Description of Locobase Power Computations

Robert LeMassena's Power Computation
Robert LeMassena's original suggestion that locomotive power could be compared by multiplying the grate area x boiler pressure
Llanso's objections:
  • Doesn't account for oil-burning locomotives.
  • Doesn't account for low-calorie, large-grate fireboxes such as the Wootten used in camelbacks.
  • Doesn't say anything about the rest of the locomotive's ability to convert the resulting heat into steam .
Same as above plus superheater percentage
First mod: factor in superheater percentage (multiply the LeMassenaR number by 1 + the percentage derived by dividing SHS into Combined Heating Surface)
Same as above plus superheater percentage
Second mod: same formula as immediately above, but substitute firebox area for grate area (LOCOBASE.BLRPRESS * LOCOBASE.FBOXAREA * (1 + SHSPCT)
Third mod that I also call the SPR for Super Power Rating:

If(number of low pressure cylinders > 0, (boiler pressure * CHSFactor * driver diameter) / (low pressure cylinder volume * 100), (boiler pressure * CHSFactor * driver diameter) / (cylinder volume * 100))

(Note the variable CHSFactor. Its formula is:

If(firebox area > 0 and LOCOBASE.CHS > 0, (((LOCOBASE.EHS - firebox area) / 6) + firebox area + (LOCOBASE.SHS * 1.5)), ''))

Translation: Take the boiler pressure, multiply by the CHS factor. This is a calculation that takes the Evaporative Heating Surface and subtracts the firebox heating surface from it. The formula then divides the remainder by 6, adds the firebox heating surface area and 1 ½ times the superheater area. Then multiply that number by the driver diameter.

Then take the product and divide by the cylinder volume x 100 (the multiplication is to reduce the number of zeros or digits in the answer -- it has no other significance).


My goal is to create a number that expresses the boiler's capacity to supply steam to the cylinders at speed. I give bonus points for a high ratio of firebox to evaporative heating surface and for higher superheat. Also, the taller the drivers, the fewer times per mile at a given speed will the cylinders require steam. So either the same amount of steam allows a higher speed or a given speed demands less steam.

It is not a replacement for LeMassena's number because I haven't quite figured out how to take the quality of the coal or the grate into account.

Take the SPR and divided it by the average axle loading in metric tons.

Any questions on the above data should be directed to Steve Llanso of Sweat House Media.

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Wes Barris