Hi Dave: According to the Clydebuilt link she was renamed twice: 1939 THEODOR WOKER / 1939-41 HMS STALWART / 1942-81 E.S. STEYTLER. The three different names reflects three different owners. 1939 South African Railway & Harbours Company Durban. 1939-41 British Admiralty London. 1942-81 Republic of South Africa (Railways & Harbours Administration) Durban.
Mr. Steytler was a cricket player: Full name Edward Spilsbury Steytler. Born 1859, Cape Town, Cape Province. Died July 17, 1947, Cape Town, Cape Province (aged 88 years). Major team: Western Province. Regards, Stein.
Also see 'A Century of South African Steam Tugs' by David Reynolds, published in South Africa in 1982, with a 2nd edition in 1992. According to this, the original name 'Theodore Woker' was considered to be rather too Germanic to be used at the time !
The twin funnelled tug on the right is the 'Sir David Hunter' built at Fergusons, Port Glasgow in 1917, scrapped in Durban in 1959 (Named after a General Manager of the Natal Government Railways.)