Bilge pumps & systems

Plumbing & Pumps

Boat Accessories - Plumbing and Pumps

Like so many aspects of life, your bilge pump falls into the category of things you don’t notice until you need them - especially if it isn’t operational or adequate for the task. It’s not enough to depend upon your hull manufacturer’s claim of intrinsic buoyancy regardless of how much water you take on - you want a bilge pump that works like it’s supposed to work when it’s supposed to work.

Boat pumps & systems

Bilge pumps


You really need it , When you need it

- a good understanding of the purposes and limitations of the typical bilge pump systems

Have you checked your bilge pump system recently? Do you have one (or more) with sufficient capacity to keep you afloat? What should you expect from this equipment?

All boats must carry at least one effective manual dewatering device (bucket, can, scoop, etc.). This requirement is in addition to any installed electrical bilge pump that the vessel may have on board.

Perhaps it’s best to use common sense. On one hand, an ordinary bilge pump system cannot be expected to keep a boat with a big hole in it afloat. It is impossible to imagine a system that could keep up with a high rate of inflow (on larger boats I have installed diversion valves on engine raw water intakes that could evacuate a large volume of water quickly).

On the other hand, an unmonitored bilge could accumulate enough rainwater and/or seepage to sink your boat over time. So, the logical conclusion is that your bilge pump system’s primary purpose is the evacuation of rainwater and seepage. To do that you can add that this system can be viewed as an early warning mechanism to alert you to the invasion of water from a preventable source (a mistakenly opened valve, a failed thru-hull fitting or hose, a poorly loaded vessel suffering from water pooping over the transom or any myriad of other imaginable causes).


The Mechanics of It All

While there are a number of manufacturers of bilge pumps, the pump’s design concept and housing shape are relatively uniform. An inverted electric motor with a paddlewheel on its shaft sits centerline and basically “flings” the water out of the discharge fitting at the base of the unit. Described as a submersible, centrifugal pump, it is simple, reliable, easy to install and inexpensive.

There is hardly a trailerboat built today that doesn’t have an electric bilge pump. See if you can find yours. It should be in the low point of your bilge. If there is more than one distinct bilge (separated by a watertight bulkhead), there should be a bilge pump for each.

There are a number of considerations when evaluating your bilge pump system. Labeled capacity should be looked at with a jaundiced eye because often this rating is at open flow with no lift and no discharge hose attached. In actual installations aboard a boat, the pump will never achieve this rate of flow. If you are adding or replacing your bilge pump, look for one that gives you flow rates at various lifts (height and distance to discharge fitting in the hull or transom) and various system voltages.

Operating features in a preferred installation will include “manual” and “automatic.” The “manual” function will include some type of switch to activate the pump. The “automatic” function is a little more complex and adds another component: a triggering device. The simplest and most common is a float switch that utilizes mercury or a rolling ball bearing to close the circuit. There have been various attempts at developing an electronic version that contains sensors that detect water contact, but I have had little experience with them other than replacing the electronic version with the float version.

For peace of mind, it’s a good idea to periodically lift the float switch to confirm that it triggers the bilge pump. With some float switch designs, the float itself is contained within a housing. Look for a push-button manual testing device on the top of the housing or a protruding shaft at the hinge point to twist and test.

Other inspection points include:

* Check to see that the pickup strainer is not clogged or blocked in some way

* Check to see that the discharge hose is not kinked or clogged

* Check to see that the exhaust fitting is not below water (make sure there is a high loop in the hose just before it attaches to the exhaust fitting)

* Inspect the wire splices for waterproofing

Backflow is a major consideration when designing a bilge pump system. Backflow is the amount of water that resides in the exhaust hose but is not evacuated out the exhaust fitting, which returns to the bilge when the pump shuts down. The key issue is the discharge hose run: How high must your pump lift the bilge water and how far must it travel to its destination? The lower and shorter, the better. Too much backflow can result in the pump continuously cycling on and off. And if it’s close, a wake that rocks your boat back and forth may also trigger a cycling episode.

A quick fix to this problem could be a check valve in-line of the discharge hose. One caution: No matter how efficient the design of a check valve, there is some restriction to the outflow.

Electrical Impulses

While we’ve addressed the manual vs. automatic triggering of the pump, the philosophy of your system is significant: The most important time to have your bilge pump functional is when you are away from the boat (and it is in the water, of course). Do you want to have to remember to turn your automatic system on every time you leave the boat, or should the system have electricity available so it works at all times?

The logical choice is to have your system active at all times. This eliminates an item from your departure checklist and guarantees that even when you are on board you don’t have to worry about whether it is on or not. The simplest way to perform this is to have a fused, direct line from the hot (positive) buss to your automatic (float switch) triggering system. Sometimes this will mean a fused connection directly to the positive stud on your battery. The chances of depleting your battery via an open circuit to the automatic switch are minimal, so let go of that outdated concern.

Another orderly method of organizing your bilge pump system is to have an indicator light. That visual indication will be an important safety feature while under way. If you locate this light strategically at the helm, an “on” light will notify you that the pump is operating and may require your attention to determine why.

Having a good understanding of the purposes and limitations of the typical bilge pump system will help you secure the most important part of your boating lifestyle: safety. While an electric, lighted, manual/automatic bilge pump system is not a requirement, it’s not a bad idea for anyone who is serious about keeping the water on the outside of the boat.