I find it intriguing that the American continent’s only native surface lift, the rope tow—arguably also the most efficient, highest capacity and most cost-effective ski lift ever built—could again play an important role in the operation of even the most sophisticated and high-tech ski resort. The function of the reborn rope tow would be to provide the simplest method of horizontal, or almost horizontal, skier transportation on skis and on the snow.
Not every ski area has the need, but many do—the need to provide, for instance, consistent skier transportation between two base areas; crossing such flat terrain as the meadows at Squaw Valley; transportation between parking lot and base area; between condominiums and lifts; to restaurants along flat ridges, as in Vail’s bowls (see also article on page 68). Many solutions have been tried, from school buses to steam engines.
Now, with some satisfaction, I would like to describe a new (patent pending) conveyance—is it a surface lift or is it a tow? The Utah tramway authorities would like to know! Or is it, as locally named, a “Yan Tow” which we have developed with the substantial assistance of Onno Wieringa, Russ Hamer, Les Fuller and “Monty” Bob Montgomery at Alta Ski Lifts in Utah?
It replaces the crosstow, familiar to many, which connected Albion Basin with the Collins/Wildcat base. Probably the most bizarre of all tows—and probably the most successful, this ropetow provided an essential link by transporting an estimated 15 million skiers in the last 30 years. Two thousand feet long, with eight international towers and a vertical rise of 90 feet, it was powered by a 25 HP electric motor, and operated at a speed of 833 feet/minute. Originally built by Chick Morton, Buck Sasaki and Hans Brogle in 1962, it was later equipped with a snatch block hanging off the rope weight, at the suggestion of Ed La Chapelle. The skier had to let go of the rope in front of the snatch block hanging off the tower crossarm, and using his/her momentum, regrab the rope on the other side of the block. If the skier failed to released the rope, the hand bumped against the block, pulled the plug and stopped the lift.
Actually, the crosstow enjoyed a surprisingly good safety record, but violated many requirements of the present safety codes, and due to the high number of stops, never offered a continuous high capacity. I had been challenged by Chick Morton and Buck Sasaki for over 20 years to come up with a better design. Finally, last spring, after Onno Wieringa threatened to confiscate my car keys until I produced the idea came.
I decided to use a modified quad chair grip and attach it to a 1-1/4-in., 6X25 rope tensioned to 25,000 lbs. This extra rigid grip (the YAN 10), with elongated jaws and non-flexible body-needle configuration, is able to transmit substantial torque without being pulled off the rope. The rigid grip/hanger connection was obtained by welding the bushing housing, located on the grip body, to the hanger pipe. (All other grips known to me have a pivoting connection between the grip and the hanger.)
[Photo] Yan Tow can be loaded and unloaded at any point and can be ridden in both directions. [Photo] Alta’s GM, Onno Wieringa, checks up. [Photo] Yan 10 grip with rigid connection between grip and hanger.
By clamping a hanger which cannot swing back to the highly tensioned chairlift haul rope, we provided a system of 104 “sky hooks” with a piece of tow rope attached to each. Those hangers are seen and felt by the towed skier as the “individual propulsion means” mentioned in the box—only with a running start and following the same ski track.
A 1-in. extra flexible, polyethylene rope was attached to the hanger through a “T clamp” and the hanger-rope connection covered by a foam bumper. Several shapes of hangers are being tested presently, as are the methods of covering the clamp, the height of the rope and the amount of rope slack between the hangers. “We’re into the sort of second generation testing that is typical when something totally new is developed,” says Wieringa. The lift has been tested at speeds ranging from 450 to 850 feet/minute. Having logged about 150,000 rides by the middle of December, Wieringa pronounced he was “very happy,” adding that “it’s just what we have been looking for: a reliable transportation system that just keeps going round and round. No challenges like before—just boring!”
[Photo] Connection protected by foam bumper. [Photo] Tow tested at capacity up to 3,000 PPH.
The comfort of grabbing the rope is high, since the tow rope tension is not accumulative. Up to three skiers fit comfortably between the hangers, spaced at 48 feet. The installation is powered by a 75 HP DC regenerative drive. The terminals and all line towers are height adjustable (16 ft.) using two horizontally mounted, 25-ton jacks. The jacks are operated by two synchronized 5 HP motors. Line tower crossarms and carriage supporting frames are connected to the screw jacks by 3/4-in., 6X37 IWRC ropes.
