Regarding Bilge Pumps
Firstly, bilge pumps should only be used for emergencies and not to keep up with the flow of water coming from leaking windows, thru-deck fittings, rub rails, stanchions,...etc. Secondly, if you do have any emergency that requires pumping, the primary pump should be a manual pump with the electric as the back-up. On smaller boats without inboard engines, the primary pump should be a manual bilge pump(operated from the cockpit) with a manually operated electric pump(w/float switch) as a backup. If you don't have a constant power source, such as an inboard with an alternator or dockside electrical hookup which can supply an electric pump with constant power, the battery can die rendering the pump useless. A manual pump will run until the crews gives up. Additionally, smaller outboard powered sailboats don't have many ways for water to get in besides a structural failure of the hull(hole), taking on water in heavy seas, or leaving the hatch open during a monsoon. At the dock, thru-hulls(sink drains, head intake) should be closed when a boat is unattended and when at sea, thru-hulls should be closed if they are not being used. Say, for example, you visit your boat on the weekends and you have an automatic electric bilge pump. The boat springs a leak on Monday and starts taking on water. Your battery powered electric bilge pump starts constantly pumping water, but soon the battery dies and the boat sinks. Once I went to the marina to find a group of people around a boat that was taking on water, bailing with buckets to keep the boat afloat. They had come upon the boat, saw it was taking on water, and immediately went aboard to turn on the bilge pump. They discovered that the automatic electric pump was turned on, but it had already killed the battery. Since the boat didn't have a manual pump they scrounged up some bailing buckets until help arrived. If the boat had an installed manual pump, the rescuers could have used it to keep the boat from sinking until help arrived.What if your boat is far from land and you have only an electric pump. The boat starts taking on water and the pump turns on until the battery dies. At this point the boat is sinking and you have to call for help on the VHF,...Oh, but wait...the pump killed the battery and you can't call for help. If the primary pump were a manual pump, then both the pump and radio would still be operational.If you don't have a constant and relatively unlimited power supply to run an electric pump, then you should have a manual pump as a primary with the electric as a back-up. Instead of having an just automatic electric pump, you may want to install a bilge alarm to warn you of a potential problem. When the alarm goes off, either pump manually or switch on the secondary electric pump. Additionally, a bilge alarm may alert others in a mooring or in a marina to a problem when you are not there and they could render assistance(manually pump until help arrives). If your boat is taking on water faster than a manual pump can empty, then what you need is not an electric pump, but a flare gun and life raft!