Specification
The vessel is powered by a twin cylinder 90 degree "V" steam engine, which has a slip eccentric reverse system and is a double-acting slide valve arrangement. The steam boiler is of the locomotive type, with 90 one and a quarter inch (35mm) steel tubes passing through the barrel. From her launch in 1859 she has been coal fired. First she used an all-copper design as used by the Furness Railway on their locomotives; this supplied steam to her engines at a maximum of 80psi (pounds per square inch). Around the beginning of the 20th century she was equipped with an all-steel boiler supplying steam at 100 psi. The boiler and the engines were taken out when she was laid up and converted to a houseboat. When she was re-launched in 1980 an all-steel design was again specified, although this time rated at a maximum working pressure of 150 psi. She still uses this boiler today. From 20 March 2008 the firing of Gondola became more green; she is now fired on Blazer Logs, these commercially produced logs being made from compressed sawdust which burns very efficiently, giving off little smoke with negligible sulphur content.
The cylinders exhaust to atmosphere after first passing through a silencer. The draft induced by the steam is used to draw the heat and waste products of combustion through the boiler and up the funnel, and so draw more air into the furnace, a force draft system. However now the ship is using a different fuel to fire the boiler a flue damper has also been fitted to produce a finer tolerance of control in the firebox; using less fuel to produce more steam, and hence greater economy. The engines produce a maximum of approximately 8,000 N·m (5,900 lb·ft) of torque at the prop shaft and this turns the 36" diameter propeller at approximately 150-160 rpm giving a hull cruising speed of about 8 knots (9.2 mph; 15 km/h). The maximum speed of 240 rpm gives a maximum hull speed of 11.7 knots (13.5 mph; 21.7 km/h). However, at this speed, although just four knots faster than cruising speed, the engines use 60% more steam.
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