• Slug weights

  • Discussion of Electro-Motive locomotive products and technology, past and present. Official web site can be found here: http://www.emdiesels.com/.
Discussion of Electro-Motive locomotive products and technology, past and present. Official web site can be found here: http://www.emdiesels.com/.

Moderator: GOLDEN-ARM

  by BR&P
During a discussion of bridge loadings, someone suggested use of a slug and mother to avoid putting too much weight on the structure in question. I was under the impression that slugs are well-ballasted for traction and would probably not offer much weight savings. What is a typical weight for a road slug? With the prime mover etc removed, and ballast added, are they lighter, heavier, or about the same as a comparable unit with insides intact? I realize slugs vary from road to road, but I'm looking for general info.


  by DutchRailnut
They are usually in same weight range as the mother unit.

  by Engineer Spike
I think that the weight savings of a slug set might be based on the axle load. Seaboard had its UxxB units with the slugs. Now the weight is spread out over more axles. There is not so much weight at any one point of the bridge structure.

  by BR&P
Spike, that's the point of my post. If a slug is LIGHTER than a regular loco, there IS a weight savings and loads on a trestle for example would be lighter, when compared with two powered locos. But if the slug is ballasted to about the same weight as a regular loco to improve traction, bridge loading would be the same - 125 tons is 125 tons for example, whether it's a prime mover & main generator, or if it's steel and concrete. I suspect, as Dutch says, the slug is about the same weight as the mother but was curious if anyone had specifics.

I'll get the weights from some of ours, when I go on duty tonight. They are heavily ballasted, as mentioned, as they are "tractive effort booster units", and that traction (adhesion) is a direct result of the weight of the unit divided by the axles being used to put the rotational torque of the motors to the rails, via the wheels. Light slugs can't supply tractive effort, as adhesion is required to operate, and adhesion is directly a result of weight on axles.

  by BR&P
Thanks GA! That's about the way I thought - the slug would be ballasted to about the maximum possible to aid traction.

The question came up in a discussion of a bridge, someone suggested using a slug & mother to save weight, and I did not feel that was correct, the slug would weigh almost as much as the mother, if not even more.

  by EDM5970
Think about it for a moment; a slug should weigh almost exactly as much as the mother unit. For sake of argument consider, say, a GP-38 with Blomberg trucks, D-77 motors, a 62:15 gear ratio, and a slug with the same trucks, motors and gears.

It the slug is lighter, it will tend to slip before the mothership. If the mother is lighter, it will slip first. It would be very similar to having a single unit with more weight on one truck than the other. All eight motors should be loaded equally, and to do this all eight should have the same adhesive weight over them.

When railroads retired the boilers on passenger Geeps or RS-3s, as an example, they either left the boilers in place, or substituted steel or concrete to make up for the weight of the removed boiler. If not, the former boiler end of the unit would tend to be slippery.

There is a trick to spreading out weight on a bridge, used by the Southern and I believe the old PGE. SOU used to run a pair of RS-3s with a heavyweight "spacer" coach between them. This coach had 21 or 27 pin MU connections at each end, and the appropriate air lines. PGE used something similar.

Today, any long freight car would suffice. You might even want to cable it up to be used with a mother and slug set.

  by scooter3798
Here is a shot of the Southern car that EDM5970 mentioned.


Also I know a guy that used to be the shop foreman for some of the Bethlehem Steel roads, and he said that he hated the slugs that they had because they were in fact heavier than the conventional units. They would ware out the ware plates between the trucks and the frames quicker, and they had to bring in extra jacks to work on them. I never asked him what the weights were on them, but I know that at least on the Beth roads that he worked for the slugs were heavier.

Well, I'm going to have to ask the foreman, on Monday. The electrician, who rode with us yesterday, trying to locate a wheel slip "bug" mentioned they weighed the same as the GP-40's, they were mated to. When asked about the weight of the Geep, he didn't know. Here's a link to the slugs we run, over the 2.2 percent grade at Nashville, and these have dynamic brakes, with extended range. We run a pair of mother/slug sets, with an additional one, or two units, either Geep 40's, or 39-2's. Maximum tonnage on the summit, is 5000 trailing tons. On dry rail, with good adhesion, we drag this hill at 3-4 mph, at maximum tonnage rating, with six units. The worst trip I've had, without needing to double the hill was 1 mile, in an hour and 5 minutes PER MILE, without stopping. (we did finally give up, after 2 miles, and made the double, due to the time factor of running to the summit) The grade is about 6.2 miles long...... SLUGS!

  by DutchRailnut
Weight should be stated on the Blueform, on both the slug and mother.

Nope, it's not. Been there, done that already.......