The height adjustment is done at a speed of 18-in. per minute. Two symmetrical, horizontal guide ropes prevent crossarms from misaligning. The entire lift line and both terminals are raised daily to allow easy grooming of the skier track by groomers using standard equipment. The line sheaves are YAN S-4’s, assembled in two sheave rockers equipped with rope position detectors (RPD’s).
The large rope bellies between the hangers are easy to load, and allow removal of the T-grip connection from the “head reach” zone.
Obviously, the tow can be loaded in both directions and at any point on the line. Significantly, operation without attendants on either terminal is conceivable.
[Schematic, p53] The terminals and all line towers are height adjustable. Line tower crossarms and carriage supporting frames are connected to screw jacks. (Elevation diagram labeled R.T. = return terminal at left, D.T.T. = drive tension terminal at right.)
[Photo] Legendary Alf Engen, 84, takes test run. [Photo] Adjustable line tower with horizontal crossarm guide cables. [Photo] Return terminal (left) and drive tension terminal (right). Tensioning is hydraulic. The installation’s drive is 75 HP DC regenerative.
Technical Specifications
- Slope length: 2,482 ft.
- Vertical rise: 108 ft.
- Max. rope speed: 850 FPM
- Max. capacity (3 skiers/rope belly): 3,000 PPH (approx.)
- Haul rope dia.: 1-1/4" 6X25 Fiber Core
- Tow rope dia.: 1" Extra Flexible Polyethylene
- No. line towers: 6
- No. torque hangers: 104
- Drive: 75 HP DC Regenerative
- Bullwheel & line gage: 11 ft.
- Max. rope tension: 25,000 lbs (hydraulic tensioning)
The Physics of Forces
The force needed to move the skier on snow at a steady speed can be determined by the formula shown in Fig. 1.
- F = Pulling force
- Q = Weight of skier
- α = Slope angle
- μ = Coefficient of friction
F = Q × sin α + Q × cos α × μ
Figure 1: free-body force diagram of a skier on an incline, showing the pulling force F (horizontal), the weight Q, and the slope angle α.
we assume a coefficient of friction of .03 (between the average groomed snow surface and reasonably flat and parallel skis) the pulling force F in the function of slope angle is illustrated by Fig. 2. The force needed to accelerate the skier from a standing position to 700 FPM (11.6 ft./sec.) depends on the acceleration rate and the mass of the skier. This is demonstrated in Fig. 3.
When looking at these figures, the limitation of pull lifts is quite obvious. The higher speed and steeper slopes are comfortable only for kids. For adults, a push lift is a must. The Push Lift (J-bar, platter and T-bar) pushes the skier, while the Pull Lift utilizes the skier holding the rope, bar or handle with his own hands.
The oldest pull lift is probably mom or dad, or on a more industrial scale, a reindeer or horse; and more recently, rope tow, Mini-Mite or the like, a snowmobile or snowcat. The “individual propulsion means” with standing starts is the most convenient pull lift, but capacities are limited and the cost-per-ride prohibitively expensive.
Rope tows are efficient, but have several major disadvantages: 1) They can provide an efficient, continuous ride only between terminals or line towers, thus imposing obvious length restriction; 2) Rope spin is difficult to control, posing serious hazards from the potential for loose clothing and hair to being wrapped around; 3) Holding onto the smooth, wet rope tensioned to about 500 lbs. is difficult; and 4) Maintenance of the snow surface directly under the rope is difficult.
Figure 2 (“Holding Force vs Incline”): Holding Force (lbs, 0–70) vs Incline (%, 2–30) for Male Skier (180#), Female Skier (140#) and Child Skier (65#) — holding force rises with incline. Figure 3 (“Holding Force vs Acceleration”): Holding Force (lbs) vs Time to Accelerate to 700 ft/min (1–6, with a secondary acceleration axis in ft/sec² from 11.7 down to 1.9) for the same three skiers — holding force falls as the acceleration time lengthens.
