We sailed from Harwich a few years ago and up the Norweign fjords. We never noticed the sea on the full 2 weeks. Again we did a cruise to the Baltic and the sea is very calm , We did both of these in July/ August time.
The North Sea can be a beggar at times and you can never take it for granted. We had a trip that included Oslo and Hamburg in July with the most attrocious weather and we were on the great ocean-going QE2 so there is always about 25% a chance of some lumps in the water but if you're an optimist there is a 75% chance of good weather just no guarantees. my last trip that way on Constellation was like a mill pond both ways in July. If you have a problem with sea-sickness there are always tablets readily available on most good cruise ships and if the worse happens a jab from the doc on board will cost you but will take all that illness away in a short time and it lasts. Hope that helps....Nei.
A party of 4 did the Fjords from Harwich Aug 08 and none of us noticed any rought seas, but we are all different. happy sailin.