The above references were taken from letter written by Alexander O'Briant to his wife Emily. They tell us some very interesting things. Alexander was in camp near Wilmington, N.C. when he wrote them and he speaks of plenty of ships making it through the blockade, but he also speaks of heavy loss to the ships. A situation that could not go on indefinably before the South ran short of ships.
Alexander also notes the high cost of food, he comments that he must be in the most expensive place in the Confederacy, but he isn’t, not by far. Alexander was actually in a place where things could still be got. Inland, away from the blockage runners ports things were disappearing from the market at any price.
The South tried to break the Northern blockade in many creative in inovative ways. For a short time after the enactment of the Union blockade the South retaliated and blockaded Washington, successfully cuting it off from the sea. The Union had to many ships for the Confederates to match and after a brief scare for Lincoln, the Potomac was reopened for traffic.
The South commisioned a sea going raider the CSS Alabama, built in England by the Laird Shipworks to disrupt Union shipping. The Alabama captured the the merchant bark Conrad which was converted to a warship and recommissioned as the CSS Tuscaloosa and susequenly joined the Alabama as a merchant raider.
The Tuscaloosa was sized by the British Navy December 27, 1863 for violating British neutrality in Simon's Bay South Africa. The Alabama was sunk by the USS Kearsarge June 19, 1864 off the coast of France. While the adventures of the Alabama and the Tuscaloosa were interesting and make good reading, they didn't have much effect on the Union blockade or upon the Union war effort.
CSS Alabama
On February 17, 1864 the USS Housatonic, on blockade duty in Charleston Harbor, exploded and sank. No ship had been seen approaching the Union vessel; only a faint phosphorescent glow under the water betrayed the presence of the CSS Hunley at all. With this single act the age of submarine warfare was begun.

The Hunley
The Hunley was a death trap, twenty men, including the inventor, died getting the ship ready for its attack. After sinking the Housatonic the Hunley herself sank drowning all eight of her crew. By WWI the Germans would have most of the bugs worked out and employed the submarine to much better effect.
Start: Port Royal