To All that have helped.

The BEC is disabled in both ESCs.

I tested the current drain on the motors and at no load 'free running' out of water only 1.3 amps was being indicated on each. The boat has not been in the water. There is no overheating at all.

I have not added suppressors, as the Graupner 700 BBs were supposed to be internally suppressed, according to a previous forum item, and it also said so on the motor instructions. I can add these, but there was no jittering, all runs smooth until one of them stops - either one.

Umi - I think that your scenario closely resembles mine although mine don't come back to life. You need to switch everything off and then start again. It then works fine until...

Regards