The jewel in Explorer’s crown is her machinery. The main propulsion is a triple expansion steam reciprocating engine powered by a Scotch boiler burning heavy fuel oil. Steam reciprocating engines ruled supreme at sea until the invention of the steam turbine by Sir Charles Parsons in 1884 and continued to dominate through the early twentieth century due to the economics and engineering expertise of the time.
The main engine was built in 1955 by Alexander Hall & Co. of Aberdeen. It is a double acting triple expansion steam engine of 1000 indicated horsepower. The HP piston is 16.5″ diameter and the IP and LP pistons 28.5″ and 47″ respectively all with a stroke of 30″ Steam inlet pressure is 220 psi and full speed RPM is 120. The Stevenson reversing gear is operated by a Brown Bros steam/hydraulic engine. The engine is both mechanically and manually lubricated. The HP cylinder is supplied by a piston valve whilst the IP and LP cylinders are serviced by slide valves. A boiler feed pump and two bilge pumps are driven by the HP crosshead.
It is quite possibly the largest and latest remaining UK example of the marine type still in its original context. It is rated at 1000 indicated horsepower and could push the ship through the seas at a quoted speed of 12 knots, as well as operate for long periods of time at smooth, low revolutions – ideal for trawling. Its efficiency, and her large heavy-oil tanks, gave ‘SS Explorer’ a range of up to 8000 nautical miles. She could be pushed beyond her stated design speed if provoked though. We have been told of a race between her and some diesel boats on the return to Aberdeen from a research trip, when 19 knots was indicated as SS Explorer beat them home, singing with the vibrations from the main engine the whole way there. A pinch of salt may need to be served with this claim.
Explorer’s boiler was built in 1954 by William Denny & Bros. Ltd, Dumbarton. It’s serial number is SO7635. It is a triple furnace, return tube Scotch type with three Deighton corrugated furnaces. The riveted shell is 16ft diameter and 11ft long with 2800 sq ft of heating surface and 3.25″ return tubes. The working pressure is 225 psig.
In a concession to developing technologies, all auxiliary pumps such as the auxy boiler feed, circulating and fuel pumps, are electrically driven rather than being powered by steam from the boiler as would normally be expected. Following the era in which SS Explorer was built, many ships were fully diesel driven and the need for such auxiliaries vanished. It would be safe to suggest that the engineering set-up of SS Explorer is therefore unique. A Ruston 4VRH and two large Ruston 6VPH engines, which may be familiar to railway enthusiasts, provide the bulk of the electrical power. The two mains produce 80kw at 220v DC and the auxiliary harbour set produces 24kw at 220v DC. An AC system was fitted for the extensive lab equipment and it was generated by a motor alternator in a compartment in the fore part of the ship. SS Explorer is fitted with shore poser receptacles though it is unclear how 230v AC was rectified.
The steering system fitted to SS Explorer is electro-hydraulic, The steering wheel on the bridge operates a telemotor which hydraulically moves a cylinder on the steering gear. Hunting gear operates the pumps to move the rudder to the desired angle proportionate to the position of the cylinder.
The telegraphs were electric and navigation was state of the art for the period with electronic gear such as Radar, Direction Finder, Gyro-Compass and Decca Navigator sets fitted. A fully electric intercom system was installed alongside the more traditional voice tubes. Many Bakelite phones remain in place and still work.
Machinery Space for Geeks
The adjacent diagram shows the layout of SS Explorer’s machinery as well as some auxilliarys. (Click to enlarge) A brief description of the machinery in a clockwise direction follows.
The general service pumps can draw water from the sea, the bilge main, the bilge direct, the ballast main and the feed system. It can discharge to all of these except the bilge in addition to supplying water to deck services and the engine condenser. These pumps have an air pump mounted above the motor to allow the pump to prime.
The fresh water pump transfers fresh water from storage tanks to the feed system.
The circulating pump provides cooling water from the sea to the engine condenser. Additionally it can pump directly from the bilges.
The aux feed pump provides feed water from the feed filter tank to the boiler when the main engine driven pump is not running.
The air pump removes air and condensate from the condenser allowing a good vacuum to be maintained.
The feed filter tank takes condensate from the condenser via the air pump and filters residual lubricating oil from it.
The 24kw generator mainly used for light load conditions such as in harbour.
The observation tanks allow condensate returns from oil fuel heating to be inspected for oil contamination due to heating coil leakage.
The domestic boiler supplies heating to the accommodation.
The fan supplies combustion air to the main boiler.
The oil fuel heaters raise the temperature of the heavy fuel oil to around 120C to reduce the viscosity to allow atomisation in the furnace.
Oil fuel strainers filter the oil before it enters the oil fuel pumps. additional hot filters (not shown) further filter the oil after it has been heated.
Oil fuel pumps supplied from ship’s bunker tanks pressurise the heavy fuel oil and supply it to the boiler burners via the heater and hot filter.
The daily service tank is a header tank holding 100 gallons of diesel oil to supply the generators and domestic boiler.
80kw generators and switchboard provide 220v DC power supply to the ship.
Tanks pressurised system provide fresh and salt water to the accommodation. They are air accumulators topped up by respective service pumps.
The compressor charges the air bottles to provide compressed air to start the generators.
Several small auxiliary pumps and the feed water heater and filter are not shown.