This is Joseph Mallord William Turner's Slave Ship (Slavers Throwing Overboard the Dead and Dying, Typhoon Coming On). It was created in 1840.
It is based on a poem which is based on the true story of a slave ship which threw overboard dying slaves so that it could collect insurance money. More information about that at the MFA website.
This painting is definitely a departure from realism. The viewer can vaguely make out the figure of a ship and could make an educated guess at where the horizon is. However, the colors and forms that are to represent the waves look nothing realistically like the ocean. Rather, it looks like an angry mass ready to consume and destroy. Upon closer viewing, one can seen chains disappearing into this mass. It is unclear whether the sun is rising or setting. Instead of painting a clear representation of what the scene might realistically have looked like, Turner chose to paint what the scene might have emotionally or abstractly looked like.