Range extender

What it means

A range extender is a small combustion generator that makes electricity for the battery while the boat runs on its electric drive. It never turns the propeller itself. Some builders call it a genverter; the principle is the same.

What it changes

It converts a range limit into a fuel limit. A boat that could do fifty miles on a charge can keep going as long as there is diesel, at the cost of the silence and the absence of exhaust that were the reason for the electric drive. Well-installed units are insulated and run at low, constant load, which is quieter and more efficient than a propulsion engine — but they are not silent.

Why it matters

It is the honest answer to the passage-making problem, and it should be read as a change of category rather than an accessory. A boat with a generator as standard is a hybrid, whatever the brochure calls it. A boat where it is an option is a pure-electric boat with a way out.