Kosciusko was converted to diesel propulsion in the 1950s and served on Sydney Harbour until 1975 when she was sent to Hobart to assist following the collapse of the Tasman bridge.

[1] Her 54 hp triple expansion steam engine was supplied by Campbell & Calderwell and pushed her to 10 knots.

Kosciusko was one of the few formerly numerous K-class ferries to survive both the 1932 opening of the Sydney Harbour Bridge and the 1950s state government rationalisation of the fleet.

Kosciusko was converted to diesel in 1959 (60 hp Crossley, 11 knots) which allowed coal-fired Kareela to be retired.

Alternatives were urgently needed, and Sydney's then new Lady Wakehurst was sent to the Tasmanian city to assist with cross-Derwent travel.