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Old 19-11-2007, 13:09   #16
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My guess is that the reason most manufacturers don't use epoxy is that most buyers don't know any better. Anytime they can cut corners on cost they stand to make more money. Less experienced boat buyers do shop around for price but generally don't take into consideration hull material. Most just think a fiberglass hull is a fiberglass hull and there is no difference.

If I don't end up buying a cat with an epoxy hull it certainly will have an epoxy barrier coat below the waterline. Ideally though, I think the best hulls are epoxy minus the gelcoat and painted with an LPU like Awlgrip or Sterling.

I don't understand the use of gelcoat either. Is it really cheaper than spraying on an LPU? Gelcoat absorbs water, is heavier than an LPU, easily stains, cracks and oxidizes..is it really better?..or is it just cheaper? Again, the boat I buy will have a LPU spray job..even if it has to be sprayed over gel coat. Perhaps someone would like to speak up for gelcoat? I would like to know, and I am sure there are others who would like to know, it's advantages.
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Old 20-11-2007, 00:00   #17
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Hallo David

Yes Gellcoat is a lot cheaper first the material is lower in price , 3 Euro per kilo for a "good" quality gellcoat, than it is sprayed into the mould or rolled or brushed. a crew of 2 can do that in one day for a 40 ft Cat and after that you can start the laminating process.
With Awl Grip the cost is close to Euro 50 per liter and we give the boat 7 coats of spray paint and in between each layer it is sanded to make sure that it comes out shiny like a new mercedes. The labor involved is 5 x as much and the mould needs to be perfect we need no filler at all because epoxy does not shrink while both polyester and vinylester have a shinkage of 3 to 5 % and this shows on the hull so filler needs to be put on and then gellcoat again, If we went to gelcoat and flowcoat we could shave 30.000 euro of the cost on the 435 but we would also gain between 600 and 800 kilo in weight in our case the complete boat is spray painted in side and outside.
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Old 20-11-2007, 10:06   #18
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It's really an aside point, but I think the St Francis is around 7000 Kgs or 15200 lbs light ship displacement. At least according to Lavranos. Is the Knysna that much more?

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24000 for the Admiral 40 and Knysna 44 or Payload 3800
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Old 20-11-2007, 10:12   #19
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Perhaps someone would like to speak up for gelcoat?
small scratches and oxidation can be buffed out and then waxed. gelcoat is thicker than paint so you have more to work with.
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Old 20-11-2007, 10:13   #20
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gelcoat

I'm really speaking in ignorance, but isn't LPU softer than gelcoat? I'd thought that those who had awlgrip hulls were more vulnerable to scratches and that you could never use any polish or compound.

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My guess is that the reason most manufacturers don't use epoxy is that most buyers don't know any better. Anytime they can cut corners on cost they stand to make more money. Less experienced boat buyers do shop around for price but generally don't take into consideration hull material. Most just think a fiberglass hull is a fiberglass hull and there is no difference.

If I don't end up buying a cat with an epoxy hull it certainly will have an epoxy barrier coat below the waterline. Ideally though, I think the best hulls are epoxy minus the gelcoat and painted with an LPU like Awlgrip or Sterling.

I don't understand the use of gelcoat either. Is it really cheaper than spraying on an LPU? Gelcoat absorbs water, is heavier than an LPU, easily stains, cracks and oxidizes..is it really better?..or is it just cheaper? Again, the boat I buy will have a LPU spray job..even if it has to be sprayed over gel coat. Perhaps someone would like to speak up for gelcoat? I would like to know, and I am sure there are others who would like to know, it's advantages.
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Old 20-11-2007, 11:08   #21
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A St. Francis 43 first weighted around 7000 kilo,s when extended to 44 the weight went up than the roof was raised and some more upgrades where done all by Duncan Lethbridge an excellent and weight conscious Cat builder and than the moulds where sold to Knysna cats , the roof was raised once more a t bar was added and a few more things changed all adding weight It is my guestimate that the weight is well over 10000 kilos now or 22000 and that leaves no payload.
Awl Grip can be polished , is slightly flexible and last a very long time in a nice way
I once owned a Airplane , a Cessna 414 twin engine that was sprayed with awl grip when new 29 years ago , when I sold the plane 6 years ago and buffed and waxed it she was almost like new with 10000 flying hours and always outside in all wheather in the Netherlands I do not think there is a better cosmetic material available , it is also very expensive but also a weight saver.
A Awl grip painted cat of 5 years still looks like new after a polish while a gell coated boat only looks new the first year. and yes gell coat is a hell of a lot cheaper to purchase and apply !!!!
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Old 20-11-2007, 11:37   #22
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Just to belabor the point on awlgrip, I've read a couple things from owners of awlgrip boats and while we're talking about it....

