What does Acts 27:42 mean?

Several weeks prior, Paul stood in Caesarea Maritima before Festus, the new governor. There, he heard the Sanhedrin re-introduce unfounded charges they hoped would lead to Paul's execution. Barring that, Paul's enemies hoped he'd be transferred to Jerusalem so they could murder him along the way. When Paul realized Festus was more concerned with pleasing the Sanhedrin than justice, he berated the governor for not doing his job and appealed his case to Caesar. Festus had no choice but to agree (Acts 25:1–12).

Now, Paul is with a group of fellow prisoners on the quickly disintegrating remains of an Alexandrian ship, likely transporting grain to Rome. The vessel has only just survived a two-week typhoon. The bow is stuck in a muddy clay reef. The waves are tearing apart the stern. The beach is just a swim away (Acts 27:6, 33, 41).

Between Paul and land, however, is a cadre of soldiers who know they will likely be executed if any prisoner escapes. If the ship had reached the beach, they could have guarded the prisoners as they climbed down the hull. As it is, they can't keep everyone under tight control while they're swimming and paddling and kicking for the shore. So, they resolve to kill them, instead.

Fortunately, their centurion, Julius, has always liked Paul and has grown to respect him greatly over the previous two weeks (Acts 27:3, 31–32). He calls the soldiers off and orders as orderly an evacuation as possible. Everyone makes it to shore, and presumably no prisoners escape (Acts 27:43–44).