They are called sponsons. Years ago I had a small 10 foot Sears Jon that me and my fishing buddy would pretty much over load. I epoxied on the sides just under the water line
some foam sponsons made for canoes. They were basically pool noodles cut in half. They added some extra flotation and stability to that overloaded boat.
Most of time I have seen them on the transom of jons to support a larger/heavier outboard. I think they also effect the boats planing performance. The rear ones are called beaver tails.