Submersible Bilge Pumps 12V

Bilge pumps for boats: 12V and 24V submersibles

The bilge pump is the quietest piece of safety equipment on the boat: you cannot see it, you cannot hear it and you only miss it when it is already too late. Its job is to clear the bilge of the water that comes in through the stuffing box, from condensation, from rain or from a leak.

At Repuestos Marinos you will find submersible bilge pumps in 12V and 24V with flow rates from 500 to 5,400 litres per hour, in manual and automatic versions with a float switch, from Rule and approved equivalents, plus manual diaphragm bilge pumps and level switches.

Types of bilge pump

Submersible centrifugal. The usual choice in the bilge. It is fitted at the lowest point and discharges through a thru-hull above the waterline. Simple, inexpensive and with a good flow rate, but it is not self-priming: it has to stay submerged to work.

Automatic with float switch. It has a switch that starts the pump when the water reaches a certain level and stops it when the level drops. This is what you want on a boat that spends time unattended on its berth. It is best wired directly to the battery with its own fuse, so that it keeps working even with the main isolator switched off.

Self-priming diaphragm pump. It can be installed outside the bilge and draw from several points. More expensive and with a lower flow rate, but it will pump the bilge almost dry and can run dry without damaging itself.

Manual pump. Compulsory in most navigation areas as a backup. It does not depend on the battery, which is precisely what can fail in an emergency.

What flow rate do I need

The flow rates manufacturers quote are at zero head and with no hose. In a real installation, with discharge height and elbows, the effective flow can drop to half. Always size with a margin.

As a guide: up to 6 m length overall, 500-800 l/h; 6 to 9 m, 1,100-1,500 l/h; 9 to 12 m, 2,000-3,000 l/h; above 12 m, 3,700-5,400 l/h or several pumps at staggered heights. On boats with accommodation the best approach is to fit two pumps: a small automatic one for the day-to-day trickle and a large emergency pump mounted somewhat higher.

Fitting it properly

Full-diameter hose, with no reducers and no unnecessary elbows: every restriction cuts the real flow rate.

Anti-siphon loop. If the outlet is close to the waterline, fit a swan neck or a non-return valve so that sea water cannot run back into the bilge when the boat heels.

Correct fuse and cabling. Work out the cable size from the current draw and the run length; undersized cable makes the pump perform below expectations.

Strainer or grille on the intake and a clean bilge. The number one cause of bilge pump failure is a rag, a cable tie or bits of laminate jamming the impeller.

Warning light at the panel. A lamp that comes on when the pump runs tells you water is getting in before it becomes a problem.

Maintenance and 24-48 h shipping

Test the pump manually every time you step aboard: it takes a second. Clean the bilge and the intake strainer every season, check the float switch (they stick with dirt and oil) and inspect the electrical terminals, which corrode easily in a bilge environment.

Shipping in 24-48 h to mainland Spain and the Balearics, 3-5 days to the Canary Islands and the rest of the EU. Orders placed before 14:00 leave the same day. Returns within 14 calendar days, plus technical support by phone and WhatsApp.

Frequently asked questions about bilge pumps

What bilge pump flow rate do I need?

As a guide: up to 6 metres length overall, 500 to 800 l/h; 6 to 9 metres, 1,100 to 1,500 l/h; 9 to 12 metres, 2,000 to 3,000 l/h; and above 12 metres, 3,700 to 5,400 l/h or several pumps at staggered heights. Size with a margin, because the quoted flow rates are at zero head and with no hose: in a real installation they can drop to half.

Should I fit an automatic bilge pump?

Yes, especially if the boat spends time unattended on its berth. An automatic pump has a float switch that starts it once the water reaches a certain level. It is best wired directly to the battery with its own fuse, so that it keeps working even with the main isolator switched off.

How many bilge pumps should a boat have?

On boats with accommodation, two electric pumps are the sensible answer: a small automatic one for the day-to-day trickle and a higher-capacity one, mounted somewhat higher, as the emergency pump. On top of that, most navigation areas require a manual pump as a backup, because it does not depend on the battery.

Why is my bilge pump not working?

The most common cause is something jamming the impeller: a rag, a cable tie or bits of laminate in the bilge. After that come a float switch stuck with dirt and oil, corroded electrical terminals and a blown fuse. Always check in that order.

Do I need a non-return valve on the discharge?

It is strongly advisable if the outlet is close to the waterline. Without an anti-siphon loop or a non-return valve, sea water can run back into the bilge when the boat heels or runs downwind. The alternative is a swan neck raised above the waterline.

Can a bilge pump run dry?

Submersible centrifugal pumps should not run dry for long, because they overheat and get damaged. Self-priming diaphragm pumps do tolerate running dry and will leave the bottom of the bilge almost dry, although their flow rate is lower and their price higher.