Bill thanks so much for your Input. Back to boat tomorrow with Nigel Calder's book to test solenoids. Still not sure if the Volvo engined boats have a ground solenoid in their starting circuit (Olivier/Joel anything to offer here?) but will search out and test as appropriate with screw driver in the morning.
One other thought is that this problem started just after work had been done reconditioning the HP fuel pump. Suspect much fuel was spilt on starter motor solenoid....perhaps causing a short?