It is a combi sorry I should have said. It is very difficult to monitor voltage at the actual time it cuts out as once the load is removed the voltage goes up.
When I had problems originally, a couple of years back I actually tried running a video camera to monitor it but the battery ran out on the recorder first.
I also tried putting the wife in charge of monitoring but the gin got to her and she went to sleep.
I think the most likely cause is a loose connection somewhere which as the previous poster said , has welded itself together
I will have a thorough check when I go to the boat. Thanks for the suggestions