In pain after getting the problem fixed. Seems the thermostat was stuck open causing too much cooling of the engine.
Replacement thermostat, gaskets, springs, belt tensioner, belt and labour ---- £192!!
At least the boat is back on the water and going well.
Had a sporty trip from Kinnego Marina on Lough Neagh to Battery Harbour on the western shore of the Lough. Straight into a wind causing lots of white horses and water spray.
Trip back with a following wind and wave formation was great