Re: Bilges - On vs. Automatic; Capacity?
There is usually water in the discharge hose which runs back down into the bilge after the float switch turns the pump off... depending on how long the hose is and how it is run. Running the pump on the manual switch may get this lower, but it's virtually impossible to get everything out (though I've done it with a Shop-Vac in an otherwise dry boat).
Having a second pump is not a bad idea. One approach would be to install a float switch on the second pump but locate it higher than the first, so that one pump would take care of "normal" seepage (wherever it comes from) and the second would kick in if there was more water than normal or the first pump/switch failed.
I've often thought of doing this on my boat (where the primary factory pump is, unfortunately, a "shower sump" pump), but the problem is drilling out the ribs to run that second discharge hose.
Hope this sort of answers your question.
1998 Jeanneau SO45.2