They Call It "The Slug"

And it Means Bigger "Muscles" For Yard Diesels

Railroaders have a knack for dressing up the equipment they use in apt and colorful nicknames.

A work crane emerges from its bout with the railroad man's imagination as the "big hook"; a note thrown or handed from a train becomes a "butterfly," a locomotive a "hog," a yard engine a "goat" and the two-unit diesel switcher "a cow and a calf." Now there's "the slug."

When the railway's mechanical department started to design a heavily weighted unit, equipped with traction motors, to add extra power to yard diesels at slow speeds, the device somehow acquired the n~9kname "the slug." The name stuck-throughout the. 'design and construction stages and during the recent "on the job" tests at John Sevier Yard in Knoxville, Tenn., where it became apparent that "the slug" was going to live up fully to the mechanical department's expectations.

Briefly, the purpose of "the slug" is to give bigger "muscles" to diesel switchers used in hump yards to shove long cuts of cars up to the hump, from which point the cars roll down into classification tracks. Made at low speeds ( about two miles an hour) the shove requires a powerful tractive effort on the part of the switching locomotive. Coupled between two units of a diesel switcher, "the slug" gives approximately as much added "push" as a third diesel unit yet costs less.

Operating tests at John Sevier Yard in Knoxville proved "the slug's" value in helping a two-unit yard switcher push long cuts of cars up to the hump.

Yard diesel switchers, like other diesel-electric locomotive units, develop power in three stages: (I) oil. fueled diesel engines turn generators which (2) produce electric current used by ( 3) electric traction motors to turn the locomotive wheels. The reason "the slug" costs less, in construction and in maintenance, is that it has only the third power stage-traction motors. The motors draw electric current from the diesel engines and generators of the other two switching locomotive units.

Power alone doesn't give a locomotive traction. There has to be weight to press the wheels against the rail. To fill the place of the absent diesel engine and generator, "the slug" is filled with alternate layers of sawed off rail ends and concrete. Consequently it tips the scales at a healthy 250,000 pounds, giving its wheels plenty of "grip" on the rails.

"The slug" sits for a portrait.

Designed by the Southern's mechanical department engineers .( with an assist from the experiences of another railroad with a somewhat similar unit) , "the slug" was built "from the blueprints up" in our diesel maintenance and repair shop at Spencer, N. C. The two trucks-each containing two traction motors and axles -came from a freight diesel unit. The car frame was once part of an old steam locomotive tender. Blowers to cool the traction motors were installed.

At every stage of planning and building, railroaders recorded with blueprints and specifications exactly how they were making this weighted unit. If the Southern's first "slug" came, through its practical yard tests with flying colors ( which it did) , they could foresee a demand for others. Minor changes made as a result of the tryout at John Sevier Yard will be incorporated into the construction of any "slugs" the Southern builds in the future. But the designers know with certainty now that basically "the slug" is sound; its performance so effective as to encourage the building of more of them as their particular services are needed.

In the operating tests, "the slug' teamed with a two unit "cow and a calf" diesel switching locomotive, being coupled between the two units. It's a practical arrangement that allows the two traction motors on the forward truck of "the slug" to draw current from the leading locomotive unit while the motors on the rear trucks tap the power supply of the other unit.

With the aid of two cranes, the body of "the slug" is lowered onto its two trucks.

Use of "the slug" cuts the top speed of the combined locomotive to about 9 miles an hour when running light, but increases the tractive effort of two diesel-powered units by 50 per cent, For shoving long cuts of cars up to the hump, this is "just what the doctor ordered," When working other yard jobs where extra "muscles" are not needed and the low speed limit would be a handicap, the engineer can disconnect the traction motors of "the slug" with the flip of a switch, Then "the slug's" weight is no more of a hindrance than a couple of loaded freight cars would be, permitting fast switching movements if desirable,

Looks as if "the slug" has found a place in railroading along with the "butterfly," the "goat" and the "cow and a calf." ,