What would be the appropriate number of diesel units (FT or F3) to replace a 2-8-2?
Generally 2-4 units.
I’ll confirm what Dan said. Obviously 2-8-2’s came in different sizes and tractive efforts, but generally to get the same drawbar HP and Tractive Effort, you would need 2-4 EMD FT, F3 or even F7 units.
The diesels would have a slight advantage on any grades and might be a little faster as well.
Sheldon
EMD figured that one A-B set of FT’s was roughly equal to a Mikado, and an A-B-B-A set was about equal to a Mallet like a 2-8-8-2.
BTW FT’s were originally designed to only be used in A-B or A-A set-ups, the two units were connected with a drawbar. They were able to rig something up to allow couplers between the units. One problem with the A-B sets is that many railroads found that for mainline trains one A-B set wasn’t enough power, and two (A-B-B-A) sets were too much horsepower. Many roads after WW2 ordered F2 or F3 engines and ran them with in A-B-A sets with FT A-B sets. If you look at pics from the forties and fifties such a set-up was pretty common.
Answer: NONE!
No mere diesel can ever replace a steam locomotive.
[C):-)]
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Unfortunately, my prototype decided that catenary motors could replace steam locomotives - but couldn’t drop the last fires until 1975. A (very) few steam locos survive in semi-revenue service to this day. (They replace DMU on selected schedules for the convenience of railfans and tourists, much more frequently than 844 gets out to play.)
Since not all lines had traffic dense enough to justify catenary, diesels were brought in to pick up the crumbs take up the slack.
Chuck (Modeling Central Japan in September, 1964 - with steam, catenary motors and diesel-hydraulics)
On paper I would agree, two FT or F3 units equals the “average” Mikado. In the real world it was not that simple.
Eaxmple: The B&O typically pulled 70 car, 3500-4500 ton trains from Baltimore to Brunswick with two Mikados. Ruling grade about 1.5%. When diesels came along it quickly became clear that 6 1500 hp units where needed to do this work if the trains were at the heavier side of this range, which the Mikados had handled easily. BUT, the diesels did improve the time from Baltimore to Brunswick.
It is possible that more modern steam like Super Power Berkshires or Heavy Mountains could have matched the diesels time, I know of no record of any regular use of 4-8-2’s on this run and the B&O never had any Berkshires - so we will never know.
But in this one application, it definately took 3 F3’s or ALCO FA’s to replace each Mike. interestingly, this is right in line with what you mentioned about F2’s and F3’s purchased seperately to make three unit sets out of existing FT’s. And Yes I have seen many photos, read lots of reports, and checked many rosters which confirm that as well.
A few more notes about the FT’s. EMD did build some ABA sets of FT’s using a shorter B unit. And by the end of production a great number of
Once a steam locomotive had been helped to either get up a grade or even to lift a train out of a yard, its cylinder cycling rate meant that it was producing maximum horsepower at track speed and that was often sufficient to handle even the ruling grade on a route if the momentum were sufficient at the base of the grade. Diesels drop off on HP to the rails as they increase their speed, the opposite of steamers. So, the net effect is that a single diesel can start a very heavy train, and may be able to crawl it up a grade, but that effort would be very hard (and hot!) on the traction motors. So, it was convenient to couple them to at least one other slaved unit that also didn’t happen to require a paid crew. HP available as needed.
Steamers would often need a shove out of a yard or up a grade, but once the locomotive was up to speed, it was only extra-heavy consists or grades steeper than the ruling grade of the route that would impose added steamer(s) …and their paid crews.
Crandell
It would be two or three diesel units, as others have posted, depending on the size of the Mikado, to haul the train. For the railroads there was another very important factor, though, namely availability. While the Mikado was off in the roundhouse getting serviced, the set of diesels would be back out on the road hauling freight, so you might have some ratio like 3 diesel sets replacing 5 Mikados.
John
Initially, many roads thought they could eliminate all steam qickly by providing enough diesel power for each train to get it over the grades on the line without needing helpers. They soon found that this was a waste as the additional units were only needed on the hills, and went back to helpers. The freed up units from the overpowered sets were then used to dieselize more trains, the true econony being the maitenance labor, ans and down time of road steam.
I have to admit, you do have a point…