I met a guy on the dry lake a while ago. He told me his friend broke some ribs in a violent crash. The guy hit something head on, and his body slid under the seatbelt (enormous beer guts might save you from this), and mashed his torso under the belt, busting the ribs.

My new friend said the guy made straps like this to keep him in place. They simply loop over the seatbelt at it's lowest point, then go around your leg, and back through the belt on top. They might also keep one's tackle from meeting the mast base or foot pedals (mini or CL-5) in the same kind of wreck.

I wouldn't recommend this for beach use; if ya flipped in the water, these things will take a bit longer to get out of

Make/use them as you see fit. I'm just passing the info along.......