The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

Chapter 26 – Interior Construction 329
Decisions on tank size and location should be made
early in the design process, especially if pre-built certified
tanks are to be used. It is important to determine
tank size and location so that the hull will eventually
float on its intended lines. <strong>The</strong> tanks should be placed
where they will have the least impact on living space.
<strong>The</strong>y should also be able to be removed at some point if
necessary. Selecting tanks early in the design process
allows you to build support around the tank rather than
trim away structure in an effort to fit a tank into an
existing space. If stringers or frames require cutting to
make room for a tank, take care to reinforce these
modified structural members to effectively carry load.
This can be done with sister frames, doublers, or fiberglass
reinforcement.
Off-the-shelf certified tanks need to be properly
supported and secured so they do not move or upend
while in use. Improper installation can cause premature
tank failure. <strong>The</strong> best way to support a tank depends on
the material the tank is made of. Issues surrounding
installation of off-the-shelf tanks can be complex
because a method that works well for one tank type
may cause a potential problem for another. Because of
this, we recommend that you contact the tank manufacturer
for their recommended installation technique.
Some tanks require mounting on support pads. Others
require a flat surface for full contact. Expandable foam
is recommended by some tank manufacturers to
support tanks while others frown on the practice.
<strong>The</strong>re are a variety of issues involved in securing tanks.
<strong>The</strong>y include the following:
• Polyethylene and polypropylene tanks are flexible and
can swell while filled. Allowances must be made for
this.
• Aluminum tanks are rigid and yet typically are not
strong enough to address stresses introduced in them
if rigidly installed in a hull that flexes.
• Aluminum tanks are known for corroding between
their support pads and the bottom of the tank. This
deficiency can be addressed by protecting the bottom
of aluminum tanks and a couple of inches up the side
with several coats of WEST SYSTEM epoxy. This isolates
the aluminum from water that eventually finds its way
between the support pads and the bottom of the tank,
effectively extending the life of the tank. (For information
on preparing aluminum for bonding with epoxy,
see Chapter 14.)
When creating storage locations for tanks, it is good
practice to build a containment area around the tank to
isolate leaks should they occur. <strong>The</strong>se areas should be
sealed with at least three coats of epoxy so the liquid
does not migrate into the wood or to other parts of
the hull.
Support platforms for tanks can be created with
plywood and installed with epoxy fillets. Saddles can be
created with fiberglass cloth and epoxy, using the
bottom of the tank as a mold. <strong>The</strong>se eventually get
glued into position in the boat to support the tank in an
exact location. Rubber pads are often used between the
bottom of a tank and its support structure to minimize
potential chaffing. Hold down straps and fittings, available
from the tank manufacturer, can be used to secure
the tank to the platform/saddle. <strong>The</strong> hold down scheme
used to secure tanks should be robust. We recommend
using glued-in fasteners and hardware bonding
techniques described in Chapter 14. Hardware bonding
will maximize the holding power of the screws involved
and seal out possible moisture intrusion that could
significantly weaken the holding power of the fastener.
Tank Construction
Holding tanks made with plywood and WEST SYSTEM
epoxy have been extremely successful, mainly because
they are inexpensive and easy to build. You can build
tanks to the exact size and shape you need and eliminate
the time and expense of preparing drawings for a
metal tank fabricator. While there are arguments in
favor of building tanks permanently into the hull, we
always make them as separate, usually removable, units
so that if the hull is damaged, we can remove the tank
to repair it.
<strong>The</strong> procedure for constructing the interior of a tank is
similar to that used for the interior of an icebox, except
that you can use cleats on the exterior corners to
assemble the plywood panels if desired. Venting is
needed to prevent buildup of gas pressure. Baffless
should be installed to reduce the surge effect that can
otherwise occur and to support the structure. If you use
them, the number and size of baffles are proportionate