Over on one of the sailing forums I participate in, there was a question about how to setup the bilge pumps on a boat. Here are my thoughts on that issue.
Ideally, the a monohull sailboat should have at least four bilge pumps. Two would be electric, and two would be manual.
The two manual pumps are the largest, highest capacity manual diaphragm pumps that money can buy. One would be mounted so it can be operated by a person in the cockpit, and one mounted where it can be operated by someone in the cabin. Ideally, both would be close enough to the companionway that they could be operated from both inside or outside the cabin. These are the pumps that are used to assist the electric bilge pumps or in the case that the electric pumps fail.
The third pump would be a fairly small, low capacity electric bilge pump that is used for bilge maintenance. It has an integrated float switch and is wired directly to the house batteries with a switch that has off, on and automatic positions. It should also have a bilge pump counter, that keeps track of how many times the pump activates.
The reason I call this a “bilge maintenance pump” is that its primary purpose is to maintain a relatively dry bilge. It is sized and designed to take care of the routine amount of water that leaks into the bilge via the stuffing box, the mast (in the case of keel-stepped masts), condensation, the air conditioning and other such water sources.
As part of your routine when closing up the boat, the captain would note the number on the bilge pump counter in the ship’s log book. When opening the boat back up, they’d compare the counter to the last number recorded. If they divided the difference between the two numbers by the number of days they were away from the boat, they’d have a rough daily average for the maintenance pump. If that daily average number starts to increase significantly, it is time to look for a leak.
The fourth pump would be a very high capacity electric bilge pump that is also wired directly to the house batteries. It has a float switch mounted about two inches above the third pump’s float switch. This is the main electric dewatering pump for the boat. It should also have a switch that has on, off, and automatic positiions. It should also be connected to a very loud high water alarm, preferably that sounds in the cockpit.
The reason this fourth pump has an alarm is to alert people at the marina that there is a problem with the boat, and that action needs to be taken. Ideally, they should contact the owner if this alarm sounds. The boat should have owner contact information posted somewhere in the cockpit that is easily located in the case someone boards the boat to see what the alarm is about. This is especially true if the boat is on a mooring.
The setup differs a bit for a trimaran, since a trimaran has three hulls to consider, and the bilge in the main hull is generally far shallower than that of a monohull sailboat. However, the fact that most multihulls won’t sink readily if only one hull is flooded is another consideration. There should be at least one bilge pump in each ama, and at least one in the main hull.
The bilge pumps in the amas should be manual, since the amas should, ideally, be water-tight and only pumped out after being inspected. Currently, I’ve been using a navy-style piston pump to dewater the amas, but not much water gets in to them, so it isn’t much of a big deal. I do plan on installing a manual diaphragm pump, to allow me to pump out the main center section of each ama, which seems to get the most water due to the large hatch on it.
I also plan on installing a three bilge pumps in the main hull. A small maintenance pump, a large electric pump and a large manual pump as described above.