76 | BoatU.S. Magazine JUNE | JULY 2014
REMOVE THRU-HULL FITTINGS
Thru-hull fittings can be jacked free with a length of
threaded rod, a stiff backing plate, and three scraps of
2x4. Drill a hole through the center of the backing plate
and the center of one of the wood scraps. Pass the threaded rod
through the wood, up through the thru-hull fitting and, inside the boat, through the backing plate. Add a washer and thread on a nut inside, then seat the plate on the inside end of
the fitting. Outside create a bridge by using the other two pieces of wood to support the
ends of the speared piece on either side of the fitting. Add a washer and a nut, tightening
until the bridge is clamped in place. Now turning the nut will pull the backing plate toward
the hull, extracting the thru-hull in the process. Putting the sealant under stress then giving it time to stretch can avoid the common result of tearing away bits of the fiberglass
laminate. If the sealant is polyurethane, a release chemical can help.
For more on choosing the right
sealant, see this article online at
6CHEMICAL REACTION: The list of solvents tried by desperate boat owners
is exhaustive: acetone, toluene, xylene, MEK,
alcohol, gasoline, WD- 40, citrus cleaners,
and more. Most have no effect on cured
polyurethane and none work well enough to
recommend. One chemical product that does
get high marks is DeBond Marine Formula.
5HEAT THINGS UP … CAREFULLY: Where both bonded surfaces are metal,
a heat gun or torch can melt the adhesive and
break its grip. However, if your boat is fiberglass, the use of heat risks permanent damage
because the temperature required to soften
cured polyurethane will also soften cured
polyester. Only heat the blade of your knife,
razor, or wire, which can help it to penetrate
the cured sealant more easily.
Unlike some other release chemicals –
there are several on the market – the DeBond
product is also compatible with most plastics,
except polycarbonate (Lexan). Without the
use of a bond releaser, plastic parts – port
light frames, for example – installed with 3M
5200 or other high-strength adhesive typically
cannot be dismantled without damage. There
is no downside to using a release chemical,
beyond expense, so going to it first rather
than last can pay dividends.
More liquid knife than solvent, it is sprayed
onto the exposed sealant after the edges have
been scored with a blade. Employing wedges
to keep the sealant under stress exposes a
fresh target to the chemical as the bonded
edge moves back with release. Given time
and repeat applications, it’s usually successful
at breaking the bond of 3M 5200 (and other
adhesive sealants as well).
Here is a takeaway about polyurethane:
The bond is permanent but the seal isn’t.
That means things may still be stuck together
just fine, but they will still be leaking. If you
don’t want to do this again, re-bed with a less
2012 Half Page Motor Treat.pdf 1 7/16/12 5:00 PM
Don Casey is the author of the classic This Old
Boat, which covers all aspects of refurbishing an
older fiberglass sailboat.
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