Hi Bill,

thanks for the suggestion. I have checked the stainless pipe and there
is no sign of any leaking water, though I have been unable to check the
aft end of the pipe yet as it is buried under storage boxes that I built
above the hot water tank.

If left at it's berth, the genset will always start normally with a good
supply of water. It's only when sailing that the water disappears. It
would seem that the forward motion sucks the water out of the system,
creating an air lock. Why water does not get forced back to the pump
when the boat is staionary and on an even keel is a mystery. Maybe if
the impeller vanes straddle the intake opening, then the air cannot pas
through the pump?

Two solutions come to mind. Install a scoop at the strainer intake.
(Haul out required and more drag), or install a non return valve just
below the impeller. I am dubious as to whether such a valve exists that
will withstand prolonged salt water immersion.

I have emailed Amel for help and will pass it along if they come up with
the answer.

Regards

Ian