In actual fact they are a 20 amp waterproof electric motor with a cage on one end protecting a propeller.
Picture a paint can with an old fashioned wire goalie mask attached to one end with a 2 blade 6 inch dia, propeller inside the cage.
The principle is A moving the water so it doesn't freeze and B drawing the warmer water off the bottom to the surface to help.
They are mounted on 6 ft. poles attached to the dock with a slight angle upward.
I could probably get away with shutting the odd one off when its sunny and near freezing but I don't want to risk having ice forming around piles and then not being able to get rid of it.
I'll post pic later showing how much area stays open now that lake is completely frozen over.