Daniel Ammen, Confederate Military History, a library of Confederate States Military History: Volume 7.2, The Atlantic Coast
Clement Anselm Evans, Ed.

[158] found to be impracticable, and a continuous rope netting was then tried, which was also swept out of position by the strong tides. The rope obstructions were then cut in lengths of one hundred feet and moored at one end, and three rows of them were then placed so as to swing with the tide, the intervals between them being about one hundred feet, and having about the same distances between the lines. A rope having a diameter of nearly two inches was secured to beer casks tarred, or to pine logs, to serve as floats at distances apart of fifteen feet. Over this rope were secured bights of smaller rope, each end being several fathoms in length. The movement of the water by a propeller, it was supposed, would draw these rope-ends within its influence, and thus foul the propeller.

A row of piles was driven across the middle ground and into the channel, just below Fort Johnson. This was intact in April, 1863, but by the autumn many of the piles had washed out.

In the Hog Island channel a heavy boom obstruction was maintained throughout the war, and several sets of torpedoes on inclined planes beneath the water, the frames resting on the bottom, having usually fifteen torpedoes on each frame.

All of the inferior channels and Cooper River were protected in like manner by torpedoes placed in sets on submarine inclined planes, upon which several of the Confederate vessels had been blown up at various times.

The main channel, leading up close under the guns of Fort Johnson, had three large boiler torpedoes, stated to be in good condition, and having one thousand or more pounds of powder within them. They were on range lines, and intended to be exploded by electricity.

At Fort Johnson and on the wharves of Charleston were a