17
Installation in a Cored Fiberglass Hull
The core (wood or foam) must be cut and sealed carefully. The core must be
protected from water seepage, and the hull must be reinforced to prevent it from
crushing under the hull nut allowing the housing to become loose.
CAUTION
: Completely seal the hull to prevent water seepage into the core.
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 (Figure 9).
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.
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.
6. Sand and clean the area around the hole, inside and outside, to ensure that the
marine sealant will adhere properly to the hull. If there is any petroleum residue
inside the hull, remove it with either mild household detergent or a weak solvent
(alcohol) before sanding.
7. Proceed with “Bedding” (page 12).
Figure 9. Preparing a cored fiberglass hull
inner skin
core
outer skin
solid or hollow cylinder
pour in
casting
epoxy
9-12 mm
(3/8-1/2")
larger than the
hole through the
hull’s outer skin
hull thickness
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