over the side is self priming as impeller is below water line. thru hull is below water line. Thru scupper needs a means of priming as impeller is above water line. Hobie uses a pick up tube with a 90 degree angle pointed forward. Momentum pushes water up to the impeller, once primed should run the duration of the battery, obviously a timer switch would be a bad idea in this configuration..........or any configuration IMO
