"Did you see which milepost that was?"
Looking back at my records I see I started to record loco performance back in the late 60's, but then it was only station passing times and often the loco type, number and/or load was missing. As time went by I started to get the hang of this aspect of the hobby so that by the early 80's I was recording what I believed to be all the essential details. In 1984 I joined the Railway Performance Society (of which I was a member for a few years) and that made me realise just how inaccurate my records actually were and also how they would also be personal to me. Any two people recording the same journey will come out with different passing times, different horsepower calculations and often that is all down to where they were sitting in the train and how accurately they noticed the timing points. Even the start and end times may differ. Often I started the watch with the first lurch of the train only to find we had stopped again for a few seconds. Similarly we would crawl into stations at what seemed to be less than walking pace so exactly when did we stop?
I have tried to use the same layout for all the timing logs you will find on this site. However the older the log, the less the detail I had recorded. This is an explanation of what each of the 'boxes' means.
Date, Locos and Train - I think those are self explanatory! If I have any photographs of this train on my website then I have added a link to them.
Weather - Only after I became a member of the Railway Performance Society did I appreciate how much the weather plays a part in train performance. By then we were towards the end of the class 25's passenger duties so many of my logs will lack this detail. You only have to think of the difference between a train forcing it way through heavy rain and high winds (wheel slip and wind resistance) and the same working on a dry, windless day to appreciate why this is useful to record for comparative purposes.
Seated - Ideally coach one, seat one but then everyone wants to be there to 'wag the thrash' especially over Talerddig so a compromise was always necessary. At the speeds class 25 locos worked trains there could be several seconds difference between the front and rear coach passing a timing point and just like with the weather I didn't appreciate that was worth recording until it was too late!
Load - Horsepower calculations require an accurate assessment of what the locos are hauling. The three essential components are net, tare and the locos themselves, each is separately treated in the calculations. The Net weight is that of the coaches themselves. Class 25 locos tended to work on Mark 1 coaching stock which weighed between 30 and 40 tons and I would add up the weights quoted on each coach (or look them up in the Platform 5 combine). Tare weight includes the passenger load. The general rule of thumb for assessing this was 10% of net weight for a full train but some of the trains out of Aberystwyth were full and standing with a lot of luggage so sometimes I added a few extra tons for that. The locos weight is the final component and that can be looked up from elsewhere on this site. You also need to know what type of coaches were being used and almost always this will be Mk.1 coaching stock. However the resistance characteristics for Mk.2 coaches is not the same as that for Mk.1 coaches and a different formula is required in those circumstances, hence that information is important and recorded.
Passing Point and Mileage - When I made these recordings in the 80's there were several quality sources for mileage information. The one I used was produced by Michael Oakley and that gave accurate mileages because he actually went out and paced the line in many places to confirm the information. The particular sheet also had the gradient profile on it. The Railway Performance Society also produced a mileage chart but the two sources tended to differ by the odd chain or two here and there. The passing points I used were stations, both in service and disused, former junctions and mileposts, particularly those that marked the start or end of an incline.
Timings - See heading for an explanation as to why timings differ from yours if you were on the same train! Often I would be in a compartment talking to my mates and trying to time at the same time. If I missed a point by a few yards I might knock a second or two off and record that as the passing time. Milepost timings tended to be accurate as I used those for speed calculations
Speed measurements - wherever possible the quoted speeds are based on milepost quarter mile timings prior to (or including) the timing point. For my older logs that is unlikely and average speeds may be given (and stated as such). Where a trains speed was compromised by speed or signal restrictions my logs show this with an asterisk (*) following the speed.
EDBHP / RAILHP - On the Railway Performance Society website (http://www.angelfire.com/pe/railperf/) you can find a link to download a horsepower calculator. Back in the early 80's you were lucky to have a programmable calculator let alone a computer and spreadsheets. Actually I did have a programmable calculator, a Casio and it connected to a small portable electrostatic printer that ran off batteries. I had programmed in the horsepower calculation and as we climbed Talerdig and passed a milepost I would press a key and within a second or two the printer would start to print the horsepower and speed calculation for the previous quarter mile. On completion of the 2 mile climb it would then print a summary. On particularly fast climbs (or slow) we would gather round the printer to see if it was a record performance, ah happy days! I still have those printouts. Because of the accuracy of these calculations, both in my timing but also inherent in the number of variables it uses, I have rounded all the calculations to the nearest 10. The following book, Clough, D.N. & Beckett, M (1988) BR Motive Power Performance (Ian Allan), has a pretty complex explanation as to the what the formula is. I'll publish the simpler version here another day!
Gradient - The only source of gradient profiles I ever had was the one produced by Ian Allan and reprinted many times. When I travelled a route many times, as I did over the Cambrian, then the source could be checked against the gradient posts otherwise I took it at face value.
Speed Limit - This was something I never had at the time but recently came to light when I reread the Railway Performance Society's Mileage Charts book as I was researching my records. On each of the tables in that booklet the PSR (Permanent Speed Restriction) between each timing point is quoted and for each direction of travel. I have included them in the tables for information and it does sometimes help to explain why the locos would be shut off in mid acceleration down a bank.
Comment - Not much to add here other than I'll mention signal stops, delays or other events that impacted on the timing.