B-Units & Slugs...

[Rik3801T]

Can anyone please enlighten me on what the main differences are between a B-Unit and a Slug? Some say that B-Units are for extra motive power on main lines and Slugs are used exclusively in Hump-Yard operations and other Yards in conjunction with standard cab units as they offer extra tractive effort without the weight.

Clearly each type of driverless unit has been developed for certain types of uses. Where I get confused is where Slugs appear in a standard mainline motive power lashup (especially on east Coast mainlines like CSX). Is this due to a shortage of other more standard Units or because there are noticeable grades on the route which favor lighter motive power units?

 

[bl4882]

A B unit is an engine, complete with prime mover, generator, and traction motors, lacking only a cab. It adds its tractive effort and horsepower to the locomotive. My understanding is that a slug does not have a prime mover or generator but does have traction motors and bleeds power off of the generators in the units in the locomotive that do. It adds only tractive effort. For example, assume you have selected two engines with 3000 horsepower and 60,000 pounds of TE each. If you add a B unit you have a locomotive with 9000 horsepower and 180,000 TE. But if you add a slug with 60,000 lbs of TE instead of the B unit, you would have a locomotive of 6000 horsepower, because you cannot have more hp than the prime movers can deliver, with 180,000 of TE.

If you are assembling a locomotive and have plenty of horsepower to keep to speed, but are shy of tractive effort, as in the case of driving a lot of tonnage over a hump at slow speed, you would use a slug rather than a B unit. The same would go for a heavy but slow main line train, as is probably the case in the CSX instance you mention.

Bernie

 

[wreeder]

Bernie is correct.

Most slugs have added weight to make up for the loss of the weight of the prime mover. They were designed for yard use. I can't imagine what use they would have on the mainline. But I guess if you have them, why not use them.

Here is what Trains magazine has to say about them.

http://trn.trains.com/en/Railroad Reference/ABCs of Railroading/2006/05/Slugs.aspx

William

 

[simulatortrain]

Road slugs are designed for slow mainline trains like locals and transfers (remember not everything outside of the yard is fast). A slug's tractive effort generally declines rapidly above around 20 mph, so most are designed to cut out there.

 

[Rik3801T]

Many thanks guys for your help & advice with my query!

Cheers


Rik