Can anyone out there give me some informed and real world (yeah, I
know this is a newsgroup but, hope springs eternal) insight as to how
vulnerable raw water cooled engines are to damage from freezing?

I just discovered that our insurance policy doesn’t have a "haul by"
clause and I’d like to sail here in Maine as late as I can. With the
cooling system filled with salt water and the water temperature not
yet fallen, I can’t imagine that my 20 HP Yanmar is going to crack
something the first few nights the temperature drops into the high 20’s.
I’d sure hate to be wrong though.

When should I start worrying?

If there was an unseasonably cold night forecast, I'd probably go down
and warm up the engine just before bed.

--

Roger Long