exceed my bilge-pump rule in total in addi-
tion to the CFR-required bilge system and fire
main.
Our example boat Fluky Flooderis based
on a real yacht my office designed, and it was
fitted with four DC submersible bilge pumps
rated at 3,700 gph (14,000 lph) each; total
14,800 gph (56,000 lph). These were the pri-
mary bilge pumps in each watertight com-
partment, each with a 1^1 / 2 - inch (31.1 mm)
discharge port (Figure 18-4). In addition, we
installed four smaller DC submersible bilge
pumps of 360 gph (1,360 lph) each, with a(^3) / 4 - inch (19 mm) discharge port. (As a plea-
sure craft in this size, she was not fitted with
the CFR-required bilge system.)
There are three disadvantages to larger
powered bilge pumps. One is that they draw
more amperage and thus put greater demand
on the battery bank. Another is that the large-
diameter discharge line holds a fair amount
of water. When the pump is turned off, the
water remaining in the discharge line runs
back down into the bilge. Assuming about
5 feet (1.52 m) of discharge line on a 1^1 / 2 - inch
(30 mm) hose, this is about half a gallon
(1.8 L) of water. The third disadvantage is
that if there’s only a little water in the bilge—
even enough to cover the pump inlet open-
ing—there won’t be enough pressure (suc-
tion head) to create sufficient flow for the
pump to work. The pump will just churn the
water around without pumping this last bit
out (recirculation).
To avoid these disadvantages, larger,
high-capacity submersible pumps are in-
stalled on pads to lift them about 5 inches
(125 mm) above the lowest point in each
bilge compartment, with each pump’s auto-
matic float switch up on the same level.
Small-capacity submersible pumps are lo-
cated right at the lowest point in the bilge
sump of each compartment, with their auto
float switches at their level.
In this way the smaller, low-powered
pumps handle the vast majority of routine
bilge pumping. This reduces battery draw
and greatly reduces the amount of water that
spills back into the bilge from their smaller
discharge lines when the pumps are shut
down. In the event of a serious flooding situ-
ation, the water rises high enough to trip the
upper, large-capacity bilge pumps.
Because the preceding configuration is
automatic and high capacity, it’s the approach
I use on almost all boats. If the boat is to be
a passenger vessel, I then add the separate
powered bilge and fire-main system to com-
ply with the CFR. This system really would
be used only in extreme emergencies, as the
automatic, submersible-pump system will
handle all ordinary problems.
Bilge-Pipe Material on
Pleasure Vessels
On yachts, plastic pipe, hose, and pipe (steel,
stainless, or aluminum) can be used for bilge
piping. Don’t use less than schedule-
40-weight pipe. Use heavy hose specifically
designed and intended for bilge piping. Use
smooth hose, not corrugated hose. Hoses
must be fastened with double stainless hose
clamps exactly per the specifications in
Chapter 4. Remember, the failure of a hose in
the bilge system will result at least in loss of
that part of the system, and likely cause serious
flooding.Plastic pipe must be strong. Most
plastic pipe becomes brittle in cold weather
and with age. Use only the best grade, and be
sure it’s properly installed and supported.
Pump Alarms and Counters
When installing small- and high-capacity
automatic pumps in the previous dual con-
figuration, you should install a high-water
alarm on the upper bilge-pump float switch.
Ideally, this should be wired to an indicator
board at the helm or at the circuit panel, with
PART SIX: PLUMBING SYSTEMS WITH NOTES ON FIRE SUPPRESSION
Figure 18-4.
Submersible bilge
pump (Courtesy
Jabsco/ITT
Industries)