Archaeology Notes

Event ID 855873

Category Descriptive Accounts

Type Archaeology Notes

Permalink http://canmore.org.uk/event/855873

NS37SW 80 3196 7465

For the loss of the original of this vessel (location cited as NR 7588 9876), see NR79NE 8001.

For monuments to Henry Bell at Helensburgh Esplanade (NS 29381 82323) and Dunglass Castle (NS 4377 7353), see NS28SE 109 and NS 47SW 123, respectively. For flywheel and anvil in Hermitage Park, Helensburgh (at NS 29855 82784), see NS28SE 236.

[No current location cited]. A replica of the 'Comet' (NR79NE 8001) was constructed by Lithgows Ltd (occupying the location of the original construction) and launched on 1 September 1962. Built on the basis of drawings held in Glasgow University, her dimensions are as follows: Length (deck) 44ft 11.5ins [13.7m]; length (water line) 42ft 6ins [12.96m], breadth (external) 15ft 9.5ins [4.81m], draught 3ft 9ins [1.14m]; displacement 21.5 tons. The location of the engine remains open to doubt. The hull, by George Thomson of Buckie, is of carvel construction, comprising 1.5in [38mm] larch planks on 3in [76mm] oak frames; the framing is at 11.5in [292mm] centres. Keel, hog, stern- and stempost are of oak, as are all deck beams; iron fastenings are used throughout. The vessel is divided into three compatrtments: a small second class passenger cabin about 7ft [2.1m] long forward, an after cabin about 9ft [2.7m] long aft, and an open machinery compartment amidships. The after cabin is entered through double doors in a sunken well, and has standing room along its length under the deckhouse roof. The machinery compartment is about 15ft [4.57m] long, and occupies the full width of the vessel. It is protected by a low bulwark, and is traversed by two paddle-shafts. The engine and horizontal boiler are set on the starboard and port sides respectively, while the coal bunkers are at the after end. Exhaust gases pass up the 25ft [7.6m] high funnel of 12ins [0.3m] diameter, which also acts as a mast. A square sail of 180 sq ft is hung from a yard 18ft [5.5m] above the deck. There is also provision for a jib, carried on the forestay.

The engine is a single-cylinder, double-acting, side-lever, jet-condensing type of 12.5ins [178mm] bore and 16ins [406mm] stroke. The throw of the single overhung crank is 7.5ins [191mm]. Working pressure is 10 psi [0.68 bar], that of the original engine being 7 psi [0.48 bar]. Power from the engine crankshaft is transmitted through gearing, the primary wheel (on the crankshaft) having 51 teeth and the secondary wheels (on the paddle shafts) having 86 teeth. The paddlewheels thus revolve at 41.5rpm when the crankshaft is revolving at 70rpm. Problems were encountered with the design and construction of the inside of the air pump, the jet condenser, the circulating pump, and the boiler feed pump, the available evidence for the last two being limited. The mean cut off was set at 83 per cent of stroke, and the gear-wheels on the paddle-shafts are mounted on squared portions with 0.25ins [6.4mm] clear all round. The wheels are centred by the eight keys in the hub. The replica engine gives about 10 bhp for a consumption of about 11ibs of coal per hp/hr.

The Comet Trust c. 1970.