Why?

[Mookie]

serious question here!

SD and GP - I know SD stands for Special Duty and GP is General Purpose.

But, w/o going into the specs, a GP39 and an SD40 - both of which we have in our yards - were they made to do the same jobs or for very different reasons?

[zardoz]

Mook-
The differences that I am aware of are that a GP (2-2 axle trucks) are more suited for locations where there are sharp curves in the tracks (such as yards, industrial trackage), as the 2-axle trucks are shorter. The SD (2-3 axle trucks) are more suited for road (main line) use. The SD's are much less likely to slip, and therefore can put more tractive effort on the rail.

As with most things, there are exceptions. The CNW used to use two pairs of SD38-2's for the hump in Proviso (Chicago). These units were esentially a SD40-2 without a turbocharger, and I believe they were geared for yard work.

[Anonymous]

QUOTE: Originally posted by zardoz

Mook-
The differences that I am aware of are that a GP (2-2 axle trucks) are more suited for locations where there are sharp curves in the tracks ......

For Example: CSX runs a gravel train to and from Winchester on the line from Harpers Ferry. they use a string of 3 GP units (Usually including a slug, the GP30 slug is common), because of the tight radius and possably something to do with older track and equiptment.

[Randy Stahl]

The SD& GP designations are ambiguous today. In the early days of the diesel
locomotive there were no 6 axle locomotives. The early passenger locomotives with 6 axles still only had 4 traction motors, the center axles were unpowered. The GP 7 was indeed a general purpose locomotive, it was a good road switcher, passenger engine, fast frieght engine, and drag engine. The SD-7 was a special duty locomotive; It was easier on old worn out track, didn't slip as much, but it wasn't very quick, it was pretty much just a drag engine for long slow trains. The bigger higher capacity generators brought a big change to the 6 axle locomotives, they became stronger and faster, putting the older 4 axle locomotives to shame. I think now the REAL special duty locomotives are the ones that need to go around sharp curves and be switch engines in the industrys.
Randy

[Overmod]

A GP39 is a special-case locomotive in the first place: it uses a smaller turbocharged engine (12-cylinder 645) to make the same basic horsepower as a GP-38 with a normally-aspirated engine. Presumably the turbo maintenance and repair costs are essentially about the same for the 12 as for the 16 in a GP40, which leaves something else... presumably either lighter weight or lower axle/suspension loadings... as the reason for doing it.

Note that the situation with track geometry is roughly reversed from what it used to be if you have radial-steering trucks. The rigid wheelbase of a six-wheel truck like a HTCR-II is essentially zero; it's more complicated to try to get a four-wheel truck to 'steer' relative to its sideframes than on a six-wheel truck which has an axle on its pivoting 'axis of symmetry'. So an SD locomotive is fundamentally more track-friendly than a GP of equivalent TM horsepower now. There's still an issue with the greater overall length (and coupler swing that results) of the big six-motor units compared to B-B locomotives, and a potential issue with the degree of permitted truck swing (between truck frame and carbody) on tight curves. But I agree with Randy: four-motor units are becoming specialty-only...

(btw, I believe it's true that EMD doesn't catalog a standard GP locomotive anymore -- and hasn't since the introduction of one of the earlier models of SD-70...)

[Mookie]

I think you all answered my question, but along with an answer - Overmod has given me a headache. Now I need to print this all out and go home and study it. It is a little more than my BB brain can absorb all at once.

Mookie

[edblysard]

EMD does market a GP, the GP15D and GP20D (MK1500 and 2000Ds).

Mookie,
simply put, the distance between the axles allows the four axel, GP type locomotives to work in very tight spaces, around sharp, really sharp curves.
Granted, the steerable trucks on the new six axels locos from EMD and GE are wonders of engineering, but take it from someone who works in yards and heavy industries, you couldnt pay me enough to take any six axel unit into some of the places we go.

The reason you see SD40s doing yard work is simple, too!

Those paticular units have reached the end of their useful "road service" life, they pose a risk of failing out on the road with a major mechanical problem.

