(Under 26ft) - Yes, if you are using the vessel for more than 18 consecutive hours, there must be at least two experienced people on board.
(Over 26ft) - Yes, for large craft being used for more than 18 consecutive hours, racing or towing water skiers (If cover is selected), as above you must have a least two experienced people on board.
NOTE: This does not apply to Narrowboats/Dutch Barges.
