These are Silver Coins that I found Metal Detecting on the beach in South England, so technically there not really shipwreck coins (but they could be!). They just look like them from the erosion and hydraulic action of the sea. They get churned up by the big storms and smahed against rocks by the waves, over the years they get more beaten up and the saltwater also slowly reacts with the metal. So it's a combination of chemical and mechanical ware that creates there distinctive appearance.
These three coins are all pretty modern. The top Right is a 925 silver Queen Victoria threepence that looks like it's been nailed to a piece of wood with an old square nail, maybe on a boat as a good luck charm! Bottom right is a 50% silver 1945 sixpence with really ragged edges. And top left is a 50% silver 2shilling piece with the rose and crown in the centre. They were probably just dropped out of pockets as people sat down on the beach, I've found hundreds of beach coins but these are the only silver's so far.