In early sailing directions, Jack Sound was described as '?little more than a cable in width? sluicing and over falling stream with its various and sudden eddies, which sets through the sound at the rate of 5-6 knots?. there is no decided mark for avoiding the bounding rocks..' However, it was extensively used by smaller coasting trade vessels and even by larger square-rigged vessels, if the conditons were right or if they had been drawn into the Jack Sound tidal stream. The two most dangerous obstacles were the Horse Rock (or Cable Rock), on the mainland side, and the Bitches off Midland Isle. The advice, when approaching from the south, was to the keep as close to the Blackstones as possible '.. and having passed them, steer towards the Tucker rock, carefully keeping the south-western extremity of Skomer Island in line with the eastern part of the Blackstones, bearing SW 1/2 W, this leads through but rather in the side of the Bitches, and when about midway between Midland isle and Wooltack point, the Bitches having been cleared, and the vessel may be hauled to the northward and westward.'

Sources:
Admiralty, 1870, Sailing Directions for the West Coast of England from Milford Haven to the Mull of Galloway including the Isle of Man, pg2-3
Historic Admiralty Chart 1410_A1, RCAHMW digital collections sourced from the UK Hydrographic Office and published in 1842

Maritime Office, RCAHMW, August 2014.