Measuring using chains

[snowball]

The confusion probably stems from the fact that speeds *are* in metric, but distance is not

This is the opposite of Manchester Metrolink where speeds are in mph but, as mentioned by LNW-GW Joint, distances are metric.

 

[zwk500]

This is the opposite of Manchester Metrolink where speeds are in mph but, as mentioned by LNW-GW Joint, distances are metric.

Indeed. There's also St Pancras HS Lines and I think Ashford International where both Mph and Kph are signed simultaneously.

 

[Snow1964]

With several thousands years of history here, I can see why you might end up with something like 4' 8 1/2", but if like Brunel you are designing something from scratch why choose 7' 0 1/4"?

As you so rightly point out, once things such as units of meaurement are embedded they are very difficult to change.

Actually Brunel‘s letters to GWR Directors, show he originally wanted 6 feet, but it was realised it was too close to then accepted 6’ 2.5 inches between tracks (so risk of running off at nose of crossovers), so Brunel suggested 6’ 10 inches to 7 feet, someone else added the quarter inch later

Incidently the river viaduct at Bradford on Avon carries signs saying located at x miles 78 chains, contact Network rail if damaged. These signs are right under the milepost on the viaduct. So signs clearly relate to distance at other side of river.

 

[Ken H]

Chains are so called because the measure used to be a chain
Here is one - https://www.tsa-uk.org.uk/media/2013/05/19-Gunters-chain.jpg
They were used because they didnt stretch. But they must have changed length due to expansion due to temperature.

Anyway
12 inches = 1 foot
3 Feet = 1 yard
22 yards in a chain
10 chains in a furlong
8 furlongs in a mile

or 1760 yards, or 63360 inches in a mile

A knot is a nautical mile per hour. A nautical mile is 1 minute of latitude. So you can measure off nautical miles on the latitude scale on the side of a nautical chart. It traditionall varies because the earth is not an accurate sphere (flattened at poles) but today its been set at 1.852 metres.

A fathom is 6 feet (Used for water depth). nautical charts now have depths in metres so they are largely unused.

A barleycorn is 1/3 inch. The difference between british adult shoe sized is 1 barleycorn.

 

[miklcct]

The confusion probably stems from the fact that speeds *are* in metric, but distance is not:
View attachment 124234

London Underground is the reverse, imperial speed with metric distances.

I wonder how people understand when incompatible units are used for speed and distances?

 

[LNW-GW Joint]

I feel like I've mentioned this numerous times before, but locations on the Cambrian line are still measured in miles and chains, not metric.

I seem to remember there are (white numbers on blue signs) km posts as well as mileposts on the Cambrian.
I need to get down there again and check!

 

[zwk500]

London Underground is the reverse, imperial speed with metric distances.

I wonder how people understand when incompatible units are used for speed and distances?

By remembering either 1.6 or 5/8. They're not 'incompatible', just in different scales.

If you're looking for jobs with NR you better get used to jumping between Yards, meters, Miles, and Kilometres. The number you'll need for engineering precision is 1.609344. You may also want to try and get your head around SLU, or Standard Length Unit (21ft).

 

[AndyPJG]

This is the opposite of Manchester Metrolink where speeds are in mph but, as mentioned by LNW-GW Joint, distances are metric.

Designed and built using metric, but speeds have to be imperial due to street running ie 'road legal'.

 

[hwl]

Alfrey's bridge, between Mortimer and Southcote Jct. has a plate giving its mileage as 41m 80ch. Spot the error!
BTW the track chart gives the mileage as 41M 64ch.
Pat

64/80 = 0.80 exactly, so an unfortunate decimalisation error...

 

[etr221]

When LU did a remeasure back at the beginning of the 1970s to metric standards, with a logical system based on a zero point at Ongar, I understand BR considered a similar project - but blanched at the cost.
(My understanding, as an aside, is that TfL/LU have now abandoned the 'Ongar' system, in favour of meterages within and between stations)

Something to bear in mind is that railway mileages/chainages/kilometerages/meterages are not actually so much 'distances' as such, but a progressive system of giving locations along the line, and as such the units aren't that important. In that sense metric units for engineering works designed in metric, to happen at locations defined in miles and chains (or yards) is not so strange.

A question: how much actual measurement in done in traditional units? Rather than in metric to be tied into the mile and chains positions?

