Airmar B744V - Manual (Page 5)

5
3. Using the 60mm or 2-3/8" hole saw, cut through the inner skin
and most of the core from inside the hull. 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.
Note: The optimal interior hole diameter is effected by the hull’s
thickness and deadrise angle. It must be large enough in
diameter to allow the core to be completely sealed.
4. Remove the plug of core material so the inside of the outer skin
and inner core of the hull is 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. Coat a hollow or solid cylinder of the correct diameter with wax
and tape it in place. Fill the gap between the cylinder and hull
with casting epoxy. After the epoxy has set, remove the cylinder
(see Figure 10).
Figure 9. Servicing the paddlewheel insert
BOW ►
flat side of
paddlewheel
O-rings
paddlewheel
pull ring
shaft
cap nut
paddlewheel
top view of
housing and
blade faces bow
paddlewheel
insert
insert
valve assembly
housing
and the valve assembly (B744V shown)
notches
key (2)
valve
assembly
insert detail
cable
6. Sand and clean the area around the hole, inside and out, so the
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” and “Installing”.
Check for Leaks
Warning: Never install a thru-hull multisensor and leave the boat
in the water unchecked for several days.
When the boat is placed in the water, immediately check around
the thru-hull multisensor for leaks. Note that very small leaks may
not be readily observed. It is best not to leave the boat in the
water for more than 3 hours before checking it again. If there is a
small leak, there may be considerable bilge water accumulation
after 24 hours (probably not enough to cause water damage). If a
leak is observed, repeat “Bedding” and “Installing” immediately.
Maintenance, Repair, and Replacement
Blanking Plug
To protect the paddlewheel, use the blanking plug when:
• The boat will be moored in salt water for more than a week
• The boat is removed from the water
• Aquatic growth buildup on the paddlewheel is suspected due to
inaccurate readings from the instrument
This multisensor incorporates a self-closing valve which
minimizes the flow of water into the vessel when the paddlewheel
insert is removed. The curved flap valve in the valve assembly is
activated by both a spring and water pressure. The flap valve is
pushed upward to block the opening, so there is no plume of
water into the boat.
WARNING: THIS IS NOT A WATERTIGHT OR SECURE SEAL!
Always use the blanking plug secured with the retaining pin,
safety rings, and safety wire to provide a watertight seal when the
paddlewheel insert is removed.
1. Inspect and lubricate the O-rings on the blanking plug with
silicone grease or petroleum jelly.
2. Remove the safety wire from the pull ring and cap nut. Remove
one safety ring and pull out the retaining pin (see Figure 8). Do
not remove the cap nut.
3. Grasp the pull ring and remove the paddlewheel insert with a
slow pulling motion (see Figure 9).
Note: In the unlikely event that the paddlewheel insert cannot
be removed, see “Servicing the Valve Assembly”.
hull’s outer skin to
hull
outer skin
solid or hollow
cylinder
pour in
casting
epoxy
core
inner skin
Figure 10. Preparing a cored fiberglass hull
Dimension equal to
the thickness of the
ensure adequate
clearance