Boat Bilge Pumps – A Type For Every Use

 Pumps ,  pumps ,  pumps , you gotta love ’em. If you have any boat larger than you can turn over by hand and dump out, you have to have them. But which  pump , what size, type, and how and where to install it? This article offers information and considerations you need to know.

Bilge  pumps . These are most important because they keep the boat afloat. There are two basic types: centrifugal and diaphragm. Centrifugal  pumps  use impellers, and are usually electrically or mechanically powered. They are dependent on an electrical source or direct mechanical power as from the engine or generator shaft. When installing electric  pumps , the wiring connections are critical. Connections must be watertight, and securely fastened as much out of the way as possible to prevent interference with the  pump  and/or float switch.

Some electric marine  pumps  include an internal float switch which, of course, activates the  pump  when water rises. These are usually smaller  pumps , and the internal switch design can render them more susceptible to blockage and sticking due to bilge debris. Most bilge  pumps  require a separate float switch allowing easy testing of the switch and  pump  (manually lifting the switch arm) and separate installation positions for the switch and  pump . For example; wisdom holds that two  pumps  may be better than one.

Both  pumps  can be strategically located in the bilge, but the switch for one  pump  can be higher than the other. This allows automatic operation of only one  pump  for regular duty, thereby reducing current draw and the life of only the one  pump . As any long time boater knows, emergencies happen. When water intake exceeds the capabilities of the primary  pump , the higher switch will activate the back-up  pump . My back-up  pump  is usually larger, because if I need it, I want to move a lot of water fast.

For smaller boats or those without power such as sailboats, rowing boats, etc., a manual suction or diaphragm type works well. These  pumps  can be inexpensive and portable. They also have the advantage of not being easily blocked by debris in the bilge. They are reliable and work great as long as you can power them. The problem is, on larger boats, how long can you man the  pumps ? While these  pumps  can also be powered mechanically or electrically, they are usually larger and heavier, so centrifugal  pumps  are the common choice; but options are good. If applicable, consider both types.

This brings us to another point. When purchasing  pumps , do not skimp; as important as life jackets, rafts, ELT’s and VHF’s can be in an emergency, the good old bilge  pump  is often your first line of defense against losing a boat and sometimes more. At the very least, in a flooding situation, good  pumps  can buy you time for options.

It is important to understand that advertised marine  pump  ratings in gallons per hour (GPH) are not accurate for normal use.  Pumps  are tested and rated in laboratory conditions with short outflow pipes on the horizontal. Under actual conditions we have to consider “head” which means overcoming both the friction of the outflow tubing and gravity to raise the water to the through-hull fitting. Common bilge  pump  tubing is a corrugated design which creates a great deal of friction. Smooth bore tubing is more expensive, but better.

Also, consider friction loss as outflow is restricted at the smaller diameter through-hull fitting. Now we have to lift the water from the bilge to overboard, usually through a through-hull fitting. Holes in a boat near the water line are to be avoided as much as possible. The through-hulls for your  pumps  should be at least eight inches above the waterline. For mono hull sailors, don’t forget you’re going to heel. For small boaters or commercial applications, remember that the water line will be higher if you heavily load the boat. You should always use a “safety loop” when piping overboard. That is, the piping should be looped higher than the through-hull to prevent water coming in if the through-hull is submerged. This loop, of course, increases the head, so it must be considered when choosing a  pump .

The following chart is only a General recommendation for boat and  pump  sizes.

Boat Length 16′ – 20′ No.  Pumps : 2 GPH: 2500

Boat Length 21′ – 26′ No.  Pumps : 2 GPH: 3000 – 3500

Boat Length 27′ – 35′ No.  Pumps : 3 GPH: 3500 – 4500

Boat Length 36′ – 42′ No.  Pumps : 3 GPH: 6000

Boat Length 43′ – 49′ No.  Pumps : 3 – 4 GPH: 8000

Boat Length 50′ – 59′ No.  Pumps : 4 – 5 GPH: 9000 – 10,000

Boat Length 60′ – 60′ No.  Pumps :4 – 5 GPH: 10,000+

Please remember that multiple  pumps , often in multiple locations, offer the most security and peace of mind. With electric  pumps , consider your power sources and connections. With installed manual  pumps , consider location and ease of access. Use all the information you can acquire with common sense. Don’t be misled by “bargain” offers. In an emergency, bilge  pumps  can be your best insurance.