The 18m proa now has diesel electric option as well as the batteries:
https://www.youtube.com/watch?v=iYKZJgFhqMM
Still in development stage with no proper ventilation in the engine box or sound proofing making it quite noisy.

The 22HP air cooled diesel drives a PMDC generator through a toothed belt with a 25% increase in speed. The generator is the same ME1009 unit as the two motors that it powers in series connection. Thus the motors each do about 60% of the diesel speed.

The proa does 5kts with the generator producing 9kW. At full speed on the diesel it gets up to 6.5kts with present gearing and calm conditions. It could be geared a bit higher as there is no indication that the diesel is lugging yet.

There is a single changeover switch to go from batteries to generator power. The two power sources are completely independent apart from the single changeover switch. Transfer from battery to diesel and back takes less than a minute.

There is no direction reversal when running on diesel. For motor sailing the proa may be motor-sailed ww hull to lee on the basis that wind would be light if the diesel motor was being used.

We have also tested the regeneration capability of the drives for battery charging. That is now another option available by dropping the drives into the water and setting the charge current.

Rick W