In other fields there have been similar divides. Indian metre gauge (3' 3.37") was always the only metric measurement on an otherwise imperial measures system (until India went fully metric, post independence) And the army adopted a metric grid on its maps at the end of 1918 (later also used for OS civil maps of GB), long before it adopted metric for anything else. (And ranges would calculated in yards from grid differences in metres)

This is the opposite of Manchester Metrolink where speeds are in mph but, as mentioned by LNW-GW Joint, distances are metric.

Croydon Tramlink is metric throughout - including speeds (and speed limits) - I always wonder how fast trams are allowed to run in Addiscombe Road, with Tramlink speed limits of up to 50 kmph, and a highway speed limit of 30 mph (slightly less).

 

[zwk500]

A question: how much actual measurement in done in traditional units? Rather than in metric to be tied into the mile and chains positions?

For scheme plans and that sort of thing, the (unconfirmed) impression I got was that the survey team would pick a known point such as a milepost or something mentioned in NESA, then convert that mileage into meters and use that point as a datum to calculate all other locations on the plan in metric. It got really fun if there was a short mile or something like that in the area as they're not mentioned in NESA and so they weren't mentioned as a mileage change on the plan, breaking the convertibility of the meterage back to mileage.
There was also one set of drawings I remembered seeing where the survey had started at Waterloo and put the Zero Metre datum on the buffers, understandably. However, because the Zero Milepost for the SWML is in fact at Waterloo East, this meant the meterage was about 3/8ths of a mile out with the mileage for all the drawings in that set.

 

[LNW-GW Joint]

OS maps have been metric for a long time (eg 1:50000 series), but I still have 1-inch scale maps with the 1km/10km squares on for accurate positioning.

 

[OVS Flatbottom]

Designed and built using metric, but speeds have to be imperial due to street running ie 'road legal'.

I believe Luas in Dublin has always had metric speed limits, even though the first lines opened to the public in 2004, whereas Ireland only metricated road speed limits in January of the following year. (Of course, it's very likely that the intention of changing the road limits was known by the time the final decision on which system to use for the tram limits was taken, but the two still had to coexist for a period.)

 

[snowball]

Designed and built using metric, but speeds have to be imperial due to street running ie 'road legal'.

Yet despite that I think most UK tram systems (other than Metrolink) have speed limits in km/h. Croydon Tramlink is mentioned above.

OS maps have been metric for a long time (eg 1:50000 series), but I still have 1-inch scale maps with the 1km/10km squares on for accurate positioning.

That goes back longer than the 1:50000 series, which was introduced in the 1970s. Use of the metric-based National Grid goes back to around WWII. Use of scales like 1:2500, which are round numbers when expressed as a fraction but not in inches to the mile, goes back well into the 19th century.

 

[Grange6843]

Alfrey's bridge, between Mortimer and Southcote Jct. has a plate giving its mileage as 41m 80ch. Spot the error!
BTW the track chart gives the mileage as 41M 64ch.
Pat

64 chains is eight tenths of a mile. Did they interpret 41.80 miles as 41m 80ch?

 

[mike57]

Brunel you are designing something from scratch why choose 7' 0 1/4"?

I dont know if it is a myth to explain the unexplainable, but I always understood that the initial design was for 7ft, but that the 1/4inch was added to allow for tolerances in wheels and track gauge, I dont know what sort of tolerances could be acheived in wagon building in the 1830s but one could envisage 6ft 11.95in track gauge with 7ft 0.05in wheel gauge.

 

[fandroid]

Of course one chain equals 4 rods (or poles) and a rod is equal to 25 links (therefore 100 links equals one chain)

I'm an old enough civil engineer to have been introduced to real chains for surveying in my first year at university. The whole civil engineering course went over to metric (strictly speaking - SI Units) in October 1968. I've never even seen a survey chain in all the years since. A bigger headache on conversions for us was the change of OS sea-level datum from Liverpool to Newlyn. When modifying existing structures it was always essential to check the original drawings to confirm which datum had been used.

 

[philthetube]

London Underground is the reverse, imperial speed with metric distances.

I wonder how people understand when incompatible units are used for speed and distances?

When training on the S stock we were told that the reason for the speedo showing mph was just because that was what all drivers were familiar with and there was no benefit in changing it.

 

[miklcct]

When training on the S stock we were told that the reason for the speedo showing mph was just because that was what all drivers were familiar with and there was no benefit in changing it.

So will that be changed in the future when the metric-educated generation who are used to work in km and km/h (i.e. those born after the 1970s) become the majority in the workplace?

It's cumbersome to work when the distance is in km and the speed is in mph, or vice versa. For example, when you are driving at 60 km/h, you pass a km post one minute; at 120 km/h, half a minute. How long do you need to drive 11 km at 60 mph? UK motorways are exactly the same as London Underground in this respect as they are also measured in km, but the speed limit are in mph.

