Steam & Excursion > Horsepower of ATSF 3751: Boiler and Drawbar???

I think the subject header pretty much asks the question that I have, which I'm confident will be answered. The horsepower rating for the ATSF 3651 in both measures.

And--while we're at it--I fear that I must be "taught" the difference between "BOILER HORSEPOWER" and "DRAWBAR HORSEPOWER". I think that the MAIN criterion here: which is more relevant? Or, put another way, let's compare the 3751 to an EMD 4300 HP SD70ACe. Or--any diesel. Which figure, DBHP or BLRHP, is going to be a more apt comparison directly with a diesel?

Now--I realize that diesels utilize their full HP output at different speed ranges than steamers--steamers having better "power utilization", and, better acceleration, in the high speed ranges, whereas the diesels develop more tractive effort, generally, in the lower speed ranges (the gap has been narrowed somewhat, too, in this area, with the so-called "High Horsepower" diesels of today, along with the tremendous tractive effort ratings of the AC-motored units--as opposed to the F-units and such that the steamers were initially compared to while they were still in service).

So: aside from answering the two "basic questions", this thread should open the way for some interesting, wide-ranging discussions.

I do recall a "4-8-4 Comparison" Website--but I do not recall if horsepower was discussed. And--I think the site may have moved. I had it in my Favorites--but hit a dead end recently.

I'm wondering how the 3751 stacks up against the ATSF 2900-Class, the "epitome," and, say, SP 4449 and the UP 844.

The 4-8-4 comparison website is on the SBRHS site: http://www.sbrhs.org/Pages/484com.html

jdc3751 Wrote:
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> The 4-8-4 comparison website is on the SBRHS site:

Excellent info there--but as I rememebered--no HP ratings. As an "aside"--there's a link to the ATSF 2926 restoration. For those of you who contribute to this type of thing--THERE is a place to send some $$$ if you're able.

Now--back to horsepower discussion--advertisement over--LOL!!! ;-)

If I can remember correctly,the 3751's were not all that impressive horsepower wise until they were rebuilt. Aftrer rebuilding,they were capable of better than 3500 drawbar horsepower at high speed. The 3776 class put out more that 4500 horsepower at speed. The 3776 class was also rated at 66,000 pounds tractive effort but put out 72,000 pounds tractive effort according to a dynanometer car. The 2900 class should have put out more than that because she was heavier than her twin 3776 cousins.

3751 class max drawbar hp was 3220 at 40mph. 3765 class maxed at 4550 drawbar, and 5450 indicated. incidentally the hp numbers for Santa Fe's big 3460 class hudsons were identical to the 3751 up to 35 mph, after which the super hudsons left the 3751 northerns in the dust. The 4-6-4 peaked at 3600 drawbar horsepower! Remember that drawbar horsepower is useable real world power.

If you want to compare steam vs diesel this story by Rich Melvin (Engineer on 765) is compelling reading. Hopefully Rich doesn't mind me repeating it here, as it is published in several places on the internet.


Steam Verses Diesel

While these incidents are interesting and good for endless hours of “roundhouse railroading,” there is one very important thing missing: We have never had the chance to make a direct A/B Comparison Of steam verses diesel on the same train under the identical weather and rail conditions. One of the never ending arguments between diesel and steam enthusiasts has always been which type of engine was best at pulling a train. Throw out all the operating and maintenance cost factors and get down to the heart of the matter: Which type of locomotive of comparable horsepower could best pull a train over the road at speed.

I found the early steam vs. diesel tests to be fascinating reading, but there never seemed to be a clear-cut “winner.” The articles varied from a rather dry statistical approach With reams of data to make whatever point the author was trying to make, To the fascinating June, 1977, Trains article by Bill Withuhn That made the point through subjective comparison that the Southern Pacific Daylight 4449 was equal to two-and-a-half E8s At anything over 40 m.p.h.

The reference to speed was always included in the test because “horsepower” is a measure of how fast a given amount of work can be done. For example, if we took in a GP38-2 and replaced its 2,000 horsepower diesel With a 200 horsepower diesel, the locomotive would still operate, but it could not move very fast with any kind of load, nor could it develop the same pulling power. In other words, it could still perform work, but not as much as before and certainly not as fast.

To do a lot of work (move a heavy train) and do it fast (40 m.p.h. and up) takes horsepower. Lots of it.

Comparing steam horsepower to diesel horsepower is also complicated because we are truly comparing apples and oranges. A diesel locomotives horsepower is converted to pulling power through the electric motors. The formula Watts = Volts x Amps defines it all. In simple terms, the Watts represent the horsepower of the diesel and generator, while Volts represent speed and Amps represent pulling power. When the speed (Volts) is low, the pulling power (Amps) is very, very high, even at low horsepower (Watts) numbers. But as the speed increases, the pulling power must come down. That’s why on a diesel, the ammeter reads very high at low speed and then drops off as the speed increases. Once they balance off, the only way to go faster is to increase the available horsepower (Watts) and this means a bigger diesel engine or more units on line. That is why a 1500-h.p. SD7 and a 4000-h.p. SD70 can pull about the same train at low speed, but the SD70 ill be able to accelerate it to a much higher speed.

