Fiberglass repair advice on keel box

[CaptnPorter]

Hi all, I’m planning on patching a relatively large perfectly round hole -6” diameter-in my keel trunk (swing keel boat) so the hole is near the water line but not on the hull.

The fiberglass in this area is relatively thin (5-6mm). The part I’m wondering about is that I have the cut out piece that was originally cut out (yes that means I’m the idiot who made the hole). So should I try and use that 6in cutout piece as a patch and just try and fill the crack? Or start completely from scratch with multiple layers of new fiberglass fabric across the whole 6in hole.

My gut says start from scratch…but going with my gut got me into this mess so I thought I’d see what people think.

Thanks!

 

[rgranger]

I am using voice texting so please excuse any typos.

You will need to fare the edges of the hole so that you have a surface for the new pieces to Matt too. You will want to tape a backing plate …a piece of hard plastic vellum is a good choice. The sheets of plastic that your teacher used to use for an overhead projector works very well and won’t stick to epoxy. You can still buy them at Staples.

use the original piece you cut out to trace (sharpie ) a circle onto a piece of flexible plastic sheeting. Then cut out circles A fiberglass cloth that are slightly larger than the trace …each circle being larger than the previous…. wet each one with resin and place on the piece of plastic until over the traced out circle until you have about six or seven pieces Of wet fiberglass cloth. squeegee out the excess resin. Then take the whole piece of plastic to your hole and tape it over the hole… smooth it out with the squeegee and let it sit until the resin sets.

 

[dlochner]

Check the West System website for their manual which will give detailed advice on how to do this repair.

Briefly, you should not use the old piece of fiberglass the joint will be too weak. If you have access to both sides of the hole, grind back an area that is 12 times half the thickness of the hull on both sides, so about 36 mm then build up successively larger pieces of fiberglass. If you only have access to one side of the hull it will be necessary to grind back the hull to 72 mm and lay up the patches. There is some debate about whether to start with the small pieces of fabric and then lay up successively larger one or start big and then go smaller. I'd follow West System's advice.

The reason for the scarf is to increase the surface area to improve adhesion and to avoid a hard spot around the patch.

Home | WEST SYSTEM Epoxy

The home of WEST SYSTEM marine-grade epoxy resins and hardeners for boat building, boat repair, home repair, and restoration.

www.westsystem.com

 

[CaptnPorter]

Thanks dlochner and rgranger!

That advice matches up with what I’ve seen - I had found west systems manual, but didn’t know if having that original piece changed anything - sounds like not! Thanks for the advice!

 

[rgranger]

but didn’t know if having that original piece changed anything -

The only significant difference between what I suggested and what West System describes is that I wet all of the 6 or 7 pieces at once onto a piece of plastic sheeting... stacking them all up. This saves a bunch of time.... Your original piece can still serve as a template to trace onto the plastic sheeting. I don't know where your hole is and if you have access to the back to set up a backing plate. If you don't here are some pics of a hole I fixed where I had to jerry rig the backing plate

The first pic is the hole I fixed... I could not access the back without removing a laz.

So I traced the hole onto some vellum and then cut out a piece of fiberglass cloth slightly larger than the trace and wet it.. (next pic)

... then I drilled two holes into it and threaded some dental floss (btw: dacron) and glued it to the inside of the hole and held it in place with the floss until the glue set (next three pics)

(glued in place with JB Weld)

Next I cut out seven pieces of cloth... the largest was the size of the original trace and each one a little smaller. I wet them all and laid them out on a plastic sheet and taped it to the hull. Unfortunately, I did not pic the sheet all tapped up but I did get a shot as I removed the plastic sheet (next two pics).

It comes out very nearly fair with the plastic sheeting in place ... just a little fairing compound and some light sanding.... paint and....

 

[rgranger]

In hind sight, it would have been a lot easier to make the backing plate out of some other scrap material, even plywood would have worked but I'm thinking a piece of plastic gutter or the cut out a piece from the lid of a PVC bucket (or even a yogurt container).