1841.
Chusan Archipelago.
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Tower hill passage. The course for vessels intending to enter by this passage, will be west by north 8 miles from Ketow point. The depth of water in this part of the passage varies from 35 to 110 fa- thoms, and no anchoring ground is to be found unless close to the shore. Vessels, therefore, not having sufficient tide to carry them round Tower hill, or wind enough to stem the current, should re- main at anchor to the eastward of Round-about island, or in the neighborhood of Singlo shan. If possible the time of starting should be so arranged as to obtain the first of the ebb after rounding Tower hill. After having rounded Tower hill, Tea island may be steered for. The depth of water between Tower hill and Bell island varies from 30 to 40 fathoms. On the northwest side of Tower hill a bank ex- tends a cable's length from the shore with 3 to 4 fathoms on it. Spring tides set at the rate of 3 to 3 knots; and vessels, in light winds, should be careful that they are not set into the archipelago between Tea and Elephant islands, where the channels are narrow, and the water deep with foul ground.
Anchorage between Bell and Tea islands. Between Bell and Tea islands good anchorage will be found in 10 to 12 fathoms. Ships intending to remain here should not open the channel between Bell island and Chusan, as the tides are stronger and the ground loose. Proceeding from thence to the inner harbor of Tinghae, another an- chorage will be found on the Chusan shore. A sunken rock, with 24 fathoms upon
it at low water, lies due south of a small hillock in the valley, and 21 cables from the shore.
Anchorage on Chusan shore. Opposite to a canal entrance is a mud bank, with 3 fathoms in the shoalest part, and deep water be- tween it and the shore. The tides are irregular at this anchorage, but it is convenient for watering In light winds vessels should avoid the strength of the ebb, when passing through the channel between Tea and Guard-house island, which otherwise is liable to set them through the Straight or Southern Passage. A ledge of rocks extends off the northeast extreme of Tea island, 1 cable. It is steep to, and between the islands 40 fathoms will be found.
Middle Ground. After passing Guard-house island it is necessary to steer for Macclesfield island, in order to avoid the Middle Ground, which has two feet in its shoalest part. The 3 fathoms line extends within 22 cables of the latter island, and Tower hill on with the slope upon the south rise of Tea island will keep you in 4 fathoms, or not to open the fort on Trumball island, with the north end of Mac- clesfield.
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