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AOSA Tip 1 - About Sailboats Floating in Winter!

The following description is about a unique weather phenomena that could also happen in the Edmonton area, given some extremely cold Fall weather.

In 1999 a huge dump of snow dropped overnight in the Vancouver area. Many boats were covered with a foot of snow and most boat house roofs collapsed under the weight. many boats suffered extensive deck damage as a result.
The following day was clear and sunny, creating a quick thaw that produced a massive fresh water runoff from the hills. There was so much of it, in such a short time, that it flowed on top of the salt water without mixing in it. The fresh water in the harbour was deep enough to enter any open through-hull fitting.
That night the air temperature dropped several degrees below freezing and the cabin temperature of any unheated boat froze as well. Any fresh water in an open through-hull fitting then froze, splitting some of them.
As the daytime heating warmed the cabins, the ice in the split fitting melted, letting seawater in.  Several boats sank in their slips that morning. 
Now wouldn't that ruin your day!

The point is, we boaters on Wabamun Lake are not that far from this scenario if we have a  mild day time temperature followed by an overnight freeze. You are less likely to have this happen at a mooring because the movement of the boat should prevent ice from freezing around the hull. On the other hand, boats huddled together at a dock might trap warm water. In any case, it is wise to close all your through hull fittings, especially in freezing weather.