Electronic level switches that are located in the bilge to operate an alarm or activate a bilge pump seem to be the least reliable piece of equipment on a boat, judging by the number of times they are condemned in sailing forums.
In my obsessive search for the ultimate bilge pump switch, I came across the report of a test completed by the UK fishing industry’s own standards organisation, a company set up to improve safety and efficiency in that industry.
Deep sea fishing boats have to carry a high water alarm to warn of flooding and the reliability of these systems, based as they are on a bilge switch operating a siren, is a problem.
This company did comprehensive testing on six or seven systems ranging in cost from nearly £1000 down to under £100. Within this group were resistive switches, optical switches, and an air pressure switch.
The systems were each installed and operated on a North Sea fishing boat for a minimum of six months. One system was removed during the test because it was clearly unreliable. Of the rest, it was noted that the Water Witch based system (the cheapest, incidentally) and the Jabsco air pressure switch were very reliable.
Of the resistive type switches it was noted that only the Water Witch sensor didn’t need to be periodically wiped clean whereas the other resistive types and the optical sensor gave false alarms, or wouldn’t switch off after the water level was reduced, if they weren’t wiped clean periodically. The report contained pictures of the conditions in which all the systems had to operate and they make the typical yacht bilge look as sanitised as an operating theatre!
I think bilge switches, whether they are expected to activate a pump or simply an alarm, have a most onerous task simply because of the hostile environment in which they perform. Salt water, oil, chemicals, debris, irregular and sometimes violent motion all contribute to nightmarish operating conditions.
I’ve come to the conclusion that all bilge switches work some of the time and no switch works all of the time. It isn’t so much that bilge switches are unreliable – it’s that they are inconsistently reliable.
I think the Water Witch would be my choice – until something better comes along.