1) While the color goes all the way through the material, awlgrip actually cures into multiple layers each with their own unique characteristics. The upper most layer is the hardest, most UV resistant portion of the paint layer and creates most of the sheen and moisture resistance. When that layer is gone there life of the Awlgrip job is greatly shortened. Using abrasive waxes or polishing compounds may temporarily return the shine to the damaged areas but they also shorten the lifespan of the finish by removing some of the surface layer

2) From a different owner one should use terry cloth over their fenders or better put their boats in slips where care is taken that they don't need fenders
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Old 20-11-2007, 12:45   #23
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Cook Composites and Polymers will raise its prices on gel coat and unsaturated polyester resin by 5 cents a pound, effective on all orders shipped on or after Dec. 17, 2007.

Hexion Specialty Chemicals is raising its prices for unsaturated polyester and vinylester resin. The price for products shipped on or after Dec. 15, 2007 will increase 4 cents a pound.
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Old 20-11-2007, 13:40   #24
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All materials that we built our boats with are going up in price like it is going out of style . just for the record Divinycell foam over the last 3 years has more than doubled in cost epoxy went from 5 euro per kg mixed to 11 in just 2 years and when talking about carbon fibre the sky is not even the limit 2004 20 euro per kilo now 85 euros per kilo.
And these product are mostly oil based copper went from 2000 usd per ton to 9000 usd in just 2 years ( we use coppercoat on the underwater ship.)
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Old 20-11-2007, 13:43   #25
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Regarding the Awl Grip we put on 7 layers of finish laquer and believe me it holds well a long time.
I own a St. Francis 48 build in 2003 , the gell coat only looked wel in the first year
there are small cracks all over the place and it has yellowed
This boat is just as old as our prototype of the FastCat 435 and this cat still looks like new once a year we polish the boat same as the st francis. both have been built with good quality materials the 435 in Awl grip and the St Francis in Gellcoat by Scott Bader.
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Old 20-11-2007, 15:45   #26
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pirate Epoxy is pretty toxic

Derek Kelsall reckons that 1/2 the people who use epoxy resin end up violently allergic to it. Vinylester resin was invented to be corrosion resistant, and it is stronger than polyester. It is used in the chemical industry to make pipes, etc. that must resist corrosive chemicals. Polyester, by the way, comes in two varieties, orthopthalic and isophthalic, with iso being stronger and more corrosion resistant, as well as more expensive. "For its more cost-sensitive J/145, the company used a carbon fiber product specially developed by Toray Carbon Fibers America (Flower Mound, Texas) to be compatible with vinyl ester resin. The use of vinyl ester brought the cost of the final laminate down vs. epoxy while reportedly maintaining 95 to 98 percent of the overall properties, says Johnstone." (-quote from Zoltek: Industry News :Carbon Fiber Manufacturer/Companies, Aerospace Composites, Carbon Fiber Uses and Applications, Carbon Fiber and Alternative Energy, Investing in Wind Power, Carbon Fiber, Alternative Energy ) My vote is for resin-infused vinylester and balsa core. Balsa is stronger and cheaper than foam. I am building a 65' cat with pre-coated balsa in the decks and topsides, but solid laminate under the waterline, all fabric to be quadraxial unidirectional e-glass, but with carbon fiber unidirectional in the crossbeams.
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Old 20-11-2007, 16:01   #27
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Quadraxial unidirectional?

Derak Kelsall must have been exaggerating a fair bit. I know probably a dozen people building epoxy boats and I know of only two with fairly mild reactions - one of them being myself.

I don't even think my reaction is allergic - I develop a cough when I am exposed to the fumes from the hardener - but that contains ammonia so it's hardly surprising. I wear a decent respirator now and have zero problems.

The other guy got a rash on his hands - but he had been largely ignoring advice to wear gloves - he does now and is fine.
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Old 20-11-2007, 16:15   #28
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Hazard Evaluation System and Information Service - EPOXY RESINS
Goto: Epoxy Resin Systems
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Old 20-11-2007, 16:35   #29
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Quadra-axial uni, meaning 4 layers of unidirectional glass, oriented at 0 degrees, +45 degrees, - 45 degrees, and 90 degrees, stitched together for quicker layout.
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Old 20-11-2007, 18:28   #30
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Yes, sorry I knew what you meant. We usually just call it quadraxial, or triaxial (warp or weft), biaxial, double-bias, or uni.

BTW welcome to the forum, do you have any pics of the project? Is it a Kelsall design? Are you building using the KSS method?
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