Bluebell Northern Extension - so what's occurring then?

Don't you mean yards. Tom?

 

Forgive me o Lord, for I have sinned... :smile:

Tom

 

With the trackbed raised, is the clearance now such that the track has to go through the middle of the arch? Obviously with the cutting only single track there will never be any need for a double track alignment under the bridge again, but was just curious.

 

Well, it could become part of an alternative London to Brighton line; then double track would be required.

Was the Bluebell line originally double track throughout? I should know, but I don't.

 

East Grinstead to Horsted Keynes only.

 

@Man of Kent: Between EG and KC, double track is already precluded by the narrow section north of KC, then by the fact the cutting hasn't been fully excavated in places, then by the bridge, then by the realignment of track away from the edge of Imberhorne viaduct, and finally by only having one platform at EG. So, yes, the Hill Place Farm bridge will now only allow a single track, but in practical terms it makes no difference.

@nanstallon: yes, the whole railway - both EG to Lewes and HK to the junction with the Brighton Line was built for double track, though the HK to Culver Junction section - on the way to Lewes - was only ever laid with one track.

As for whether it will ever be a suitable diversion when the BML is shut - not really my field of expertise, but the general opinion from those more knowledgeable, including some career railwaymen, is that the forecast is for flying porcine creatures...

Tom

 

He was quite correct. One of the myriad oddities of the imperial system was that yards were never used for vertical measurement.

 

The standard measure was Cubits
and for weight it was the Firkin

Too Firkin heavy etc

 

I thought beer was measured in Firkins, about 9 gallons if my memory serves me correctly. I should know as they were heavy to carry round the ship when we couldn't get the smaller casks. I blame NAAFI.

 

I realise that this section never can be double track again so it doesn't matter, I just wondered what the clearance at the bridge was. I assume Imberhorne lane Bridge will be the same.

 

I'm not 100% sure but I think the bridge at Imberhorne Lane was a little bit higher so might still be OK. All a moot point of course!

Tom

 

Latest official update from Chris White, courtesy the Bluebell online newsletter:

 

Actually, looking at the pictures, I suspect the height of the bridge was based on the height (relative to the track) of the road and track (for the two bridges, respectively) which the bridge carries over the track; i.e. they didn't just gratuitously make the bridges much higher than they needed to be to clear the trains, they just wanted the roads to be level going across the track.

I'm not sure why they made the cutting that deep, though - maybe they were really focused on minimizing the amount of climbing the trains had to do - or perhaps they wanted to minimize the height of the viaduct to the north of the cutting, or something like that?

Noel

 

Yes, sorry, sloppy drafting by me! Obviously, didn't mean to imply they would wilfully build anything bigger than it needed to be, but rather fitted the bridge to the road it had to carry. A similar example is Three Arch (Nobles) bridge, south of HK, which is very high.

I suspect it was probably about maintaining a single ruling grade. Before the Bluebell started mucking about with things :smile: the steepest gradient anywhere else on the line was 1:75. So a deeper cutting maintained that grade. Obviously, if you have one small section of line at a steeper gradient than most, it effects the motive power you need and loadings along the whole line - witness the issues around e.g. the Lickey incline, requiring special working arrangements. So in that case, it is better to spend more on construction to save future running costs.

Tom

 

Ha anyone done the sums to establish whether the Bluebell's collection of vintage engines will be able to surmount the new gradient with more than just a single carriage? (or perhaps I should say even a single carriage?). I really hope this new gradient is not so challenging as to preclude the little engines from doing their share.

 

Haven't seen official figures, but here is a very rough calculation. My feeling is that we will be increasing the strain on locos, but our core sets we currently run would probably still be possible without change.

Our current load limit for our smallest regular passenger engine is 70 tons trailing load for a P class, which weighs 28.5 tons. That is based on a current maximum gradient of 1:60.

New steepest gradient is 1:55 - that means roughly 60/55 increase in gravitational resistance of the whole load (loco + train). So new load limit would be 55/60 * (70 +28.5) = 90.5 tons. Take off the weight of the loco and you are left with a useful load of 62 tons with the same working margin of available TE to gravitational load. (Assuming rolling resistance doesn't change).

So a cut in 8 tons of actual load. That would allow a two coach vintage train (e.g. a 100 seater + birdcage brake) but maybe not adding on a 4 wheel first, which we did sometimes in the summer. (That was 72.5 tons, i.e. 2.5 tons over our supposed load limit, but not a major problem).

A Terrier (which has more TE than a P class) is allowed 80 tons, which equates to the 4 Mets; that will probably end up being too much unless the current load limit has been deliberately set at a conservative figure.

The E4 I think is currently allowed 150 tons normally, but 185 tons at the discretion of the relevant director and workshop manager. Loco weight is 57 tons. So doing the same calculation gives 133 tons normally / 164 tons with discretion. Probably still allows a core 4 coach mixed Bulleid / Mk 1 set under normal conditions, i.e. no practical change from now.

Tom

 

A quick bash on the calculator shows that an 'on spec' P has the TE to drag about 120 tons up a 1 in 55 but, at what speed? A 60 ton payload at a sustained 20 mph is going to need about 200hp. I'd say that a P's continuous rating is going to be more like 100hp but steam locos aren't as simple as that. It's a relatively short grade and can probably be overcome without too much winding.

I've no speed /TE curves or other info necessary to come to a more accurate conclusion.

Edit,
Tom's post above largely agrees with my conclusion. I'd have thought that a Terrier would be up to more than the BB currently allow as they've a fair bit more TE than a P. Boiler limitations, perhaps?

 

For our Terriers at least, Stepney is so mechanically frail that she is effectively on "special duties" and limited to a load of one carriage.

For Fenchurch, the increase in TE over a P class would suggest a load limit much greater than 80 tons. However, I suspect water capacity would come into play, i.e. our small locos could safely move bigger locos on our gradients while keeping to time, but may not have enough water capcity to get from one end of the line to the other reliably while doing so. Certainly I have seen on occasion a P class take our 3 coach Wealden Rambler set which is theoretically way over the weight limit, so I suspect the limit is deliberately conservative if only gradients were considered, but is chosen to mean that even an "average" fireman can do the job and still have a useful reserve of water capacity. Remember, when setting load limits, you have to think not "what could an excellent fireman do with an engine in prime condition when nothing went wrong", but "what could a novice third man do with an engine due a washout and near shopping for overhaul do on a day when everything conspires against you..."

Certainly I have been on 323 with a load of 72.5 tons (i.e. over our nominal limit for the current line) and done a round trip of the line and still had about a third of a tank left when getting back to SP, having not taken water at KC. So I think the current limit is probably fairly conservative, though I doubt anyone will be going all the way to EG on a small engine with a big load and choosing not to take water when they get there!

Tom

 

Compared with the Isle of Wight the Bluebell "Terriers" do seem to have an easy existence although mechanical condition is obviously a factor. A round trip on the IOW involves ten miles between water stops although the air braking may (I don't know if this is actually so) consume less water than the vacuum system.

Paul H.

 

For Fenchurch at least, you have both the vacuum ejector and in addition a Westinghouse pump running all the time for the locomotive brakes, so that is more running than on the IoW. Plus you have to think about steam heating for some of the year, which is another drain on the boiler - the load limits are based around a worst case scenario, i.e. on the assumption you are also drawing steam for heating. So I suspect we are being conservative to make sure we have plenty of spare water capacity, rather than running right up to the loads that theoretically the engines could manage on our gradients.

Tom