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To seaward of the Challenger, the principal dangers to be avoided are situated on the Five Fathoms Bank, and consist of Seaward Reef, a small patch, six or seven feet under water, about three miles and a quarter W. by N. (magnetic) from the north end of Carnac; and the Casuarina Shoal, with one and two fathoms upon it, about two miles and a half of W. ½ N. from the north-west point of Garden Island. Further to the south lies Coventry Reef, a small patch of rocks just awash, bearing S. 18½° W., and distant eight miles from some remarkable sand-hills on the coast near the middle of Garden Island, called “Sandown.”
Lambert Channel, through which his Majesty’s ship Alligator got to sea from Owen’s Anchorage on the 19th of December, is a valuable outlet to sea or to Cockburn Sound, from Owen’s Anchorage or Gage’s Roads, without passing round Rottnest Island, which, during strong northerly winds that would distress a ship in either of these situations, may be considered almost impracticable. In the absence of means at the present time for buoying this channel, it may be found by keeping the summit of Buckland Downs a very little open to the south of the Mewstone, in the direction of N. E. ¾ E. and S. W. ¾ W. (magnetic). This mark will carry a ship through in not less than four fathoms, and about 100 yards to the northward of a small rock four or five feet under water, which is detached about a cable’s length to the north-east of the breakers on the western bank, and is called the Passage Rock. At a cable’s length to the north-west of it is a small patch of two fathoms and three-quarters. A ship must pass between them in four to five fathoms water, and then haul up to the W. by S. to avoid a small shoal spot with 3¼ upon it.
The soundings will then quickly deepen to 7, 5, 6, 8, and 9 fathoms, and a course may be shaped to pass half a mile to the westward of the Challenger Buoy. This channel being narrow, and not yet buoyed off, should not be attempted by a stranger without previously securing a boat or conspicuous cask near the Passage Rock, and another near the patch of two fathoms and three-quarters to the north-westward of it.
