Passenger transport connected with recreational activities or airport car parking: Boats
Boat rides to, from or within a place of entertainment or cultural interest etc are standard-rated except where independently supplied.
However, ferries, canal boat trips, and other round trips or excursions by boats, without other facilities, on the open sea or other waterways to which the public have free and unrestricted access are zero-rated, providing the general conditions of item 4 are met.
See VTRANS021340 for the liability position of supplies such as disco cruises, dinner cruises, wedding reception cruises and other similar entertainment cruises on public waterways.
The liability of trips for the purpose of diving will depend on the exact nature of the supply. If there is an element of instruction or training the whole supply will be standard rate. If it is simply the supply of the transportation to the dive the supply is of zero-rated transport.