Robert
As a one off I can't think of any problems, moving ice can cause hull damaged but it would need to be very extreme to crush the hull!
Long term continuous immersion in water, fresh is said to be worse than fresh, can cause osmosis problems.
Security can be another issue, is the dyke accessable, could the boat be liable for break-ins and damage if not theft?
Philip
ss26 rascal, out of the water each winter.