In 1866 Thornycroft took over Chesterman's yard completely, and John I. Thornycroft & Company was formally established, but at the beginning, John Thornycroft did not work there full-time.
I 1866 overtog Thornycroft Chestermans værft, og John I. Thornycroft & Company blev formelt grundlagt, men de første år arbejdede John Thornycroft ikke på fuld tid i virksomheden.