Unless it changed recently, there is a regular hydrofoil line linking Vienna to Bratislava on the Danube. I rode it in 2015, it's a wonderfully kitsch piece of Soviet era kit, but does this beast fly!
I rode one 20 years ago to islands off the coast of Greece. One of the trips was rough though due to choppy seas. I recall seatbelts were required and barf bags were utilized by a few passengers.
Regardless of type of boat, waves need to be considered and managed. Most of the time speed needs to be reduced. The same for Candela, when a wave is to high it works to operate just like a regular boat.
