Bilge Pump Sizing Calculator
Bilge Pump Sizing
Determine the right bilge pump capacity for your boat based on hull size, number of through-hull fittings, and worst-case flooding scenarios.
Formula
Bilge Volume = Length x Beam x 0.5 x Hull Factor; Minimum GPH = Bilge Volume x 5 x (1 + Through-Hulls x 0.1); Head Loss = Minimum GPH x (Discharge Height x 5%); Required GPH = Minimum GPH + Head Loss
Frequently Asked Questions
How do I choose a bilge pump size?
Select a bilge pump that can handle at least the volume of your bilge area times 5 per hour. Consider the discharge head height, as pump capacity drops significantly with increased vertical lift.
Should I have two bilge pumps?
Yes, the Coast Guard recommends a primary automatic bilge pump and a secondary manual backup. Larger boats should have an additional high-water alarm and a secondary automatic pump.
How much capacity do bilge pumps lose at height?
Bilge pumps lose 5 to 10 percent of their rated capacity for every foot of vertical lift. A pump rated at 2,000 GPH at zero head may only deliver 1,400 GPH at a 4-foot discharge height.
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