Alta loading every other chair - what does this accomplish?

powderstudpowderstud intermediate
A quick scan suggests that the best skiing in the country is right here in the East, for a change.  I noticed on Alta's website that because of the thin snowpack, they are loading only every-other chair with skiers.  I assume this is to put fewer people per hour on the mountain. 

As a question for the numerous Mountain Ops folks who visit Snowjournal, can someone explain the logic behind that for me?  Wouldn't it be better (and cheaper) simply to run the lifts slower?  Or to just tell skiers that the skiing currently sucks (a 25" mid-mountain base at Alta is completely sucky--it only starts getting good at around 50").  Is there a better explanation than the one I'm assuming?

Comments

  • lotsoskiinglotsoskiing expert
    Posts: 927
    No idea, but man, those web cams are depressing.
  • LiftGuyLiftGuy advanced
    Posts: 147

     As a question for the numerous Mountain Ops folks who visit Snowjournal, can someone explain the logic behind that for me?  Wouldn't it be better (and cheaper) simply to run the lifts slower?  Or to just tell skiers that the skiing currently sucks (a 25" mid-mountain base at Alta is completely sucky--it only starts getting good at around 50").  Is there a better explanation than the one I'm assuming?

    Simply put, lifts are engineered to run at a certain speed- "design speed". When you slow them down, the electric motor is less efficient and can use more current (electricity=$$). Also, the carriers are designed to travel around the bull wheels at design speed and when you slow the lift they lose the centrifugal force needed to keep them in the proper plane which causes them to swing in as they enter the bullwheel and out as they exit. This causes empty carriers to swing on the down hill side which can contribute to sheave flange contact, contact with the sheave assembly or in extreme cases contact with the towers.
    My experience is running the lift at design speed is the most efficient.
    The other factor is you would double the ride time- don't think anyone would like that!
  • joshua_segaljoshua_segal expert
    Posts: 1,946
    The Castlerock Chair at Sugarbush has about double the normal chair spacing to reduce traffic on the pod.  

    Reducing the speed creates a customer comfort issue, by doubling the length of the ride.
  • powderstudpowderstud intermediate
    Posts: 43
    Thanks, LiftGuy!  That was really helpful and interesting to learn. 
  • ciscokidciscokid expert
    Posts: 1,875
    LiftGuy said:

     As a question for the numerous Mountain Ops folks who visit Snowjournal, can someone explain the logic behind that for me?  Wouldn't it be better (and cheaper) simply to run the lifts slower?  Or to just tell skiers that the skiing currently sucks (a 25" mid-mountain base at Alta is completely sucky--it only starts getting good at around 50").  Is there a better explanation than the one I'm assuming?

    Simply put, lifts are engineered to run at a certain speed- "design speed". When you slow them down, the electric motor is less efficient and can use more current (electricity=$$). Also, the carriers are designed to travel around the bull wheels at design speed and when you slow the lift they lose the centrifugal force needed to keep them in the proper plane which causes them to swing in as they enter the bullwheel and out as they exit. This causes empty carriers to swing on the down hill side which can contribute to sheave flange contact, contact with the sheave assembly or in extreme cases contact with the towers.
    My experience is running the lift at design speed is the most efficient.
    The other factor is you would double the ride time- don't think anyone would like that!
    I'm going to liftguy if I got questions, heck w Ibrake4tbars. Sounds like Mapnut ⛷⛷
  • joshua_segaljoshua_segal expert
    Posts: 1,946
    I'm not sure if what LiftGuy said was true: Bromley, Killington and I am sure others, run their HSQs at less than full-speed on weekdays and at low volume times. I assume it is to save money as well as the wear and tear on the haul-rope going around the bull-wheel.  If it were less efficient to run it slower, I suspect they wouldn't.
  • CannonballCannonball advanced
    Posts: 154
    I don't know what's up at Alta. And I don't know much about lift mechanics. But as a customer I would MUCH rather ride every-other at full speed versus every chair at half speed. Being on the lift exposes you to the elements more, exposes you to being stuck on broken lifts, limits your options, etc. So if they are really making that choice, they are making the right one.
  • LiftGuyLiftGuy advanced
    Posts: 147

    I'm not sure if what LiftGuy said was true: Bromley, Killington and I am sure others, run their HSQs at less than full-speed on
    weekdays and at low volume times. I assume it is to save money as well as the wear and tear on the haul-rope going around the bull-wheel.  If it were less efficient to run it slower, I suspect they wouldn't.



