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Old 07-12-2008, 11:07   #1
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Hull fairing recommendations?

I just had OWTW's bottom soda blasted and I got a surprise. The bottom's nowhere near fair, thanks to a myriad of tiny pock marks (old, popped blisters, I assume) as well as at least a couple of patches in the hull. We've owned the boat for 15 years and done nothing to the bottom, save for repainting after hauling for the winter (done every two years). The previous owner had the bottom painted with Devoe Bar-Rust, a two-part epoxy used to coat bridges (and boat hulls). FWIW, Devoe is now part of Interlux.

Sooooo... the question is how best to fair the hull next spring. The original plan had been to put a couple of coats of epoxy sealer on the bottom but, after seeing the bottom with the old paint off, it's going to take a little more than that. Input and experiences with fairing the hull are welcome. BTW, OWTW has a full keel, with the prop in an aperture.
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Old 07-12-2008, 11:18   #2
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Well... you are in for a big job. I have seen lumpy bottoms before. Realistically, it wont make any diffence in your speed to speak of. You need a set of "boards". These are like long flexible sanding blocks that bend to the hull shape. It would be easier if there was some paint on the bottom. Normally you would sand the surface with the Boards, then you can see the scuffed up high spots and fill between using a lightweight filler and a long flexible piece to wipe in and approximate the surface as you fill in the low spots. Then board the surface again and repeat as many times as necessary. It is a big back breaking job best left to some athletic youngster with a lot of energy! Be sure to use lightweight /easily sanded filler or it will be very difficult. (you are going to epoxy after anyway right?) BTW, epoxy primer (like Interlux etc) will not provide the barrier coat like real epoxy resin will.
Maybe you should just hit the worst spots and leave it. Only the fish will care...
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Old 07-12-2008, 11:20   #3
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I think you will need a fairing board from Jamestown distributors.
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Old 07-12-2008, 13:15   #4
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Good point about fairing boards - I'd forgotten about them. My real challenge, though, is what to use for a filler. Trust me, the bottom is rough enough that this isn't just a matter of cosmetics. There's enough roughness to the bottom that fairing really is called for.
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Old 07-12-2008, 13:21   #5
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I used WEST system epoxie.
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Old 07-12-2008, 13:48   #6
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Particulars (e.g., micro-balloons, "cat hair", other stuff for bulk as well as making it sand-able)?
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Old 07-12-2008, 13:54   #7
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I've been mixing my own bog using a general purpose epoxy mixed with phenolic microspheres. Try not to aerate it when mixing, as that creates pinholes when sanding.

Don't use Q-cels below the waterline.

Sand using a longboard, which you can make yourself from 8mm ply, with a couple of doorknobs and some velcro glued on. Make it to fit the sandpaper you want to use. Longer is better, one pro boatbuilder I know has a board which needs 3 men to swing it.

Realistically, a board around 1 metre should be plenty for what you're doing. For more fiddly bits a single handed board around 300mm is good.
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Old 07-12-2008, 13:56   #8
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I used a lot of West 410. It has been 6.5 years and I have not had any problem with what I used. I wet out the hundreds of areas ,some very large then filled and faired. I was a little concerned that the 410 was to soft for some of the large areas that I had filled but it worked very very well and the 410 is the easiest to work with. It is a BIG BIG job to do.
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Old 07-12-2008, 14:02   #9
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Hi Rick,
The very first thing is to check your moisture content, it sounds like you will be hauled out for awhile...do not fill large voids or barrier coat a wet hull. I simply vote that whatever you do use epoxy and not polyester. Ensueing battle on the horizon, best of luck!
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Old 07-12-2008, 22:06   #10
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Any work is at least four months away. I'll probably suck it up and buy a moisture meter to keep an eye on changes.

The good news is that the bottom generally simple for much of the surface, save for the leading edge and bottom of the keel and a chine from the stem to the keel. Now to find two more willing souls to swing a 3m long board sander...
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Old 19-12-2008, 12:26   #11
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What is the difference between epoxy resin and fibre glass resin?
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Old 19-12-2008, 13:56   #12
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There are 3 resins commonly used in GRP (glass reinforced plastic) - epoxy, polyester and vinylester. Epoxy is considered to be the best, it's the most waterproof, usually stronger and has much stronger secondary bond strength. If you are trying to bond to existing cured GRP, especially if you're unsure what the existing resin is, epoxy is the best choice.

Of course it's also the most expensive.
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Old 19-12-2008, 14:45   #13
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Quote:
Originally Posted by perchance View Post
What is the difference between epoxy resin and fibre glass resin?
The quick and literal answer is epoxy resin is the stuff that can be squeezed between glass fibers (woven, loose, or chopped), the other is somewhat loose terminology. Past that, there's a world of technology wrapped up in the fine points of resin and glass.
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Old 24-12-2008, 02:30   #14
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I think I would use an epoxy fairing compound. Awlgrip makes one that as I remember was good. The number 545 seems to stick in my head. I use to make my own fairing boards with width strips(4"X48") of T-111 ply with the 4" spaced serrations and a holding block at each end. After the fairing is done, maybe use Interlux 2000 barrier coat.
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Old 24-12-2008, 05:33   #15
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I like the idea of using T1-11 strips and, in fact, have a bunch of it handy. Where does the sandpaper come from (kinda think West is a tad short on 48 x 4 in. paper of any grit) and how's it attached?
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