My Hunter 340 came (to me) with a Rule bilge pump, it is the kind that automatically fires every 7 minutes. If there is no resistance on the pump, indicating no water to pump out, it shuts down. So far this season (May – September) the pump has fired 70,000 times according to the counter at the Nav station.
While I appreciate the security of a pump that is always checking, I can’t imagine it is doing anything but slowly, unnecessarily wearing the pump out. It also makes a racket that I’ve gotten used to. Given I’ve got solar panels I don’t worry about the battery drain either, but that could be an issue for some owners.
My bilge is dry, the only moisture coming from the fridge drain or the odd bit of rain water from accidentally left open ports. If there is a bit of water in the bilge, the pump makes a splashing-gurgling noise that echoes in the empty chamber – it is a good indicator that I need to sponge the bilge dry!
A friend stayed on the boat and remarked that my boat sounds like Star Wars, full of strange mechanical noises in the night, startling him awake as he drifted to sleep. The bilge pump whirrs, the fridge breathes like Darth Vader and the old water pump would hammer for half a second every half an hour or so. The pump is gone, the fridge stays so this leaves me wondering about the whirr in the bilge.
Quick web research reveals that the floating hinged (ball bearing or a tube of mercury) types (Rule, Seasense, Seaflo ) are generally only good for a couple of years at best. These also tend to foul on debris. Given my bilge access is beneath the dining table, there is a frequent stream of cheerios, crumbs and craft bits like string, paper and beads falling into the finger holes in floor/hatch, I would like something that can’t be easily fouled.
I looked into the electronic current sensor types, the most popular brand being the Water Witch. The drawback seems to be that the sensors stop reading if the water is contaminated oil or grease. The sensors use the conductivity of bilge water to pass current between two electronic probes, if oily, the sensors don’t receive the current.
Also, Water Witch seems to have hit and miss user reviews despite their claims that they are used on US and Canadian coast guard vessels.
Finally, there are physical switches in enclosures. The leader of this segment appears to be Ultra Saftey Systems, Aqualarm appears to be a cheaper knock-off of Ultra.
the benefit of these is they should not foul from debris and are less prone to firing from boat motion.