From what I've seen over the years a lot of folk don't think a pontoon needs to be secured. I mean, like, their heavy.
Back in 1974 I was running a lowboy for a road construction outfit. When I started one of the foremen told me about the importance of ALWAYS chaining the equipment down. A few years before they were moving a D8 dozer a little over a half mile so driver figured he'd go slow and wouldn't need to chain it. About a quarter mile down the road there was a left hand curve and when he took it the dozer gracefully slid half way off the lowboy. Oops.