As a developing technology, inboard electric propulsion for boats has seen winners and losers. Some brands and ideas have proved short-lived, while others like Oceanvolt, Bell Marine and Torqeedo are dug in for the long haul. There are also some well-funded new entrants looking to shake things up.
What is sure is that the switch to electric is only becoming more attractive as fuel prices rocket.
If you’re mulling the idea, it is key to understand that a smaller electric motor can do the same work as a bigger diesel engine. This is mainly because motors engage optimum torque from zero to nearly maximum speed, whereas a marine diesel reaches its sweet spot only at around 2000rpm, dropping off on either side. Finland’s Oceanvolt is quite punchy in comparing the performance of its 10kW (13hp) electric AXC motor to that of a 30hp diesel. “Typically maximum boat speed will be somewhat lower (0.5-1.0kt) than with a comparable diesel engine, but the boat will maintain the speed better in heavy seas and headwind due to the higher torque,” says European sales manager Alec von Weissenberg.
Top speed under electric power is calculated just as it is with a diesel engine – that is a function of waterline length for displacement vessels, or using the designer’s polars for planing craft. The difference is that rpm is generally around half that of a diesel engine, so the propeller needs to be pitched and sized accordingly.
Range depends completely on the weight of the
