She looked like a veritable phantom ship of tradition as she glided past. No ghost could have moved more silently, or looked more mysterious; and we all felt a sort of mystical enchantment as we watched her rapid, stealthy progress. She was painted a smoky gray color, and could scarcely be distinguished in the light mist which enveloped her. Not a lamp gleamed aboard; no sound could be heard, except very faint echos from her revolving wheels,and no smoke seemed to be thrown out by her engines. Everything to ensure a successful trip had been carefully studied and prearranged. She passed like a spirit through the midst of the blockading squadron, and twenty-four hours later dropped anchor in the sparkling tropical waters of Nassau.
Apparently a lot of blockade runners got through. A visiting British colonel noted in 1863 that they were seldom captured.
In his book "Lifeline of the Confederacy: Blockade Running During the Civil War" Stephen Wise shows that it wasn't the blockade that halted the flow of supplies to the confederacy, it was the loss of ports to the advancing Union armies.