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Old 30-04-2009, 10:59   #1
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Question Fillling in holes in hull,

What is the best way to remove a thru hull and ensure a good repair on a fiberglass boat?
I have 13 Thru hulls, and would like to reduce that number.

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Old 30-04-2009, 16:21   #2
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West system guide is available at most chandleries or see here: WEST SYSTEM | Projects | Fiberglass Boat Repair & Restoration - Repairing machined holes in fiberglass
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Old 30-04-2009, 16:30   #3
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It is said that you want at least 3 times the hole size tapered with a grinder around the hole. The outside would be the most important as the water pressure is "in". So for a 1" hole grind a tapered circle maybe 3" all the way around. Fill the hole with epoxy saturated disc's of fibreglass graduating from 1" to the maximum size. Ditto on the inside, albeit it is less important to go so big on the grinding. Once hardened, grind the outside off flush. fair and coat. I did this on my 44 footer, what with all the odd ball fittings I had to make into manifolds etc in order to use less throughhulls, as well as the extra length of hoses running everywhere, I was then worried about the weight of all that bronze hanging on the remaining seacocks when I was done, Frankly, unless you have shorts runs, lots of room and a good plan..... I dont think it was worth it....
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Old 30-04-2009, 16:37   #4
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I filled a few holes from unwanted thru-hulls on Insatiable. The hull is solid fibreglass / kevlar about 20mm thick. I ground out a bowl shaped recess about 150mm diameter both inside and outside. The "bowl" was only 1-2mm deep at the edge and about 5-6 deep in the middle. I made a plug to fit into the hole (marine ply, coated with 3-4 coats of timber preserver, then laid glass / resin both inside and out. The point of having a tpered bowl recess is that you can cut circular pieces of glass mat of increasing diameter. We used about 4 laters of glass each one larger than the last, with the last one being the diameter of the outside of the recess.

when the glass/resin was nice and hard, we sanded it back smooth. On the inboard side we laid flowcoat straight over the top. On the ouside we laid a screed of filler over the area, and indeed over a bigger area and sanded / faired it back to smooth before painting.

Whether the above method is strictly the professional way to do it; I don't know, but it worked fine for us.
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Old 01-05-2009, 04:22   #5
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It is said that you want at least 3 times the hole size tapered with a grinder around the hole....
I think that the laminate thickness (not hole diameter) determines the amount of bevel, according to the ratio 12:1.
Accordingly, a hole through a 1" thick laminate will be bevelled out (tapered) 12" beyond the circumference of the original hole.
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Old 01-05-2009, 15:36   #6
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What is the best way to remove a thru hull and ensure a good repair on a fiberglass boat?
Solid or cored?
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Old 02-05-2009, 00:37   #7
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It is said that you want at least 3 times the hole size tapered with a grinder around the hole. The outside would be the most important as the water pressure is "in". So for a 1" hole grind a tapered circle maybe 3" all the way around. Fill the hole with epoxy saturated disc's of fibreglass graduating from 1" to the maximum size. Ditto on the inside, albeit it is less important to go so big on the grinding. Once hardened, grind the outside off flush. fair and coat. I did this on my 44 footer, what with all the odd ball fittings I had to make into manifolds etc in order to use less throughhulls, as well as the extra length of hoses running everywhere, I was then worried about the weight of all that bronze hanging on the remaining seacocks when I was done, Frankly, unless you have shorts runs, lots of room and a good plan..... I dont think it was worth it....
This is the way I do mine too. It seems every boat I have bought except this latest one had waaaaay too many thru-hulls. One thing I will add to your good description Cheech is to use X-Mat cloth. It is one of the strongest for weight and quick build up.
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Old 02-05-2009, 07:13   #8
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Thanks all for your reply s.
I understand now what to do.
I think I can get rid of 4 Thru hulls. Now if I can just get my boat out of the #$@&^%$# damn marina where they won't let me on it cause its a "contractor only" yard and into the do it yourself yard a 25 miles north... I will be happy.
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Old 02-05-2009, 07:40   #9
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I was told that when filling in the ground out 12:1 area, the LARGEST piece of cloth should be placed first, followed by the smaller. Reason is you will have a much larger surface area bond, compared to just the edges of each sequentially larger patch. BTW, Gord is right...@12:1 your cone is gonna be close to 12" for a 1" thick hull, 6" for a 1/2" er.
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Old 02-05-2009, 11:31   #10
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Hate to be a stickler about this subject but I feel doing 12:1 when using epoxy is ridiculous. 4:1 at the most.
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