7 MPH to 0 MPH in a foot or so
That is the thing: You keep going 7 mph until you hit something solid, then you stop is something like 0.25 inch. Just like falling over walking. If you land wrong, or on the wrong thing, you might get hurt. There are a lot of wrong things to land on in and about sailboats.
I seem to remember reading of some cruiser who would sleep with his feet forward, so if he hit something he wouldn't break his neck (might have been Alvah Simon).