The tug Lyttelton and her engines were built in Scotland in 1907 by Ferguson brothers Ltd. of Port Glasgow, and was sailed out to Lyttelton through the Suez canal which had been open for almost forty years. The machinery has been very little altered throughout the ship's long period of service with the Lyttelton Harbour Board and gives the visitor a glimpse back in time to the heyday of British steam engineering. On a visit to the engine room and stokehold you can very easily imagine the ship steaming out across the Indian ocean in 1907 lit only by oil lamps, with every spare space loaded with coal for the long voyage.
To feel the heat and the movement of the ship, and hear the rasp of shovels on the stokehold floor and the hissing and pulsing of the engines puts you in close touch with the conditions many of our ancestors would have encountered as they made their way across the world in the early years of last century.
The ship's boiler is of a type known as a Scotch Marine Boiler. It is hand fired by coal and when the tug was new, produced steam at 110 lbs per square inch and was rated at 1000 horsepower. Since 1974 the maximum working pressure has been reduced to 80 lbs per square inch.
The boiler consists of a drum 17 feet in diameter and 11 feet long and holds 30 tons of water. The body is made of 7/8 inch steel plates riveted together and the two large forged end plates are connected by stay rods. There are four corrugated furnace tubes which feed the hot gases into four separate combustion chambers and back through the boiling water via 300 fire tubes of 4 inches in diameter and thence up to the smokestack. This is 5 feet in diameter and 22 feet high and induces a natural draught up through the boiler. The four furnaces have a total grate area of 78 square feet.
We control the steam output by use of a damper at the bottom of the stack and also by semicircular damper plates controlling the air fed in under each grate. There are coal bunkers each side of the stokehold and each of these holds 17 tons of steaming coal.
When the tug is steaming along it consumes approximately one third of a ton of coal an hour. We normally have at least two firemen who do half hour watches during a voyage and they are required to keep the steam pressure up in the 70 PSI region and not to have too much fire on at the end of each voyage when the use of steam ceases.
From a cold boiler we light warming fires 48 hours before each voyage and gradually increase the heat until all four fires are burning as we leave the wharf. The boiler is surveyed annually by qualified marine surveyors.
The boiler water is treated chemically to minimise corrosion. The boiler has all the usual auxiliary pipe work valves and gauges which would be found on a boiler of its age and type.
Steam is lead
through to the main engines through a main steam line 6 inches in diameter.
The Main Engines
The tug's two main engines are compound, reciprocating steam engines, fitted with steam assisted Stephenson's reversing gear and built in condensers. They were rated at 500 horsepower each when fed with steam at 110 lbs per square inch. Steam from the boiler is led via a throttling valve into the high pressure cylinder which is 20 inches in diameter. It is exhausted from this engine at about atmospheric pressure and is fed through ports in the cylinder casting into the low pressure cylinder which is 40 inches in diameter. Both cylinders have a stroke of 27 inches.
The exhaust from the low pressure cylinder is lead through a large pipe into the top of the condenser where a vacuum is produced as the steam is cooled by contact with a bank of brass tubes which have cold seawater pumping through them. The water which collects in the bottom of each condenser is pumped back into the boiler.
Each engine drives a large propeller 8 feet in diameter with a 12 foot pitch as befitting a tugboat. There are two thrust bearings just behind each engine which take up the thrust from the screws onto the structure of the ship which is specially strengthened at that point.
Each engine drives a bank of reciprocating pumps which circulate cooling water through and maintain a vacuum in the condensers. These pumps also return condensate to the boiler and empty the bilges.
The engines are reversed by bringing in to use separate eccentrics on the crankshaft which time the valve gear opening and closing to make the engine rotate in the required direction. Lubrication is by a drip feed of oil through wicks into all the principal bearing surfaces in the engine.
We have three people in the engine room. The Chief Engineer is in charge of all the machinery and the boiler on the ship and he is assisted by a Second Engineer and a Greaser. We run the main engines at around 70 R.P.M. these days but, they ran at over 100 R.P.M. when the tug was younger and towing a heavy load. Each engine is controlled in the engine room as ordered by the mechanical telegraph from the bridge.
There are numerous auxiliary engines around the ship fed with steam from the boiler. The Tug being originally fitted out as a sea-going salvage tug, has a large fire pump in the engine room which could be used to pump out another ship at sea.
There is also a general service pump which can be connected in numerous ways to pump water around the ship and a single cylinder steam engine driving a 5KW, 110Volt DC generator. The ship was fitted out with electricity for lighting in Wellington in the 1920's, and until then had only oil wick lamps for illumination below decks and at night.
On the foredeck is a winch for raising and lowering the anchors and on the afterdeck is a capstan for handling ropes. The ships rudder control is power assisted by a steam engine in the wheelhouse. This engine is coupled with chains and pulleys to a quadrant directly over the rudder shaft.
Fresh tanks under the crews quarters hold 20 tons of fresh water to make up the boiler water lost as steam from auxiliary machinery and exhausted to atmosphere. We use about a ton of water in this way on each voyage.