The unfortunate soul disappeared under the water several times before resurfacing, so Tristan worried that he was a poor swimmer. Why was nobody helping that man!?

Because Zechariah Meijer was on the boat closest to him. That was probably why!

Tristan abandoned his post completely to join Tobias in shouting when he saw Tobias' brother go overboard too. "Turn round! Turn round! We have to help them!" he shouted at the captain.

Oh thank God! And he didn't even believe in one! Bless constable Crane. At least the men had something to hold on to.