Small pumps for separate compartments in boats and other vessels can either be electrically powered or run off of 12v or 24 volt marine batteries. As a rule, every compartment that doesn't allow free flow of water from one to the other needs to have a bilge pump. Smaller boats under 16 feet in length should bilge pumps of at least 800 gallons per hour and more if possible. Boats between 20' and 40' can use bilge pumps or multiple units that should give evacuations of from 2500 GPH to 6000 GPH as the vessel size increases. Buy the largest capacity pumps that will fit your space and ensure hoses and discharges are sized properly.Anyone who does any long range cruising should have an emergency bilge pump.
Diaphragm pumps are re self-priming and act like a wet-vac to draw out bilge water. Water is pulled in through an intake valve, then pushed out through an output valve.
Centrifugal pumps are less expensive but are not self-priming .Advantages include low maintenance, good reliability, and the ability to pass intermediate solids without clogging. They can also run dry for extended periods without immediate damage. They are prone to loss of effectiveness the farther they have to push water vertically.