LED lights to indicate which compartment
has tripped the alarm.
On the same indicator board, it’s also
ideal to set up a run counter for the small-
capacity bilge pumps. These can be set up to
record the number of times the pump cycles
on. If you see that the pump has switched on
once or twice in a few weeks or months, no
problem. If you notice the frequency increas-
ing, however, you need to find the cause. I
slightly prefer a total-hour counter. This
gives the total hours the small-capacity
pump has run. If you note the hours in the
log every time you come aboard, it’s a sim-
ple matter to divide by the days since the
past entry and get the hours per day of oper-
ation. (On a new, well-fitted boat it may be
close to zero.) In any case, an increase in the
number of hours per day is cause for thorough
investigation.
Bilge-Discharge Hull-Exit
Location
The bilge system should discharge to a
through-hull above the waterline—about
12 inches (20 cm) above on boats up to 60 feet
(18.2 m) waterline and about 18 inches
(45 cm) above on boats over 60 feet (18.2 m)
waterline.
Notes on Float Switches
The standard float switch works fine. It’s
simply a buoyant flapper on a hinge. When
the water level rises, it lifts the hinged flap
of the float, and a sliding or rolling bead in
the flap closes the electric connection, turn-
ing on the pump. One drawback is obvious.
Debris can jam the float down so it won’t lift
and activate, or jam under the float and keep
it from shutting off. Most manufacturers sell
plastic cover guards that surround the float
switch to protect it from debris (Figure 18-5).
These are so inexpensive that there’s no ex-
cuse for not installing them.
Another less obvious drawback is that
some float switches use a drop of liquid mer-
cury to complete the electric connection. The
quantity of mercury is tiny and so really not
much of a hazard, but on steel or aluminum
boats (especially aluminum), severe corro-
sion can result if the mercury escapes from a
cracked float. For metal boats, be sure to
specify float switches without mercury. There
are modern (and slightly more expensive) au-
tomatic switches, such as those that use two
Mirus detector cells to sense the presence of
water by using a low-impedance electric field.
Other standard float switches use a simple
ball bearing rather than a drop of mercury.Fire Mains and Fire Suppression
Fire suppression of some form or other is re-
quired under law for all boats. Most boats un-
der 75 feet (23 m) or so will rely exclusively
on fire extinguishers of various types; how-
ever, small commercial vessels are required to
have fire mains under CFR Commercial, and
this is a good precaution for large yachts too.Fire Mains
A fire main is nothing more than a powerful
pump connected to a piping system to deliver
plenty of water to fire hoses at strategically
located hydrants throughout the boat. The
hydrant connects to a fire hose with a noz-
zle, usually stored on a rack. Figure 18-6
shows a typical installation on a 110-foot
(34 m) motoryacht.
As mentioned earlier, the pump for the
fire main can be shared with the bilge system,
which usually makes the most sense. You can
see the layout in Figure 18-2. As a general
rule, I recommend that fire mains be installed
on all yachts over 90 feet (27.5 m), though
this is not a legal requirement for pleasureChapter 18: Bilge Systems, Fire Mains, and Fire Extinguishers
Figure 18-5. Float
switch (right) and
cover guard
(Courtesy
Jabsco/ITT
Industries)