Bill, I use a 500mm on day trips a 400 mm on extended trips. The 500 mm is a big lens and as I get older it gets bigger. I do shoot handheld from a kayak. For sharp pictures I try to shoot at a shutter speed on 1/1000 or higher but I have been successful at a fraction of that speed. I keep my elbows down tucked against my pfd (it is almost always good technique to plant your elbows on your chest), my rear end and knees are firmly planted, my back and arms stay pretty lose and considering everything is moving you need good panning skills. I use both a full sized sensor and a crop sensor, I like the reach of crop sized sensors but I find full format has a larger pixel so it blurs less.