A good way to judge the current is to use the Miragedrive speedo pitot tube in conjunction with a GPS. Roadrunner posted about it here:
http://www.hobiecat.com/community/viewt ... ight=pitot
I use both tube and GPS and find the combination useful. Current isn't really an issue in the AI if the wind is right of course. Turbo fins are a real improvement when the wind dies and you're fighting a current by yourself. I have been in our local tidal current a few times and have made steady progress against the current with turbos. The AI ama's when windless and level don't seem to add much drag.