We went through the exact same questions in 2011 when faced with the same dilemma. On all our past vessels we always took the larger HP motor upgrade options so our natural preference is certainly for the larger horse power where possible.

In the case of the Amel we got lucky and ended up with a never cruised 2001 SM model in pristine condition with just 590 engine hrs on the 75 HP Yanmar and even less on the Onan generator. Despite our preference for the 100HP we were completely surprised to find that our 75 Yanmar could keep us motoring at 9.3 kts (top speed - clean bottom) and cruise at 7.3 kts on just 1800 revs approx. for days on end, comfortably non stop. Based on this, and now almost 1000 engine hours later after motoring across large sections of the Pacific, we are completely happy with the Yanmar 75 / Super Maramu combination, particularly when calculating fuel consumption and motoring range which is absolutely HUGE!!! as the 75 Yanmar is very frugal indeed.

In terms of batteries, obviously the more amp hours the better, but the 9 batteries do us perfectly fine and we are now adding 600w solar on a new davit arch and changing all lights to LED so no problem there too.

At the end of the day it comes down to a price / benefit decision and different people will make different decisions. For me, if we needed to repower and the same 75HP Yanmar was still around then, that's exactly what I would be putting back in.

Colin & Lauren Streeter

Island Pearl II, sm #332

Brisbane, Australia.