This is an idiot question, and I should have tried to find out the answer years ago.
Steam locomotive specifications typically include "BMOD": boiler maximum outside diameter. (Given the slightly conical design of typical boilers, this is there outside diameter just in front of the fire box.) But the diameter given is that of the steel boiler shell. This would have been covered by "boiler lagging" (= insulation-- typically asbestos in the period of 20th century steam production), and an outer layer of sheet metal covering this. How thick would these outer layers (typically) have been?
In other words, if a locomotive "officially" had a BMOD of, say, 100 inches (like the New York Central Niagara), what was the VISIBLE outside diameter?
Or to look at it another way... Suppose a locomotive (like PRR Decapod 4483 in its current location at a museum in western New York State) is preserved with a "stripped" boiler: if you look for recent photos, you can see the rivets, which would have been hidden under lagging and exterior sheet metal in service.(1) How much "skinnier" does it appear than it would have "in life"?
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(1) When I last visited 4483, at its previous location outside the Westinghouse plant in Turtle Creek PA, in the mid 1970s, some of the sheet metal had deteriorated, even splitting open in places. And, of course, modern safety regulations would necessitate removal of asbestos lagging. (I think there is a modern substitute, involving fibreglass.). The long-term hope, of course, is to restore the locomotive to its original appearance, but railroad museums are under-funded, so for the moment the best that can be done is to give the boiler a good coat of (I hope weatherproof!) paint to protect it from rusting.
Steam locomotive specifications typically include "BMOD": boiler maximum outside diameter. (Given the slightly conical design of typical boilers, this is there outside diameter just in front of the fire box.) But the diameter given is that of the steel boiler shell. This would have been covered by "boiler lagging" (= insulation-- typically asbestos in the period of 20th century steam production), and an outer layer of sheet metal covering this. How thick would these outer layers (typically) have been?
In other words, if a locomotive "officially" had a BMOD of, say, 100 inches (like the New York Central Niagara), what was the VISIBLE outside diameter?
Or to look at it another way... Suppose a locomotive (like PRR Decapod 4483 in its current location at a museum in western New York State) is preserved with a "stripped" boiler: if you look for recent photos, you can see the rivets, which would have been hidden under lagging and exterior sheet metal in service.(1) How much "skinnier" does it appear than it would have "in life"?
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(1) When I last visited 4483, at its previous location outside the Westinghouse plant in Turtle Creek PA, in the mid 1970s, some of the sheet metal had deteriorated, even splitting open in places. And, of course, modern safety regulations would necessitate removal of asbestos lagging. (I think there is a modern substitute, involving fibreglass.). The long-term hope, of course, is to restore the locomotive to its original appearance, but railroad museums are under-funded, so for the moment the best that can be done is to give the boiler a good coat of (I hope weatherproof!) paint to protect it from rusting.
