"21—(1) A person shall not in Irish waters navigate or operate a vessel in a manner (including at a speed) which, having regard to all the circumstances of the case (including the condition of the vessel or class of vessel, the nature, condition and use of the waters and the amount of maritime traffic, or number of people, which or who then actually are, or might reasonably be expected then to be, on or in those waters) is dangerous to persons in or on those waters or land, within the State, adjacent to those waters.