OR, if it's pouring rain, you could always slow down a bit...that's saved my fish-tailing boat many a time. I have a strict "65 or less" speed limit when I'm dragging the love of my life behind me, 55 or less in heavy rain. And that's with just one boat.

But 6 of them stacked? I think 55 might be the max on a dry road, less in rain. And then there is the cross wind issue too, on a stack like that, was it blowing hard when this happened and from what direction?