The inlet where the ship is docked is NOT Crystal Lake
This installment reveals that a fairly large river flows from Crystal Lake to an inlet with access to the ocean. The yacht in the beginning, wherein the couple are slain, drifts down the river to the bay where the ship is docked. This is how Jason inconspicuously reaches the inlet and proceeds to board the vessel.
If there’s any doubt about this -- due to the mistaken claim that the docking inlet IS Crystal Lake -- pay close attention to what the doom-prophesying deckhand says later on.