Dear Iain I think the person you are looking for is Joseph, son of Jemima (nee Davey)and William ( my grans brother)he was one of 14 children, all born Pentewan, he was married to Mary they had 7 children, James, Joseph,Frank,Ernest,Jessie, May,William.
In the 1891census He was in Bristol with his brother William on the vessel Marian sailing schooner, her tonnage was 84 she was a sailng schooner coasting trade, place belonged Padstow, William was master and Joseph was mate.
In 1881census he was Mate on the Enginner with his brother William Master,Chalestown surname index William Matta Master ship Enginner.
Joseph is the 6th generation I have of the Matta's going back to 1725
I was in touch with your Uncle Chris about 20 years ago, Jean Selwood