There is a difference in 30 degrees when you are towing or sitting still. If the boats engine compartment vents are not covered the air is being forced into the engine compartment. The area cools quickly and could potential cause a freezing problem.
You may be able to pull the temperatures from the National Weather service for the date, time and location in question to verify that the temperature was actually 30 degrees. Good Luck!

the fiberglass hull will act as an insulator, so if the boat was in 30 degree weather, inside the engine compartment will be at least 3 or 4 degrees warmer. from the few car engine i have looked at that cracked it took lower 20's for several hours to cause this, the bad thing about boat engines though is that the bottoms of the block will have silt and mud trapped at the bottom, so if it packs up bad enough even if you drain the block the silt will hold some water and can freeze and crack the block, on your friends boat Gino sounds like someone is not being honest with you, sounds like the boat sat outside in very cold weather [below 23*] for at least 6 or 7 hours or longer[ most likely longer]

Sometimes when boats sit in water the ocean/lake water will keep them from freezing because the lake has not had a chance to drop that low - so it can work like a weak heater. I think that when you are moving on the highway the cool air could definately flow through the engine via the blowers and accelerate the process. Like driving a car down the highway- if its wet and its below freezing your car will likely have ice on it way before the bridges are frozen over.

Not an expert....

And in Florida, that means wearing pants!!!

Seriously, something's fishy here.

Possibly the owner should have winterized it prior to coming north a couple of months ago...wind chill can do it it had a way in....yes in 4 hours IF it had a way in!...who would send a boat north and not winterize it...

Wind chill, yes it can happen

Gino,
Your answer is yes it can happen. I had a Drag Racing customer that was going down south to race one year, He alos had to travel through very low 30's winter weather heading to Gainsville,Fl. I had recommended him to at least drain the water from the engine block and radiator before he leaves. He didn't and ended up getting to the race track to find a busted cylinder block! The temperatures where right near freezing also.

I thought wind chill only had effect on living tissue??

Would have thought the freeze plugs would have popped first

Sitting still no way 30 degree did it.....moving down the highway, well??? I just don't know. When daytime highs are over 40 I don't sweat nighttime lows in the mid-upper 20's.