Open Water 2: Adrift (2006)

A weekend cruise on a luxurious party yacht goes horribly wrong for a group of old high-school friends. They forget to let the ladder down before they jump into the ocean for a swim. The boat proves impossible to climb. They are stuck in the water many miles from shore, with baby Sara left alone on board. Sara's mother Amy must contend with her aqua-phobia as well as the group's increasing desperation, as the friends begin to turn on each other. Soon the exhaustion of keeping afloat and the struggle to get back on board begin to take a terrible toll. The happy reunion turns into a fight for survival...

Source: TMDb