Often using any kind of "prototypical practice/methods" results in calculations
that don't really "work" for the layout. At the very minimum you will have to
make some decisions that "map" the horsepower in the locos to the trains you
are able to run on your layout - because, among other reasons, the prototype
ratings don't apply directly to our model trains.
I'm saying that using the same formulas that were used on the prototype
often results in 'errors' when applied to our layouts.
Another approach is to do -actual- motive power measurements ... on your layout.
This is easily done by first finding the ruling grade and then pulling a 'typical' train
up that grade and changing the number of cars until the loco handles it (with? or
without? any slipping is up to you/the layout owner).
Finally - create "locomotive cards" that are the same size as your car cards and
include the rating/pulling power for the loco. It helps if all of the cars on the
layout are the same weight (for the same size car). Using a rating that is right
on the edge of being the max the loco can carry may result in "emergency calls
for a helper" which although fun can seriously affect the 'flow' of the Op (so
decide whether or not you want this to happen and set your ratings based upon
that decision). The loco card "travels with the loco/train" just like the car cards -
so it is always available to anyone (the YM/hostler?) who is making the decisions
about what power to use on the trains. (Many layouts also have "caboose cards".)
Many layouts include specifying the locos that will be used on trains that are
made up during the session in the 'packets of stuff' that are used to assign the
trains to operators and/or given to the yards to use to make up the train(s).
Most layouts do not have much capability for/include in the operations the
ability to add helpers for "Just The Grade(s)" ... and so the motive power assigned
to the train is done in the originating yard or staging.
With this approach what you do is to "assign enough power for the train to get
itself over the RR". And, usually, the layout owner decides to not specify different
power requirements for different directions (even if that is possible) - if for no
other reason than to keep the number of locos 'balanced' on the ends/in the
yards. But some Ops include "light power moves" to re-balance. *G*
I operate on a lot of different layouts. One of them has a helper district and
many of the trains truly -require- a helper in order to get up the grade. They
won't make it without one. The way the Op works is that the train pulls up to
the departure point in the yard/town, the helper is added (and at the correct
placement/specified place in the train), and then clearance to proceed is gotten.
At the top of the grade the helpers are cut off and the train proceeds without
them. This is an "all steam" Ops (OK, only mostly steam) and so each locomotive
has its own crew/engineer (no consisting with the head end).
Helper operations can be/are a lot of fun - but in order to do them
effectively you may have to add Ops jobs such as "hostler" and "Helper
Engineer(s)" ... and you also have to allow time in the schedule to add/remove
helpers. Luckily, it is usually fairly easy to find a window where a helper/helper
set can be returned back down the hill - where it goes into the engine facility
to wait for its next assignment. *Great Stuff!!!*
- Jim B.