Question about Repairing Fiberglass Hull

[Dennis Marshall]

Hello, a friend of mine recently purchased a Larsen M16 one design scow. While beached, he discovered a hole in the hull. I am wondering if there is anyone here who can give us some advice on how to repair it, or point us in the direction of a good resource (book) that explains such things precisely and clearly.

Thanks,

Dennis

[Bruce Hooke]

Well, this is supposed to be a wooden boat forum but since a lot of stuff posted here has MUCH less to do with boats than this does I think there are some folks around here who can and will help you. Having done this sort of thing myself I tell you what I do:

The first big question is what size hole are we talking about? Repairing a hole that is, say, 2" in diameter or smaller, is fairly easy. As you get into larger holes then it gets somewhat harder because the curve of the hull needs to be recreated.

The basic methodology I use is to feather the edges of the hole to a knife edge. I like to do this mostly on the inside but some on the outside too to provide a key. For a 1/4" thick hull I would probably fair back 2" all around. An angle ginder with a course sanding disc is great for this step. Where lots of clothing to keep the glass off your skin. Then lay in fiberglass matt in fiberglass resin from both sides until you have built up to the hull surface on the outside and at least to the hull surface on the inside and usually somewhat beyond for extra strength. Once the resin sets you can sand the outside flush. This approach will work fine for a small hole below the waterline. For larger holes, or holes above the waterline where you need to restore the gelcoat as well, things get a bit more complecated so let us know if either of those situations apply.

[mmd]

Bruce is pretty much on the money. Standard ratio for feathering ground edges for same-strength repairs is 12:1; i.e., a 1/4" thk hull skin gets feathered out to 3 inches. Little bitty holes can be repaired with mat & resin, bigger than 1" diam (feathering spans 7 - 8 inches) you should include alternating layers of biaxial or triaxial cloth in the matrix.

[Dennis Marshall]

Bruce, it appears that the affected area is between 4-6" in diameter. Given what you have said about patching the hole, does the procedure change that much?

Dennis

[Cedarhill Boatworks]

I do it differently. I'm not saying my way is any better, just different.
Do all the grinding from the outside. Bring it to a knife edge. 2" sounds just right for a 1/4" hull. Clean the hull on the inside down to bare glass. Theres probably some funky white sprayed on stipple that is the industry norm, it will grind off fairly easily. Lay a fully saturated patch of chop over the hole from the inside. The patch should be slightly larger than the outside edge of the ground area. When the epoxy kicks and is still tacky lay a patch of cloth on the outside that is just about the same size as the hole. Squeegee as much of the resin out of the weave as you can, the strength comes from the glass not the goop. When this patch kicks but is still tacky cut a slightly larger peice and do the same thing. The idea is to fill the void with ever larger peices of cloth until you have overlapped the ground area and come slightly higher than the surrounding hull.
Let the whole thing cure and then grind it smooth and fair. Go over the whole thing with a thinned coat of resin and when it cures,wet or dry sand before prep.
Wear a respirator when you grind the glass,Like Bruce said lots of clothes. Ilike tyvek suits with a hood. Duct tape the cuffs over your gloves.

[AngWood]

First of all, I'm sorry to hear that your friend was beached. Were you able to drag him back to sea? ( smile.gif sorry, dangling modifiers just amuse me).

Second, how about covering the entire hull with a thin layer of wood? (in the interest of counterbalancing the unjust fiberglassing of thousands of wooden boats). ;)

Okay, okay. I'm a smart aleck.

[Donn]

I'd say with a 4-6" hole in the hull, he was lucky he was beached.

[Scott Rosen]

Cover the entire fiberglass hull with mold release wax. Then apply five layers of cedar veneers with epoxy, alternating the direction of the veneers, diagonal, fore and aft. Remove the fiberglass "plug" and, violla, you have a wooden boat.

[Memphis Mike]

Ignor that last comment. He's a smart
alec lawyer. Use mahogany instead
of cedar. You'll be much happier
with the results.

[Cedarhill Boatworks]

If you use Scott's method you can make lots and lots of wooden boats.

[Buddy Sharpton]

Go to the national chain boat supply store, WEST, BoatUS, or the like and get the Gougeon WEST booklet for $3 ( the one for repairing fiberglass boats, not the wooden boat repair one)and it will have words and pictures and info of what to buy for materials. You can do this job yourself, and well.

[Dennis Marshall]

Thanks to all, even the smart alecks, who have been kind enough to share there expertise and humor here. I've passed the comments along to my well holed and beached friend (that sounds quite obscene). After reading the comments, it makes me happy that I have a wooden boat

[Bruce Hooke]

The only issues that I think a 4-6" hole raises are:

1. You might need to put something over the outside of the hole while you are laying in the first layers of fiberglass from the inside so that the 'glass doesn't sag too much.

2. The same approach (of laying something over the hole on the outside to support the 'glass while the resin cures) might also help to cut down on the amount of grinding required to fair the outside of the hull after the 'glass work is done. Otherwise it might be harder to lay the glass in such that it is close to fair...