Long Exposure

My first photography trip since Baby was born, and I finally had the chance to try out my neutral density filter. I popped along to North Berwick to experiment with capturing long exposure shots of the waves. It threw me off a bit that I couldn't see what I was pointing the camera at while the filter was on. Do those of you who use ND filters take the filter off between shots so you can get the correct composition? Or do you do what I did and guess, then adjust until it's good enough?

I also managed to get some photos of a tower (it looks like an old dovecot) in a field I sometimes drive past on my way to North Berwick. It's different to the one I posted about last month, but I thought they were the same tower until after I had tried to photograph the other one ...