Yanmar 2GM loss of prime whilst sailing

[DufourJon]

All,
I have a problem! And, whilst scouring the web for an answer I found this site, so joined and hopefully there may just be an experienced sea dog out there who could help. Here goes with the symptons of the problem...
1. Starting with boat in marina and raw water primed through filter.
2. Engine starts and runs fine whilst flat in marina etc, but when the yacht starts to keel or is in rough choppy water the prime in the raw filter slowly goes down until it is dry.
3. The engine a Yanmar 2GM, there is a single through hull sea **** for the engine, there is an anit-syphon valve and the exhaust has just been replaced with a new waterlock. Impellor looks good with no scouring on the plate.
4. There is no fresh water on the Yamar
Having just had to be rescued which was a trifle embarrasing in a Force 5 HELP Please...
The only thing I can think of, and this come from this site is that the strainer is quite high up... about the hight of the pump... maybe a little higher, I would need to check - but people are saying it should be low?

[DrB]

Where on the bottom is the inlet for the engine cooling water located? Is near the centerline of the boat on the bottom or more towards waterline? If you heel the boat (while the motor is running) does the side to which the heel is being done make a difference, ie if the boat is heeled to port the problem is noticable, but when heeled to starboard it doesn't, or vice versa?

[DufourJon]

Thanks for the message - the strainer sea **** (feed) is just off the centre line to s'bd but the problem does not seem to change irrespective of tack... it does it even if the boat pitches for and aft.