tank). Such large tanks may also be further
restrained with netting wrapped over the en-
tire tank and fastened to the hull.
As main “built-in” fuel tanks, standard
bladder tanks are best suited for smaller sail-
boats. Their small size, light weight, and free-
dom from corrosion make installation easy
and attractive.
The usual fill vent and takeoff lines
are required for bladder tanks. (Yes, vents
are required even for flexible bladder tanks.)
Be sure to check with the manufacturer
about the intended fuel. Some tanks are rated
only for diesel, others for gasoline and diesel.
The ultimate in bladder tanks are bladder
tanks completely filled with reticulated foam
(Figure 6-5). These tanks aren’t fully flexible
but are held in their designed shape by their
internal foam. The foam looks much like ordi-
nary seat-cushion foam, but reticulated foam
has had the walls between the individual foam
cells chemically removed. This makes reticu-
lated foam incredibly porous—so much so
that the foam takes up a mere 2 to 3 percent
of the volume of the tank. Reticulated-foam
tanks require no baffles as the foam essentially
divides the tank into millions of tiny cham-
bers. There is no sloshing at all. For gasoline,
these tanks are nonexplosive and—with the
right high-end bladder material and external
jacket—self-sealing and self-extinguishing.
Because of this, reticulated-foam bladdertanks can be a good choice for very high-speed
racing craft and for rescue and patrol boats.
Ordinary level gauges won’t function in
reticulated-foam tanks. The manufacturer pro-
vides capacitance-gauge level indicators. As
far as I’m aware, none of the bladder tanks
have been approved for use on passenger ves-
sels, not even reticulated foam.
Reticulated-foam bladder tank costs vary
from somewhat higher than comparable cus-
tom aluminum tanks, to more than twice the
price for ballistic, self-sealing tanks with an exter-
nal flame shield. Of course, no aluminum tank
is ballistic or self-sealing. Aluminum tanks are
also heavier. Obviously—like fiberglass and
poly tanks—all bladder tanks are immune to
corrosion. ATL (Aero Tech Laboratories, Inc.)
and Aircraft Rubber Manufacturing, Inc., both
make reticulated-foam bladder tanks in stock
or custom sizes. Aircraft Rubber also manufac-
tures standard bladder tanks without the foam.Wide Tanks Reduce
Stability: The GM Reduction
Except when completely filled with ab-
solutely no air in the tank at all—a condition
termed “pressed up”—the fluid in all tanks
of any size or shape reduces a boat’s stabil-
ity. This is because—even with baffles—the
fluid in the tank moves from side to side as
the vessel rolls. Both the shift in weight andPART TWO:FUEL SYSTEMS
Figure 6-5. ATL
reticulated-foam
bladder tanks