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You will feel movement occasionally. depends on the weather & if you are traversing somewhere like the Bay of Biscay & the sixe of the ship (bigger the better in my experience). Most of the time it is hardly noticable. If you do not take travel sickness pills with you, the Guest Relations staff will be only too happy to provide you with one or two (one, taken at the time, will invariably cure you & set you straight for the rest of your cruise).
I have been on Legend several times and the answer to your question is that if you hit rough weather even with the stabilisers out there will be pitching and rolling. Some areas of the world are more prone to rough weather but it is a fact of life that any stretch of water can play up. My advice is that you try to get a cabin amidships where the least movement can be experienced and should you not feel well ask for some sea-sickness tablets which most ships provide free of charge. If then you still feel unwell ask for an injection for which they will charge but after a rest period are apparently very effective. I'm lucky and have never missed a breakfast yet even though I have been in Force 10 gales.
Good luck, Neil Down.
It is highly unlikely that you will feel much if any movement. If you do feel sick the ship's shop sells exellent pills under the brand name of Bonine (they are the best product I have ever used). I am an appallingly seasick traveller on cross channel ferries etc but have never had a problem even in rough seas on a modern cruise shi.