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I've managed to travel from Khor's Deep to Island of Spears. BUT - I forgot that i had one unexplored location on previous island, so I've turned back. And that's where my troubles begin - I've returned to the Gull South Dock. But when i've tried to travel from this place one more time, it tooks me to the island I've explored before Gull Island. I've checked the Khor's Deep once more, but there is no boat anymore.

Does anyone know, where is the boat that I should travel to Island of Spears?
This question / problem has been solved by Star_Sageimage
It's one area east of there, I believe it's called Gull Island North Docks. You must have skipped that part of the text box that told you about that.