Bilge alarm and float switch fundamentals

Every boat needs at least two independent bilge pump circuits per bilge compartment: an auto-cycle pump (float switch triggers) and a high-water alarm (separate float switch, separate wire run, separate audible alarm at the helm). ABYC H-22 requires this separation so a single failure doesn't leave you sinking. Common failures: (1) Float switch stuck by debris, mechanical float switches (Rule, Attwood) will jam on packing peanuts, wire ties, or dead marine life. Electronic sensors (Ultra Safety Systems, Water Witch) have no moving parts and are more reliable but need clean 12V power. (2) Pump running dry from a stuck-on switch, kills the pump impeller in an hour. Check bilge state daily. (3) Cracked pump housing from age or freeze, replace pumps every 5-7 years regardless of function, they're cheap insurance. (4) Discharge hose siphon, install an anti-siphon loop above the waterline OR a check valve at the pump. Without one, water siphons back into the bilge after the pump stops, cycling the pump forever until it fails. High-water alarm: mount 6 inches above the auto-pump switch. Test both circuits monthly by manually lifting the float. Wire the high-water alarm to a battery that STAYS powered even with the main switch off, you want the alarm working when you're not aboard.