You're a bit dogmatic here - the torque is less important on a boat, but it still reduces the time a propeller takes to get up to full revs in an emergency. My comparison was a 40 hp diesel running a heavy alternator load - say 200 amps - versus a 20kw electric drive. 40 hp is pretty much 30kw. The alternators alone, with a charitable 60% efficiency, would absorb 4 Kw and the drive train maybe another Kw, resulting in around 25 Kw at the prop. The 20Kw electric motor should deliver 20Kw at the prop and take maybe 23 kw out of the electrical system - most are specified with peak ratings higher than nominal, so even higher kw bursts are feasible. A 5kw difference at the propeller will make no difference on the canal and a minor difference of perhaps 1 mph in top speed on the river, which no-one does with a diesel, because they're worried about overheating and noise. Several US electric boat vendors use serial LiFePO4 installations and Victron have all the necessary control equipment to do it available in the UK. Not cheap but, in my opinion, worth it for mostly quiet cruising, with maximum use of shore power and solar for charging and the genset cocooned for those occasions when it is necessary to use it.