Just found this info -
Visas for Cruise Passengers
Cruise ship passengers can currently visit Russia on visa-waiver scheme provided that the stop in the port of call doesn't exceed 72 hours and tourists stay overnight on board of the cruise ship. This rule doesn't apply to passengers of Finnish and some other cruise companies. This rule doesn't apply either if there is only one port of call during a voyage.
Cruise passengers may disembark from the ship without a tourist visa if they participate in tours organized by cruise companies. Passengers, who are not participating in tours and wishing to disembark will need to obtain a Russia tourist visa. Passengers won't be permitted ashore if they don't present a valid passpost, a Russian visa and a voucher issued by a Russian travel company or another athorized organization.
Cruise passengers cannot obtain a visa in Russia. Visas are issued in the country of residence before departure.
We recommend that you check information on organized cruise tours and visas with your cruise company in advance.
Claire