BILGE PUMPS CYCLING
When we bought our boat it had a large capacity bilge pump with a large diameter hose that ran for half the length of the boat. I fitted a relay that switched a car horn on when the bilge pump switch was activated, the idea being that this would warn us of serious water leaks in the boat.
When we went on our first coastal cruise and the ocean swells hit, the car horn sounded and the consternation onboard was considerable. It seemed we were sinking. I looked in the bilge and there was little water. The problem was that as soon as the bilge pump stopped, the water in the outlet hose would return to the bilge and switched the pump on and sounded the alarm horn again. We were not sinking.
After fiddling about with the float switch level the problem remained.
The solution was simple. I fitted a second bilge pump of low capacity with an inbuilt switch and a half inch exit hose. This cleared the bilge of large quantities of water caused by the large capacity bilge pump hose returning water to the bilge and the cycling stopped. If a serious leak occurs the large capacity pump still operates but the small capacity pump takes care of minor leaks and we now get no false alarms.