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How late can I leave my boat in?

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How late can I leave my boat in the water? If the lake hasn’t actually frozen, is there any reason to haul it out?
—Louisa May, via e-mail

It’s not the ice on the lake you should be worried about (although moving ice can definitely damage the hull); it’s the dropping air temperature and the possibility of damage to the boat’s engine. Happily, the lake’s natural tendency to retain heat as the summer fades to fall works in your favour: Even when the outside 
air temperature goes down, the water temperature can stay well above zero—and the water will help to insulate the boat from the cold. “The engine compartment stays the same temperature 
as the water,” explains Adam Paris, the service manager at Paris Marine in Peterborough.

So it depends on the weather—and 
it also depends on your engine. An outboard will be able to handle the cold 
better and could stay out longer than an inboard or sterndrive, says Rob Davidson, the coordinator for the Marine and Small Engines Program and Apprenticeship at Georgian College, and owner of Rob’s Marine Service in Orillia. This is because water, trapped in the engine block of a sterndrive or an inboard, can freeze and cause damage. But, in most outboards, the water can drain out (provided, of course, that the engine is left 
in the down position).

Davidson says he’s kept boats in 
the water as late as Christmas. “But typically, for a sterndrive, the end of October is as far as you want to push 
it.” An outboard would be okay until mid-November, he says, but he warns that marine insurers won’t cover your boat if it’s still in service past the date specified in your policy.

Check with your insurer, and then watch the five-day forecast. “If it’s about –5°C or warmer out, I wouldn’t even bat an eye at leaving it,” says Paris. But if the weatherman predicts three nights in a row of –10°C? To be safe, you’d better pull that boat out. “It takes a lot to bust an engine block in a sterndrive,” says Paris. “However, I have seen it happen.”