Hi Ed
I think you will find that most boats discharge their exhaust water in spurts – certainly at low revs. This happens because of the swan neck in the exhaust hose. The exhaust gases can only ‘pump’ the water up the hill when sufficient collects at the bottom. At higher revs, with a higher flow rate of cooling water, this happens more frequently and may appear almost continuous.
That said, 30 seconds does sound like a long time. Mine glugs every 10 seconds or so on tickover.
Best of luck with your Spanish trip – keep the mast up this time! We are heading for La Rochelle (all being well) a week or so behind you.
Roger
