Thanks guys for your replies.
Last friday I tried it for the first time at sea, together with a friend of mine. He is more experienced with the SOT.
We had a strong current along the coastline, going north. Fishing was manageable but compared to flyfishing out of a U-boat I found time spent on fishing was less and on managing the kayak more, but this is of course mainly due to my inexperience. These things do get blown away easily, especially if the wind and current work together. Getting back against the current was something different. We did manage but it puts an extra dimension into flyfishing. If I do this more regularly I will be able to cast effortless with #12 rods
Although I did not catch anything that day it was great fun to do. I will keep your advise in mind next time and look for shallow water to fish wading and just troll on the way.