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1. Drill a 3mm or 1/8" pilot hole from inside the hull. If there is a rib, strut,
or other hull irregularity near the selected mounting location, drill from
the outside. (If the hole is drilled in the wrong location, drill a second
hole in a better location. Apply masking tape to the outside of the hull
over the incorrect hole and fill it with epoxy.)
2. Using a 51mm or 2" hole saw, cut the hole from outside the hull through
the outer skin only (see Figure 5).
Figure 5. Preparing a cored fiberglass hull
3. From inside the hull, use a 60mm or 2-3/8" hole saw to cut through the
inner skin and most of the core. The core material can be very soft.
Apply only light pressure to the hole saw after cutting through the inner
skin to avoid accidentally cutting the outer skin.
4. Remove the plug of core material so the inside of the outer skin and the
inner core of the hull are fully exposed. Sand and clean the inner skin,
core, and the outer skin around the hole.
Caution: Completely seal the hull to prevent water seepage into the
core.
5. If you are skilled with fiberglass, saturate a layer of fiberglass cloth with
a suitable resin and lay it inside the hole to seal and strengthen the
core. Add layers until the hole is the correct diameter.
Alternatively, a hollow or solid cylinder of the correct diameter can be
coated with wax and taped in place. Fill the gap between the cylinder
and hull with casting epoxy. After the epoxy has set, remove the
cylinder.
9-12 mm (3/8-1/2")
larger than the hole
through the hulls
outer skin
pour in
casting epoxy
hull thickness
outer skin solid or hollow cylinder
outer skin
core
inner skin