Re: extending the season a bit
Never leave a running heater in an unattended boat! That is a recipe for disaster.
Here in the middle Chesapeake, there is no, or very little, risk to your engine until well into December. Even when the temps get down into the mid 20's on land, there is no risk. First, it takes most of the night to drop that low and it doesn't stay there long (due to sunrise). Second, temps on the water remains significantly higher than on land due to moisture saturation in the air from proximity to water and it remains above freezing even when land temps drop into the upper 20s, unless there's a stiff wind blowing off the land. Third, your engine is low in the hull and is partly below water level. Water warms the hull, and therefore the boat, and keeps it above freezing. Fourth, inside the hull, there is no wind to remove heat, and the entire environment must cool below freezing before there is a risk. There just isn't enough time before sunrise unless it drops into the mid 20s and stays there for a day.
Pragmatically, winterize your water system in late Nov and you can easily sail into December if you like sailing in that kind of weather. I usually go on the hard in late November or early December, myself, mostly because I don't like sailing when it is in the 30s and 40s, but also because my marina won't haul past then.
T. P. Donnelly
S/V Tranquility Base
1984 Islander 30 Bahama