The steam engine’s power curve, on the other hand, is exactly the opposite. A steam locomotive applies its power directly through the reciprocating engine, meaning the power is developed and pulses as the pistons move back and forth to turn the wheels. At slow speeds, those “power pulse” repeat at a slow rate and are far apart, So the power developed is not very high. For example, under 30m.p.h., the best the 765 can do is about 2,100 drawbar horsepower. But, as the engine accelerates, the power pulses get closer together and occur more often, So the power level increases. Or, said another way, in a fixed amount of time (remember “horsepower” is a measure of how fast a given amount of work can be performed), More power pulses occur at high speeds than at low speeds. Thus the power developed is greater. Eventually, even a steam locomotive’s power curve will begin to fall off as the machinery reaches a rotational speed where so much power is being absorbed to turn the wheels that less is available to pull the train.

With an electrical "transmission" between the reciprocating diesel engine and the rail, a diesel can be producing nearly all of its potential horsepower while standing still, as the diesel engine swings the generator at full design r.p.m. That maximum horsepower is thus available just above stall speed, thanks to the electric motors. Imagine, however, a diesel engine with its crankshaft locked directly to the wheels like a steam locomotive's pistons are to the drivers. You couldn't even get the diesel to fire, because it has to be rotating to "inhale" for combustion to begin.

Further complicating the issue are the other ways that horsepower is expressed when referring to steam locomotives, namely "boiler horsepower" and "cylinder horsepower." These are numbers arrived at with the slide rule, not from actual on-the-road performance data, and the numbers can be misleading. The Nickel Plate 700s are capable of nearly 4500 drawbar horsepower, yet their boiler horsepower rating is 3164 and the cylinder horesepower rating is only 2754. But the number that really mattered when it came to pulling a train was the drawbar horsepower, which can only be measured in service on the road with a dynamometer car actually measuring the pulling force at the coupler and the speed of the train. Confusing, isn't it?

765 versus a Dash-7

Maybe we can clear up some of the confusion with a little test, not purely scientific, mind you, but worthy of note nonetheless. Let's compare the 765 with a fairly new, high-horsepower diesel, say a General Electric B36-7. We'll put this 3600-h.p. diesel head-to-head with a 2754- or 3164- or 4500-h.p. steam engine, depending on which number you care to use.

This "test" occurred on September 123, 1993, on an excursion from Cincinnati to Indianapolis, Indiana, on the former B&O. Now, for those of you who picture the state of Indiana as flat as a billiard table; well, you folks haven't seen southern Indiana. This route offered a couple of tough grades, one out of Hamilton, Ohio, and the other at Connersville, Indiana. With 29 cars, the 765 would be hard-pressed to maintain any kind of speed at all on these grades. But we needed to keep moving fairly well to keep the running times manageable. So, we tucked CSX B36-7 5843 in behind our A-tank and m.u.'d it to our diesel controller in the cab of the 765.

On the way to Indianapolis, we stopped in Hamilton to pick up passengers. When we stopped we were about half-way across the bridge over the Greater Miami River, and I could clearly see the grade start at the west end of the bridge. When we got the okay to proceed west, I eased the 765 into motion. As soon as we had everything moving, I began to notch up the diesel.

By the time we got to the end of the bridge, the diesel was in Run 8, and the 765 was in run 51. (There are 51 notches on the throttle quadrant in the 765. John Snyder counted 'em.) Even with both engines wide open, we could manage onlu 25 m.p.h. up the hill. Without the diesel, our speed would have been around 10 m.p.h., and we would have spent the better part of an hour climbing this hill.

During our layover in Indianapolis, the 765's other engineer, Tom Stephens, wondered aloud about just how strong this diesel really was. I had used the diesel on the two big hills and for a little help in accelerating, but otherwise I had run the train pretty much the same way I always did. Tom decided that on the return leg of the trip, he was going to put this big 3600 horsepower diesel to the test. We had been pulling it and the train all day at 50 m.p.h., using the diesel sparingly. Today's 29-car train was not the longest or heaviest that we had pulled, not by a long shot. At 32 to 34 coaches the New River Trains hold that honor. We have pulled those trains -- unassisted -- in excess of 65 m.p.h. numerous times, with ease.

