What exactly did Union Pacific gain by buying the “double diesel” engines, such as EMD DDA35, ALCO C855, and GE U-50? (Forgive me, I pulled model numbers from memory.) Was there really anything to gain from ordering semi-custom units, that couldn’t be accomplished by just buying "off the shelf " models, and hooking 2 of them together? It seems that if it was such a great idea other railroads besides Southern Pacific, would have bought into the idea too?
The idea was that certain operating costs are based on the number of locomotives needed rather than how many engines each locomotive has. ( i.e. only one brakestand, two less trucks, only one cab, etc.). It turned out that the complexity and operational inflexibility costs outweighed the savings. Only the Espee followed the UP, because you needed First Class trackage to handle the very heavy locomotives. Many railroads could have operated the double-diesels over some parts of their systems, but only the UP could operate them over most of their mainlines. Especially in the timeframe when these locomotives operated. For many railroads this was a time of deferred maintenance.
I suspect it was because they needed the horsepower. UP had been buying GP B-units, including GP9B’s and GP30B’s and running long strings of GP’s on fast freights. The DD35 was essentially a GP35 A and B unit on a single frame - same number of traction motors per prime mover. The Centenials were the first single unit diesels to match the horsepower of a Big Boy so that much horsepower in a single unit wasn’t new to UP. Even with that much power, Centenials often ran in pairs with a fast SD40 in between. The U50’s were ‘recycled’ by GE from the early gas turbines.
there are operational limits as to how many locomotives can be used at the head end of a train. UP is frequently at that limit on Sherman Hill and Echo Canyon. I have seen two trains with 8 engines in the last 3 months. The “double diesels” were one approach to addressing their horsepower needs. The 8500 series 6000 hp units were another approach. I am wondering that with the improved reliability of today’s locomotive, a double engined unit might again be practical.
dd
One set of systems controls for two units gives more bang for the buck. What helped do them in was that modular circuit board controls that could be swapped easily to get a unit back on the road quick, and not have to worry bout monster units runnin into size related problems.
Adrianspeeder
The various double diesels were basically the idea of the CMO at the time, for most of the reasons cited above. Runthrough arrangements with connections were still relatively uncommon, so motive power that basically restricted to UP’s main lines was not a problem. With the retirement of the CMO and increasing numbers of runthroughs, commonality of power with connecting roads became more important so the double diesels were retired.
The Centennials were the first EMD diesels to use modular circuit cards for controls, although the modules were custom designed and so not interchangeable with later Dash-2 locomotives.
Would the operational limits have to do with coupler strength? I would think that pairs of standard diesel units could have been semi-permanently coupled together pretty easily to accomplish same end result ?
The most important limitation is coupler strength, reliability of MU signal indication is another, dynamic braking force, etc. Semi-permanent coupling solves almost nothing and creates other problems unless one part lacked cab controls.
i wasn’t sure what the dd35’s look like so i searched. figure id post it up on here!
That’s a DD35B - there were “A” units as well. Just add a cab on one end…
Holy cow! There’s a whole generation of fans who never saw these engines[:0].Makes me feel like an old [censored].
DD35As had spartan cabs to be exact (std cab) and the DDA40Xs had wide cabs.
Welcome to the forum.[:)]
Go here http://utahrails.net/webpubs/up-dd35.php for an in depth article on the DD35s and DDA35s by Don Strack. Strack explains why the UP originally went with the double diesels. This article was originally published in Diesel Era.
Another Don Strack article here about the Centennials http://utahrails.net/webpubs/up-dda40x.php This one was also originally published in Diesel Era.
IMO, a quick and dirty solution would have been to permanently connect an A and cabless B unit together, creating an articulated B+B+B+B double diesel that would have been easier on tracks with sharper curves than the non-articulated DD35/40s. I believe EMD did something similar with some of their early FT units by using drawbars instead of couplers, and railroads who used this option considered an FT A-B-B-A combination as a single engine.
To me the most compelling “double diesel” had to have been the Alco Century 855 it was ugly, for one thing(not that that would bother UP, then or now) then it was an oddball,which meant that if anything went wrong,it got stored until it’s unique parts arrived. Then too,they had aluminum wiring,like the later and equally disastrous U50Cs (which deserved a better fate,too)which made them a major maintence headache which was not appreciated at all, by any one concerned. I would have loved to see the A-B-A set[wow] (60-60B-61) accelerating out of Laramie, smoking it up with those 16 cyl. 251Cs![yeah] Not to mention, seeing them in the current “Building America” paint scheme![:p] Ah, but ponder this the whole set in Cornell Red with a white outlined LV herald over white chevrons on the nose and the LV flag on the lead hood and 48" Lehigh Valley lettering on the rear hood![:p][;)][wow][wow]
SSW9389: Thanks for the links! They were quite interesting. Don Strack states that UP did a study that determined that yearly maintenace for a diesel locomotive ran about $7000 per year, regardless of the H.P. Wouldn’t a DDA35 have just about the same number of maintenance-requiring parts as two GP35’s?
No, it only had one brakestand, this is a significant expense as it must be completely disassembled and inspected each year, also only one controlstand with throttle and reverser, one toilet, etc. The other parts would be the same. If one of the GP35s was a cabless booster then they would be close.