Jet boats were once mostly hairpin-­happy thrill rides, with the reflexes of a slot-car. Today, they’ve matured into hot-selling family models, viable alternatives to craft propelled by propellers.

We recently had a look at a man from Washington who decided his PWC would be better off with a Chevrolet V8 inside. As this kind of watercraft should be light and agile, that might not be the best ...