ALCO-HAULICS - Hydraulic drive Alcos on the SP

What became of the six axle hydraulic drive Alcos tested on SP?

I think there were only three, not 6, Alco DH-643. (SP seems to have felt three was a good number for experimentals: their DD-35 and U50 were also trios.)
I am morally certain they were scrapped, but don't know the exact date. Steinbrenner's "Alco: a centennial history" would probably say: it also has some details about the design, and mentions a more powerful follow-on design Alco offered, but that SP didn't buy.
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The diesel hydraulic idea seems to have been very tempting: lighter weight and the promise of lower purchase price (given economies of scale from series production: SP's experimentals, being experimental prototypes, may not have been cheap) than electric transmission. Experience seems to be that the diesel electric locomotive was a better buy in the long run. One can argue that SP's experiment was stacked: small number of K-M and Alco diesel hydraulics on a railroad whose operating and mechanical departments were used to diesel electrics. This is a point at which overseas experience can illuminate U.S. railroad history: British Rail staged a better-controlled experiment. Their Western Region (basically the pre-nationalization Great Western Railway, so a large pike whose operations and maintenance were largely autonomous from the rest) concentrated on diesel hydraulics for their first generation diesel locomotives, while the other regions used diesel electrics. With comparison data available, Western Region's diesel hydraulic fleet were retired in favor of diesel electrics.

Three ALCO DH-643s were built. Each locomotive had six axles and 4,300 horsepower. The three units were Southern Pacific #9018, #9019, and #9020 all built in 1964. These three units joined the 21 Krauss-Maffei diesel-hydraulics that were already on Southern Pacific's roster. All three Alco DH-643s have since been scrapped.

Ummm... I'd take the "4300 horsepower" with a grain of salt. The engines used (12-251C) were, I think, the same as those used on the C-420. The usual convention, in the U.S., that the power rating of a locomotive is the power delivered by the engine to the main generator. Since the DH-643, being a diesel hydraulic, didn't HAVE main generators, Alco felt free to use a more impressive sounding figure: I think the engines' BRAKE horsepower. So probably it is better tto think of them as 4000 hp units: what a diesel electric with their engines would have been called.

How powerful were they when it comes to actually pulling trains? Well, I think diesel hydraulics tend to be slightly LESS efficient than diesel electrics at translating their engine horseposer into train-pulling. They probably had better adhesion than contemporary diesel electrics: the various manufacturers (EMD, GE and Alco) put a lot of work into improving anti-wheelslip control over the next few years.

Curious, I Googled "Alco DH-643" to see if I could find out more. Several sites said the three units were scrapped in 1973, one adding that one of them had been set aside for cannibalization (parts supply) a few years earlier. The 1973 version of the DPA-LTA locomotive rosters book (no, not an infallible source, but what I had at home to consult) showed the DH-643 as already gone (i.e. it didn't show them), but the U50 and DD-35 as still on the roster.

Note that the DH-643, the DD-35 and the U50 were all acquired in 1964: three units each. (SP management was clearly in a mood to experiment.) All used diesel engines the SP mechanical people were familiar with (The 2000hp Alco 12-251C was used on the ten Dl-721 of 1961; SP had also had experience with the earlier, 1800hp, version of the engine in Dl-701 and Dl-712. The turbocharged EMD 567D had been tried out in a dozen and a half GP30 bought in 1963; in 1964-1965 SP bought a significant number of GP-35 and SD-35 with the same, 2500hp, version of the engine as the DD-35. As for the GE FDL-16, in 1964 SP finished acquiring the country's second-biggest U25B fleet.)

For a railroad the size of SP to buy 9 experimental units to try out various new technical ideas probably made sense. ... Better adhesion and lower continuous speed (since no traction motors to burn up) were selling points for the diesel-hydraulic idea, but SP apparently found that the DH-643 weren't much good in the mountains and used them primarily on flat districts. The "two of everything on a raft" concept represented by the DD-35 and U50 seems, in retrospect, to have been just silly, but UP's motive power director claimed there were cost savings. And, I suppose, in a period where train weights and speeds were increasing and very long motive power lashups becoming the norm, maybe reducing the number of couplers and m.u. connections was an attractive idea.

The DH643 had a gross rating of 4300 hp, 3600 continuous (traction).
All were sold to Chrome and scrapped at Sacramento in fall 1973.

Allen and all,

A couple corrections regarding the hydro's.

- DH-643 is the Alco specification, not a model. As far as I can tell, these units were never assigned a model number.
- Alco considered the 3 units delivered to the SP to be prototypes.
- To quote from an Alco presentation book "They went into service in 1964 and were then rated at 3600 HP, this rating being limited by the transmission capability. Since then however the units have been raised to 4000 HP with the permission of the transmission manufacturer."
- Alco planned to offer the SP a DH-650, 4600 HP for traction, for delivery in 1966.
- I do not believe that the Hydro's should be considered as Century Series models. However, I have an Alco generated list of current, 6-67, Century Series models that do not include the hydros, but does include a C-860, while in the same book, there is a Locomotive Application Chart that includes a 650-H under a Century model heading.

As far as I can tell, the SP was satisfied with the 3 units. I spoke to a former SP shop foreman awhile back, and he said that the hydros took a long time to lube, but I do not remember him being negative about them. An excellent source for information on them is Volume 2 of joe Strapac's Southern Pacific Historic Diesels series, which covers all the SP hydros.

