Large and Small locomotive economics, ex-West Somerset Railway developments

Why do all the interesting threads (to me, anyway) happen whilst I'm away from a PC?
Putting a bit of practical engineering into all this, raising steam is basically a question of heat required to boil the water and bring it up to a working pressure. The fundamental in all this is the amount of water in the boiler and not the size or type of grate. It is not a question of grate area. The bigger the boiler water capacity and higher the pressure, the more coal that is needed to reach the red line (or an operable state). Small boilers don't require as much heat input to raise steam as big ones, it's as simple as that. A wide firebox loco is probably going to have a larger water space than an equivalent narrow firebox loco simply because of its design. There is going to be some variation in terms of heat energy lost up the chimney but that is going to be affected more by the steam raiser/fireman than boiler design. It's the same when it comes to standby losses; a smaller boiler has less surface area and therefore less heat loss, which has to be replaced. When it comes to steam used in hauling trains, the big difference is usually the steam required to haul the dead weight of the loco; the bigger the loco, the more steam required to move it. That required to move the train will be fairly constant There is some variation in efficiency between locos, just as in any thermodynamic system but it is far more complex than simply looking at size.

 

It's interesting that the WSR record the amount of coal used by their locos. I wonder how they do it? I've long advocated that the NYMR fit load cells to the coaling tower and record coal usage. It would provide some interesting info on coal usage. Perhaps not so much on which loco uses the most coal but which fireman/driver does! There's an old (and true) saying that, if you can't measure it, you can't manage it.

 

Wouldn't a larger boiler, containing more water, retain more heat than a smaller boiler?

 

Like most corporate accounts the IoWSR published accounts can be impenetrable when you try to mine them for detail. I'm sure that the internal management accounts are more specific.

Anyway in 2012 and 2013 the railway ran about 14000 steam loco miles per year at a cost for "Coal & Fuel" which works out at £4.75/mile. There is also an entry entitled "Locomotive Running Costs" which is clearly a much wider category but appears to include coal which works out at £11.10/mile.

Also in the 2013 accounts are some other interesting statistics:-
Individual Loco mileages range from 34 to 5747;
There were 70500 carriage miles with the bogie vehicles typically running 10000 each and the 4 wheelers 5500 each
Average passengers per train was 87. At first sight this looks small, but this average includes all public trains from off season quiet times to peak trains at the August bank holiday.

It would be very interesting to see some comparative costs from other railways.

Nick

 

On the Bluebell, for 2013

Coal cost works out at £5.56 per mile. Perhaps more germane, the per passenger cost of coal works out at £1.15 per passenger.

Repair costs are impossible to work out from the published figures for two reasons: firstly because they don't account for money put in by external locomotive owning groups; secondly because (the way our accounts are presented) the locomotive workshop cost includes materials and direct contractor costs, but doesn't include staff costs, which are in a different line in the budget grouped with all staff costs. That is probably understandable in a small organisation, since if you split the salary costs for each department, in some cases you would inadvertently reveal the specific salary of an individual member of staff, which would be a potential invasion of privacy.

Tom

 

It would, in terms of heat energy, if the starting conditions were otherwise the same. However, that is only one of many factors that need to be accounted for. The surface area of the boiler will contribute to the rate of cooling and bigger boilers have greater surface area. Putting a chimney cap on can reduce the flow of cooling air and help retain the heat. If we assume that the boilers start off from the same water temperature then the amount of heat required (and hence coal used) to get it up to working pressure is largely a function of the amount of water in the boiler. The next most important factor will be the heat loss up the chimney, which is going to be quite variable and largely influenced by the quality and skill of the steamraiser.

 

When we were running 6024 on the mainline, after a run on a Sunday a cap was put on the chimney, after what little fire was left was pulled to the back. When we went to dispose on the following Thursday the boiler would be still warm, and working in the firebox and smokebox was a warm job. The boiler had modern ceramic blanket insulation on it. The amount of heat lost through standing losses(radiation and convection) pales into insignificance compared to what goes up the chimney.

Rob

 

I may be wrong, but I don't think the surface area of a boiler relates linearly to it its volume, so a bigger boiler has relatively less volume than a smaller one.