But, in yard service and yard to yard transfer work, where they are not to far away from a repair facility, or too far away from where they can be replaced easily with another locomotive, they still can earn their keep.

The GP units you see are de-tuned and set up for yard work, they too no longer have a realible road service life, but using them in yard work , again, allows the railroad to get the last little bit of use out of them.

As they continue to become un-usable even for that job, or too expensive to maintain anymore, they will be scrapped, and either replaced with other GP units, or something like the MK1500/2000s.

Dont look for GP style locomotives to become extinct anytime soon....

Ed[:D]

[Junctionfan]

What does the P stand for in P-42 and F stand for in F40

[dharmon]

QUOTE: Originally posted by M.W. Hemphill

P for Passenger. F for Full Cowl Carbody -- just like an F45. When Santa Fe requested a modified F45 for passenger service, EMD cataloged that as an FP45.

I should add that E in E unit originally stood for Eighteen hundred horsepower, and F in F unit for Fifty-Four hundred horsepower (four FTs at 1350 hp each).

Yes, I know. Consistency doesn't exist.

On the earthmoving side, everyone is wondering what Caterpillar will do when it runs out of letters of the alphabet. D is for Dozer there, and each new major design series moves up in the alphabet. A D9G is a mid-60s machine, a D9L an early 90s machine. Last I looked they were up to R.

They're also made by different folks..the P42s being GEs and the F40's being Ferrari's ..... sorry wrong F40.....being EMDs. EMDs use F .... F59PH, F50PHI, F40PH...except for that crazy SDP40F thing....but I know why they did it that way. GE seems to use P for passenger diesels..P30CH, P42, etc...but they too broke that with the U34CH...

Maybe Cat will do like GE and go to Dash line up.....D9R-0 or something..how do you do the first decade anyway???

[Junctionfan]

A little confusing isn't it

[Anonymous]

QUOTE:
On the earthmoving side, everyone is wondering what Caterpillar will do when it runs out of letters of the alphabet. D is for Dozer there, and each new major design series moves up in the alphabet. A D9G is a mid-60s machine, a D9L an early 90s machine. Last I looked they were up to R.

I used to drive a D9G. I thought it was big until I saw a D11R-CD, which has a blade that is twice as big as a regular D11R. BTW a D11 requires 3 rail cars to transport. One to haul the main part of the tractor, one for the blade,hyd. cyls.and arms, and one for the tracks. The wet weight of a D11 is about 220,000lbs. [:D]

I forgot that they have to take the cab off too.

[Junctionfan]

Oops; how rude of me.

Thankyou M.W Hemphill and dharmon for the information. What does the H stand for in SD90MAC-H

[Junctionfan]

I heard it refered to CP's few 6000 hp SD90s

[CShaveRR]

QUOTE: Originally posted by zardoz
The CNW used to use two pairs of SD38-2's for the hump in Proviso (Chicago). These units were esentially a SD40-2 without a turbocharger, and I believe they were geared for yard work.

No special gearing that I'm aware of...they used to go out on transfer runs, and were occasionally seen on road trips, too. They're geared for 70 m.p.h., just like the SD40-2s of the same era. Nowadays we use only one of them at a time on the hump jobs. The first thing UP did was move half of the CNW fleet to North Platte (in fact, it was one of the SD38-2s that was the first CNW unit repainted into UP colors). The units that stayed here have all been equipped for remote-control operation; they've all been repainted and renumbered (CNW 6650-6659 are now UPY 806-815), and they've been joined by a newcomer: UPY 863, which was rebuilt from a UP SD40-2 (and still has three radiator fans, in reference to the discussion on another thread).

[locomutt]

QUOTE: Originally posted by Junctionfan

Oops; how rude of me.

Thankyou M.W Hemphill and dharmon for the information. What does the H stand for in SD90MAC-H

Not sure about that one,but I would consider that with head end power(HEP)[:)]

[Anonymous]

Often, when a locomotive has a designation which is not part of a standard class (such as the "H" here), it refers to a rebuilding of the locomotive, especially if the locomotive were rebuilt by an outside company. My guess is that the "H" indicates the rebuilder.