The Paddle Steamer OSCAR ‘W’ is powered by a 16 horse power Marshall steam engine which obtains its steam supply from the Forbes loco type boiler below on which the engine is mounted.

The 1908 engine is original. The boiler was built by Forbes Engineering in 1996 to replace the original Marshall boiler, which was removed at that time.

The boiler produces steam by burning wood in the firebox of the boiler (4’ or 1.2 meters long) The fire box is surrounded by water. The fire sits on a grate with air flowing from the front under the grate and through the fire, exiting through tubes in the barrel of the boiler to the smoke box and flue. Air flow is controlled by use of the damper, located at the base of the boiler front.

The water level in the boiler is visible in the gauge glasses, this is controlled by pumping water into the boiler, steam usage and blowing down the boiler. The water level is extremely important – if too low the fire box crown could be damaged – if too high priming (water carry over to engine) can occur.

The boiler can run at up to 1,000 K.P.A. (150 P.S.I.) but normal working pressure would be 120 – 140 P.S.I., this being the range where the machinery runs most efficiently without lifting the safety valves (set at 150 P.S.I.).

Warming up time

When the boiler has not been used for some time, we allow 3 hours from the time we light a fire in the boiler until it is near operating pressure. If the boiler has been in use the day before, we usually allow 2 hours due to the fact that the boiler does not cool down completely for several days.

How it works

The steam produced by the boiler is used to drive the engine, the steam enters the engine block and by way of ports within the block travels to slide valves on either side. These valves allow steam to enter the cylinder and then drive the pistons. At the same time steam is allowed to exhaust from the other side of the piston. The pistons are connected to the crankshaft and when moved drive the paddle wheels on either side of the boat.

The crankshaft also has eccentrics fitted to it, these cause the slide valves to move allowing steam to enter or exit the cylinders as required.

The exhaust steam from the engine exits via the smoke box to the stack, this exhaust also helps with airflow entering and leaving the boiler and so aids firing of the boiler.

Blow down

From time to time there is a need to get rid of accumulated mud, chemicals etc. from the boiler. This is achieved by blowing down (opening a valve at the bottom of the boiler), a somewhat spectacular and often disconcerting event for the uninitiated, with water and steam being released on the port side of the boat.

Lubrication

Normal lubrication of bearings etc. takes place, but steam cylinders and slide valves require special oils. Special lubricators on the engine achieve lubrication of steam parts. These work by condensing steam from the engine which displaces oil from a reservoir, the oil then drops back into the engine parts to lubricate them.

Some commonly asked questions

Do we carry water?

No, we use the water straight from the River.

What is the water quality like?

Not good, which causes us to blow down more often and add chemicals to the boiler.

Can the paddles turn independently?

No, we can only go forward and reverse together and rely on the rudder to turn.

Do we heat the water going to the boiler?

Yes, some exhaust steam is used to preheat water (improves efficiency – burn less wood)

How many ways to get water into the boiler?

What are all the parts on the crankshaft?

There are 5 eccentrics attached, 4 to move slide valves and one to drive short stroke pump.

How can the engine reverse?

Each slide valve has 2 eccentrics attached – by moving the gear lever the other eccentric is brought into play (alters relationship of valve to piston) allowing engine to reverse.

Who controls the engine?

The gears and stop/start of engine is controlled from the boiler front. Speed is controlled from the wheelhouse.

How much wood do we burn?

The estimate is 1/3 to ½ ton per hour.

What speed to we travel at?

Approx 6 – 7 miles per hour, depending on River conditions.