Edit - I think I meant to say relatively less surface area!

 

WSR coal measurement is by counting digger bucket loads of known weight.Steve, as ever,is making excellent points,not least in the human factor.There are still those who think constant use of safety valves is evidence of their ability, not lack of it ! WSR practice is to stable an engine with a dying fire (if not, you stay with it until it is!)and full boiler.The remaining heat and pressure contribute to a reduction in coal usage in steam raising.Smokebox and dead fire are dealt with next day-usually takes about 30 minutes, with a new fire making steam not long after.

 

I think the real number to look at, when looking at this facet, is the volume/surface-area ratio. Heat loss per unit of water (which is probably what one really cares about) will be a factor of this, not just the surface area and temperature differential. And on that measure, sadly, small boilers fare worse than large ones, since smaller things always have a larger surface-area/volume ratio than big ones. (Which is why elephants have thick legs - mass goes up faster than leg cross section - and huge ears for cooling.)

PS: I see someone else already made the same point. Sorry! That will teach me the be careful and read the thread all the way through before posting a reply...

Noel

 

The idea of quantifying all of the consumables & repairs in order to really get an accurate idea cost per mile/cost per passenger allocated to a specific loco is interesting. I suspect that it would be very hard to achieve without producing averages over a long period of time to give any level of certainty. There are an awful lot of variables that would need to somehow be monitored- those that immediately spring to mind are;

-Crew variance
-Coal variance (quality and weight)
-Weather
-Boiler Cycling
-Loadings
-Water usage
-Oil usage
-Preparation/disposal procedures

Drawing a like for like comparison is going to be very challenging as there cannot be very many railways where it would be possible to produce similar enough conditions loco to loco I wouldn't have thought (please feel free to correct me if I am wrong in this assumption) NYMR maybe- having 45428/44806/61264 collectively in traffic would probably give a good sample to give an accurate indicator of running costs of a class 5 loco?

Chris


(edited as I had repeated myself)

 

It's worth getting the coal consumption into perspective. On the Bluebell at least, the coal bill is about 5 - 6% of the annual expenditure. If there was some way to make, say, a 10% efficiency saving that would be very welcome, but it would be a marginal impact on the railway's finances, not a transformational one. Indeed, it would have roughly the same impact on the bottom line as being able to attract about six extra passengers on every running day - say two extra cars in the car park. Arguably, it would be a better use of management resources to think of ways to reliably bring six extra passengers to the railway every day than to save 10% of the coal bill.

Tom

 

On the Isle of Wight I calculate about 60 pence per passenger for coal from the published accounts. Given the differing journey lengths between the Bluebell & the IoWSR that seems reasonable.

 

But that is too simplistic. A boiler has tubes and a firebox. Bigger boilers have more tubes and bigger fireboxes, all of which contribute to surface area and hence heat loss. As I said, a chimney cap can reduce this heat loss but heat loss via the smokebox and chimney remains a significant factor.

 

The NYMR has no way of measuring the amount of coal individual locos use because the coal is loaded via the coal hopper. I've said many times that, if you can't measure it, you can't manage it. Please Mr Bean Counter, can we have the coaling stage fitted with load cells? The results would be interesting and may lead to different decisions being made.

 

That was news to me. Having spent a week on 34053, plus a week or so on 1501 and some days on 4566, I offer the following:

A "round" on 4566 12 - 15 shovels 6 coaches

A "round" on 1501 12 - 15 shovels 6 coaches

A "round" on 34053 60 shovels 7 coaches (time of year) loaded to 9 one day

A round on the tank engines would take you from, say, Bridgnorth to Sterns, where you would top up again.

A round on the Bulleid would take you comfortably to Hampton Loade and, with a little patching as necessary, to Highley. I noticed I was really only firing it 3 times between Bridgnorth and Kidderminster. Like all the big 'uns, once you've got them warm, they will go a long way. It still used a lot of coal and water though.

Regards,

jtx

 

What happened to little and often?

 

That was little and often. It takes 60 shovels to cover the grate of a Bulleid Pacific. That's only one layer of coal thick with some extra in the back and corners. Likewise on the tank engines. I usually run with a "thin, bright fire."

jtx