This engineering group traces its history back to the earliest days of propeller manufacturing in the 19th century. Its Stone Marine division designs, supplies and services marine propellers for customers worldwide, and demand for its fuel-saving products boosted exports to £17.5m last year. The group also makes light alloy castings for the aerospace industry, and owns the former naval base at Portland, Dorset, which it has developed into a commercial port. Managing director Chris Langham, 64, leads the family-owned business.