You could code it as a Cat. 6 vessel;
Area Category 6 - to sea, within 3 miles from a nominated departure point(s) named in the
certificate and never more than 3 miles from land, in favourable weather and daylight;
but then you still have to have a liferaft;
13.2.3 Vessels Operating in Area Category 2,3,4,5 & 6:-
.1 should be provided with liferaft capacity to accommodate at least the total number of
persons on board;
Plus lifebuoys, grab bag (TPAs, Medikit, Flares, Tools)...
Honestly by the time you have fitted all of these on your thundercat I don't think there's gonna be space for many passengers...
[All info from the MCA's 'The Small Commercial Vessel and Pilot Boat Code']
But drop the MCA a line, there may be exceptions I've missed (148 page doc)...