Bilge pumps : yes, they can save your boats and your family
So... you buy this shinny new boat, the latest
model from a reputable builder with all the fancy gadgets you've
ever wanted. All is well, right ?
Well, why don't you take you eyes off the flat
screen TV and soft upholstery and take a look in the bilge... you
know, the space under the cabin floor and under the engines builders
never show in the brochure; chances are your builder cut a few corners
in there and delivered the boat with only marginal bilge pumps.
"But it's a small boat, a 20' bow rider
The smaller the boat, the more critical bilge
pumps are, for a number of reasons. First, it's more likely to take
on water from a wake or wave over the bow or stern than a larger,
higher more enclosed boat. This is particularly important with bow
riders... Second, a small boat has small bilges and water will quickly
reach critical components like electrical connections, batteries,
alternators, etc.. Finally a smaller boat will be more affected
by water sloshing around the bilge than a larger boat; just 50 gallons
of water sloshing around will noticeably affect the stability of
a small boat. So you want that water out of there, now, and the
tiny bitty factory installed 500gph cartridge pump isn't going to
"But I never go far offshore !"
So what ? many people have died or seen their
boat sink in a small lake or near shore, even at the dock. You'd
be surprised how quickly a boat will go under as soon as enough
water gets in and major openings finish the job.
"Electric bilge pumps aren't going to
save my boat if I get a hole in it"
True... but it will buy you some time, probably
enough time to fine the hole and plug it or at least call for help
and be ready to abandon ship with enough gear to make it till help
arrives. Let's face it, few boats sink because they have get a 2'
gapping hole in the hull and when this happens, you're not going
to have much time to do anything about it. But for the most realistic
scenarios like dropping a shaft, loosing a rudder, a failing thru-hull
or a minor hull breach, adequate pumping capacity will buy you time
to find the problem and temporarily plug the hole...
ex... a one inch hole, two feet below waterline,
will bring in about 1800 gallons of water an hour. Now one inch
isn't very big, that's more or less what you may have on an air
conditioning inlet or some cooling hose. Take a two inch hole, also
two feet below the waterline and you're looking at almost 7000 GPH.
While a 1500 and a 3700gph pumps aren't going
to keep afloat, remember that real world figures are less than the
rating on the pump, it sure will buy you enough time to plug the
hole with rags and a wooden dowel.
How many pumps should I have ?
First thing to remember is that bilge pump capacities
are best case scenario at full voltage and no head (the height between
the pump and the discharge). So out there, in the real worked, that
500gph pump is probably only pumping 300 gallons out of your boat
For small to medium boats, I think that boat size
times 200 is a good start.
Ex.: 20' boat x 200 = 4000... 30' x 200 = 6000...
50' x 200 = 10 000.
It's simplistic and I know it may sounds like
an overkill to have two 2000GPH pump on a 20 footer so you may reduce
that a little to a 1000gph primary pump and a 2000gph back up. Don't
forget that pumps and float switches are not the most reliable thing
on board your boat and that you need to consider that one of them
might fail. The cost is irrelevant since a 1500gph pump and float
switch cost well under $100...
You need to consider the boat layout in deciding
what will work best. On the typical small to medium boat, the engine
room bilge is sealed from the cabin bilge so that any fuel or oil
spilled in the engine bilge doesn't' get under the cabin. Obviously,
putting all your bilge pumps aft is not going to help if you get
water up front ! Because most leaks are likely to occur in the engine
room, it's worth having more pumping capacity there so on a 30ft
boat, a 1500gph everyday pump, backed up by a 2000 is a good start
in the ER, with a pair of 1500 in the forward bilge. On a larger
boat or inboard or a boat with more systems, upgrading the engine
room back up to a 3700 gph is a good idea. Again, bilge pumps are
cheap and not something you want to cut corners on.
It's best to have a smaller everyday pump at the
bottom of the bilge, with both float and helm switch, and have a
large backup pump mounted higher so that it only comes on if the
first pump either fails or doesn't keep up with the water flow.
This way, the larger back up stays dry and clean until it's needed.
So, for a small boat, a 1500GPH pump with a 2000GPH back up is a
Pumps should always be mounted in locations where
they can be accessed and tested; this sounds pretty obvious but
way too many builders bury the bilge pumps under the engine or in
spots where a normal size person can't reach it. You want to test
the pump regularly, at least once a month, ideally every time you
go down in the engine compartment to check your fluid levels. If
the pump is right there it takes a second to flip the float up...
Discharge hoses should be kept as short as possible
but always include a rising loop at least 12" above the thru-hull
This is especially critical if the thruhull is near the water line
or if it can get under water due to load, rolling, etc... in that
case, the rising loop should be even higher. Make sure the hose
is supported so that it doesn't put any load on the fitting. Check
valves should be avoided at all cost ! While they sound like a good
idea, they are even less reliable that float switches and prone
to clogging or failing.
Normally, each pump should have it's own discharge
thruhull but if you really can't bear the thought of drilling a
hole in your hull, you could use an existing thruhull although not
ideal. If you do, care must be taken so that water from either source
(ex your new pump and a sink) can't back into the bilge. Again,
rising loops are better than check valves... Make sure you are not
using a thruhull which is likely to be used while the bilge pump
is on, like another bilge pump or an air conditioning pump.
Standard pumps are wired with a switch and indicator
light at the helm and a float switch. The float switch should be
wired directly to the batteries so that it is always on, even when
the battery switches are off. When adding a back up pump, it doesn't
really need to have a switch at the helm and should be wired to
the batteries, with a fuse. If your boat has multiple battery banks,
spread the loads but try to wire the largest pump to the largest
if you have a larger boat that you routinely operate
offshore, you may consider carrying an emergency gas powered pump...
these things will pump thousands of gallons of water an hour even
after your electrical system is under water.
Adding engine driven pumps can help although impeller
driven pumps can't run dry so you must attend to them. The same
goes for Tee valves to redirect the intake for your engines raw
water pumps to the bilge; they can save the boat but again requires
that someone makes sure they don't' run dry or you could be left
But I passed a Coast Guard Vessel Safety Check
and they gave be a nice sticker even though I only have a manual
Correct, like charts, anchors, lines and fenders,
bilge pumps are "discussion items" during a safety check,they
are not mandatory. Is your boat really safe ? you decide !
A couple of hundred dollars and a couple of hours
of your time may save your boat one day... and your family.