I have ridden it a couple of different times while preggers. Its very smooth but there is one very small slide (its more like a dip), nothing major. Just one word of caution.. you do have to step down into and step up out of the boat so just please watch your step. I always had a hard time seeing my feet so DH just helped me in just to make sure.
Plus if your going when its hot, it is a wonderful place to cool off.