What is the purpose of raising the hoods on Alco RS models and high-hoods in general?

[punchy71]

Greetings,
Can somebody please explain to me the purpose of high-nose diesel locomotives in comparison to low-nose models? I am especially interested in what its purpose would be in modifying a low-nose to make a high-nose 'hammerhead' (like a hammerhead shark I presume), in this photo of an Alco RSD 5 for CNW railroad.
Additionally, I've seen the polar opposite of this also. Where the long part of the back end was raised up high and the nose was left low. (scratches head)... Which makes the locomotive look like Quasimodo of the hunchback of Notre Dame fame.. though I can't find a photo of an example right now...
Thank you

 

[Damon Hill]

Diesel locomotives can run equally well in both directions, and some railroads preferred to run them long hood forward. I suppose that was a holdover from steam days, and crews apparently felt safer with the bulk between them and whatever they had the misfortune of running into.

The short high hood was probably somewhat the same reasoning. The disadvantage in either case was the very limited forward visibility, pretty requiring a second crewman on the opposite side to call out signals on that side and generally help keep an eye out both forward and back.

Also, the short high hood probably contained additional equipment such as air compressors/tanks. This may be why some locomotives were uniquely modified, perhaps for special purposes or simply a different engine type, dynamic brake grids and fans, or whatever. Some converted hybrid locomotives had their long hoods lowered because the multiple gensets were that much lower.

Contemporary practice is short hood forward for better visibility, with isolated cabs for crew comfort. Frames are generally longer so all equipment can fit behind the cab, and the short forward hood now contains a (cramped) toilet. Locomotives are now designed with better internal crash protection to address that concern.

 

[Bill Anderson]

Most first generation high-hooded units were rebuilt so the short hood served as the front of the unit if the unit was originally manufactured to run long hood forward. The high short hood was replaced with a low short hood to facilitate the forward view of the engineer and fireman. In some cases like the C&NW "Hammerhead" unit, a unit of one manufacturer was rebuilt using a diesel engine and other parts from another manufacturer. Clearances did not always match and roofs had to be raised to accommodate the "foreign" engine and equipment.

 

[bcp]

The hoods weren't raised. That was normal for early diesels. Later the short hood was lowered.

The high short hood often contained a steam generator so the locomotive could pull passenger cars, which depended on steam for heat, etc.

Some, like some switchers, and early ALCo RS locomotives had hoods that were normally lower than cab roof height. EMD road switchers had hoods near cab height.

This diagram is typical of many early diesel locomotives.
http://www.irm.org/dieseldept/technicaldata/EMD/SD24/

Bruce