Clean the inside of the hull, in a non-cored area, where you want to place
the thru hull fitting. I use Dupont Y-3919S Prep-Sol solvent and 16 to 25
grit sanding disks on a right-angle sander. Cut a disk of 3/4" to 1" thick
teak about 4 to 6 inches bigger in diameter than the base of your seacock.
Round the top edge with a router. Stick it to the cleaned area of the hull
with thickened epoxy and use the excess epoxy to shape a rounded taper where
the teak meets the hull. Tongue depressors work great for this. The area of
the cleaned hull should be at least 8 inches in diameter larger than the
teak disk.

After the epoxy has set cover the teak disk and out to the edge of the
cleaned hull area with two or more layers of fiberglass and straight epoxy.
Smooth it down over the teak, over the rounded edges, and on to the hull.
Work out all air bubbles. After it's cured, clean it with water and paint it
your favorite color. I use three coats of Pettit Easypoxy deck paint over
two coats of Pettit white undercoater. Don't forget the primer coats, I've
seen the top coats not cure when placed over non-primered epoxy.

When all is dry, drill through the middle of the teak disk and the hull
using the correct hole saw to fit your non-tapered thread thru-hull. Check
the length of the thru-hull and trim it if it hits the works on the inside
of the seacock. Coat the inside of the hole with 3M 4200 Marine Adhesive
Sealant and put a bead on the thru-hull and the seacock. Fit the thru-hull
in place and screw the seacock to it. For final fitting hold the seacock in
position and have someone tighten the thru-hull from the outside. The ridges
inside the thru-hull are there just for this. You can even get a tool that
fits inside several different sizes of thru-hulls and lets you do this
easily. The excess 4200 can be cleaned off with paint thinner.

Use a 1/8" pilot bit to start screw holes for the seacock mounting holes.
Use 3/4" or 1" long #10 stainless steel pan head sheet metal screws and
washers to fasten the seacock to the teak disk. Ace Hardware has a good
supply of these. Just screw into the teak, not the hull. A little MaryKate
Tek Gel on the hardware will help prevent corrosion.

A lot of work, but worth it.

Rusty O