You're quite welcome Adrian.
I have a lot of difficulty finding something out in Riga, Latvia, myself. But in the Netherlands it's virtually impossible to find out what old records are still saved from about 1774 till 1810.
I'm looking for Andele (or Andle) Bonnes Brouwer (Brouwer means Brewer in English), who left as a skipper from Harlingen, Friesland with his ship for Riga, Latvia in february 1774. His younger sisters, Dieuwcke and Jaijke Andeles Brouwer left with him, but returned and married respectively in Harlingen and Amsterdam.

Cheers, Nick