MacGregorSailors.com

"Freak" freezes of lakes don't happen overnight. In order for a lake of any reasonable size to freeze, the average (not instantaneous or overnight) temperature has to remain below freezing for quite a number of days. How many days it takes is determined by how much below freezing the average temp is.

My boat has been in the water late in the season when there was ice along the shoreline, a small layer around the boat itself, and up to two inches on the upper surfaces of the boat form a freak early storm, but the ballast never froze.

As long as the lake isn't frozen, the ballast won't freeze either.

You should have ample warning to get your boat out of the water and empty the ballast.

Just last week I got energetic and went out to clean the inside of my boat in preparation for April fools day moorage. After cleaning the inside fiberglass, I proceeded to clean out the bilges of rain water. Much to my surprise it was frozen so I was able to break some of the pieces out and throw them over the side instead of bucketing the water out. I know this is only a small volume of water, but it does not get that cold here and even though we were getting -1 to -3 I did not think water inside the boat would freeze, but it did. I am inclined to believe the ballast water would freeze before the lake does. I would not leave water in the ballast during winter.

http://www.boatus.com/goodoldboat/winteragitation.htm

This bubbler is used to keep the water from freezing around your boat. I would think if the water outside wasnt frozen the water inside probably wouldnt be either. Leave all your curtains down so the sun can warm the interior too.

Thanks for the helpful replies. I will get the boat removed from the water as the safest option.