Differences, FP-45 against SDP40F

Does anyone know the differences between these two locomotive models?

Clearly, the SDP-40F had something different from the FP-45, that caused the -40F to derail.

This has been long debated... the theory that I've bought into was the water storage tanks for the steam boilers. In mariner terms, they had issues with slack tanks...

On the SDP40F, the tanks were mounted high, and supposedly didn't have baffles inside. As the water tanks emptied, the momentum of the water sloshing around it possibly introduced sideways forces that could have caused the derailments.

On the FP45, the water storage was below the frame and between the trucks (aft of the fuel tank).

One other difference was that different trucks were used between the two models. The FP45 had Flexicoil trucks, while the SDP40F had HT-C. The Flexicoil had coil springs and one motor faced the opposite direction in the truck from the others. The HT-C used rubber blocks for suspension. Supposedly the SDP40F used a lightweight version which was one speculation as a cause of the derailments. Some say that because of this debacle over trucks is why Contrail ordered all SD40-2 and most SD50 with Flexicoil. I don't buy it because ex EL SD45-2 had HT-C, and it was likely because of the supply of used trucks from traded in units.

Engineer Spike wrote: ↑Thu Nov 03, 2022 8:01 pmSome say that because of this debacle over trucks is why Contrail ordered all SD40-2 and most SD50 with Flexicoil. I don't buy it because ex EL SD45-2 had HT-C, and it was likely because of the supply of used trucks from traded in units.

Sure, but Conrail didn’t order those SD45-2s, EL did, and they were built in 1972, before any SDP40F was built.
Conrail also pretty much only used the SD45-2s as helpers in the Altoona area, so it ‘d seem that they weren’t too comfortable with the idea of running them at high speed. Conrail also wouldn’t have been trading in power that used that version of the Flexicoil truck at the time they were buying SD40-2s and the early SD50s.

Both were 72'4" long, but the truck center spacing was different: 45 feet on the FP-45, 46 on the SDP40F. (This MAY be a design change to accommodate the different trucks, and may not.). These are both long by the standards of freight diesels of the era, but shorter than the truck center spacing on such more modern diesels as theSD-70 and GE's Dash-9, so I'd be surprised if the SDP40F's derailment history is attributable to it.

eolesen wrote: ↑Thu May 19, 2022 8:27 pm This has been long debated... the theory that I've bought into was the water storage tanks for the steam boilers. In mariner terms, they had issues with slack tanks...

On the SDP40F, the tanks were mounted high, and supposedly didn't have baffles inside. As the water tanks emptied, the momentum of the water sloshing around it possibly introduced sideways forces that could have caused the derailments.

On the FP45, the water storage was below the frame and between the trucks (aft of the fuel tank).

That makes sense to me since the derailments generally involved the outer rail being rolled over outside the curve. But I think we might also suspect deferred track maintenance too, as a contributor?

Perhaps a combination of both.