Thank you all for your comments. Taking these shots presented a number of challenges - getting the entire boat and wake in frame, getting the %#%$@ thing in focus, dealing with the light (it was mid afternoon & the sun was high in the sky) and, finally, getting a good feel of action in the shot. Using a CP on the lens and getting on top of the panning process helped a lot as did the lens 70-200 VR lens - next time I hope to do better
Wayne - I'll try a tighter crop, thanks
Andrew - tell me about it. As it is I've actually added a bit of bow into the image that wasn't in the shot
Mitchell - trouble is working out what gives that sense of speed. I've been experimenting with tighter cropping and in some cases that seems to have worked.
Mark - 3rd shot is the best of these I got, but I have a few others on my SmugMug site where the other boat is just disappearing off the LHS.