Bilge Pump Calculator
Size a bilge pump by boat length, measured ingress, safety factor, and single vs dual-pump strategy. Returns required capacity, ABYC minimum, pump count, and a 12-volt current estimate for battery planning.
Marine Toolkit runs this math past cell range
Worked example
25 ft boat, measured leak 300 GPH, safety factor 2.0, single-pump install.
ABYC bilge pump capacity reference
| Boat LOA (ft) | ABYC minimum (GPH) | Recommended for heavy use |
|---|---|---|
| <16 | 500 | 800–1,000 |
| 16–24 | 1,000 | 1,500 |
| 24–32 | 1,500 | 2,000 |
| 32–40 | 2,000 | 3,000 |
| 40–50 | 3,000 | 4,000 |
| 50+ | 3,000+ | 5,000+ |
Common mistakes
- Sizing to nameplate, not installed flow. A 2,000 GPH pump delivers ~1,200–1,400 GPH once hose, head, and voltage drop are included. Pick the next size up.
- Single-pump boats without a high-water alarm. Float switches stick. If the primary fails and there's no alarm, the first sign of flooding is water over the sole.
- Undersized wire. 16 AWG on a 30 ft run to an 1,100 GPH pump sags voltage enough to drop flow 20–30% and overheat the conductor.
- Using a check valve instead of an anti-siphon loop. Check valves fail closed or open — either mode floods the boat. ABYC wants a vented loop.
FAQ
What is a bilge pump?
A pump installed in the bilge — the lowest interior space of a boat — to remove accumulated water before it damages equipment or rises to an unsafe level. On most small boats it is a 12-volt electric pump controlled automatically by a float switch.
What capacity bilge pump do I need?
The larger of two values: the ABYC minimum for your boat length, or your measured leak rate multiplied by a safety factor (usually 1.5–2.0). That prevents a minor leak from driving the pump below a reasonable baseline while still covering abnormal inflow.
Should I install dual bilge pumps?
Often yes. Dual pumps add redundancy and surge capacity. A common arrangement uses one smaller automatic pump for routine water plus one larger higher-mounted pump that activates only when water rises unusually high.
What is ABYC standard for bilge pumps?
ABYC A-16 covers powered dewatering on recreational boats. It's a voluntary standard, but marine insurers and surveyors use it as the compliance baseline. See our ABYC A-16 reference.
How much battery capacity does a bilge pump need?
Depends on pump current draw and expected run time. A rough planning figure for 12-volt systems is about 1 A per 250 GPH of installed capacity, but real demand depends on discharge head, voltage drop, and duty cycle. Size battery reserve for the worst credible pumping duration.
Sources
The web page can't load once the boat leaves coverage
Marine Toolkit keeps ABYC E-11 ampacity and tank/scope math on the phone, saves each run, and works in the engine room and offshore. Pay once, own it.
Related
CalcSpec is a sizing estimator for boat owners and marine professionals. ABYC A-16 and E-11 are voluntary standards; installed systems subject to survey or insurance underwriting should be verified by an ABYC-certified technician. 33 CFR 183 is federal law for covered recreational vessels.