The Western Channel is two cables wide, with a depth, in the shoalest part, of 10 fathoms; it is formed by the Middle Ground on the eastern side, and the Yellow Rock Reef on the western; the latter is an extensive patch of kelp, with a double light-coloured rock near its extremity.  The least water on it at low-water is 6 feet; from the Shear Beacon, it bears North 50 degrees West five-tenths of a mile, and from the lighthouse, South 52 degrees West eight-tenths of a mile.  The Shear Beacon and the flagstaff at George Town in a line lead over the outer extreme.  There is generally a white buoy in its vicinity, and a black one on the western edge of the Middle Ground.  The Barrel Rock red beacon, and the high and low white beacons, erected by the Beagle’s crew on the shore over Lagoon Bay, kept in one, lead through the Western Channel.  When abreast of the Shear Beacon, steer for the next beyond on the west side of the channel, to avoid a long patch of kelp, with three and five fathoms in it, extending two cables and a half to the South-South-West of the Barrel Rock.

The high part of the Western Reef, bearing South by East leads into the fairway of the Western Channel, when will be seen the white beacons over Lagoon Bay.  The latter is the second sandy beach inside the lighthouse on the eastern shore.  The Western Reefs are those fronting Point Friend; the part above-mentioned, the only spot uncovered at high-water, is a black patch of rocks near their northern extreme.

The only danger near the entrance of the Tamar is the Hebe Reef, named after a ship lost on it in 1808; it occupies a space of a quarter of a mile, chiefly in an east direction.  A small portion of its centre is nearly dry at low-water; this part bears South 89 degrees West, three miles and three-tenths from the lighthouse on Low Head; inside it there is a channel of 7 fathoms.  The guide for passing northward of it, is a white spot on the North-West extreme of Low Head in one with the lighthouse; the latter will then bear East 16 degrees South.

The shoals, on either side, within the entrance of the river, are marked with beacons.  Those on the western shore, have a letter V sideways with a vertical bar on the top; and those on the eastern a dagger.  Shoals marked with chequered buoys, may be passed on either side; a red or black buoy, signifies that the danger extends from the eastern shore; and a white one, that it extends from the western.

The result of 115 tidal observations, taken three miles within the entrance, gives 12 hours 06 minutes for the time of high-water on the full and change day.  The rise of tide was irregular, the least being 4, and the greatest 10 feet.  The highest noticed in the Beagle was during the neaps, caused by a strong North-West gale forcing the water into the river.  The tides flow 5 hours 50 minutes, and ebb 6 hours 25 minutes, with a velocity varying from two to five miles an hour, according as the river is confined or open.  The ebb-stream setting round Low Head into the bay to the eastward, is apt to drift vessels in that direction.  Three miles in the offing the flood-stream runs from one to two knots to the West-North-West.