[normie3000]

Which part of the Baltic takes 18 hours to cross?

Anyway it wouldn't be too surprising it's less rough than the North Atlantic given the Baltic is closely wrapped in land.

[precommunicator]

Nynäshamn - Gdańsk. I've also did shorter routes like Ystad - Świnoujście and Helsinki - Tallinn

[mzi]

Stockholm - Helsinki, for example.