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jaschrumpf 03-01-2009 04:06 PM

Glassing over old through hull openings
While surveying my boat's plumbing, I've found that there's one old unused through hull and one old unused depth finding sensor. (At least that's what it looks like, though I don't know why someone would go to the trouble of making a new hole instead of replacing the existing sensor.)

Anyway, what's the process for glassing in an old through hull? I've never done any glass work ever, but is this something that a glass kit you'd buy from West Marine could take care of? Do you fill the hole with some kind of hardening putty, then just glass over the bottom, sand and repaint?

Or is this something best left to a pro if you've never done it before? Considering you need that hole to stay filled, I'd think "pro" in my case, but I'm still curious.

scottyt 03-01-2009 04:16 PM

jas use the west system guide for this its perfect for what you want. if you want some help doing it i can come down and help ya.

yes you have the basic idea, grind it out to a 12 to one taper then fill in layers with glass, fill then smooth and paint

edit if you have access to the inside you can also do the repair from the inside to have less to paint, but then the water pressure is pushing the patch in, not onto the whole. the best is do a couple of layers inside and more out side to form a sandwich

Keldee 03-01-2009 04:27 PM

Also if you get Don Casey- This Old Boat-chapter 6 on fiberglassing it is very helpfull if you have no idea.As scottyt says the west system guide is very good. Make sure you use epoxy.

sailingfool 03-01-2009 04:33 PM

54 Attachment(s)
I think you have the right idea - this is the bottom of your boat, you can't afford a learning experience from making a mistake. Although the work is not technical or complicated, I'd have a pro do it. Find some other projects where you can learn how to use epoxy and fg where a mistake or two wouldn't carry such a downside.

scottyt 03-01-2009 05:37 PM

sailing fool you would have had a cow if you saw the side of my boat. at the water line it had a 10 by 18 inch area of the gelcoat scrubbed off. after grinding it back to good glass and further i had a 24 by 36 inch taper that was in the center 12 by 18 area was just the last layer of glass . i left the last layer to have something to lay the new glass on. the repair has held fine including when i had to beach the boat and it laid on that side on the repair.

its not hard to do, if you follow directions.

jas i even have some of the strong filler left to thicken the epoxy with, you wont need much, so let me know if you want to do the repair i can give some to you

Bene505 03-01-2009 06:50 PM

Is this true for large through-hulls too?

scottyt 03-01-2009 07:20 PM

bene this works for any hole. but if you go too big you need something to back it up to hold the cloth. a trick that works well is to lay some cloth on the hull right next to the hole on top of some saran wrap. when it gets like leather peel it off, mix a little more epoxy and spread it on the inside of hull around the hole, then put the leathery FG over the hole. work out the bulbs, and let it cure. this will give you a good back up for the repair. if the hole is say over 6 inches, just let the leathery piece cure till real stiff but still bendable. it should be flexible enough to match hull shape but be solid enough to hold its shape.

if the hole was over 6 inches i would feather out both sides first and use the leathery piece as the first layer on the inside.

Bene505 03-01-2009 07:27 PM

Thanks, I think my large through hulls are maybe 1 1/2 inches in size. This is a great thread. Thanks.

jaschrumpf 03-01-2009 09:04 PM

What's a "12 to one taper"? Does that mean if the hole is 1 1/2 in diameter you grind an area 18" in diameter? Sounds kinda big. Do you fill the hole through the hull with anything?

scottyt 03-01-2009 09:12 PM

nope it means 12 to one of the thickness of the hull, so a 1/4 inch thick hull would be 3 inches of taper past the edge of the hole

not being rude but go read west systems stuff i will edit with a link in a sec

edit link

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