If you are planning on walking the outer route of the St. Olavsleden path, you will need a boat lift to get from Tautra to Trondheim. Since there is no ordinary passenger route across the fjord, the Stiklestad Pilgrim Centre has made an agreement with a local boat owner.
The boat leaves Tautra harbor every Tuesday at 3 pm between June 15th and August 30th. It costs 500 NOK pr passenger, paid in the boat.
Groups can hire the boat on other dates if available. An extra trip costs 2500,- NOK with a maximum of 7 passengers.
It is also possible to get a lift from Frosta to Steinvikholmen with the boat. Ask for availability. This trip MUST be preordered.
See this post for information about how to get from Tautra to Aasen train station.