This is a question I have had for a long time but could never find a good answer to. Why is horsepower mainly what manufacturers, regulations, and laws go by when it comes to outboards and why is that unique to the outboard industry? Why does every outboard have to come with the hp rating label on it, or is it that even required, and why are boats with inboard motors not like that and exempt from HP regulations as well? In many cases it makes very little since to regulate, and advertize them that way. Why not go by displacement instead like ever other motor industry? Does anyone know the history of how it came to be this way?