This is indeed very hard to answer at this moment, as Greece in its very awful financial situation is right now trying to create new financial sources wherever it can.
An Info from November 2009: yachts that stay in greek waters more than 40 days have to pay a special tax if they are over 15 meters (Sailing yachts) Â*or over 10 meters (Motor yachts) long.
The last info I found (german source
), dates from beginning of march. It confirms that this tax has to be paid by boats of the above sizes. Boats below these sizes have to check in at the marina or harbour offices and they pay one â‚¬ per meter. You need the ships papers and the personal ID of the owner.Â*
So, you should be fine as your yacht is under 15 meters.
But... one never knows what greek authorities think about next in their urgent need of money. Will check the net and will let you know as soon as something new comes up.
(On top of that there is still the topic of importing a yacht into the EU... )