Seaboard Air Line 4-6-2 "Pacific" Locomotives of the USA

Class Details by Steve Llanso of Sweat House Media

Class P (Locobase 2812)

Data from for 1929 locomotive diagrams, supplemented and amended by DeGolyer, Volume 48, p. 27 and SAL 9 - 1918 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection.. See also "Pacific Type Locomotives for the Seaboard Air Line," Railway and Engineering Review, Volume 52, No 2 (1 February 1913), p. 95-97. (Thanks to Chris Hohl for his 16 September 2015 email and spreadsheet noting several differences in data.) Baldwin works numbers for road numbers 85-89 were 38763-38767 in 1912, Alco's numbers for the Richmond Works engines were 50262-50271 in September 1911 and 54030-54036 in September1913.

Speedy Pacifics that proved to be a bit light. Baldwin built five, Richmond turned out seventeen. The first 91 and 93 destroyed each other in a head-on collision on 19 November 1912, killing six people. They were replaced by two engines in 1913.

Firebox heating surface includes 24.2 sq ft (2.25 sq m) of arch tubes. 12" (305 mm) diameter piston valves supplied steam to the cylinders. The locomotives had modified Hodges trailing trucks with an arrangement of swings, links, and equalizers that reduced "to a large extent, any tendency to throw the spring out of alignment with the truck frame when the locomotive is curving."

Later increases in tender capacity to 15 tons (13.6 tonnes) of coal and 9,000 US gallons (34,065 litres) of water resulted in a loaded tender weight of 151,640 lb (79,061 kg). The larger tender extended the engine-and-tender length to 66 ft 3 in (21.9 m). The last

At least the 865, 867, and 868 were shrouded in streamliner casings that resembled those of the Milwaukee Road's A-class Atlantics. The color scheme was a dark green overall decorated with a broad gold band near the top and thin yellow and red stripes just below the footboard.

Most of the class operated through World War II and were retired in the late 1940s. The last two -- 858 and 862--were scrapped in November 1951.

Locobase had estimated the superheater area, which was not given in the diagrams, as 540 sq ft based on similar installations in other locomotives. The 1918 diagrams gave the superheater area as 638 sq ft (59.27 sq m).

Class P-1 (Locobase 1400)

Data from "Pacific Type Locomotives for the Seaboard Air Line," Railway and Engineering Review, Vol 53, No 5 (1 February 1913), p. 95-97, supplemented by DeGolyer, Volume 48, p. 27. See also SAL 9 1918 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection. (Thanks to Chris Hohl for his 30 May 2016 email suggesting some changes in the tender weights and capacities.) Works numbers were 38596-38601, 38634-38635 in October 1912 and 38665-38668, 38721-38723 in November

Firebox heating surface includes 24.2 sq ft (2.25 sq m) of arch tubes. These fast-freight Pacifics had the same driver diameter as the Mikados. R&ER's report noted that the "freight locomotives are well proportioned to meet conditions on a line which, like the Seaboard, is free from excessive grades and handles large quantities of perishable materials at fairly high speeds." Thirteen-inch diameter (330 mm) piston valves admitted steam to the cylinders. Although the specification gave 180 psi, boiler pressure was described as 185 psi (12.76 bar) only a few months after its delivery.

The Baldwin estimates for tender weight came close to the actual figure given in the 1913 report on their service entry on the Seaboard. The 1918 diagrams show several clear differences from either the Baldwin specs or the 1913 story. Superheater area for the same superheater installation is given as 638 sq ft (59.73 sq m). Locobase hasn't quite deduced the reason for the 63 sq ft difference. Weight on the drivers increased to 144,500 lb (65,544 kg) and engine weight grew to 220,000 lb (99,790 kg). Loaded tender weight (same capacity as delivered) now came to 151,640 lb (68,783 kg).

See Locobase 8748 for the P-1/P-2 69" drivered passenger variant.

Class P-2 (Locobase 8748)

Data from SAL 9-1918 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive Raildata collection . See also "Pacific Type Locomotives for the Seaboard Air Line," Railway and Engineering Review, Vol 53, No. 5 (1 February 1913), p. 95-97 and the 20 May 2012 entry "Sunday Streamline #65: Seaboard Pacifics" at Ramat Gan's, last accessed 4 May 2015. (Thanks to Chris Hohl for his 3 April 2015 email correcting the valve gear.) Works numbers were 54000-54015, 53995-53999, 54016-54030 in September 1913.

Although the first fifteen locomotives of this design were delivered as P-1 mixed-traffic engines with 63" drivers (Locobase 1400), most were completed as 69"-drivered passenger engines. They were delivered with the same cylinder volume, but later saw a 1" (25.4 mm) increase in diameter, presumably to compensate for the taller drivers.

Firebox heating surface includes 26 sq ft (2.4 sq m) of arch tubes and steam was admitted through 13" (330 mm) piston valves.

Other than the 832, which suffered a head-on collision with Mountain 220 near Stark Florida in a December 1931 wreck, the entire class served the SAL throughout World War II before being cut up in the late 1940s, early 1950s.

Specifications by Steve Llanso of Sweat House Media
Locobase ID2812 1400 8748
RailroadSeaboard Air Line (SAL)Seaboard Air Line (SAL)Seaboard Air Line (SAL)
Number in Class201535
Road Numbers85-104/1-20/851-870800-814815-849
Number Built201535
Valve GearBakerBakerWalschaert
Locomotive Length and Weight
Driver Wheelbase12.50'12.50'12.50'
Engine Wheelbase32.75'32.75'32.75'
Ratio of driving wheelbase to overall engine wheebase 0.38 0.38 0.38
Overall Wheelbase (engine & tender)66.25'62.89'62.89'
Axle Loading (Maximum Weight per Axle)48200 lbs49600 lbs52164 lbs
Weight on Drivers137700 lbs133900 lbs148690 lbs
Engine Weight214700 lbs211600 lbs230600 lbs
Tender Light Weight147000 lbs148400 lbs174300 lbs
Total Engine and Tender Weight361700 lbs360000 lbs404900 lbs
Tender Water Capacity8000 gals8000 gals9000 gals
Tender Fuel Capacity (oil/coal)14 tons14 tons15 tons
Minimum weight of rail (calculated)77 lb/yard74 lb/yard83 lb/yard
Geometry Relating to Tractive Effort
Driver Diameter72"63"69"
Boiler Pressure195 psi185 psi180 psi
Cylinders (dia x stroke)23" x 28"22" x 28"22" x 28"
Tractive Effort34098 lbs33826 lbs30050 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort) 4.04 3.96 4.95
Heating Ability
Firebox Area210 sq. ft208.20 sq. ft210 sq. ft
Grate Area53.10 sq. ft53.10 sq. ft53.10 sq. ft
Evaporative Heating Surface2820 sq. ft2820 sq. ft2820 sq. ft
Superheating Surface575 sq. ft575 sq. ft540 sq. ft
Combined Heating Surface3395 sq. ft3395 sq. ft3360 sq. ft
Evaporative Heating Surface/Cylinder Volume209.44228.91228.91
Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation1035598249558
Same as above plus superheater percentage121151149311087
Same as above but substitute firebox area for grate area479124506543848
Power L1157191424814669
Power MT755.00703.77652.49


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