The Slaves Diet While on The Ship

Since food could potentially take up a great deal of room on a ship, captains were careful about the food they brought. They wanted to squeeze as many slaves as they possibly could, into the smallest space possible, so they were sure not to take up too much space with food.

A daily ration of food commonly included the following:
*yams
*a biscuit
*beans
*flour and salted beef

Sometimes slaves would be forced to take a sip of lime juice or vinegar to help avoid scurvy.
Water caskets that were necessary for long voyages took up a great deal of space and were often limited to the smallest size possible. This forced many slaves to spend their time dehydrated, as well as the fact that they were sailing close to the equator in tightly packed ships.

http://www.mariner.org/captivepassage/middlepassage/mid007.html