Hi - Im trying to find out if you can travel by boat to St Petersburg from Helsinki without a Russian Visa THANKS
It's possible, but there are strict rules: http://www.stpeterline.com/en/Goodtoknow/Visafreerule.aspx
Yes, there is a new ferry service that allows up to 72 hours (I believe) visa free. I forget the service name but a Google search would give you the details.
Needing a Visa is based on your nationality not on how you arrived. When you show up, you will need a Visa to enter the country. Russia does "waive" the normal Visa requirement if you are on a guided tour (technically your Visa is provided by the tour). There are train based guided tours of St. Petersburg out of Helsinki but I don't know all the details. I expect there are also ferry based tours.
The link above provides more details on the ferry service and the waiver for a visa under the restrictions. This is a pretty new service so not everyone is aware of it. I assume Anna is a US citizen since she is from the Windy City.
I recently asked a question entitled "Travel to St Petersburg" in "To The North" section of this Helpline and received some helpful answers that may be useful to you as well. You may want to take a look at that thread. The last responses were on about Aug 24, I believe.