To prevent this, use a good bedding com-
pound between the tank and the Neoprene.
A nonadhesive compound such as Woolsey
Dolphinite or a silicone sealant is best. If you
use an adhesive sealant like 3M 5200, you’ll
have to sand the pads off should you ever
want to remove them. Whatever you do, don’t
use any padding that can hold water.
The following materials are neveraccept-
able for use in padding or cushioning fuel
tanks:
- cardboard
- carpeting
- unpainted wood
- felt (tarred or otherwise)
- canvas (tarred or otherwise)
- foams
All of these will absorb water and cause
corrosion.
Other acceptable nonabsorbent materi-
als for tank padding or cushioning are Teflon
and high-density plastics (e.g., UHMWPE)
that are not degraded by exposure to any
petroleum fuel, water, or any standard boat-
ing cleaner or solvent.
Welded-on Tank Attachment
Metal tanks can also be secured by welding
heavy bars or angles along the length of the
tank corners (welded-on lugs). Again, the
total weld strength must equal at least 4 times
the total combined weight of the tank and its
contents. The angles are drilled for through-
bolts or lag bolts with UHMWPE (ultra-high-
molecular-weight polyethylene) bushings to
isolate the bolts from the tank material. The
sheer or axial strength of the bolts (depend-
ing on how they’re being loaded) has to equal
at least 4 times the total combined weight of
the tank and its contents (as does the bear-
ing strength of the UHMWPE bushings and
the wood or FRP structure). Of course, you
need large-diameter heavy washers or back-
ing plates under the nuts of all through-bolts
where they contact wood or FRP. Tanks fas-
tened with welded-on lugs don’t require
chocks or support stringers. Take care that
tanks fastened that way don’t make contact
with any other material or object and that
they have clear ventilation all around.Tank Location
Fuel tanks carry large variable loads. Proper
location is critical to performance, stability,
and proper boat trim. Diesel is 7.13 pounds
per U.S. gallon (0.851 kg/L), and gasoline is
6 .06 pounds per gallon (0.73 kg/L). A long-
range motoryacht with 2,000 gallons (7,570 L)
of diesel fuel will vary 6.3 tons between full
and empty! A large, high-speed, twin-dieselChapter 5: Fuel Tanks and Fittings
Figure 5-3. Installed tank. Note the Neoprene insulation under the
hold-downs and the ball valves on the takeoffs.