I once saw the awesome sight of a classic Jaguar, stationary in the middle of an intersection, with a boat on its roof. Boat was not on a roof rack! It was your average power boat that had been on its trailer aft the Jag. The Jag's roof had a V-shaped crease that matched the ship's keel. Seemed the car had stopped suddenly.
Boat trailers have rollers to assist with launch and recovery and a post