Why were most slave revolts on ships unsuccessful?

Though African slaves outnumbered their captors by a large margin on slave ships, there are many factors to consider as to why they were unsuccessful in capturing the ships. First, the Africans were packed in quite tightly and were unarmed. Secondly, not all of the Africans spoke the same language; Africa is a culturally diverse land with many languages.  While there are some linguistic similarities in Africa, it would have been difficult for these Africans to understand one another, especially in the heat of a battle against armed slave captains. There was also the issue of slaves being malnourished and weakened, especially towards the end of the voyage. Even if the slaves did overthrow their slave captains, there was the question of steering the ship. Most slaves lacked the skill needed to sail such a large vessel, and in open water it would have been hard to locate a port that would provide refuge for a ship full of captives.