hole repair, HELP!

[Troy Scott]

Folks,

I'm eliminating a seacock. This leaves a nice round two inch hole in my boat. I have done a lot of fiberglass work. But I thought I would check out Don Casey's advice before tending to this "repair". Don wrote that I need a 15 to one scarf. The hull is about 7/16" thick in this area, so a 15 to one scarf would be 6.56" long! This means that I would need a repair extending 6.56 inches from the edge of the 2" hole. The resulting circle would be 15 1/8" in diameter! This seems really ridiculous to me. I can't imagine that I really need to grind this large an area to repair a 2" diameter hole. Not only would this be a HUGE job, imagine the fairing work to get this area back to the nice shape it has now. Thoughts?

I think I have a more reasonable plan: I would clean/sand/grind the inside of the hull around the hole. I would prepare a 6" diameter round "patch" for the inside, using the same manufactured fiberglass material I've been using for through-hull backing plates. I would clean/sand/grind the surface of this patch. I would use West epoxy to prime the roughed-up surfaces of the hull and the patch. While this is still wet I would mix some milled fiber into the remaining wet epoxy in the pot, and use that as a bonding and sealing agent to install the patch over the inside of the 2" hole. My experience tell me that, once cured, the only way this patch would ever come off is with a chisel or a grinder. Now that the hole is sealed, I would grind out some of the original fiberglass around the hole to create what would look like a "countersunk" area six inches in diameter. Then I would put back enough layers of fiberglass and mat to fill the "countersink". I would then sand the area to match the original contours, and paint it. I would end up with a solid glass area (thicker than the original by the thickness of the backing plate material) that I believe would be as good as new with a lot less work, and I would be disturbing far less of the original (perfectly good) structure. THOUGHTS?

[Duncan]

The 6 inch diameter "countersink" you propose would only give you a 2:1 scarf, and this is much less than I've seen recommended anywhere. I'd do it the way the experts recommend.

[Troy Scott]

Duncan,

I'm confused. A two inch wide scarf in 7/16" thick material would provide a 4.57 to one scarf. A 7/8" wide scarf would be a 2 to one scarf in 7/16" material.

Duncan and all,

I'm not trying to do something cheap or easy or to just "get by". I'm just thinking that if a fifteen to one scarf is appropriate when the repaired area will end up the same thickness as it was originally, then a smaller scarf would be reasonable if a substantial fiberglass backing plate is permanently bonded inside the hull.

More thoughts, please?

[Duncan]

Hi Troy
I think your calculation is correct, i.e width/depth=scarf ratio. Maybe I should call it a "bevel", which would be the more usual term when talking about holes?

When I said 2:1, I was comparing the 6" width of the proposed bevel to the 2" hole, but I was (incorrectly) ignoring the scarf depth, as you say.

Since every "how-to" I recall is similar to the one Don Casey recommends, I'd say you're likely to be safer doing it that way. It is a proven method for repairing fiberglass hulls, and it integrates the repair with the surrounding area.

On the other hand, what you propose is probably just as strong as the seacock installation you removed, so maybe it would work out fine. I'd just be conservative, since the recommended way seems to have stood the test of time, and you don't have to worry about some factor that may have been overlooked.

[winthrop fisher]

for what its worth,

i would cut a fiber glass cloth 4"x4" put west on it and put it on the inside of the boat first,

then go on the outside and fill it in at least an two inchs outside of the hole, let it dry over night,

then the next day sand and put gelcoat over it and your done.

its so easy, it will be like steal later....

i have done little jobs like that for at twenty five plus and never had any thing go wrong...
winthrop

[SurryMark]

I did this to fill a 1 1/4" hole on the bottom of an old runabout, in about 1988. The bottom was about 1/2" thick.

Carved out a bevel, about like a countersink, on the outside.
Put two layers of roving, about 6"x6", on the inside.
Drilled a hole through the roving in the center of the original 1" hole, and put in a 3/8" coarse-thread screw, as a mechanical fastener.
Put a few more layers of glass on the inside.
Filled the hole from the outside with resin and glass fibers.
Covered with gelcoat (I think) and smoothed.

It was not a kosher fix, but it is still going after 20 years of pounding and runs up on the beach. I'd do it more by the book on the Cape Dory.

[SPIBob]

Troy,

As I recall, Casey recommends the 12 to 1 bevel grind on the INSIDE of the hull. This leaves only the original sized hole, 2" for you, to fair on the outside.

Bob

[S/V Necessity]

The reason for a long shallow scarf joint is not just strength of the initial bond. It's so that over the long run of things moving and flexing, that you don't get a stress riser.

[ocean31]

All of my boats (except for the current one) have always been wreck/insurance jobs. Looking at the previous posts and thinking about what always has worked for me, I find my repairs are kinda a middle ground.

On removing and filling a thru hull. What has worked for me is:
1. Always use epoxy, They say epoxy has 5 times the adhesive qualitys over polyester resin. I do know I have never had a epoxy repair fail
2. I bevel out (scarf) on both sides always. It is a matter of spreading the stress in the cloth over all larger area.
3. Majority of the times my bevel inside the hull is larger then the outside of the hull.
4. I do a large bevel but do not worry about the ratio. More often then not, there is a bulkhead or other item in the way when beveling the inside of the hull
5. On a thruhull I do not belive I have ever beveled out greater then a 6 diameter. Just seemed a 6 inch wide bevel is large enough.
6. You have to be careful with mat, some of the older styles did not set right with epoxy resin
7. If you take you time, you should not have a problem keeping the hull shape. What I have done is bevel the outside slightly, put a couple layers on the outside then bevel the inside,building the greater thickness of the patch from the outside inward
8. Remember, any grinding on the inside always creates a mess.

Anyway, just my thoughts, one thing I have always liked about fiberglass; Don't like how it come out, just grind it back again.

JSB

[CruiseAlong]

On my CD26 I had a dry filament of wroving which caused wicking into the boat at the turn of the hull to keel location (bottom of companion way stair). The hull there is 3/8" thick and the "dry" area (no resin) was about the diameter of a finger which was removed for rebuilding. I scarfed a bevel on the outside of the hull which extended ~6-7" outside of the hole, with an intent of 12 to 1 bevel/hull thickness ratio. The CD factory used 18 oz wroving and 1 oz mat in a total of 7 layers. Using a cardboard sheet on the inside of the boat to match the hull shape I layed up and duplicated their layup with alternate layers of wroving and mat using WEST Expoxy Resin for the repair. You can normally handle a few layers at a time without too much heat build up. For my build up it took 9 total layers. The layup pieces overlapped the piece below it (~1 inch all the way around). Then fair the outside (more tough with epoxy..I know) and then the inside if the surface is exposed to normal viewing (like mine was). If the repair area is below the water line, you may or may not elect to gel coat. Since this was a Do It Your Self job for me I recieved a lot of questions and looks from other boat owners as the work progressed. I can tell you the repair looked excellent, not noticeable, and has lasted over 7 years so far. I stress the use of the epoxy resin for repair.....
Dana

[SurryMark]

Everybody knows that epoxy is better than polyester for lot of things, but here is a warning. I had to abandon a wrecked but pretty little Signet 20 because layers of old patches, put on by a previous owner, were coming off. The yard said there were two causes. One was that patches had been put over gel coat, without grinding to bare glass. The other was that epoxy had been used in places, and the polyester resin would not adhere to it, over the long term. Maybe a more knowledgeable workman can comment on this.

[Matt Cawthorne]

Troy,
Do 1/2 of the patch on the inside and 1/2 on the outside. 7/16*1/2=7/32. 15*7/32= less than 3.3 inches so the repair is closer to 8 inches in diameter.

Matt

[Maine Sail]

West System calls for a 12:1 bevel repair based on the thickness of the laminate not the hole diameter. Preferable the repair would be beveled on both teh interior and exterior

For a 7/16" thick laminate you'll need a total bevel of 5.25" from the edge of the hole. It is best to lay the largest circular patch in the hole first then laminate the increasingly smaller circles on top of the first largest patch as this gives the strongest secondary bond to the bevel..

[Maine Sail]

The other was that epoxy had been used in places, and the polyester resin would not adhere to it, over the long term. Maybe a more knowledgeable workman can comment on this.

Mark this yard is clearly "in the darK' on this one. ALL bonds to cured polyester resinated laminates are SECONDARY bonds meaning no chemical cross linking has occurred.

Polyester resins have VERY, VERY low secondary (glue) bonds and can range from well under 100 PSI to the 300-375 PSI MAX range if PERFECTLY prepped. Vinylester resins have a max secondary bond strength (glue bonds) of about 500 PSI. By the way 5200 bonds to fiberglass at well over 500 PSI more than polyester resin when used as a secondary bond.

Most epoxies have a secondary bond strength to polyester resinated laminates of between 1500 PSI on the very low end to over 2000 PSI!

There is no stronger secondary bonding resin than epoxy. My guess is that the person doing the work never properly de-waxed or prepped the surface and used polyester NOT epoxy..

[Steve Laume]

It is best to lay the largest circular patch in the hole first then laminate the increasingly smaller circles on top of the first largest patch as this gives the strongest secondary bond to the bevel..

It is counter intuitive to lay the largest piece of fabric on first. In some of my first messing about with fiberglass on canoes and kayaks I would fill in with the small pieces and build up the largest on the outside. One of the problems with this approach is that you will cut through the fibers of the largest layer when you sand to fair the area.

In a description I read some where the author suggested making up the entire stack of glass laminate off of the boat on a bench. You could then lay a piece of wax paper over it and press the whole thing into place. A piece of aluminium flashing duct taped to the curve of the hull over the patch would go a long way towards establishing the shape.

A vacuum bag would be the bomb for this application, Steve.