Any tips for travel by sea to Santorini from Venice?

The only way by sea is on an expensive cruise ship that stops at many ports along the way. There is no ferry from Venice to Santorini. From Venice you will take a ferry to either Igoumenitsa or Patras, depending on the ferry, then a bus overland to Athens/Piraeus, then another ferry the rest of the way to Santorini. Expect that trip to take a minimum of 36 hours.

http://www.greekferries.gr

Thank you, we may consider leaving from Ancona on overnight ferry. I appreciate your input.

You can take a ferry from Ancona to Santorini? direct?

There is no direct ferry from Italy to Santorini.

There is not direct ferry from Venice to Santorini but you can take the boat from Venice to Patras on Minoan Lines then train to athens and on from there or you can check and see if they are still running special on the $99 flights Venice to Athens.http://www.edreams.net/
they run all kind of cheapie specials.