Ready to depart east from Hamilton Ohio, the stafe was set for the big test. Tom got the clearance to proceed, whistled off and eased the train into motion with the diesel, working only enough steam on the 765 to keep lubrication flowing into the cylinders. In other words, the 765 was just pulling itself, while the big GE was pulling the train. Tom quickly notched up the diesel to Run 8, and we could hear the FDL-16 prime mover barking with that distinctive GE sound. Speed began to build at a pretty respectable rate.

At low speeds, the diesel was capable of accelerating the train somewhat faster than the 765 could (remember the power curves), and initially we thought that maybe it would be able to handle this train at track speed all by itself. But by the time we reached 30 m.p.h. the rate of acceleration had slowed markedly. Tom had continued to adjust the throttle and reverse on the 765 so as to keep it set to just carry its own load. It took a long time to get from 30 to 35, but we were still accelerating. Finally we reached a point where we just "hung," and there was no more speed to be had. All 3600 horses in the GE diesel were on line and galloping as fast and as hard as they could, and they had us moving at the astounding speed of...38 m.p.h. That was it. There was no more.

Finally the CSX road foreman asked Tom why he was "doggin' it," since we were already late. Tom answered by widening out on the 765 and throttling the diesel back down to idle. Within a mile or so, the 765 had us up to 50 m.p.h. with hardly any effort at all. It was a graphic display of the difference in the horsepower curves of the diesel and the steam engine. At 38 m.p.h., the diesel's drawbar horsepower had reached the point where even in Run 8 it could not accelerate the train any faster, while the 765 was just approaching the peak of its horsepower curve with plenty of power in reserve.

This is exactly what Will Woodard had in mind when he developed the steam "Super Power" concept. As the speed increased, so did the horsepower! The Lima literature of the era used the words "Horsepower at Speed" to describe their new approach to steam locomotive design. After witnessing this steam vs. diesel test, the words still ring true today, 50 years after the 765 was built.

Thank you very much for posting this information. I was just thinking of asking this kind of question as I am assembling a presentation about steam locomotives for a college class.

Are there any websites that show this kind of data? I have to make a chart and would love to see charts on Horsepower vs. speed for Steam and diesel to help get some ideas.
Thanks for any help.
Howeld

I don't mean to take away from Red's post but here is something to ponder in regards to diesel vs. steam:

An old head steam engineer once told me that a steam engine could pull more than it could start and that a diesel could start more than it could pull. It makes sense to me. I have had a diesel consist start a heavy train on a grade but it never could get that same tonnage up to speed. In other words, I never got above 1 or 2 mph. The horsepower of a diesel was immaterial if you can't keep the wheels from slipping.

I've also heard that a steam engine that is rated for say, 3000 hp has the ability (if that's the way to put it) to develop that same horsepower at 0.1mph and, for the sake of arguement, at 40mph. Is this true?

JDE

A steam engine generates more horsepower the faster it goes. The limiting factor becomes the amount of steam the boiler can provide.

Boiler size, firebox capacity, cylinder size (dia and stroke)and driver size had to be proprtioned to the work to be done.

CP/SP's Master Mechanic, A.J.Stevens, built some very successful 4-8-0's in the 1880's. He reasoned that a 4-10-0 with bigger boiler and cylinders would be equally successful. It wasn't, the firebox was too small because it had to fit between the frames. Even with two firemen it couldn't make enough steam to pull a train over Tehachapi.

Boiler h.p. is the amount of h.p. the boiler is capable of generating at max. firing rate and water input. Cylinder or "indicated" h.p. is the amount actually delivered by the cylinders/pistons to the drivers. This is the figure the PRR's Altoona test plant preferred to use. As Rich points out, the drawbar h.p., the amount of h.p. actually available at the tender's coupler to move the train, is the important figure. The most d.b.h.p. ever documented from a steamer was delivered by C&O Lima-built 2-6-6-6 No. 1608 during a dyna test on the road in Southern Ohio in 1943, when the big H-8 hit 7,498 d.b.h.p. at about 43 mph, a figure that would have required the use of 6 or 7 contemporary EMD FT's. Yet, at starting, 2 of the F's could just about match the H-8's pull. In 1952, 3-unit F-7's replaced the H-8's on the Russell-Toledo line, despite the much greater dbhp at speed of the Lima product. The F's could walk 12,000 tons up Powell Hill north from Columbus with no assistance, while the steamer needed a Mike helper on the roughly 12 mile grade. And, over the Allegheny climb, 4 early Geeps replaced 2 H-8's on e.b. coal drags. On the NKP the speeds were such that the 700's were able to put all their h.p. to work, just as Mr. Woodard intended. When diesels finally came, it took 3 Geeps to get a train over the road as fast as a 700 could.

To add to what Steamjockey said: If a steam engine could start a train rolling it could usually pull it FAST ENOUGH to satisfy its owner but, a diesel could start half of hell, and only barely keep it moving. It took 3 F-7's to roll the same train AS FAST as a T&P 2-10-4 could even tho the F's tractive effort totaled about 151,000 lbs and the 2-10-4 only 97,300 lbs.

