Most inboard boats pull in water to cool them don't have a radiator as suck. When you winterize them you are taking the water and other fluids that are still inside the engine from its last use and other impurities out. You actually don't have to winterize it as long as you are good with maintenance and live somewhere it does not get to cold. Here in Texas its hit or miss risk cracking the block or pay the money. Another option a lot of people use that keep there boat on the water is a block heater in the winter much like a diesel.