The proper way to patch a thru-hull hole in a GRP hull is
with polyesther resin and not epoxy resin.

The hole should be tapered in a radius of approximately
four times the radius of the hole itself. In other words if
the hole is two inches the taper should be eight inches.

The taper should be made on both the inside and the
outside of the hull equally. One should then attempt to
determine the layup schedule of the hull and duplicate it
with roving, mat, etc. one should first repair the outside
of the hull. This is the difficult part because one must
work upside down. The secret is to cut the layers to
size, wet them sparingly with resin and keep them in
order of application from small to large to fill the tapered
hole layer by layer rolling with a roller with light pressure
to remove all bubbles. Once the area is filled, a thin, smooth,
flexible board covered with wax paper should be pressed
against the hull and secured there with a jack stand and wedges
so it conforms to the shape of the hull. The area should be
allowed to set up for a couple hours.

Then the inside of the hull can be repaired. This is the easy part.
Wet out the cut-to-size layers and apply layer by layer
using a roller to remove all air bubbles. Go easy on the
resin. If you have resin streams draining down the inside
of the hull the cloth and mat is too wet. Let the resin kick
off for about four hours. The outside wooden form can
be removed. Allow a day before doing any final sanding
or grinding to smooth the surfaces. It might be a good
idea to apply a couple layers of barrier coat to the
patch to keep water away from it to eliminate possible
osmotic blisters in the future.

I hope this helps.

S.Simon - learned how to fill in thru-hull holes when working
for Irwin Yachts.



"Jonathan Ganz" wrote in message ...

Thanks for the pic and the advice. I used the 5200 to make
sure I got all the gaps filled in, though I guess it was overkill.

I'm not sure what you mean about leaving a tapered area
around the hole. Why would this give it better bonding?


"DSK" wrote in message
...


Jonathan Ganz wrote:

I had an illegal head on my Cal 20. For that boat, I cut out the
fitting,
then somewhat closely matched a piece of wood to the hole. Then,
filled in the gaps with 5200, then glassed over the whole thing from
both sides. I don't know if that was the best way to do it, but it
doesn't leak and I suspect it's stronger than the rest of the hull.

Is there another method that's as or more effective?

Sure. Just fiberglass over the whole thing, then fair it.

I filled in a thru-hull in our tugboat this spring, which gave an
opportunity
to check the hull lay-up (3/4" thick) also. Using a side grinder to create
a
hollow area inside & out, then I taped a piece of wax paper over the
outside
of the hole, then used WEST system resin & low density filler to fill the
hole, then put three layers of 28oz cloth with bonding filler on the
inside.
Then I put on another three layers of heavy cloth plus some lighter
stuff,
and used the side grinder again to smooth it over. There is no doubt that
this patch is stronger than the rest of the hull, and thoroughly bonded.

Here is a picture of the inside of the finished patch. That yellowish
thready
on the left
http://community.webshots.com/photo/...73346002sUSTvu

A side grinder is a GREAT tool, but I used up a lot of expensive masks &
respirators (to protect my even-more-expensive lungs).

Why did you use 5200 inside a layer of fiberglass? Why not just glue the
wood
in place with resin? BTW it's a good idea to cut away a tapered area
around
the hole for better bonding.

Fresh Breezes- Doug King