Poseidon's Tollgate

THE STRAIT OF THE EARTH-SHAKER

Ithaca was one strait away. Poseidon, still sulking over his son's eye, parked himself in it and opened a toll booth. He takes payment in fish, answers only in numbers, and explains nothing. Those who understand his moods may pass.

Ships are announced by the harbour master. Open this challenge on CTFd and use its link to approach the strait.