Try some of the following links for information:
I would think this is the important section of the Naval Institute report:
Assessing the Blockade’s Effectiveness
Southern supply bases greatly simplified the U.S. Navy’s job, but maintaining the blockade remained a challenging and often thankless task. The general pattern of trade was for conventional cargo vessels from Europe to bring their goods to a neutral port such as St. George in Bermuda, Nassau in the Bahamas, or Havana, Cuba. There the cargoes were off-loaded into low, fast blockade runners. The vessels, almost always unarmed, then attempted to run into a blockaded port, usually at night. Blacked out and painted a dark gray, they sought to dash past Union warships without being sighted, or if they were spotted, to outrun their pursuers. Those that made it into port would later attempt to dash out to sea, usually loaded with cotton or other exports.
Given the difficulty of spotting or catching them, it is not surprising that most of the ships that tried to run the blockade did so successfully. A more important factor, however, was that relatively few ships tried it. In the last full year of peace, some 20,000 ships entered or left Southern ports, but during the war, that number dropped to only 2,000 ships per year. Even more telling, cotton exports from the South dropped from just under 3 million bales a year before the war to just over 50,000 in the first year of the conflict—less than 2 percent of the prewar total.5
A precise calculation of just how much the Union blockade hurt the Confederacy is elusive. On the one hand, the South was able to import the essential matériel it needed to sustain its economy and war effort—including 400,000 rifles, 3 million pounds of lead, and more than 2.2 million pounds of saltpeter for manufacturing gunpowder. Historian Stephen Wise is undoubtedly correct in concluding that “without blockade running the nation’s military would have been without proper supplies of arms, bullets, and powder.”6
On the other hand, the blockade had a cumulative eroding effect on the Southern economy and contributed to inflation and war weariness within both the civilian population and the Army, thereby undermining the Confederate war effort. As historian William H. Roberts put it, if the blockade was “never airtight” it “was constricting enough that the South was constantly gasping for economic breath.” It is likely that the Union would have won the war even without the blockade, as long as the Northern population sustained the Lincoln administration, but almost as surely the war would have lasted longer and been more costly. So it is possible to argue that the blockade probably saved many thousands of lives.
Thank You Damon !