Article by Capt. Steve Katz
Battle of the Bilge
While bilge pumps may seem like an unexciting subject, it is a very popular service call for marine technicians and crew alike. ABYC standard H-22 defines the common electric bilge pump as “intended for control of spray, rainwater and normal accumulation of water due to seepage and spillage”. The ABYC standard does not cover pumps intended for damage control, though we often rely on these same pumps in an emergency.
Bilge pumping systems are comprised of three main parts; the pump itself, the plumbing and the electrical wiring.
Pumps and capacity
As most can imagine, any hole in a boat (or seawater hose, strainer, etc) is bad! But the farther below the water line the hole is, the worse it is. For example, a one-inch hole, one-foot below the water line will flow 1,140 gallons per hour. A two-inch hole, two-feet below the water line will flow 6,600 gallons per hour.
Most bilge pumps are rated by their capacity in Gallons Per Hour. The most popular bilge pump, the Rule 1500, is rated to be able to pump 1,500 gallons per hour in an open flow, no output hose while supplied with steady 13.6 volts or 27.2 volts depending on the model. Once discharge plumbing is added and battery voltage drops, the capacity is reduced rather quickly.
As you can see in the above example, a common electric bilge pump or pumps will not be able to keep up with any sizable opening in the hull, hose or other leak but will work fine for controlling spray, rainwater and normal accumulation of water in the bilge. There is no generic formula to determine the size and capacity of bilge pumps for your boat. You need to take into account the boats design, compartment sizes, water accumulation potential and other vessel specific factors to determine what is best for your boat. Locating pumps in the appropriate areas within the bilge is important with the best set-up generally in each independent compartment and at the lowest practical point
Type of pumps
The most common type of bilge pump is the submersible centrifugal pump, like the Rule 1500. This pump is designed to operate while submerged and requires a minimum amount of water under the pump to operate.
The diaphragm pump is still a popular pump as it is remotely mounted and requires an intake hose be run from the pump to the bilge area. The nice feature of these pumps is that they can almost pump the bilge dry, since they do not need a minimum water level. Additionally, the suction hose can be easily located where it is most effective. Compared to centrifugal submersible bilge pumps, these diaphragm pumps can clog more easily, have reduced capacity in a similar physical size and contain diaphragms that may need replacement if worn or damaged.
Plumbing
A good installation will use smooth wall hoses, (the common corrugated flexible hose can reduce flow buy 30%), short straight hose runs, fittings that do not restrict flow and no check valves or other devices in the discharge hose. Check valves are only permitted by ABYC to eliminate pump cycling. If the discharge overboard fitting is close to the boat’s waterline, a vented loop needs to be installed to prevent water from siphoning back through the pump and into the bilge. Each pump needs to have its own discharge fitting. Do not connect two pumps to one thru-hull since bilge water can re-enter the non operating pump and fill that area with water.
Wiring
Even if you have the biggest and best bilge pump, combined with the best float switch, it needs to be wired and fused properly to provide the best and safest discharge. A stuck float switch or pump jam can cause an overheated or melted bilge pump, which is a common occurrence. You want to be sure that a pump malfunction does not cause a fire. A recommended set-up includes the DC powered pump, an automatic float switch and two properly fused power feed(s), one for the manual switch operation of the pump and one for the automatic operation by the float switch. Additionally an indicator light panel on the helm is a very useful way to know when your bilge pumps are operating.
There are many different types of switch mechanisms that will automatically actuate a bilge pump when the water level rises. The most popular is the cantilevered float switch that turns the pump on when the buoyant float rises to a predetermined level of bilge water. Other less popular actuators include air pressure, conductivity sensors and pump resistance. I often see the typical float switch that has become inoperable due to debris in the bilge, water accumulating within the sealed float, a float switch dislodged from its mounting point and worn or defects parts. Regular testing the automatic function of your bilge pump system is a good idea.
An automatic switch should be supplied with a constant power source – usually a direct circuit from a battery (NOT through the battery switch or other switch where it could be accidently turned off) and properly fused for the exact pump it controls. Most bilge pumps have the recommended fuse size printed on the pump itself for reference since this fuse is needed to protect the pump in the event of a failure. Oversizing the fuse can cause the pump to melt or catch fire in the event of a locked rotor or other failure.
Be sure that the DC positive feed is fused and connected through the float switch. Do not connect the ground to the float switch. You do not want a “hot” DC power source at the pump unless it is running. In the event of a pump failure, stray DC current could enter the bilge water and bonding system, causing stray current corrosion of metals.
Installing the correct size pump in each compartment, routinely checking the automatic/manual operation and monitoring pump activity will help you avoid a surprise pump failure and keep you prepared when you need the pump in an emergency.
Captain Steve Katz is the owner of Steve’s Marine Service and holds NMEA, AMEI and NMEA2000 certificates along with ABYC Master Technician certification and factory training from many manufacturers.
