Class M (Locobase 5008)

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.

The first group of Mountains built for the Richmond-Hamlet-Atlanta service. According to the 16 July 1915 Railway Age Gazette, the particular section assigned to this new class was challenging. In the 160 miles between Richmond to Raleigh NC, "... there are several grades of 1.2 per cent, 2 1/2 miles long; and from Raleigh to Columbia. 207 miles, on which there are grades of 1.25 per cent, 3 1/2 miles long."

RAG's comment on the reason for resorting to a 4-8-2 sounds very similar to the French reasoning behind adopting 2-8-2s: "The introduction of the Mountain type engines was because of the inability of the locomotives of the Pacific type to maintain a sufficient speed up the grades with 10 or more steel cars to avoid the necessity of exceeding the maximum speed limit of 50 miles per hour on other parts of the run."

These were the only Seaboard Mountains with Walschaerts gear.

Firebox heating surface included 26 sq ft of arch tubes.

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)

Data from SAL 1 - 1948 Locomotive Diagrams supplied in May 2005 by Allen Stanley from his extensive collection. Works numbers were 58074-58083 in November 1924; 58681- 58682 in September 1925; 58724-58728, 58748-58751, 58760-58764 in October; 58992-58996 in January 1926; 59047-59051 in March.

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 all of the Mountains it would want. They remained in service until 1956.