He soon entered into a partnership at Plymouth with
Nathaniel Beardmore, and his practice rapidly grew. In 1826 he erected
Bowcombe Bridge, near
Kingsbridge, Devon, when
hydraulic power was first applied to the machinery for making
swing bridges. In 1831 he introduced a new system of crossing rivers by means of
chain ferries worked by steam, and in 1832 he constructed a
floating bridge on this principle, crossing the
Dart at
Dartmouth. Between 1832 and 1834 similar floating bridges were erected at
Torpoint and
Saltash across the
Tamar, which greatly facilitated the intercourse between Devon and
Cornwall. For these achievements a second Telford medal was awarded to Rendel in 1838. The
Torpoint Ferry still operates, albeit much updated. A similar
floating bridge was implemented as the
Woolston ferry between
Woolston, Hampshire and
Southampton in 1836. During this period Rendel was also engaged in reporting on harbours and rivers in the southwest of England, and thus acquired that mastery of hydraulic engineering on which his fame chiefly rests. In 1829 he designed the harbour which was afterwards executed at
Par Docks in Cornwall; in 1835 he carried out works on the
Bude harbour, dock, and
Bude Canal, and in 1836 he designed
Brixham harbour and the breakwater at
Torquay. In 1836–37 he designed, as a terminus to the
Great Western Railway, the
Millbay Docks, Plymouth, afterwards executed by
Isambard Kingdom Brunel. In 1843–44 he constructed
canals in Devon, and was engaged in the Colchester and Arundel navigation; and in 1844 he designed harbour improvements for
Newhaven and
Littlehampton in
Sussex. At the same time he was largely employed on marine works by the
Admiralty and other government departments, as well as by public companies. The
Exchequer Loan Commissioners engaged him in 1835–37 in the repair of the Montrose suspension bridge after its fall. There he introduced the principle of
trussing the framing of the roadway. This system of preventing the undulation, by which so many structures of this kind have been destroyed, was quickly acknowledged to be essential to their safety. ==London practice==