Slave ship

Slave ships were large cargo ships specially converted for the purpose of taking slaves, especially newly captured African slaves to the Americas. Living conditions for slaves on these ships was awful. Men, women and children were crowded into every possible space, leaving no room to move or even breathe. There was little food and the smell could not be described. Between 1526 and 1867 about 12.5 million slaves were sent by slave ships from Africa to the Americas. But only about 10.7 million slaves actually arrived. Of all human migrations it caused the most human deaths. The average time to sail across the Atlantic was 60 to 90 days. Sometimes the trips took up to four months.
Saleable slaves.
Ship captains were under orders by slavers to deliver only saleable slaves. Starving, sick or troublesome slaves were often thrown overboard into the ocean to drown. Sometimes Africans were kept on deck chained together with long chains. There were times when they would jump overboard, taking every other chained slave with them, to avoid their unknown fate. Many ships kept extra crew members on deck to prevent this from happening. At other times crew members would throw slaves overboard as a warning to other slaves. If the ship was running out of food or water, all the slaves would be killed to save the crew from starving.
"Zong" massacre.
Slave ships could at times get insurance on their cargos of slaves. But insurance would not pay if the slavers starved the slaves or they got sick. Insurance paid out if the slaves drowned, but not if they were severely starved to death. In 1781 the slave ship "Zong" was hauling 470 slaves—more than the ship could handle. Many began to get sick. By the time the ship reached the Doldrums, a mid-Atlantic region that at times had no wind, several of the crew had died from the spreading diseases. To save themselves, the remaining crew threw 132 dying and sick slaves into the ocean. Another 10 slaves jumped with them. When they tried to collect the insurance the Insurance underwriter denied the claim. In 1782 in a court in Jamaica, ruled for the owners. The insurance company appealed the decision. This brought a good deal of public attention. It began to be called the "Zong" massacre. No member of the crew or the owners were ever charged with murder. 
Slave ship takeovers.
About 15% to 20% of the ships leaving Africa never arrived in the Americas. In thousands of cases the crews were overtaken by captured slaves, some of them warriors. Often the crew was killed and the Africans managed to sail back to Africa. In other cases the ships were lost at sea.
Some of the documented slave ship revolts are: