13. The discharge into the sea of a Category D residual mixture is prohibited except where—
(a)(i)the ship is proceeding on its way at a speed of at least 7 knots in the case of a self-propelled ship or at least 4 knots in the case of a ship which is not self-propelled;
(ii)the concentration of the substance in the effluent is not greater than one part of the substance to ten parts of water; and
(iii)the discharge is made at a distance of not less than 12 nautical miles from the nearest land; or
(b)the discharge is made in accordance with regulation 11 as it applies to Category C residual mixtures.