Can someone explain the reasoning for the large “back porch” found behind the boiler on the cab forwards from SP?I have never heard what they were thinking.
Take a look at the side view drawing here: http://www.steamlocomotive.com/cabforward/ That should explain a lot of it since the rear cylinders and trailing truck are both aft of the smokebox. There’s no need for a in that area and the tender is connected by a drawbar. Might as well make it a straight shot.
Now take a look at a DM&IR 2-8-8-4. http://www.steamlocomotive.com/yellowstone/ . Notice that the front cylinders are forward of the smokbox front. If you remove the pilot and extend the front deck until just forward of the pilot truck, you’d get pretty much the same effect. IOW, the big back porch is just one of the quirks of the later (4-8-8-2) design.
I tried to find pics of the earlier 2-8-8-2’s that showed how their front decks were constructed but couldn’t find any that gave a good shot of the rear deck (called a “monkey deck” by SP enginemen).
Andre