What is Notice of Abandon?

Notice of abandon is a formal notice of relinquishment or unconditional surrender of all rights to a property, cargo, or ship by its insured owner to the insurer in the event of a constructive total loss.
By this notice the insured party declares its intention to treat the loss as actual total loss. The notice must be given with reasonable diligence otherwise (or in the absence of a notice) the loss may be considered partial.