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bilge pumps for boats comparison, in stock
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What it does and the types available
A bilge pump removes water that collects in the bottom of the boat: rain, spray, condensation, small leaks or water coming in from a serious problem. No pump replaces a major repair, but a good bilge system buys you time to act.
- Submersible electric: the most common. Sits at the bottom of the bilge and runs on 12 V. Compact and simple to install.
- Electric diaphragm: mounts out of the water and draws through a hose. It handles debris better and can run dry without damage.
- Manual: works with no power, by lever or handle. Essential as a backup.
- Portable or bucket-style: for small boats, dinghies or as a supplement.
How much flow you need
Flow is rated in gallons per hour (GPH) or liters per hour (l/h). Remember that the manufacturer's number is in ideal conditions. With a long hose, bends and low battery voltage, real flow drops noticeably.
| Boat | Typical flow | Notes |
|---|---|---|
| Open boat or dinghy (up to 13 ft) | 350-500 GPH | A small pump plus a manual pump is enough |
| Boat of 13-20 ft | 500-1,000 GPH | One main pump with float |
| Sailboat or cruiser, 20-30 ft | 1,000-1,500 GPH | Automatic main pump plus a backup |
| Boat over 30 ft | 1,500 GPH or more, several pumps | One in every watertight compartment |
Tip: two medium pumps in different spots beat one very large pump. If one fails or jams, the other keeps working.
Float switch and automatic operation
A pump without automatic control only helps if you are aboard. For a boat on a mooring or at the dock, the usual answer is a float switch that starts the pump when water rises. There are three options:
- Mechanical float: simple, but it can jam with debris.
- Electronic or sensor switch: no moving parts, less prone to sticking.
- Manual switch at the panel: lets you run the pump by hand and pairs with the automatic switch.
The ideal setup is both automatic and manual control, with a high-water alarm that warns you if the pump is running too often. Review the whole electrical system, including the battery switches, so the pump always has direct power from the house battery or a dedicated one.
Installing it correctly
- Mount the pump at the lowest point of the bilge, where water gathers, and secure it so it does not shift with the motion of the boat.
- Use hose of adequate diameter with as few bends as possible, and avoid kinks.
- Discharge above the waterline, with a high loop (vented loop) to stop water siphoning back in.
- Fit a fuse sized for the pump in the positive wire, close to the battery.
- Use correctly sized wire and waterproof connectors. Enough voltage must reach the pump.
- Test the system by pouring water into the bilge and checking that it starts and discharges.
Warning: a discharge below the waterline without a check valve or high loop can sink a boat by siphoning. For offshore use, follow the equipment rules for your waters and ISO 15083, the international standard for bilge-pumping systems on small craft.
Maintenance that prevents failures
- Test the pump at the start of the season and at least once a month if the boat stays in the water.
- Clean the bilge and the intake strainer. Leaves, hair, grease and plastic bags jam pumps. See our bilge cleaners for degreasing without harming the equipment.
- Check the float. It must move freely and not stick.
- Inspect connections and the fuse: a corroded terminal is the most common reason a pump «will not start».
- Check battery condition regularly. A weak battery leaves the pump short of power. See lithium batteries or the right charger.
Make the pump test part of your routine before leaving the dock. It is included in our pre-departure checklist.
Common mistakes
- Relying on one pump and having no manual backup.
- Buying by maximum flow without considering the hose, discharge height and battery voltage.
- Placing the float where it snags on wiring or bilge hardware.
- Skipping the fuse or using wire that is too thin.
- Ignoring the high-water alarm. A pump that runs nonstop is warning you that water is coming in.
Frequently asked questions
What flow rate does a bilge pump need for a 20-foot boat?
For a boat of about 20 feet, 500 to 1,000 GPH is usually enough as the main pump. It is better to add a second backup pump and a manual one than to rely on a single very large pump.
Is a manual bilge pump worth having?
Yes, especially as a backup. It does not depend on the battery and is the last line of defense when the others fail. Keep it accessible with the hose already attached.
How many bilge pumps should I have aboard?
A good setup is an automatic electric pump in the bilge, a second backup pump and a manual pump. On boats with watertight compartments, fit one per compartment.
Why does my bilge pump run but not move water?
Common causes are a clogged intake, a crushed or sharply bent hose, air in the pump or a badly installed discharge. Clean the strainer, check the hose and make sure the pump is fully submerged.