    First- On a detachable lift the carriers don’t go around the bull wheels, so you are correct that the chair swing is not an effect.
    As for running at reduced speed, the savings they are looking for is related to wear and tear on the moving parts which are obviously more numerous and more expensive on a detachable. The difference in efficiency between 80% and 100% speed on a detachable may not affect a large areas total consumption by a large amount.
    The question was about a fixed grip lift running at 50% of design speed.
    Hope this helps-
  • obienickobienick expert
    Posts: 1,008
    From my limited knowledge of ops, it's my understanding that no lift runs at its design speed.  Every lift is run slower for either maintenance issues (limiting cycles for detachable grip rebuilds) or for ease of loading/unloading of fixed grip lifts.  Seems many/most lifts run ~50 fpm less than what's advertised in the published specs.
  • patrick_torsellpatrick_torsell intermediate
    edited December 2017 Posts: 22

    I'm not sure if what LiftGuy said was true: Bromley, Killington and I am sure others, run their HSQs at less than full-speed on weekdays and at low volume times. I assume it is to save money as well as the wear and tear on the haul-rope going around the bull-wheel.  If it were less efficient to run it slower, I suspect they wouldn't.

    It depends entirely on the type of lift. I think LiftGuy was referring specifically to the OP's scenario at Alta. In that case, he's right: fixed-grip lifts are not meant to be run at slow speeds for extended periods. Detachables are a different animal. Since the carriers are not on the line at the terminals, the speed factor is irrelevant in that sense. In fact, running detachables at a slower speed means fewer grip cycles, and therefore less wear & tear.

    With respect to energy efficiency, it depends on the type of motor and drive. An old AC wound rotor induction motor would use resistor banks to reduce speed, making slow operation excessively inefficient. Long-term slow operation is even dangerous due to resistor heat. Until relatively recently ('05-ish), most big lifts were powered by DC motors with SCR (thyristor) drives. With these drives, power factor suffers when high torque is required at low speeds (high current, low voltage). In more modern large lifts, variable frequency drives power AC motors and can supply 100% torque across all speeds. These motors/drives can be operated efficiently at any speed.

    Anyway... there's a lot to it. In simple terms, fixed grip lifts like to run near their design speed. Detachables are more flexible about slower operation over long periods.
  • joshua_segaljoshua_segal expert
    Posts: 1,946
    LiftGuy said:

    I'm not sure if what LiftGuy said was true: Bromley, Killington and I am sure others, run their HSQs at less than full-speed on
    weekdays and at low volume times. I assume it is to save money as well as the wear and tear on the haul-rope going around the bull-wheel.  If it were less efficient to run it slower, I suspect they wouldn't.



    First- On a detachable lift the carriers don’t go around the bull wheels, so you are correct that the chair swing is not an effect.
    As for running at reduced speed, the savings they are looking for is related to wear and tear on the moving parts which are obviously more numerous and more expensive on a detachable. The difference in efficiency between 80% and 100% speed on a detachable may not affect a large areas total consumption by a large amount.
    The question was about a fixed grip lift running at 50% of design speed.
    Hope this helps-
    It does help.  Thank you.
  • Frers33Frers33 novice
    edited December 2017 Posts: 9
    Snow preservation, top of Alta home page and from first hand experience,

    Not much natural snow terrain open and it is slick in spots on snowmaking trails. 



