Hello Howard, I had a hatch fitted in the aft cabin top and it works extremely well especially whilst at anchor. See message nos 1781 and 1804 for a description and Bali Hai SM 317 photo album for more details.
I had problems with my bilge pump but it was a self inflicted injury because I was using the pump on manual switching when it had already emptied the sump to its preset level. This caused the electric pump to suck air thus emptying the pump above its top flap valve. The valve then failed to do its duty as it relies on the head of water above it to make it seal. The flap was only made of neoprene unlike the ones in Whale Gulper pumps which have flaps with a slice of something heavy like lead moulded in to make them seat properly.
