People are often baffled by the problem that the typical rotary vane bilge pump (such as Rule) does not remove all the water from the bilge. In fact, most pumps will leave as much as 1-1/2" of water. Plus there is also the matter that the remaining water in the hose when the pump turns off then runs back into the bilge.

You should not use a check valve in the bilge pump line to prevent the back flow of water. The use of a check valve is not recommended due to the potential for sticking and causing the pumping system to fail.

On a sail boat with a deep keel sump, that's probably not a problem, but on a power boat where the bilge bottom may be nearly flat, that much water remaining in the bilge can cause big problems. For one thing, when the boat gets up on plane, all that water is likely to go rushing aft where it sloshes and splashes around, causing corrosion damage to other things under the deck that shouldn't get wet.

Further, when the weather is hot, and the sun is beating down on the deck, this causes a high evaporation rate that creates very high humidity in the bilge that can cause other components, especially things like steel pump bodies and generator sets to rust up. Therefore, it's a good idea to remove as much of that water as possible.

Fortunately, there is a solution for this, which is to install a diaphragm pump that is capable of removing nearly all of the water from the bilge. Usually, these can remove up to the final 1/4" of water. For this purpose, we recommend the Jabsco - PAR single diaphragm pump, shown at left top, which is reasonably priced. We like it because it has mostly plastic parts that don't rust, and the diaphragm can easily be replaced. You'll also need to have an inline strainer so that no debris gets into the pump, but fortunately this is provided with the pump.

This pump has to be operated manually since no float switch can function in an inch of water. Therefore, it gets wired to a manual on/off switch

The installation of such a pump is straightforward. First, you need to determine where is the lowest point in the bilge when the boat is at rest, and where the water will accumulate. This is the point to install the pump and it's remote pickup. The beauty of this type of self-priming pump is that it can be mounted well above the bilge water and out of harm's way of leaking hatches where water might get to it.

Be aware that boat building is a low capital investment manufacturing business that is easy to enter but hard to prosper in. During the last ten years, an estimated 80% of all builders went under, most leaving unresolved warranty claims. If warranties are important to you, choose your builder carefully.

You can also double up to an existing bilge pump port by the same method. Your existing pump should have a riser loop already in the line, in which case all you need to do is install the "Y" and duplicate the riser for the new discharge line. It's wise to have a riser of at least a 12" above the waterline for power boats.