Hope this helps,

Stephen McMillan

According to this web page, the model was DH-643, while the spec number was DH-400. I'm just putting this out here - I don't know which is true...

http://smg.railfan.net/Diesel/basicdiesel.html

Hope this helps,

Stephen McMillan--
Thanks for details! Steinbrenner, when he wrote "Alco: a centennial history," may have had access to an Alco document similar to the one you have: certainly, his information (as well as I can remember) is much in keeping with yours.
By 1966, the 16-251 had been applied in 3000hp locomotives (C630,C430): the same per-cylinder rating in the 12-cylinder engine would give 2250hp (allowing a notional "C423" as a direct competitor to GE's later U23B), so an up-rated Diesel Hydraulic with 4600 hp for traction would have been feasible.
As for SP being satisfied... They DID stay in service longer than the K-M diesel hydraulics. The only evidence of dissatisfaction I have is the report (on several WWWebsites: I don't know the original source (all together now, repeat after me: "The Internet is NOT a reliable source for research purposes!")) that they were found to be ill-suited to mountains, and were used primarily on flat terrain.
N. Todd--
I'm happy to believe that Alco was not consistent in its own nomenclature, and used different designations on different documents!

From what I have read the biggest issue that faced all diesel hydraulics was wheelslip control. I have read that the transmision on both the KM's and the DH643's tied all three axles together on each truck. At the time the only way to detect wheel slip would have been via a speed differantial between each truck (as opposed to each wheelset via an axle alternator, or currant flow via the balancing paths between motors, as used on a diesel electric) With such a limited source of speed inputs it would be very easy to have the locomotive have a wheelslip on both trucks, leaving the loco without a fixed referance of actual speed.

Alco advertised the model in question in the 1966 Car & Locomotive Cyclopedia as the "Century 643-H"
Question answered.
I talked to a former SP trainman, he mentioned the bleeding obvious as to why the Alcohaulics outlasted the K-M units but left so soon: maintenance. The DH643 had numerous parts that were interchangeable with other Alco road units (esp. RS11's, C628s). Whereas the KM's were orphan-engined and required metric tooling. The transmission was the primary reason for retirement, lack of parts.

A few additions: First, most manufacturers in Europe considered the adhesion qualities of diesel-hydraulic locomotives to be higher than that of diesel-electric locomotives with axles powered singly and uncoupled; adhesions of 30% were commonly quoted. The idea was that since weight transfer between axles was a leading cause of wheel slip, the coupling of three axles in a truck (in the case of both the Krauss-Maffei units and the ALCO units on D&RGW and SP) would eliminate the chance of a single axle slipping.

This is of course not to say that such units could not, and did not slip; on such a unit, one engine-truck combination could break loose and slip. This was clearly demonstrated during tests of two Rio Grande Krauss-Maffei units on the B&A portion of the NYC system, although in point of fact the units were greatly overloaded in terms of tonnage since the assumption was that one unit was roughly equal to two standard four axle units. With a unit weight of only about 331,000 lbs obviously there wasn't enough weight for this to be a valid comparison.

There has been much confusion over the actual horsepower rating of these units in general; in point of fact, the original Krauss-Maffei units were rated 4000 brake horsepower per unit, which was then derated or reduced by modification since the engines could not develop this output at the high altitudes experienced on the two purchasing railroads in the Western United States. (Information published at the time gives a brake horsepower rating PER ENGINE of about 1900 BHP at 2950 ft and about 1700 BHP at 7450 feet, or the altitude at Soldier Summit.) The next series of Krauss-Maffei units, the production roadswitcher type units for SP, were modified in design to allow a full 4000 brake horsepower at any altitude up to 7000 feet. Keep in mind that this is not the usual "horsepower for traction" rating of a US diesel, and that you will find ratings for the Krauss-Maffei units of either 3540 or 3600 horsepower for traction in official documents. I can only imagine that the ALCO units' published rating of 4300 HP is a brake horsepower rating. I recall reading the transcript of a lecture given to the RFOOA by ALCO's sales director in which he described the locomotives, and said clearly that some of the transmission limits had not yet been determined and that they only could be through experimentation and over-the-road testing. This meshes well with the previous description of originally under-rating, then uprating the ALCO hydraulic-drive locomotives.

As a final note, the continuous speed rating of a diesel-hydraulic wasn't or isn't necessarily lower than that of a diesel-electric in broad terms. The rated continuous speed of the first Krauss-Maffei units at 3800 brake horsepower, 3540 HP traction input to transmissions was 76,000 lbs at 10.5 MPH. The final Krauss-Maffei units were rated 80,000 lbs continuously at about 10 MPH. What is important to note here though is that on test on the NYC, the two Rio Grande units employed experienced violent wheelslips when wide open (Run 17) as speed dropped down to about 12 MPH - a speed above the continuous rated speed which was based on transmission heating primarily.

-Will Davis

Typewriters wrote:What is important to note here though is that on test on the NYC, the two Rio Grande units employed experienced violent wheelslips when wide open (Run 17) as speed dropped down to about 12 MPH - a speed above the continuous rated speed which was based on transmission heating primarily.

-Will Davis

Can you explain a bit more about the above? Why is it important to note?

Btw, someone wondered what was the reason for SP purchasing these higher horsepower-per-unit locomotives? On an SP site several former employees generally agreed, the underlying reason for the K-Ms and the Alco hydraulics was to force EMD to build a higher horsepower unit. By 1962 SP was operating road freights with as many as five or six 1500-1750 HP units. From SP's perspective this was too many. They wanted EMD to offer a higher horsepower unit but EMD was satisfied to just squeeze a little more power out of the existing prime mover with the 2000 HP GP-20 and 2250 HP GP-30.

Thus SP 'went shopping' for a builder who was willing to build a more powerful unit. EMD got the message and began development of what became the 3600 HP SD-45. SP bought them in quantity, too, with a fleet of many hundreds of units.