Bilge high-water alarm
Monitoring
A float switch set above the bilge pump's normal level that sounds a buzzer, light or horn if water keeps rising. It warns that the pump can't keep up or has failed, and it can save a boat, especially one left at the dock.
How it works
The alarm's switch sits higher than the bilge pump's own float switch, so normal pumping doesn't set it off. If water reaches it, it sounds an alarm; some owners wire it to the boat's horn so neighbours notice when nobody's aboard. Switches come as hinged float arms, enclosed vertical floats, or electronic sensors. ABYC standards call for high-water alarms, so boats built to them have one; boats built earlier or to other standards may not.
Using it
- If the alarm sounds, find the source fast. BoatUS insurance files point first to the engine room: stern-drive bellows, raw-water plumbing, stuffing boxes and through-hulls.
- If water is gaining on the pumps, call for help early on VHF rather than waiting.
- Know which compartment each alarm covers. BoatUS suggests a separate alarm, light and label for each bilge area on boats with several.
- Consider wiring the alarm to the horn; BoatUS Marine Insurance found most sinkings happen while boats sit at the dock.
Looking after it
- Test each alarm float switch at least once a year, as BoatUS advises, by lifting the float and confirming the alarm sounds.
- Look for corroded wire connections and debris jamming the float, the same faults that stop bilge pumps.
- Mount the switch high enough to ignore water the pump normally handles, but low enough to warn early of a real problem.
- A magazine test of switches found hinged float arms work in calm water but can be less dependable when water surges; keep them free of debris.
Troubleshooting
Alarm sounds
- Check the water level and whether the bilge pump is running.
- Search for the leak, starting in the engine room.
- If the pump is running and water is still rising, call for help and prepare to act.
Alarm doesn't sound when the float is lifted
- Check the fuse and power supply.
- Check wiring connections for corrosion.
- Check the float isn't jammed with debris.
- Test the buzzer on its own.
Frequent false alarms
- The switch may be mounted too low, catching water the pump normally handles.
- Water sloshing underway can trigger it; check the mounting height and location.
- Clean out debris around the switch.
Buying a boat that has one
- Find out whether there's a high-water alarm at all; a boat not built to ABYC's standards may never have had one.
- Test each alarm and find where each switch is mounted.
- Ask about the bilge pumps' and alarms' service history.
Sources (2)
General guidance for recreational boaters, researched from the sources listed and written in our own words. Your equipment manuals, local knowledge, the Navigation Rules and a qualified instructor come first.