Doug, If the water your boat sits on forms ice..
then it could be cold enough to freeze the water in your ballast tank. But, the water in your tank will take a lot lower temp to freeze as it has the boat structure surrounding it as a heat sink.Simply said, if the lake or bay where your boat is moored freezes up then pull the boat out and drain the tank.The major problem area is in the head and sink lines. They don't have the protection of the surrounding water temps and can very easily freeze and break at temps as high as 32 to 34 degrees. Drain and blow out all water lines and the toilet system/holding tank (if so equiped) and you will be in good shape.Good luck with your 240, it's a beautiful sailing boat.Raysv Speedy 95 H26