See full version: Installing a Bilge Pump
If the discharge is submerged when the pump runs, the ocean siphons back through the pump into the bilge when the pump shuts off. When enough water has entered to float the switch, the pump will eject it, only to have it siphon back again. This continues until the battery is depleted, then the water floods the boat until it reaches a level that gets the crew's attention.
Bends and long runs also reduce pump output, so make the hose run as straight and as short as possible. That may mean discharging the pump through the side of the hull rather than through the transom. However. . .
The discharge fitting must never go below the waterline. If the fitting is through the transom, be sure it is high enough not to submerge when the stern squats. And if it is through the side of the hull, it must be high enough to remain above the water at the deepest angle of heel.
Do not strip the ends of the supply wires and loop them beneath the battery terminal wing nuts. Install crimp-on ring terminals the proper size to fit the threaded posts on your battery. Use a copper washer-not steel-between the wing nut and the ring terminal. [links]
When you turn the power off to leave the boat unattended, you don't want to turn off the bilge pump. Connect an automatic bilge pump directly to the battery, not through the distribution panel. here
The ideal bilge pump arrangement is a small (400 gph) automatic bilge pump mounted in the sump to dispense with rain and shaft-gland leakage, combined with a high capacity pump (3,500 gph) mounted higher to deal with more serious ingress.
The through-hull fitting can further reduce pump capacity. To minimize this restriction, use a fitting with the largest possible opening. more
Corrugated hose reduces pump output by as much as 30%, so always connect the pump to the discharge fitting with hose that has a smooth interior surface.
A bilge pump big enough to deal with a real emergency will do a poor job of keeping the bilge dry because the water in the discharge hose drains back into the bilge when the pump shuts off. And a big pump requires a big hose.
Mount your bilge pump float switch to the hull of the boat using the instructions that came with the float switch. There are many mounting methods used, as they vary according to the different models. When you are working on your hull you always have to be cautious. here
The 3-way switch will replace the manual bilge pump switch. The powered wire from the manual switch is connected with the line terminal of the 3-way switch. Connect the bilge pump wire to the switched terminals of the 3-way switch. Now connect the float switch by connecting a wire to each switched terminal on the 3-way switch.
Disconnect the wire that is on the negative battery terminal. This is to avoid the chance of electrocution. more
A bilge pump float switch turns the bilge pump on automatically when the water passes a certain level in the boat. Here are a few instructions on how to install a bilge pump float switch.
The wiring of the switch has to run to the manual bilge pump control switch. When you are running the wires, try using an area that is out the way. Many people choose to run the wire through the bilge. Nonetheless, if you do it this way be sure to avoid running the wire where it will be continuously wet.
Position the float switch in the bilge near the bilge pump. The float switch should be at the same level or slightly higher than the bilge pump so that the switch does not trigger the pump before the water level has reached the pump. here
Disconnect the negative wire from your boat's negative battery terminal. more
Replace the current bilge pump manual switch with a three-way switch. Connect the powered wire from the original switch to the line terminal on the three-way switch. Connect the wire that runs directly to the bilge pump to one of the switched terminals on the three-way switch. Connect one of the wires from the float switch to each of the switched terminals on the three-way switch.
Purchase a float switch that is compatible with your bilge pump. Most bilge pumps run on 12V DC power so it is important to get a switch intended for 12V power and rated for slightly more than the maximum wattage draw of your bilge pump. Purchase a float switch with long enough wires to run from your bilge pump to the pump control switch. more
Run the wiring from the float switch to the current manual bilge pump control switch. Try to run the wiring in an area where it is out of the way, for example through the bilge, but avoid running it through an area where it will be continuously wet. [links]