At the top, from left to right, are the MPI Sure Bail DEL-30 and the Rule-A-Matic Plus Model 40. In the center is the West Marine model 543561. On the bottom, from left to right, are the Ultra Safety Mini, the 36152 from Johnson Pumps, and the Water Witch 230.

The automatic bilge pump switch is the lowly guardian of a boat’s bowels. Its sole purpose: Switch on the pump when a predetermined level of water is detected in the bilge, and turn off the pump when the bilge is dry. The task may sound simple, but the bilge itself—with its corrosive mix of seawater, oil, shards of fiberglass, and other debris—makes it a tough job.

What We Tested

Thirty different automatic switches flood the market today. They are grouped into three main categories: the pivoting arm, the vertical float, and the electronic pump switch. We tested 17 switches: eight verticals, five pivoting arms, and four electronic. …