As said, prohibiting the trade did but increase the profits of those who disregarded the law, but a more memorable result of prohibition was the effect upon the unfortunate victims of the trade--the increase in the horrors of the middle passage. A brief description of the ships used in the trade will help one to understand how the slaves were affected.
The American slave-ships were usually small vessels, say 100 feet or so long, and 10 or 12 deep. On the way to the coast what was called the slave-deck was laid. By means of beams, stanchions, and rough planks a temporary deck was built 3 feet below the regular deck. The naked slaves were placed upon this deck. In the days of the lawful trade they were compelled to lie down on their backs, shoulder to shoulder, with heads outboard in a row all around the slave-deck. Then other rows of the kind were made on the deck inside of the first row until the deck was entirely covered. When the law prohibited the trade, the slavers increased the number carried to the utmost capacity of their vessels, in order to increase the profits and cover the risks. To do this they compelled the negroes to lie down on their sides breast to back,--"spoon fashion,"--or else they were made to sit in rows, breast to back, from the wall of the ship to the centre. When sitting thus, the only air-space between the two decks was that over the rows of shoulders and between the rows of heads. When lying down, the air-space was greater, but whenever the vessel heeled to the wind, those on the lee side had to lie with their feet higher than their heads, and when the vessel rolled to the waves all of them sawed to and fro over the cracks between the unplaned deck boards. Moreover, the slaves were kept fastened to the deck--they were not allowed to leave their cramped berths for any purpose save only at fixed hours, when they were fed and, in small gangs, were taken to the upper deck for a short airing. In storms the washing of the waves across the deck compelled the crew to put on the hatches and keep them on sometimes for days at a stretch.
Meantime the allowance of water was a pint a day. In short, the slave-ship was a horrible floating cesspool. How the inhuman drivers added to the sufferings of the wretched slaves by the use of the whip, and other means of torture, may be suggested by one story.