It depends on how long your docking takes at Riga airport.

In particular: a visa for Russian citizens will not be needed in the case of transit through the territory of Latvia to countries that are not members of the Schengen, when it is planned to transfer from one flight to another within 24 hours. But, please note that the exit from the transit zone of the airport is prohibited at the same time.

If your docking takes more than 24 hours, then you need to get a transit visa.

In detail about the visa to Latvia you can read here