Looking for an old cartoon about pirates

From the plot I remember that there were pirates who had infiltrated the ship in the guise of the good guys. Was painted swallow that poisoned by feeding her a bug-blot (if I am not mistaken did the pirates, like a Gypsy). There was a moment with a storm, during which the pirates opened up and tried to seize the ship. And in the cartoon the pirates were on the ship alone, and they hide the fact that they are pirates from the rest of the team.
Many were tied to correspondence/letters like. It's not exactly treasure island. The cartoon in dark colors, a little bit of psychedelia.
Tell me the name, please.