I have always heard that you don't have anything to worry about as long as the ice is off the water. Your I/O will sit about half way under the water line. The water temp is 38 or so right now so with your boat in the water, the temp of the water will radiate up and keep it from freezing. I personally dry dock my boat so if i have it up there this time of year, I open the drains on the engine block and risers then pop off the lower hoses. It takes me about 15 minutes but it get me fishing earlier.....