 

[Oxfordblues]

"Is it an urban myth or did it really happen" No.97: in the 1970s BR wanted to embrace modern Continental-style metrication and eliminate old-fashioned miles, furlongs and chains. The Western Region main line was chosen for a pilot project and kilometre posts were installed from the buffer-stops at Paddington all the way to those at Penzance. It took a lot of surveying, a long time and considerable expense. However, just as the final post was put in place on the approach to Penzance, it was decided to extend the Lawn at Paddington by a few metres and the buffer-stops were duly moved a few metres west. This at a stroke rendered all the new posts inaccurate. Shortly afterward the whole scheme was quietly dropped. At least, that's what a fellow-railwayman told me in a pub once. Can anyone corroborate this sad story?

 

[Peter Mugridge]

"Is it an urban myth or did it really happen" No.97: in the 1970s BR wanted to embrace modern Continental-style metrication and eliminate old-fashioned miles, furlongs and chains. The Western Region main line was chosen for a pilot project and kilometre posts were installed from the buffer-stops at Paddington all the way to those at Penzance. It took a lot of surveying, a long time and considerable expense. However, just as the final post was put in place on the approach to Penzance, it was decided to extend the Lawn at Paddington by a few metres and the buffer-stops were duly moved a few metres west. This at a stroke rendered all the new posts inaccurate. Shortly afterward the whole scheme was quietly dropped. At least, that's what a fellow-railwayman told me in a pub once. Can anyone corroborate this sad story?

Moving the stops back would render the miles based measurements slightly out as well, surely?

Are there any rules that, in these circumstances, would have prevented them saying the buffer stops were at "minus distance"?

 

[LNW-GW Joint]

Trackmaps shows a P1-8 datum at Paddington at 0m06c, P9-10 at 05c and P11-12 at 04c.
The Euston equivalent is at -03c, presumably after rebuilding in the 1960s.
St Pancras has a zero (km) for the CTRL platforms.

 

[etr221]

I believe that, certainly at some terminals, the datum (zero point) was the property line, and not the end (or should I say start) of track - Paddington may well be such.

 

[Ploughman]

There is an unsubstantiated story circulating, which starts off describing why the Space Shuttle booster rockets were that size. That story leads onto the 4 feet 8½ inch gauge on the railway.

As it goes on it says that that gauge was chosen as it was the one used for plateways in coal mines - which was the gauge for wheels on carts on the roads - which were that width because they fitted in to the ruts that most roads had (otherwise it would lead to axles breaking). That the ruts were that width in the first place was, allegedly, because that was the distance between wheels of a Roman chariot.

How true that all is remains to be seen.

And the reason why the distance between the Roman chariot wheels is what it is.

It is because that was the average width of a Horses Ass

 

[swt_passenger]

It is because that was the average width of a Horses Ass

I think you might need the “Americanisms” thread now…

 

[Ediswan]

And the reason why the distance between the Roman chariot wheels is what it is.

It is because that was the average width of a Horses Ass

Two horses, according to numerous online sources.

 

[59CosG95]

Since the remodelling work, some of the new assets in King's X (e.g. retaining walls) have been listed in kilometres and metres, rather than miles and yards.

I suppose it'd make sense to start with the zero point...

 

[CEN60]

Another point to consider (and I have to on a daily basis) - mileposts, quarters, half and three quarters on the track can be notoriously inaccurate - this is demonstrated by modern software “Chaining” up topographical survey information - they should be 402.34m apart - routinely 5-10m out have seen one 100 odd metres in the wrong location, and have seen 2 mileposts of the same value 20m apart! Also re the use of chains - a lot of the old NR / BR records are in miles & chains.

 

[DerekC]

I recall when commissioning the Seltrac system on Docklands Light Railway's Beckton Extension, the final check of the data tables against reality revealed that the platforms had been bult 5 metres too far west (or east - I forget which) and nobody had noticed, the station being pretty much in the middle of nowhere in those days. A speedy technical variation to change the software cured the problem!

 

[XAM2175]

At least, that's what a fellow-railwayman told me in a pub once. Can anyone corroborate this sad story?

Yeah that's tripe.

Moving the stops back would render the miles based measurements slightly out as well, surely?

Exactly. And even if it were true; since the buffers moved west at Paddington, they could have easily left the datum in the same place and declared that it was x metres east of the buffers - after all, the actual distance down the line from the exact current location of the buffers at any given time is totally irrelevant.