(1)This section applies to—
(a)a professional master of a ship,
(b)a professional pilot of a ship, and
(c)a professional seaman in a ship while on duty.
(2)A person to whom this section applies commits an offence if his ability to carry out his duties is impaired because of drink or drugs.
(3)A person to whom this section applies commits an offence if the proportion of alcohol in his breath, blood or urine exceeds the prescribed limit.
(4)For the purposes of this section a master, pilot or seaman is professional if (and only if) he acts as master, pilot or seaman in the course of a business or employment.
(5)Where a person is charged with an offence under this section in respect of the effect of a drug on his ability to carry out duties on a fishing vessel, it is a defence for him to show that—
(a)he took the drug for a medicinal purpose on, and in accordance with, medical advice, or
(b)he took the drug for a medicinal purpose and had no reason to believe that it would impair his ability to carry out his duties.