It's always the captian's responsibility to ensure the safety of everybody onboard the vessel.
See the CE-plate in the back of the immersed cockpit or your Owners Manual.
Your boat is registered for a certain amount of people within a category (C-Coastal or B-Offshore). At Goldfish, we set the numbers typically quite conservatively and limited them to the number of good seats as your boat certified for open water and rough elements.
It is not illegal to carry more passengers, but it is captain/driver’s responsibility to make sure the passengers remain safe and the boat is driveable under the prevailing conditions.
Often used definitions of the different classes:
Designed for extended voyages where conditions may exceed wind force 8 (Beaufort scale) and significant wave heights of 4 m and above but excluding abnormal conditions, and vessels largely self-sufficient.
Designed for offshore voyages where conditions up to, and including, wind force 8 and significant wave heights up to, and including, 4 m may be experienced.
Designed for voyages in coastal waters, large bays, estuaries, lakes and rivers where conditions up to, and including, wind force 6 and significant wave heights up to, and including, 2 m may be experienced.
D: SHELTERED WATERS,
Designed for voyages on sheltered coastal waters, small bays, small lakes, rivers and canals when conditions up to, and including, wind force 4 and significant wave heights up to, and including, 0,3 m may be experienced, with occasional waves of 0,5 m maximum height, for example from passing vessels.