[obican]

It's movement after all, I'm not surprised IS could counter the movement of the boat. I did not have many lenses with IS but I don't think I ever ended up thinking IS wasn't working in one situtation when I thought it would work. What I'd go for if I were trying to cheat the IS would be putting it through so much lateral acceleration (in a cornering car, for example), it would think I was holding the camera in horizontal orientation when it was actually vertical.

 

Ps. I live in the area, if you need to ask anything, don't hesitate