  • 210210 intermediate
    Posts: 21
    I was there last week and it the "every-other-lift" loading seemed to work well.  The few trails that were open weren't that crowded.  Less crowded than the few open trails at Deer Valley the day before.
  • obienickobienick expert
    edited December 2017 Posts: 1,008
    I'm having a hard time believing that.  If you can't run FGs slow for extended periods, then how did ski areas run scenic lift rides in the past (and still today in some places)? You have to have slow enough rope speed for foot passengers to load/unload. Usually 150-200 fpm.
  • newmannewman advanced
    Posts: 278
    Every scenic lift ride I went on including amusement parks was faster than 200 fpm
  • teighsteighs intermediate
    Posts: 73
    A lot depends on how the speed control is achieved.  On the t-bars at Hogback various resisters were switched in line with the motor to change the speed, but it didn't do anything for the amount of power being used.

    Many lifts use hydraulic couplings, again the motor runs full speed, no energy savings.

    More modern speed control systems utilize VFD's here because power if a square function, slowing the motor does save energy.
  • patrick_torsellpatrick_torsell intermediate
    edited December 2017 Posts: 22
    obienick said:I'm having a hard time believing that.  If you can't run FGs slow for extended periods, then how did ski areas run scenic lift rides in the past (and still today in some places)? You have to have slow enough rope speed for foot passengers to load/unload. Usually 150-200 fpm.

    It's not that you
    can't. It's just that it's less than ideal to run a fixed-grip lift for extended periods at very low speeds. The only type of lift that you really can't run on slow for too long without unnecessary risk is a lift driven by a resistor-controlled AC wound rotor induction motor. DC SCR drives/motors are fine running slow. AC VFDs are happy running slow. As for chair swing and other fixed-grip concerns, it all depends on the design of the particular lift. Each lift is a very specialized chunk of engineering. Some are designed with downloading and slow summer operations in mind. Some are retrofitted for that purpose. Some were designed only for full-speed uphill loads. This isn't one of those topics where you can paint with a broad brush and say definitively that lifts
    can or cannot operate at a certain speed. It depends on the lift.
  • LiftGuyLiftGuy advanced
    Posts: 147

    obienick said:

    I'm having a hard time believing that.  If you can't run FGs slow for extended periods, then how did ski areas run scenic lift rides in the past (and still today in some places)? You have to have slow enough rope speed for foot passengers to load/unload. Usually 150-200 fpm.

    It's not that you can't. It's just that it's less than ideal to run a fixed-grip lift for extended periods at very low speeds. The only type of lift that you really can't run on slow for too long without unnecessary risk is a lift driven by a resistor-controlled AC wound rotor induction motor. DC SCR drives/motors are fine running slow. AC VFDs are happy running slow. As for chair swing and other fixed-grip concerns, it all depends on the design of the particular lift. Each lift is a very specialized chunk of engineering. Some are designed with downloading and slow summer operations in mind. Some are retrofitted for that purpose. Some were designed only for full-speed uphill loads. This isn't one of those topics where you can paint with a broad brush and say definitively that lifts can or cannot operate at a certain speed. It depends on the lift.

    +1



  • ciscokidciscokid expert
    Posts: 1,875
    I should stay out of this one but in layman's terms I would say let the ski area that runs their own liftsrun them the way they think best, whichever it is economically and safely ,that's all got to say
  • Stan51Stan51 novice
    Posts: 9
    I just got back from Alta.  They were loading all of their running chairs at every second chair intervals.  The stated, and probably real reason, was snow preservation. I think the high speed lifts were also running at less than full speed,  probably 80% of normal weekend speeds.  There was plenty of terrain open, especially when compared with Snowbird, but when venturing off the snowmaking pistes, you did have to be a bit light on your feet in places.  Brush was more of an obstacle than rocks, but there were definitely rocks. The snowmaking slopes were pretty slick in places, but well covered.
    I understand that they will open the new Supreme lift this weekend.  No snowmaking on that terrain, but I am told that there is enough natural snow.
    Interesting that they bombed some of the snowmaking whales with hand charges, just to make sure they were stable,.
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