The most common types of bilge pumps (and the primary focus of this article) are centrifugal and diaphragm electrical pumps. Centrifugal pumps move water by kinetic energy using a rotating, solid impeller, similar in design to a turbine. Water enters the pump, picks up speed as the impeller rotates, and is then forced out by its own momentum. Centrifugal pumps are submersible but not self-priming, meaning they must be sitting in water in order to pump it.

Centrifugal pumps are relatively inexpensive and can move a lot of water. Other advantages include low maintenance, excellent reliability, and the ability to pass small amounts of debris without clogging. They can also run dry for extended periods without damage, although this does wear the bearing and will cause it to fail eventually. Disadvantages include their inability to self-prime and their loss of effectiveness the farther they have to push water vertically.

A diaphragm pump acts like a little wet-vac to suck out bilge water. Water is pulled in through an intake valve, then pushed out through an output valve. Diaphragm pumps are self-priming (meaning they develop suction and prime themselves when dry), can be run dry without damage, and are better able to push water uphill than centrifugal pumps. As to downsides, they can't move as much water as a comparable centrifugal pump and most can't tolerate even small bits of trash or debris, which can lodge in the pump's valves, causing leaks or failure.

Nothing beats the simplicity and pumping power of a centrifugal pump. However, diaphragm pumps can be a better choice where water has to be pumped more than a few feet uphill, and they can be installed in a drier, more convenient place than the bottom of the bilge. Adding a filter before the pump to remove debris reduces the risk of failure.