In article ,
Roger Long wrote:
"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.

You assume correctly. (Neal is just as ass.) See my other post if you haven't already.

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.

I have two choices about where to locate a loop. One is near the transom. The other is in the engine space, which is perhaps 3 feet from the pump. I'm inclined to think that the latter would make it much more difficult for the pump, having to overcome the height in short distance. The former solution might cause some backflow/pump cycling, but I can't know until I try it. It's certainly easier for the former solution.

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.

I would never try to discharge on the side. It's a stern discharge now, and it will remain that way.