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July 2018

Know Your Capacity

How much lift capacity are you losing to inefficiency? It's easy to find out.

Written by Nils Ericksen | 0 comment

What’s your area’s lift capacity? Many resorts tout the hourly capacities of their lifts in their marketing. But the actual capacity is often less, and in some cases, far less. And that matters.

Many managers do not fully appreciate the difference between the actual uphill capacity (AC) and the original design capacity (DC) of any chairlift. Measuring the difference, and correcting the causes of a drop in capacity, is not simply a matter of efficiency. Maximizing the AC can cut operating costs, improve customer satisfaction, and even reduce the chances for lawsuits.

Most lift-related capacity shortcomings stem from a belief that dynamic, actual capacity is not measurable or, worse still, is of no consequence. However, learning how to measure and correct capacity shortcomings is fairly straightforward. That’s because most shortcomings stem from misloads, inefficient loading and unloading areas, and associated stops.

There is a simple method to determine the design capacity if you don’t already know it. First, there are 3,600 seconds per hour; divide that by the loading interval of the carriers (typically, six to eight seconds). That figure is the number of carriers that load per hour. Then, multiply that figure by the number of people each carrier can accommodate, i.e., two for a double chair, six for a six-pack. Thus, for a quad chair with a six-second loading interval, the design capacity is 3,600 / 6 = 600 carriers per hour x 4 = 2,400 pph. If that same quad chair uses an eight-second load interval, the design capacity is 3,600 / 8 = 450 carriers per hour x 4 = 1,800 pph.

But the actual capacity at an eight-second interval may be closer to, or even exceed, that of the same lift at six-second intervals.

It’s All About the Interval
Note that design capacity is not dependent upon rope speed, but upon the loading interval. Rope speed only determines how long the trip will take. For example: compare a fixed grip quad running at 400 fpm that’s parallel to a detachable quad running at 800 fpm. If both lifts operate with, say, a six-second load interval, each has the same capacity of 2,400 pph. The detachable is traveling at twice the speed, but the carriers for both lifts are passing through the loading and unloading areas every six seconds, so their capacity is the same. This magic happens because the detach carriers are spaced more widely—80 feet v. 40 feet, say.

Loading interval always controls the maximum capacity and the number of riders that can be loaded successfully within a certain time period. This is important to remember.

Several approaches can be used to create the maximum working capacity for a selected lift. For example, an area might organize the lift operation to fill every chair to its capacity. How many customers can be stuffed into the passing carriers within the shortest period of time? However, this approach almost always fails to achieve maximum capacity, because it focuses on just one aspect of operations.

To achieve the greatest efficiency, it’s necessary to design the entire operation—maze area, “wait here” area, and loading zone at the bottom, and at the top, the breakover point, unloading area, and runout—as a whole. It helps, too, to begin with a realistic loading interval and make minor adjustments as necessary to attain maximum efficiency. Often, the actual capacity will not be the same as the DC. The DC is a target and assumes flawless operation with no stops for any reason.

Factors affecting actual Capacity
Maximizing capacity and setting the loading interval depend upon many factors, not the least of which is the ability level of the skiers using a particular lift on a particular day. For example, experience has dictated over the years that a 10- to 12-second load interval works best for beginners, as it gives them time to reach the loading zone and prepare to load. For a lift serving advanced skiers, a six-second interval may well be possible.

To be realistic, design parameters such as interval and rope speed must always respect the lowest ability-level rider expected to use the lift. Also, remember that snowboarders may be unable or unwilling to occupy all seats available.

Other factors include challenging weather and, more generally, rope speed, on both fixed- and detachable-grip lifts. Although this may not seem relevant, high rope speeds can cause rider anxiety, not only during the loading but also the unloading process.
Perhaps the most prevalent but unrecognized capacity reducer is the unload area of fixed-grip lifts. That’s because the breakover point, where the rider must transition from the level unloading deck to the inclined discharge ramp (see diagram above), must be located properly, and that location must be maintained at all times throughout the day.

What makes the breakover point so critical? This point must allow the rider to stand up and gain enough speed to stay ahead of the carrier as it passes around the bullwheel. In addition, the ramp and outrun must accommodate the riders’ ability levels so they remain standing as they ski down the ramp without colliding with milling skiers in the outrun.

The location of the break point is reasonably specific. One rule of thumb: the breakover point should be at least six feet downhill from the bullwheel center for a double, seven feet for a triple, and eight feet for a quad. (See illustration, previous page.) Contact your lift manufacturer, if possible, for its recommendation.

Generally speaking, the wider the carrier and faster the rope speed, the more critical this point becomes. If the breakover point is too close to the terminal bullwheel tangent point, the riders’ exit speed is insufficient to allow them to clear the ramp prior to the carrier passing around the wheel. In addition, the outside edge of the carrier rotates at a faster speed than the inside and will, quite often, contact riders, causing them to fall on the ramp and forcing the operator to stop the lift.

During daily operation, the breakover point typically moves uphill, as tips of skis and boards pick up snow during touchdown and deposit it just uphill of the point. Be sure to reestablish the proper point before the lift opens the following day. (The best time to check for and correct the breakover point is summer).

Still other factors that can reduce capacity include seat height (refer to ANSI B77.1: 3 and, poor maze layout, poor preparation of snow surface in and around “wait here” locations, lack of pre-load organizing of riders, inattentive operators, and inadequate marshaling assistants. All deserve attention.

How to identify problems with any of these? Measure.

FINDING Actual Capacity
Measuring actual capacity is typically a manual exercise. The number of carriers that pass a certain point within a certain time—and the number of riders in those carriers—can be counted, and the totals collected, by using simple manual counters and a timer.

High-tech solutions can also yield useful results. For areas using LRFD readers, counting at the load gate provides actual numbers of users, which can be combined with other available lift data for a near perfect marriage. Using electric eyes on four-place “load gates” has, in the past, yielded reasonable results, if you track the number and duration of stops concurrently.

Any of these measurement methods will help reveal how often your lifts are stopping, and how effectively you are filling seats while the lifts are running. If you’re not operating close to the design capacity, find the weak points in the overall system and fix them.