You might want to look into this family further.
1851 census Woolwich
John Martin 59, machinist, born Taunton
Elizabeth Martin 50 born ---Sanford ?
Francis Martin 21 born Barnstable, machinist – (he eventually ends up as a chief engineer with Royal Navy)
James Martin 18 born Barnstable, machinist
Same family in 1841 census Barnstaple Devon
John Martin 45, Smith
Elizabeth Martin 45
Francis Martin 12
Mary Martin 10
James Martin 6
Sarah Martin 2
James MARTIN (b abt 1832) Marriage in 1853 Erith Kent to Louisa YALE
On marriage is an engineer and son of John Martin
James’ brother Francis Martin is witness
By 1861 census Louisa Martin is alone, claims to be a widow, has 3 children: Joseph Francis 6, A Louisa 3, George Edwin 1.
Louisa Martin remarries in 1863.
When son Joseph Francis Martin marries in 1876 he names his father as James Martin - Engineer with Royal Navy