Join Date: May 2006
Location: Ottawa, Canada
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Re: Easy only if you know the answer
O.N. Official number This is the boats registration number. In the US it's the documentation number.
R.T. (In Canada this should be N.R.T.) Registered tonnage
In Canada, both the official number and register tonnage shown on the Certificate of Registry must be clearly marked and permanently fixed to the hull. In the US this is probably the requirement for documented vessels.