I'm not quite sure what to put on a Risk Assessment form for a model yacht. Maybe a one word answer?
'None'.............
Off the top of my head, I can think of a few..
Old RC TX with telescopic antennas that can take your eye out. Cure, a ping pong ball, or practice golf ball, to cap the end of the antenna.
Masts, bowsprits and booms can be a hazard.
Auxiliary motors, and props.
If servos are powered by Lithium batteries.
Boat stands, trip hazard.
Pond side risks common to all boat users
etc. etc.