normal grade polyester costs 2.00 euro per kilo or 3 usd per 2.2 lbs
a normal grade vinylester costs 3.50 per kilo or 5,25 usd per 2.2 LBS
The grade epoxy we use made by SP systems called Prime LV 20 costs 11.00 euro per kilo or 16 usd per 2.2 lbs over 5 fold , you are right it is better and stronger material and after postcuring it is is almost indestructable , no probklems with osmosis or water ingress launching an epoxy boat of 5 tons willl still weight 5 tons after a month while an polyester boat wil gain 200 kilo,s of moist in the same period , these are guestimates so do not pin me down on these figures
Greetings Gideon Goudsmit
builder of the African Cats
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Old 18-11-2007, 11:44   #6
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Interesting... I only know retail prices in the US but they are less extreme. From one retail supplier Polyester costs $122.15 / 5 gal, Vinylester costs $207.53 / 5 gal, and System 3 Epoxy costs $313.80 / 5 gal, less than 3x polyester and 1.5x vinylester. I guess the price difference is more pronounced when you buy it by the truck load.

Fiberglass Supply - Product Catalog

OK I'm going to back-of-the-envelope this. A properly made layup is about half resin by weight. Add in coring materials let's say 1/3 resin by weight. Let's say we're talking about a half million dollar catamaran that displaces 16,000 lbs. I'm guessing about 1/3 that weight is composites, hence 1777 lbs of resin. Round up to 2200 lbs for waste. Using fastcat's numbers that's $11,000 for resin in an epoxy boat, $5250 for resin in a vinylester boat, and $3000 for resin in a polyester boat. That's ignoring the fact that the epoxy boat can be built both lighter and stronger using less materials -- less resin, and less of those expensive fabrics. Even with the most fantastic markup that is still less money than some people pay for their nav station. Nowhere near twice as expensive -- that's ridiculous. It really seems penny-wise pound-foolish to do anything else. Yet a lot of supposedly performance offshore boats (*cough* Outremer) use vinylester. I really don't get it.

Martin
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Old 18-11-2007, 13:53   #7
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I thought epoxy (at least west systems stuff) gets kind of mushy around 130 degrees f. Not sure if that's even remotely the same thing you would build a boat with, but the rather low temperature that it gets kind of mushy is why I know a lot of shipwrights who swear by resorcinol.
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Old 18-11-2007, 20:09   #8
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I've also done the math and although my calculations came out somewhat higher than Sparahok, the idea is pretty much the same. On a 1/2 million dollar boat the difference is between $10,000 and $15,000. Who would argue that it's not worth the price? The boat would start life more rigid, and literally never wear out due to composite fatigue.

Like I said earlier in the thread, I've often wondered about this.
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Old 18-11-2007, 20:11   #9
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Get's kind of mushy? They use epoxies to hold jumbo jets together. They will experience higher temperatures than a boat is likely to. Around 130 f (under 55 c) might be a good post cure temp for epoxy but it isn't going to turn to mush.

The reasons builders use polyester are basically financial - it's cheaper than epoxy, and you can control the cure rate better - it suits production line methods better. The downsides are that it is weaker than epoxy, it is more prone to osmosis, and it will burn like a blast furnace given the chance.
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Old 18-11-2007, 22:04   #10
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If you can’t take the heat ...

Here is an artical about how much heat epoxy will take...........

http://www.epoxyworks.com/indexprojects.html

Goto: Epoxy Techniques & Materials and scroll down to "If you can't take the heat..."

as for the ratios...................

EPOXYWORKS
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Old 18-11-2007, 23:14   #11
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Epoxy resin can be found from 4.00 euro per KG up to 40 euro per KG , that is the aviation grade that will not even burn
In the example of sparohok for a 16000 lbs boat half that weight will be the hull deck , bulkheads and furniture in the boat or 8000 lbs 40 % of this will be the resin used or 3200 LBS + 20 % wastage , we in fact use 1600 kg plus 10 % wastage = 1760 x 2.2 = 3872 LBS , that is 29040 USD , had we used polyester the cost for this resin would have been 5280 usd , with using epoxy other high tech materials come around the corner like Kevlar/carbon/Basalt fibre and unfortunately these materials all cost much more than glass
if glass is 1 for arguments sake than basalt is 4 , kevlar is 11 and carbon is 22
or in USD
4 usd per kg for glass
16 usd per kg for basalt
44 usd for kevlar and
88 usd for carbon fibre
also in these materials there are different qualitys
for carbon the difference between 3 k and 24 k is almost double in price if one can get it it is not only expensive but also hard to get.
Using all these materials does not only increase the cost of the materials but the work is also more than using CSM ( chopped strand mat ) and hand lamination
we for instance resin infuse under vacuum every part of the boat built in composite material and the total time involved to built a FastCat 435 is around 12000
If we look at the old St Francis , the same size cat or the maxim 39 also abou the same size but both built in wet lay up and vacuum bagged , the maxim takes 4500 hours to build and the st francis around 6000 hours another time consumer is the spray painting we do instead of using gell coat , the complete cat is spray painted in 4 layers of Awl grip paint in order to save around 800 to 1000 kilo,s or 1700 to 2200 lbs.
It all costs but the result is a boat that weights half of what a comparable sized cat weights
11000 lbs for the FastCat 435 , ( our aim is 10000 ) Payload 12000
24000 for the Admiral 40 and Knysna 44 or Payload 3800
20000 for the Privilege 445 Payload 4000
23000 for the Catana 431 Payload 3600
26000 for the Broadbleu 435 Payload 4000
all according to CE A certification

About Mushy , that must have been a 1 euro per kilo type of epoxy and the mixture ratios where probably off
If epoxy is well mixed and post cured it is the hardest possible resin available , they make artificial tooths and limbs from epoxy
The Fokker 100 Aircraft is gleud together completely with epoxy gleu and the new 787 dream liner has a carbon epoxy fuselage and partial wing structure
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Old 18-11-2007, 23:33   #12
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Quote:
Originally Posted by delmarrey View Post
Here is an artical about how much heat epoxy will take...........

http://www.epoxyworks.com/indexprojects.html

Goto: Epoxy Techniques & Materials and scroll down to "If you can't take the heat..."

as for the ratios...................

EPOXYWORKS

After 3 hours at 200' C the epoxy was stronger than the timber substrate. Long way from going "kind of mushy" at 55' C....
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Old 18-11-2007, 23:44   #13
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We postcure the complete boat in a oven once all structural parts are in place for 8 hours at 80 degrees Centegrade
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Old 19-11-2007, 10:59   #14
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Prime LV 20 costs 16 usd per 2.2 lbs
well I guess that leaves hunters and catalinas for the rest of us
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Old 19-11-2007, 11:16   #15
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Not really ! there are a couple of high quality monohulls that can be build in epoxy optionally, one is Hanse boats in Germany and the other is Grand Soleil in Italy
they both offer a couple of yachts both in Polyester/Vinylester or optionally in Epoxy
and I believe there is also a American yacht builder building in Epoxy
The extra cost for the Hanse is around Euro 20.000 for the 40 ft version
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