Article by Capt. Steve Katz
Bilge Pumps
While we will dedicate this column to bilge pumps, we can’t come close to all the information available on bilge pumps. There is even a book written by Thomas J. Oertling, titled Ships' Bilge Pumps that covers the 500 year evolution of boat bilge pumps. It seems that the wooden ships of the 16th century had leaks just as today’s boats.
While bilge pumps may seem like a boring subject, it is a very popular service call for marine technicians and boat owners 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 standard does not cover pumps intended for damage control.
Bilge pumping systems are often compromised by pump capacity, plumbing and wiring.
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 can be. For example, a one-inch hole, one foot below the water line will create a flow of 19 gallons per minute. A two-inch hole, two foot below the water line will flow 110 gallons per minute.
The most popular bilge pump, “1500” will pump 1,500 gallons per hour or 25 gallons per minute, in a perfect world with no restrictions. As you can easily see, the common electric bilge pump will not be able to keep up with any sizable opening in the hull, hose or other leak.
In regard to damage control pumps, larger diesel powered boats often have what is called a “crash pump” which is an emergency suction pump operated by opening a valve on the main engine raw water intakes. A medium size diesel engine at cruising speed can pump at least 5,000 gallons per hour (Sherwood 18000 pump at 2,000 RPM). This can be a great way to pump large volumes of water in an emergency.
As a practical note, in damage control situations, effort is best spent in an attempt to reduce the amount of water entering the boat using popular methods such as tapered wooden plugs, collision mats or any other means of slowing the water flow.
PLUMBING
Bilge pumps are labeled and advertised by pumping capacity in gallons per hour. This rating is for a pump operating unrestricted in a perfect environment. Many common real world factors such as, discharge hose type and size, length of discharge hose, number and radius of bends, size of fittings and thru-hulls and intake screens effect the actual pump capacity on a given day on your boat. Installing larger or additional pumps is recommended. Locating pumps in the appropriate areas within the bilge is important, generally being placed in independent compartments at the lowest practical point.
A good installation will use smooth wall hoses (the common corrugated flexible hose can reduce flow buy 30%), short straight 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 hose is close to the boat’s waterline, a vented loop needs to be installed to prevent water from siphoning back through the pump. Each pump needs to have its own discharge fitting so do not connect two pumps to one thru-hull, because bilge water can re-enter the non operating pump area.
WIRING
So your boat is equipped with the best, largest pump so now we need to get it wired properly. Don’t blindly rely on the boat builder to design a bilge pump system that meets your needs. A recommended set-up includes the DC powered pump, an automatic float switch and properly fused power feed(s), one for the manual operation of the pump and one for the operation of the float switch.
There are many different types of automatic switch mechanisms that will activate a bilge pump when the water level rises. The most popular is the float switch that turns the pump on when the buoyant float rises to a predetermined level. Other less popular actuators include air pressure, conductivity sensors and pump resistance.
Problems that I often see with a typical float switch that has become inoperable is usually due to debris in the bilge water accumulating around the float, a float switch dislodged from its mounting point or worn out or defective parts. Testing the automatic function of your bilge pump system is a good idea for all boat owners. This automatic switch should be fed with a constant DC power source – usually directly from the 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 fuse size printed on the pump itself for reference.
Be sure that the positive feed is fused and connected through the float switch. You do not want a “hot” DC power source at the pump unless it is running. A pump failure could allow stray DC current into the bilge water and bonding system, causing stray current corrosion of metals. The power lead for the manual operation of the pump needs to be fused too, and often the switch includes a light to indicate the pump is operating.
Keeping an eye on these few areas will help maximize your bilge pumping system function and reliability.
Captain Steve Katz is owner of Steve’s Marine Service serving Baltimore, Annapolis and Ocean City, MD.