"Mounting hardware directly
through cored decking without taking the proper precautions is
just asking for trouble. Here a leaky lifeline stanchion has
caused the coring beneath its base to rot. The mounting nuts are
drawn up so tight they're crushing the panel, no doubt an
attempt by the owner to not only keep the stanchion from
wiggling, but probably to try and stop the leak as well (note
the inadequately sized washers and lack of a backing plate).
Anytime you screw or drill through a cored
panel, the first rule is properly sealing the core against
moisture entry. There are a number of ways to do this, but the
best one is to avoid breaching the core material in the first
place. In a perfect world, your boat's manufacturer has
anticipated where all deck penetrations are necessary (stanchion
bases, cleats, etc) and has "de-cored" these areas by reverting
to solid fiberglass, allowing you to mount hardware without
drilling into the core. But, in the case of new installations
(particularly if you're lucks like mine) your chances are
slim-to-none that any of these areas will coincide with whatever
aftermarket doo-dad you want to mount, meaning you're going to
have to do it the hard way. The good new is the hard way is
fairly easy, as long as you have access to the underside of the
deck where you're doing the mounting.
What you're going to do is a
little de-coring of your own. The easiest way to remove coring
is with a hole saw and a little caution. Let's say you want to
mount a new cleat on your foredeck, but the entire area is
cored. First step is marking and drilling the appropriate sized
bolt holes. Then, take a 2 inch hole saw (or larger, depending
on the size of your backing washers) and remove the coring from
the underside of the deck where each bolt is to be installed,
being careful NOT to drill through or damage the upper layer of
fiberglass (you also have the option of removing a single
section of coring large enough to encompass both bolts). I find
it works best to drill almost through the coring, but leave the
last 1/4" or so to be removed by hand (to avoid any chance of
damaging that outer fiberglass layer).
Once the cutout and coring is
removed, seal the exposed edges of the coring in the holes with
thickened epoxy paste. Now all you have to do is mount the cleat
using properly sized backing washers and a good bedding compound
(under both cleat and washers) and Whaa-la! You've got a
properly mounted cleat that won't leak and has no chance of
letting water into the core.
I like the above method of
dealing with mounting holes in cored panels, but it's not the
only way to address the problem. An excellent reference for this
and just about any other type of fiberglass repair or
maintenance issue is "Fiberglass Boat Repair And Maintenance"
published by Gougeon Brothers, Inc. (517) 684-7286. It's a good
how to booklet and well worth space on any vessel's bookshelf.
"The right way to do it. Here the deck beneath a lifeline
stanchion has been "de-cored" to prevent water entry into the
core (note the substantial backing plate)."