Seaboard Air Line 4-8-2 "Mountain" Type Locomotives

Class M (Locobase 5008)

The first group of Mountains built for the Richmond-Hamlet-Atlanta service. These were the only Seaboard Mountains with Walschaerts gear.

Firebox heating surface included 26 sq ft of arch tubes.

Much of the data comes from http://www.dnaco.net/~gelwood/other/sal-steambk.html for 1929 locomotive diagrams. Superheat surface area originally was estimated from the calculation of the area of the flues and a calculated average ratio based on more that 350 locomotive entries in Locobase where both flue surface area and superheater areas are known. At the time, 857 sq ft seemed a close fit that likely slightly understated the real area.

In fact, according to the table in the January 1917 issue of Railway Mechanical Engineer, the actual area was 865 sq ft. Not bad.

Class M-1 (Locobase 5007)

The second group of Mountains built for the Richmond-Hamlet-Atlanta service.

Firebox heating surface included 26 sq ft of arch tubes.

Much of the data comes from http://www.dnaco.net/~gelwood/other/sal-steambk.html for 1929 locomotive diagrams. Superheat surface area is estimated from the calculation of the area of the flues and a calculated average ratio based on more that 350 locomotive entries in Locobase where both flue surface area and superheater areas are known. It's a close fit that likely slightly understates the real area.

Class M-2 (Locobase 225)

These were enlarged M-class Mountains with a larger boiler holding 11 more superheater flues and a commensurately larger superheating surface. The firebox heating surface expanded as well, but the same system of arch tubes contributed a similar 26 sq ft to the overall value. Also, the combustion chamber length increased by almost 30%. Taken with the 3" taller drivers, the result is a design that emphasized steaming capacity over tractive effort.

With this batch, the SAL had its Mountains. They remained in service until 1956.

Specifications
Class	M	M-1	M-2
Locobase ID	5008	5007	225
Railroad	Seaboard Air Line (SAL)	Seaboard Air Line (SAL)	Seaboard Air Line (SAL)
Whyte	4-8-2	4-8-2	4-8-2
Road Numbers	210-214	215-224	235-270
Gauge	Std	Std	Std
Builder	Alco-Schenectady	Alco-Schenectady	Baldwin
Year	1917	1922	1924
Valve Gear	Walschaert	Baker	Baker
	Locomotive Length and Weight
Driver Wheelbase	18'	18'	19.25'
Engine Wheelbase	38.92'	38.92'	40.66'
Ratio of driving wheelbase to overall engine wheebase	0.46	0.46	0.47
Overall Wheelbase (engine & tender)	76.39'	76.31'	78.38'
Axle Loading (Maximum Weight per Axle)	52900 lbs	52500 lbs	53250 lbs
Weight on Drivers	210500 lbs	209000 lbs	213000 lbs
Engine Weight	316000 lbs	315000 lbs	320500 lbs
Tender Light Weight	183800 lbs	183800 lbs	188600 lbs
Total Engine and Tender Weight	499800 lbs	498800 lbs	509100 lbs
Tender Water Capacity	9000 gals	9000 gals	9000 gals
Tender Fuel Capacity (oil/coal)	17 tons	17 tons	17 tons
Minimum weight per yard of rail on which locomotive could run	87.71 lb rail	87.08 lb rail	88.75 lb rail
	Geometry Relating to Tractive Effort
Driver Diameter	69"	69"	72"
Boiler Pressure	190 psi	190 psi	200 psi
Cylinders (dia x stroke)	27" x 28"	27" x 28"	27" x 28"
Tractive Effort	47776 lbs	47776 lbs	48195 lbs
Factor of Adhesion (Weight on Drivers/Tractive Effort)	4.41	4.37	4.42
	Heating Ability
Firebox Area	319 sq. ft	319 sq. ft	343 sq. ft
Grate Area	66.70 sq. ft	66.70 sq. ft	66.70 sq. ft
Evaporative Heating Surface	3715	3715	4039
Superheating Surface	865	857	1136
Combined Heating Surface	4580	4572	5175
Evaporative Heating Surface/Cylinder Volume	200.22	200.22	217.68
	Computations Relating to Power Output (More Information)
Robert LeMassena's Power Computation	12673	12673	13340
Same as above plus superheater percentage	15066.48	15048.49	16268.36
Same as above but substitute firebox area for grate area	72057.09	71971.06	83658.86
Power L1	15420.39	15335.60	20666.74
Power MT	646.01	647.07	855.63