Passenger ships engaged only on domestic voyages in sea areas where the probability of significant wave heights exceeding 1. 5 meters is less than 10% over a one year period for all year round operation, or over a specific restricted period of the year for operation exclusively in such period, in the course of which they are at no time more than 6 miles from a place of refuge, nor more than 3 miles from the line of the coast, where shipwrecked persons can land, corresponding to the medium tide height. Class D ships are equivalent to UK Class VI(A) ships.