Surveyor's report didn't says so and recommended testing, but based on the operator's manual, you don't need to keep a batter switch on since they were supposed to be directly wired to a power source. That guidance is contradicted by the wiring diagram, which shows the bilge pumps to be powered from a sub panel and thruster battery. Most owners aren't going to be electricians so would be expected to rely on the written word describing intended function. The surveyor expressed the opinion that the flapper valve that is supposed to prevent the inevitable water from sloshing into the sponson was inadequate. However you cut it, this Cutwater was very poorly thought out with the result that whatever the failings of the owner or dealer, the vessel capsized.
I took a look at the 302 wiring diagrams and my read is a bit different. I agree it’s not super clear, but here’s my take.
First, according to the surveys, there are three pumps; two in the main bilge and found on the inboard as well as the outboard versions of the 302. Then a 3rd pump in the sponson, obviously unique to the outboard version of the 302.
The wiring diagram shows the dual main bulge pumps, but down NOT show the wiring on the outboard sponson pump. So we have no idea how it’s wired, and whether it’s the same or different from the main pumps.
The main pumps appear to be wired from two power sources; the thruster battery, and the house bank. This part is unclear, but I suspect this relates to the typical on, auto, off switches commonly used for bilge pumps. The power from the thruster battery runs through float switches, so would be the Auto power source. And the power from the thruster battery is always present for the pumps, even if the thruster switch is off. The switch only controls power to the thruster itself. This all seems reasonable, and agrees with the operators manual.
The second power source from the house bank is indeed switched by the battery switches, and there will be no power if the battery switches are turned off. I suspect this power source is only used for the Manual On operation of the pumps, but can’t tell for certain.
What’s completely unknown is how the sponson pump is wired. It might be the same as the other pumps, which would be fine, or it could be different with unknown implications.
Regardless of the wiring, the pump arrangement in the sponson seems problematic. The top of the sponson is barely above the water line, and that the highest any anti siphon loop could be for the pump. And there was no mention of an anti siphon in that hose run, making it highly susceptible to siphoning. The check flap would slow any back flow, but is never a substitute for an anti siphon vent. If the outlet remained submerged after the pump ran due to wave action, it would immediately start to siphon back into the sponson. Get enough water in the sponson, and the pump outlet would be permanently below the waterline with constant siphoning. The amount of water flow would be impeded by the flap, but definitely not a perfect seal, and perhaps a very poor seal if any debris got in it. Any pump failure and its curtains. Plus the pump could be running constantly and rapidly drain the battery. I suspect this was the first element in the chain of failures.
Now add the weight ( or lost buoyancy) of a flooded sponson that places the penetrations to the main hull below the water line. At that point it’s all a done deal.