A "Do Not Hump" question

[mu26aeh]

I obviously understand most situations where a car is marked "Do Not Hump" but while sitting at a crossing today in Wormleysburg, PA, a string of rapid discharge hoppers lettered for WIMX (Wimpey Minerals) have it marked on the ends of cars.  Why would a pretty standard ballast/stone car be marked as such ?  I have included a picture where you can see most of it printed

http://www.rrpicturearchives.net/showPicture.aspx?id=2484900

[nkalanaga]

I have no idea.  When my father worked at the Pasco yard in the 60s and early 70s they humped gravel and rock hoppers all the time.  It's also odd that the stencil is on the end of the car, as usually it's on the side, where the pin-puller can see it.  If the car made it to the crest, the entire train had to be pushed into the proper track, the car left there, and the rest of the train pulled back to continue humping.

One of his worst nights was when the pin-puller missed the stencils and they actually humped a cut of cars waybilled "CHLORINE".  What made it worse was that they were NOT chlorine tank cars, but DODX boxcars, and probably contained nerve gas, bound for the Umatilla Army Depot.  The military pulled tricks like that all the time, and, out of an abundance of caution, the railroad tried not to hump any DODX car, regardless of what it said on the waybill or car, unless it was a flatcar and they could see the load.  Fortunately this one went through safely.

[ljudice]

Not sure, but...

A short, very heavy car may have some sort of restriction or be un-stoppable on the retarders???

[Chris333]

The shortline RR around here has those red do not hump cards on all their boxcars.

[C855B]

... A short, very heavy car may have some sort of restriction or be un-stoppable on the retarders??? ...

I think that's close. I surmise it could be that the owner simply wants to avoid the damage (and subsequent repair costs) of humping. Hump classification is hard on cars without cushioned draft gear, and given that this kind of loaded car is going to be at max weight, likelihood of damage from overspeed couplings in the bowl is pretty high. It also could play that these cars normally are transported in blocks, anyway, so the special handling costs of flat-switched classification might not apply, and the "do not hump" is a reminder.

I dunno. Edu-guesses.

[nkalanaga]

That's a real possibility, but it would be due to the weight, not the length.  A bigger problem is a long car, where only one truck is in the retarder at a time for much of its pass.  As long as both trucks are in the retarder, the length of the car doesn't affect the braking force.  Too many short, heavy cars can be a problem, but these aren't that short.  Loaded iron ore cars might be a another story.

"It also could play that these cars normally are transported in blocks" is very likely to be a factor.  If a group of cars is going to the same destination, the natural action is to hump them as a group.  Remember the limited length of the retarder?  The weight not yet in is pushing, and the weight already out is pulling, making a long cut much harder to control. 

I saw the results once, while in the retarder office with my father.  Picture a cut of grain hoppers, roughly 60 feet long each, going through a 120 foot retarder.  Two will brake fine.  Three can be controlled.  That was the limit for loaded cars when the retarders were run manually, which was my father's job.  The railroad bought a computer right after the BN merger.  A big improvement, right?  No more rough joints, right?  The programmers, with the yardmaster's approval, left out the limit on cut lengths.  Eight loaded 100 ton cars came down the hump.  The master retarder had no effect on them.  The computer tried slowing them with the group retarder, and the first couple cars barely slowed.  It then applied maximum pressure, which would have stopped any normal loads dead.  The momentum pulled the cast iron "brake shoes" out of the retarder.  Those things were about 15 feet long, and weighed who-knows-how much.  That group was closed while the maintainers repaired things.  The cars ended up going all the way to the end of the track, which fortunately was empty, and were stopped by the spring loaded mini-retarders designed to keep cars from rolling out of the bowl.

I also saw the results of a boxcar crushed by a following load.  The Walla Walla branch had bridge weight restrictions, and the jumbo hoppers had to be separated by empty boxcars.  Naturally, the BN used the oldest, most decrepit cars they could find, to keep from idling revenue cars.  I THINK they all had a steel centersill, not truss rods, but that was about all that could be said for some of them.  These were routinely humped in pairs, a hopper and a boxcar, to make sure they stayed together, as they were being run as dedicated pairs (before unit grain trains).  One pair got caught by the group retarder, either a mechanical failure or operator error (not my father, fortunately).  The following pair rammed them, and splinters went for several car lengths in all directions.  Most of the boxcar was a lump of shattered boards piled in the retarder.  No significant damage, except to the boxcar, which should have been scrapped anyway, but it took most of a day to clean all the pieces out of the retarder and get the hump working again.