IMHO it largely depends on the anti fouling's consistency.
I had to stretch pretty much to cover the 44 square meters Lagoon indicates for the 380's underwater
hull with 5.3 liters of Attiva's self polishing "Giralia", so I wouldn't call it ample...
However, this one coat prooved enough for cruising Spanish waters between Ibiza and Almeria April to October: just slime when dry
docking it for the
winter. The older coat (different colour) was shining through in large spots, though, so I guess one full year in these waters indeed requires two coats.