Greenwich Park - this geometry can't be right, can it?

[Lacathedrale]

 

In an attempt to fill a pretty dull evening in a hotel I thought about working out the templot overlay for Greenwich Park terminus - it had an unusual throat,  and a pair of symmetrical three-way turnouts - one of the strangest things appears to be the turnout highlighted below - with less than a 1:4 crossing angle:

 

The original OS grid map link is here; https://maps.nls.uk/geo/explore/#zoom=18.65666666666667&lat=51.4785&lon=-0.0100&layers=168&b=1

 

After some poking around I can get it to an A4 but it still seems like a pretty intense curve. The middle track would only have been used for locos running around (and at that only aged 1860's 0-4-2 tanks - which were fitted with push-pull apparatus and thus just shuttled in and out of the bays).

 

The rest of the geometry fits fine into B6 and B8 turnouts - but this one is a real doozy. Am I doing something hilariously wrong?

[Siberian Snooper]

I wouldn't take to much notice of the OS geometry, they are notorious for getting  it wrong, they are more interested in boundaries. The black line just beyond the template, I think indicates the toe of the turnout.

 

 

[Siberian Snooper]

Take a look at the 1:1056 map and see if it's any better.

 

https://maps.nls.uk/view/101202513

 

 

[Clive Mortimore]

Looking at the point in question it is a Y point so with both lines curving away from each other you will have a greater crossing angle and a shorter length of point.

[Guy Rixon]

When Greenwich Park was laid out, the 0-4-2 engines were not working motor ("push-pull") trains. That came later, under the SECR. On a model of a later period, you might be able to avoid running round, but the full-size railway definately needed to do it 

 

Also, a Sturrock 0-4-2 has a very long, rigid wheelbase, so will not be happy on the tightest curves. As Clive points out, the crossing angle is great because both roads curve, but the turnout radii will be more important.

 

For comparison, some inner-London layouts really were too tight for the stock. Mansion House, pre-electrification, was notorious for near derailments, particularly with the rigid 8-wheeled coaches of the Met. Railwaymen reported the Met. stock lifting clear of the outer rail on the curves into the bays and then falling back on again. Only extreme slow speed saved matters.

[eastglosmog]

Bear in mind that the relative accuracy of a 1/2500 map is only +-1.9m over 100m now - it was worse when that map was drawn up - so it probably is not accurate enough to tell the difference between a 1:4 or 1:8. 

[jim.snowdon]

Looking at your Templot plot, if you reduce the angle of the turnout labelled TR013, you will find that the  turnout on the centre road, whilst still a Y will become flatter, at the same time moving its switch tips closer to where they are marked on the underlying map. The radius will change quite significantly for what appears to be a rellatively minor change.

 

Jim

[Lacathedrale]

Thank you all for the very astute observations - I'll review and report back shortly