Complex sentence: Cofresí then selected six of them and traveled to the main island (Puerto Rico) where they hijacked a schooner named "Ana" forcing the crew to jump into the ocean, an incident which they survived.
Split into simpler sentences: Cofresí then selected six of them and traveled to the main island (Puerto Rico) where they hijacked a schooner named "Ana". The crew of the "Ana" were forced to jump into the ocean, an incident which they survived.