I'm closing in on finishing up my trackplan for my years in waiting basement empire. While fine tuning thngs and adding some of the flavor I want, I've run into something I've never really dealt with before. First, the background:
Nominally, the mainline is two tracks, with the exception of the hidden track that feeds into one of the staging yards. Originally, I had a curved turnout in the tunnel. Both mainlines feed into the same track going into the yard ladder. There are several reasons I did this, and it is compatible with my planned operational cadence (no train will ever be trying to enter the staging yard at the same time one is leaving). Access was not an issue, as it was only a few inches from the front edge of the layout and readily accessible when I made a test section of the layout. Easier to reach than, say, the headlight bulbs in my car. I did get a little edgy about having more hidden turnouts than I'd absolutely need.
Moving the turnout into the open got me thinking. Given that the track is going into a tunnel, I thought what if the tunnel was single tracked. The layout backstory has some engineering concern why they couldn't notch the tunnel or drop the floor to accomodate double stacked containers. I know that there are places that Conrail did this sort of thing (which is fitting, because my layout is NS territory that's ex-CR and exx-PRR). So, you've got a two track mainline pinching down to one, but centered on the common centerline of the two tracks as to fit down the center of the tunnel. The real trains call those equilateral turnouts, turns out. No pun intended.
As I went looking for wye turnouts, I noticed that most pre-made wye turnouts are the lone offering in their catalog or have fairly low numbers like a #3. I suspect that this is more like a #6 turnout, because you have two different angles working against each other in the frog number. From my sketching, it is my understanding that you'd have a small section of curved track between the turnout and two tangents. I do plan on running full length passenger trains, so this pinch point must accomodate them.
This is where we finally get to my questions. Are those curves going to be large enough that they're not really worth worrying about? Do I really need to worry about the frog number on a wye? Any S-curve considerations?
I can't answer any of your questions but Modeltrainstuff.com has 3's, 4's and 5's
https://tinyurl.com/24g99kzu
Henry
COB Potomac & Northern
Shenandoah Valley
Here's a good reference on layout turnouts:
http://www.pcrnmra.org/pcr/clinics/Kolm-TurnoutsWhatYouNeedtoKnow-PCR2008-handout.pdf
Rule of thumb as you point out is that a wye frog is essentially half the ratio of what a tangent angle frog would be.
16-30m by George Hamlin, on Flickr
Regards, Ed
The number on a wye track is going to be half of its equivalent of a regular turnout since the track diverges in both directions. A 3 is the equivalent of a 6. A 4 the equivalent of an 8. If I were planning to run full length passenger cars, I would opt for a 4 wye if you can fit it in although you could get by with a 3.
If you want to get fancy, you could opt for a gauntlet track. This is another means of pinching a double track main to run in a space of a single track. This explains it better than I could:
Gauntlet track - Wikipedia
It was done where double track replaced single track lines without having to rebuild single track bridges or rebore single track tunnels.
I don't know if commercial gauntlet tracks are made so you would probably have to scratchbuild them if you wanted to go that route.
I believe I've read a variation of the gauntlet track was used in double track tunnels to bring one or both tracks into the center of a tunnel so that hi-profile cars could take advantage of the higher clearance in the middle of the bore.