This coin is a copper twopence dated 1797 and weighs about 2 ounces. The diameter is about 40mm or 1 9/16". The reverse features Brittania and because of the rim and weight the coin was known as a Cartwheel.
Either side of the hole is the initials HC and EA, the coin would have most likely been holed, initialed and hammered into a keel of a boat behind the mast as a good luck talisman. On the obverse is a mark where the coin had been levered off. A fine maritime artefact I beleive.