Just realised, most of these companies are up north. What's wrong with us southerners?
I supposed it's not unlike cars' chasiss. Manufactourers spent millions on a floorpan and naturally they would want the most out of it. So we see many models from one manufacturer as well as from different manufacturers, think, Audi A3, VW Golf and Seat Octavia.
I read it somewhere Raider's hull is based on the Shetland family 4, not sure how true it is. As with Quicksilver and Jenneave, and all the European makes with a 'q' in their names, based their boats on the same mould.