frednz: A friend has a launch that takes about 5000 litres of diesel and he goes through that every 2 months or so. And the marina is full of diesel guzzling boats. So what are we doing about them?
Boats are an issue. Much more energy wasted on hydro-drag and much worse traction (esp with petrol engines) than road vehicles.
My boat weight about 1800kg light with two crew. 140HP/100kW (at the prop shaft) pushes is at a max speed of only 50km/h - that's assuming calm conditions.
There are some applications where battery electrics are being used, but they tend to be flat-water, short range, applications; with shallow hulls and minimal payload.
Skinny hulled, light catamarans with modest seem to suit the tech (e.g. torqeedo) well.
I've done the spreadsheet exercise of powering my boat with electric motors an batteries for a 25 kmh cruise at 2 hours rwith another our in reserve in case of poor weather or miscalculation. Even using best the tech available (unaffordable) and favourable assumptions - it sinks under the weight of the required batteries.
An advantage of electric is that the torque allows you to swing a bigger prop at a lower speed and that means you get less prop slip. That means more thrust per prop-shaft kW.



