Given that the drawback of a single engine configuration is lack of back-up should the one and only engine fail, I chose to fit a hybrid engine when I decided my ancient bobtail Yanmar was past it. I now have a 30hp Beta diesel, with a 5Kva generator
driven off a toothed belt, which (should the diesel fail or I wish a silent exit/entry in or out of a mooring) becomes a 10Kva motor
when power is fed from the batteries. Of all the options, it satisified KISS, was the lightest and simplest to fit. The only marginally complicated task was to make a 50mm pad for the transom, so as to move the Sillette leg far enough back to allow space for a hydraulic gearbox
needed to disengage the motor
from the engine. Check out Hybrid Marine
on the Isle of Wight.