James Russell Soley, Professor U. S. Navy, Confederate Military History, a library of Confederate States Military History: Volume 7.1, The blockade and the cruisers
Clement Anselm Evans, Ed.

[108] drove the Confederates out of their works on the Island, and the monitors took their station inside, somewhat to the southward of Cumming's Point. Blockade-runners were then driven to the use of the Beach channel, at the northern side of the harbor. This channel skirted the shore of Sullivan's Island, and opened into the harbor through a narrow passage close to Fort Moultrie. Its outer end lay abreast of Breach Inlet, near which was Fort Marshall; and from this point to Fort Beauregard, and thence to Fort Moultrie, heavy batteries lined the beach. It became usual to send a vessel at night to this entrance, which, weighing early, got away from the Breach Inlet batteries before daybreak. Occasionally it happened that blockade-runners, which had come in during the night, would be seen in the morning hard and fast aground at the inner entrance. No attempt could be made to seize them, lying as they did directly under the guns of Moultrie; but they could be destroyed by the fire of the monitors, and a collection of wrecks was gradually accumulated at this point.

Toward the close of the war the blockade of Charleston, like that of Wilmington, increased in stringency. Dahlgren describes it as being perfectly close, until a few very fast steamers of trifling draft were built in England expressly for the purpose of evading it, and these did not pass with impunity. So keen did the watch afterward become that a vessel on the way out, whose presence was only known by seeing her two masts cut off the light on Sumter, was captured by the observer's signalling the cruisers outside. But even then the port could not be absolutely closed. The ‘very fast steamers of trifling draft’ were so difficult to catch that up to the last moment they were occasionally going in and out; and three or four of them were at the wharves of Charleston when the city was taken.