"Wilbur Hubbard" wrote

To put one on a bilge pump is folly - pure folly. In order to keep a bilge
pump from siphoning all one needs do is have the bilge pump discharge
above the LWL of the vessel.


I assume though, that he is looking for a solution that doesn't involve
hauling the boat to relocate a through hull fitting.

With a long hose run, a vented loop can cut the amount of back flow
considerably if placed close to the pump. This makes for a less water in
the bilge even if back flow cycling is not a problem.

As far as keeping the discharge above the waterline, it has to be above the
HEELED waterline. This means near the centerline, thus the stern, on any
boat which is sailed hard which brings up the long hose run issue. The
heeling problem might not be apparent on a 27 foot boat that just sits in
one place but, if you really sail, a discharge near any probable bilge pump
location could start a back siphon while driving hard if the pump goes on
and stops. On a long tack, such as might be done on a passage, you could
end up with a significant amount of water in the boat if the pump failed to
restart.

--
Roger Long