Our Navigator (42' motoryacht) came from the factory with two standard issue 1500/3000 Rule bilge pumps in places where water really never collects. One is midships under the stateroom/head and the other in the rudder box. My plan is to relocate the rudder box pump to a low spot between the engines and replace it with a much larger capacity pump for emergencies. I will need to add a larger thru-hull to accommodate this install. My question is about the placement. Can it be placed just above the waterline where the others currently reside, or should it be higher? My thought is that if the boat has taken on enough water for the emergency pump to activate, would not the boat now be lower down in the water, effectively restricting the output, perhaps even siphoning water back into the bilge? Or, can a pump easily overcome the backpressure without a significant reduction in flow?
Bilge Pump Exit Placement
- Thread starter GonzoF1
- Start date
The bilge covers a small space within the hull. The water level in the bilge section can be high and the boat will not drop any. The backup pump is usually set higher than the primary so that it will activate only if the primary fails. You can set your primary in the floor of the bilge. I would suggest you save your money and the hull from an additional hole. A 1500 GPH and a 3000 GPH bilge pumps are more than adequate. It is the small boats that need a larger pump as they will fill up faster. Kidding aside, the bilge pumps are merely convenience fixtures to automatically discharge incidental water that collects in the bilge. They do not have the capacity nor are designed or intended to tackle a significant inflow of water. The small electrical bilge pumps like Rule are bench rated with no loads; add a length of discharge hose and a couple of heads or water to be lifted and their rated capacity in GPH is cut in half. Operate the pump uninterrupted for any length of time and the heat produced will cut the capacity even further. It is not unusual the pump rated for 1500 GPH may only deliver 500GPH in a good day. The bilge should be located at the low spot in the hull and the pumps installed within the bilge. All other areas where water may collect should be connected to the bilge by small holes or conduits with the exception of the pan under the engine(s). Oil and fuel residues cannot legally be discharge into our waterways. I understand you are not a sailboat but all the principles should apply with the added factor of speed where the water collected in the hull may be pushed to the stern as the boat gets on plane. Perhaps you may not have a deep bilge to stage a primary and backup pumps so I would look for places around the stern and the low point when the boat is just floating at the dock. I'm sure your boat designers may have chosen the best locations. For an emergency you may likely need a 120V gusher pump that can run off a generator or shorepower. The small bilge pumps will not do it.
