Data from "The Isle of Man Railway.," Locomotive Magazine, Volume VII (December 1902), p. 202; and "No.14 Thornhill (M.N.Ry. No.3)" on the Isle of Man Steam Railway Supporters' Association at [], last accessed 16 July 2025. See also "Manx Northern Railway" in Wikipedia at [], last accessed 14 July 2025; and Brunel Revidivus [pseudonym], "Manx Northern", Railway Magazine, Volume V [5] (July 1899), pp. 59-68. Works number was 2028 in 1879.
The Manx Northern opened its mainline between St John's and Ramsey on the Isle of Man in 1879. The Isle of Man Railway had opened several years earlier. The MN's construction yielded a 1% ruling grade and relatively mild curves despite "the nature of the country and the secondary character of the railway" said the Railway Magazine report. Its timetable called for an average of 25 mph (40 kph) speeds between stops "so that a fairly high rate is at times attained."
As the Isle of Man Railway took delivery of its nonet of four-coupled six-wheel tanks (Locobase 10245), its northern competitor ordered another of the same design to join the two Sharp, Stewart engines Ramsey and Northern acquired a few years earlier..
According to the 1902 LM report, the B-Ps on the IoM performed as desired pleasing both the company and footplate crews. The Thornhill found similar success on the MN; the IoMRA's entry notes that its frame accumulated 803,728 miles (1,294,002 km) before its retirement in 1963.
As the website notes, boiler mileage differed: "After the merger it [Thornhill, by now #14 on the Isle of Man Railway] received the 1896 boiler from No.4 Loch in 1910 which remained until 1913 when the 1893 boiler from No.2 Derby was fitted in its place. There was a further swap in 1916 when the boiler provided in 1895 for No.5 Mona was installed in the locomotive. The final swap came in 1921 when another boiler from No.5 dating from 1914 was placed in the frames and it is this boiler that remained in use until the end of the locomotive's service career."
| Principal Dimensions by Steve Llanso of Middle Run Media | |
|---|---|
| Class | Thornhill |
| Locobase ID | 21257 |
| Railroad | Manx Northern |
| Country | Isle of Man |
| Whyte | 2-4-0T |
| Number in Class | 1 |
| Road Numbers | 14 |
| Gauge | 3' |
| Number Built | 1 |
| Builder | Beyer, Peacock |
| Year | 1879 |
| Valve Gear | Allan |
| Locomotive Length and Weight | |
| Driver Wheelbase (ft / m) | 6.50 / 1.98 |
| Engine Wheelbase (ft / m) | 14.50 / 4.42 |
| Ratio of driving wheelbase to overall engine wheelbase | 0.45 |
| Overall Wheelbase (engine & tender) (ft / m) | 14.50 / 4.42 |
| Axle Loading (Maximum Weight per Axle) (lbs / kg) | |
| Weight on Drivers (lbs / kg) | |
| Engine Weight (lbs / kg) | 40,796 / 18,505 |
| Tender Loaded Weight (lbs / kg) | |
| Total Engine and Tender Weight (lbs / kg) | |
| Tender Water Capacity (gals / ML) | 576 / 2.18 |
| Tender Fuel Capacity (oil/coal) (gals/tons / Liters/MT) | 0.60 / 1 |
| Minimum weight of rail (calculated) (lb/yd / kg/m) | |
| Geometry Relating to Tractive Effort | |
| Driver Diameter (in / mm) | 45.30 / 1151 |
| Boiler Pressure (psi / kPa) | 160 / 1100 |
| High Pressure Cylinders (dia x stroke) (in / mm) | 11" x 18" / 279x457 |
| Tractive Effort (lbs / kg) | 6539 / 2966.04 |
| Factor of Adhesion (Weight on Drivers/Tractive Effort) | |
| Heating Ability | |
| Tubes (number - dia) (in / mm) | 121 - 1.625" / 41 |
| Flues (number - dia) (in / mm) | |
| Flue/Tube length (ft / m) | 7.69 / 2.34 |
| Firebox Area (sq ft / m2) | 51.40 / 4.78 |
| Grate Area (sq ft / m2) | 6.25 / 0.58 |
| Evaporative Heating Surface (sq ft / m2) | 461 / 42.84 |
| Superheating Surface (sq ft / m2) | |
| Combined Heating Surface (sq ft / m2) | 461 / 42.84 |
| Evaporative Heating Surface/Cylinder Volume | 232.84 |
| Computations Relating to Power Output (More Information) | |
| Robert LeMassena's Power Computation | 1000 |
| Same as above plus superheater percentage | 1000 |
| Same as above but substitute firebox area for grate area | 8224 |
| Power L1 | 4381 |
| Power MT | |