height would call for 12 ft. × 0 .43 psi/ft.× 1. 5 =
7 .74 psi, or 3.66 m× 9 .7 kPa/m× 1. 5 = 53 kPa
pressure. (One foot of standpipe height
equals 0.43 psi of tank pressure—fresh water.
One meter standpipe height equals 9.7 kPa of
tank pressure—fresh water.)
Pressure Testing of the
Entire Fuel System
The entire fuel system should be pressure
tested to the same pressure as the tanks;
however, the fuel tanks should be pressure
tested separately first.
Level Gauging
In the “good ol’ days,” you would check the
tank level by sliding a sounding stick down the
fill pipe or down a dedicated sounding pipe.
Withdrawing the sounding stick, you would
read the level (like a car oil dipstick), though
this isn’t easy to do at night in a storm. These
days, it’s not unusual for tanks to be located
where a direct fill run for a sounding rod is im-
possible. Still—if it’ll fit—the sounding stick is
thebulletproof backup for modern tank gauges,
despite its inconvenience for regular use. For
obvious reasons, you’re required to have a level
indicator, and any of the standard tank gauges
will work if properly installed. (The sounding
stick alone meets legal requirements.) Glass or
plastic-tube sight gauges are too easily bro-
ken—they would cause a major spill. I don’t
recommend these in place of a proper marine
tank-level indicator system. Such sight gauges
are illegal for gasoline in any case.
FloScan
In addition to level gauges, I like to install
FloScan fuel-flow meters to provide the crew
with accurate real-time information on fuel
consumption. On twin-engine vessels—when
possible—I prefer to install a single FloScan
sender in the lines feeding and returning from
both engines but separate from the line feed-
ing the generator(s). This way, it’s easy to get
engine mile-per-gallon numbers. The genera-
tor consumption can be estimated adequately
and added, or a separate FloScan can be in-
stalled on the generator feed and return lines.
Be sure to install a FloScan meter that reads
in the range of flow rate of your engine (or
engines). Multiply total horsepower by 0. 054
for gph, or multiply kilowatts by 0.274 for
liters per hour. Twin 350 hp (261 kW)
engines—monitored by a single FloScan—
would burn about 37.8 gallons per hour
(143L/hr.) combined, at max. (For gasoline:
gal./hr.= 0. 10 × hp, or L/hr.= 0. 508 × kW.)Tank Materials
Table 5-2 lists proper tank materials and
thicknesses for nonintegral tanks with baffles
spaced no more than 30 inches (76 cm).
Tinned copper was the old standard for gaso-
line, but as the tanks aged, the tin reacted
with the gas, creating a gum that fouled the
carburetor. (There are fewer carburetor en-
gines around every day, but I imagine the
effect would be even worse on injectors.)
Similarly, diesel tanks must never be galva-
nized inside. The zinc reacts with the fuel oil,
ruining the diesel. Copper also reacts with the
sulfur in diesel and can be eaten away. Plain
old-fashioned marine aluminum, iron, or steel
is the answer (Monel is the ultimate); how-
ever, iron and steel aren’t acceptable for gas
unless hot-dipped galvanized inside and out.
A long time ago, terneplate steel (sheet iron or
steel coated with an alloy of about 4 parts
lead to 1 part tin) was a common inexpensive
tank material. It isn’t acceptable for any fuel
tank, however. You’ll often come across ref-
erences to “black iron” tanks. I don’t know
where this term came from. Black iron tanks
are simply ordinary mild steel.
Stainless steel tanks must be of only 316L
or 317L (“L” for low carbon) and welded with
the TIG process, per ABYC. An even better
alloy (not ABYC approved) is 321 stainless
(see sidebar). ABYC has now approved stain-
less steel for diesel, but notfor gasoline fuel
tanks. The one exception is that ABYC does
permit stainless gasoline tanks if they are less
than 20 gallons (75 L), are of cylindrical con-
struction, and have domed ends. I personally
can’t see any reason to use such small stain-
less gas tanks. Polyethylene tanks are avail-
able in many shapes in this size range and are
much superior for this application.
Except for integral tanks, no part of any
fuel tank may be used for structural support
or hull reinforcement.Chapter 5: Fuel Tanks and Fittings