A mortgage is a legal document. If you own a vessel, or own a share in a vessel, registered in the general part of the Canadian Register of Vessel (commonly known as the Large Vessel Register), you can use it as security for a loan or other valuable consideration.
If you're using your vessel as security and receiving a loan, you're called the "mortgagor". If you're taking the vessel as security (which usually means you're giving the loan), you are the "mortgagee".
If you want a builder's mortgage for a vessel that's under construction, you must first record the vessel in the Canadian Register of Vessels.