Diesel locos designations

What do the letters designations for diesel locomotives mean? I see GP, SD, F7, etc. Is it possible to look at a loco and know what its
designation is? Is there a table some where that lists all the designations?
Karl
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On 2/6/2008 9:47 PM Karl P Anderson spake thus:

They mean nothing.
To be more specific, they mean (or meant) whatever the locomotive maker wanted them to mean. There were, however, some conventions followed:
GP = general purpose (called "geeps") SD = special ... mumble mumble [something]
Welcome to trainspotting.
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On 2/6/2008 9:54 PM David Nebenzahl spake thus:

Special duty, yeah, that's the ticket.
Although, aren't all SDs six-axle?
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Yes. And the GPs are four-axle.
I understand the Geeps were the originals, and the six-axle SDs started out as variants that were essentially the same locos, but the six axles gave them lighter wheel loadings, and therefore they could run on lighter-railed branch lines that the Geeps couldn't manage.
It was shortly discovered that dividing the same engine output into six traction motors instead of four gave the SD models much more "oomph" at low speeds, and they rapidly became favorites as mountain engines.
Modern day SDs have given up the idea of having a lighter axle loading because of their humongous size. They need six axles just to distribute that tremendous weight.
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Am Thu, 07 Feb 2008 00:26:06 -0800 schrieb P. Roehling:

Not true. Most of the SDs were essentially 50% heavier than the corresponding Geeps, for increased tractive effort. Only the SDL-39 built for the Milwaukee Road was lightweight, and Alco had six-axle versions of its RS-series with lower axle load. As a matter of fact, six-axle engines are often not allowed on branch lines, as three-axle trucks put more strain on the track than the two-axle trucks.
Toby
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Could you cite that please? Everything I can find on the early SDs (7s and 9s) indicates that normally the only extra weight in them was a somewhat longer frame, 6-wheel instead of four-wheel trucks, and a pair of extra wheels and traction motors. That would hardly add up to 50% more weight than the GP models they sprang from, as everything else on the SDs was the same as the GPs.
Now there *were* some early SDs that were built with added weight: two of the S.P.'s early SD7s (numbers 5288 and 5289) had an extra 15 tons of concrete in their frames, but according to John Signor on P. 221 of his book "Southern Pacific's Coast Line", "it made little difference in practise", and I've seen nothing that suggests any more of the S.P.'s SD models were ever ballasted after that.
Pete
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Am Thu, 07 Feb 2008 23:19:39 -0800 schrieb P. Roehling:

The Fallen Flags website (www.rr-fallenflags.org) has the operating manual of the SD7, which says that it was available in either 300,000 or 360,000 pound versions. SD18 is 386,460 pounds, SD24 between 330,000 and 390,000, depending on the amount of ballasting. GP7 is 240,000 pounds. So yes, the "light" SD7 actually has a slightly lower axle load than the GP7 (25 tons vs. 30 tons), but most others are 50% heavier than the Geeps.
You also said in your original mail that modern SDs need the six axles to distribute the weight, implying that a similarly powerful engine could not be built light enough to use four axles. I don't agree with that, as there were both GP60s and SD60s, both with a 3,800 hp prime mover. I don't think it would be a problem to build a GP70ACe or whatever it would be called, it's just that nobody would buy it, as they wouldn't be able to develop the tractive effort necessary to get all that power on the rails. NS even orders their new locos downgraded to 4,000 hp (ES40DC).
Toby
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Go back and read my original post. I was speaking only of the early SDs when I said "they *started out* as variants that were essentially the same locos, but the six axles gave them a lighter wheel loading".
I said what I meant, and I meant what I said; so if you wanna play nit-picking word games, go find someone else to bother.
Me, I'm anti-semantic.
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Since semantics has to do with the meaning of the words we write, we should all be pro-semantic. Otherwise there will be misunderstandings -- like the one in this thread.
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Whoooooosh!
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David Nebenzahl wrote:

"F" was Freight.
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On 2/7/2008 11:38 AM Greg Procter spake thus:

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On 2/7/2008 11:38 AM Greg Procter spake thus:

But Greg, in your heart of hearts, don't you just *know* that that couldn't possibly be correct? After all, it should be "goods", should it not?
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David Nebenzahl wrote:

In English the word can either be a noun or a verb. I set them up, you dash yourself to shreads against them.
Regards, Greg.P.
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On Fri, 08 Feb 2008 16:18:21 +1300, I said, "Pick a card, any card"

English or metric? -- Ray
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Ray Haddad wrote:

You've got me there, I thought shreads were truely international!
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On Fri, 08 Feb 2008 19:55:44 +1300, I said, "Pick a card, any card"

"Shreads?" No such word. Perhaps you meant shreds? Or some word in some other language than English? -- Ray
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Ray Haddad wrote:

Hey, you're right and I'm wrong - treasure the moment, but there's no call to build a shrine.

There's always the possibility!
Greg.P.
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On Sat, 09 Feb 2008 15:52:09 +1300, I said, "Pick a card, any card"

We know. -- Ray
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On Fri, 08 Feb 2008 16:18:21 +1300, Greg Procter wrote:

Don't you mean shreuds?
--
Steve

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