No Brown is not a Swedish name. The closest equivalent is probably Braun, which is the name of a originally German noble family introduced in the Swedish House of Nobility in 1611, but they would hardly have become common seamen. There are some families called Brun (ie the colour Brown in Swedish), but I think it is much more likely your seamen adopted the name as they moved to Britain. Before 1900 most Swedes were called by their patronymic names, but would often start using a different name if they were employed in trades or moved into town to or to another part of the country.

By the way, isn't Brown is a typically English name, like Smith or Wright?