Back to the OP's question.
All aspects of Hovercraft (design, build, flying) used to be controlled by the aviation authorities (latterly CAA) but it was eventually realised that this simply added cost for no good reason and they were then 'reclassified' as ships. This then meant that they could be built as per boats and operated by sailors rather than 'pilots'. Not sure when the change occured but am guessing sometime around 1980.