> I've also heard that a steam engine that is rated
> for say, 3000 hp has the ability (if that's the
> way to put it) to develop that same horsepower at
> 0.1mph and, for the sake of arguement, at 40mph.
> Is this true?

No locomotive (steam, diesel or elec) can produce anywhere near 3000 useful horsepower --or 1000 hp, either-- at 0.1 mph.

> I fear that I must be
> "taught" the difference between "BOILER
> HORSEPOWER" and "DRAWBAR HORSEPOWER"

When books speak of a steam engine's "boiler horsepower" they're usually referring to an estimate of the locomotive's capability, calculated from its square footage of heating surface. It's a first guess-- you don't use it if you have anything better.

Drawbar horsepower is also calculated, but it's calculated from the measured drawbar pull. Getting the measurement right is no cinch, but if you can get it then it's by far the most useful figure.

> ... steamers having better "power
> utilization", and, better acceleration, in the
> high speed ranges...

Lots of fans like to think so. In the US we're not much for measuring actual acceleration with any locomotive, so nobody knows for sure.

Finderskeepers Wrote:

> All 3600 horses in the GE
> diesel were on line and galloping as fast and as
> hard as they could, and they had us moving at the
> astounding speed of...38 m.p.h. [with 29 cars] That was it. There
> was no more.

Uphill, that is. On the level 3600 hp would do ... maybe 60 mph.

IMHO, trains got slower when diesels came calling. Sure they could start the planet,but they needed so many more just to get anywhere.Just mow many diesels per train did it take to replace steam on the same tonnage? An example on the ATSF the 5000,5001,and 5011 class locomotives could run away and leave FT's on flat ground,and excluding water stops,would make better time. In the mountains however,the diesels' superior slow speed lugging ability killed them. My late uncle fired almost every type of steam locomotive the ATSF had,and he absolutely loved the 2900's for their ability to just flat run with anything you tied to her coupler. Having run a few steam freights, the axiom is true....

timz Wrote:
-------------------------------------------------------
> Finderskeepers Wrote:
>
> > All 3600 horses in the GE
> > diesel were on line and galloping as fast and
> as
> > hard as they could, and they had us moving at
> the
> > astounding speed of...38 m.p.h. That was it.
> There
> > was no more.
>
> Uphill, that is. On the level 3600 hp would do ...
> maybe 60 mph.

Timz, My reading of FK's account mentions NO hill, and my understanding is that 38MPH was "on the level", and remember, when questioned, the engineer "powered up" the 765, and took the train quickly to 50MPH. Please let us know your thoughts AFTER re-reading FK's post. And I am curious as to how you arrived at the 60MPH figure, and if you have DATA, please share that with us. Thank you, AA

Stanford White
Carmel Valley, CA

> I am curious as to how you arrived at
> the 60MPH figure, and if you have DATA,
> please share that with us.

Nope, nobody has data. The Davis formula says
a 29-car 2100-ton 116-axle train would require
less than 1100 dbhp at 38 mph on the level,
but no one knows the actual figure.

px320 wrote:

> CP/SP's Master Mechanic, A.J.Stevens, built some
very successful 4-8-0's (sic) in the 1880's (sic). He reasoned that a 4-10-0 with bigger boiler and
cylinders would be equally successful. It wasn't,
the firebox was too small because it had to fit
between the frames. Even with two firemen it
couldn't make enough steam to pull a train over
Tehachapi.


If it was true that 4-10-0 El Gobernador "couldn't make enough steam to pull a train over Tehachapi," then the engine would never have seen Tehachapi service for 7 1/2 years - from November 1884 to June 1892.

The reason for the engine being withdrawn from service had to do with economics - it cost 30% more to operate per ton hauled than the 12-wheelers the SP was using on the Tehachapi line.

Whish I had them handy, but don't, but there are power curve charts which illustrate graphically, and easy on the brain, the relative strength/weakness of steam vs diesel. Whereas, on the road, steam, when up to speed,clearly outperforms diesel, with steam's power higher on the speed curve than diesel. Steam, with it's need for water/fuel stops, oiling around, and other maintainance items, is what slowed it compared to diesel. Passenger schedules went off the chart vs steam when diesels took over, no more of the maintainance issues, PLUS engine changes. Freight train speeds went into the tank with diesel mostly because trainsize increased dramatically, frequency went way down, sidings were removed, and the rest is history...can't hardly get one oversized train across the line. Give me the fast, frequent and fliud thing every time. But, in the end, it all came down to money, once again. Subtract the artificial value of money from the formula, and I wonder what life would be like?? That would certainly be easier to accomplish than, say, to subtract greed from the formula, a very human component, which probably led to the formation of money. AA

Stanford White
Carmel Valley, CA