"21.—(1) A person in command or in charge of a vessel in Irish waters or an Irish ship in waters anywhere shall not, or shall not allow another to, operate or control or attempt to operate or control the vessel or carry out any task or duty in relation to such operation or control while he or she or the other is under the influence of alcohol or a drug or any combination of drugs or drugs and alcohol to such an extent as to be incapable of properly controlling or operating the vessel or carrying out the task or duty.