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.
