With the recent weather in Colo. I am a little concerned with my boat. I had it in the water last weekend, and now I'm watching it snow. How long does the weather need to be freezing before it will crack the block.
Anything in the upper 20's and low 30's should not really be anything to worry about for a few days. There are a lot of easy ways to protect the boat if you are overly concerned, including the use of anti freeze or a small block heater.
I heard if you put a mechanics light(trouble light) and leave it on in the bilge area, as long as the temps dont drop that far, you should be fine with that much heat. At least that is what my marine mechanic told us to do in that event.