Always deduct 2% for internal framing,
baffles, and small air pockets:
148 L ×0.02 =2.96 L148 L −2.96 =145.04 LThis is a 145-liter tank.Flexible Bladder Tanks
Another tank option is flexible bladder tanks.
Basically sacks of reinforced rubberlike fab-
ric, these are available in almost every size and
shape imaginable, from 4 or 5 gallons (15 L) up
to 10,000 gallons (38,000 L) or more. Two
sources of marine bladder tanks in the United
States are Imtra, which imports the Nauta line
of bladder tanks manufactured by the French
company Pennel, and Vetus den Ouden, Inc.
Both companies also offer flexible portable
gasoline tanks for outboard craft.
Standard sizes and shapes are available,
as well as custom tanks on special order.
Nauta tanks are fabricated of Neoprene
nitrile, while Vetus uses Alcryn. Both are
incredibly tough, puncture resistant, and
abrasion resistant. Nevertheless, bladder fuel
tanks are usually add-ons or replacements.
Commercial fisherman or voyaging cruisers
can use temporary deck-mounted bladder
tanks to extend range. The tank is carefully
secured on deck or in the cockpit; then it is
fed into the built-in fuel tank’s fills when the
built-in is near empty. With the bladder tank
drained, it can be rolled up and stowed out
of the way.
Flexible bladder tanks can also be used to
replace damaged built-in tanks. Rather than
pull and replace old damaged fuel tanks, cut
a hole or two in the original tank—large
enough to get in and clean it out and smooth
off any rough interior edges inside. Then insert
a bladder tank. This is not a small undertak-
ing, but it’s less extensive than cutting out
large portions of interior or deck to get an old
tank out, as can be necessary on some boats.
As tough as bladder tank material is, it
still must be protected against long-term
chafe. The area where the tank is to be
mounted must be carefully sanded smooth
and all protrusions must be removed. Small
tanks, usually less than 100 gallons or so, are
fitted with corner grommets used to secure
them. Larger tanks would place too much
load on these grommets; so they are installed
in a strong built-in box (almost a partial integralChapter 6:Tank Capacity and Range
Figure 6-4. Tank
half-sections (in
metric units)