Norfolk is regularly downright chilly by late December. Used to see the late snow birds coming through covered in Ice. I'd want to get to at least Southern Georgia if I was truly flleeing cold weather and it can freeze even there in January-March. Why are you doing the ditch?? If you want to get south in a hurry, go outside. You can sail 24 hours a day and easily double your miles than the ICW. You can sail/power at night on the ditch but have your kedge anchor and dinghy ready for instant deployment. Tried travelling at night with 100% success, ran aground every time we tried. Non functioning lights, very narrow dredged channels, confusing buoyage, etc. Probably easier with GPS but I still would want to put in every mark as a waypoint which could get very tiresome.