It was nearly 1 a.m. on Friday when Gabriel Korty, sitting on the deck of a 30-foot sailboat moored off Crete, felt the hypervigilance of the previous days begin to ebb. His boat rocked gently in the dark, and around him were anchored dozens of other vessels festooned with Palestinian flags that flapped gently in the wind.
The placid sea was a stark contrast to the scene two nights earlier, when Mr. Korty and…