Date: 11/24/2020
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True Vertical Lift: When Should You Choose A Single-Reeved Vs. Double-Reeved Hoist?
Across the industries we serve, we see examples of applications that have specific lifting needs – from precise placement of a load onto a pin or location, small capacity lifts of only a 1/2 ton or heavy lifting that requires rigorous and reliable components. And as facility managers begin to research the single-reeved and double-reeved hoist options that best suit their application, many have similar questions, especially around double-reeved hoist’s perceived value of achieving true vertical lift.
True vertical lift is necessary in some extremely precise applications, though through advanced design, single-reeved hoists can minimize hook drift and fit many applications where less precise lifting is sufficient. This is especially salient for projects where cost is a key factor; if your application can be safely performed using a single-reeved hoist instead of a double-reeved hoist, you can save 20-25% of the cost for new installs and an ongoing 40-50% savings for recurring maintenance.
Today we explore: What is the difference between a single-reeved and double-reeved hoist? What does true vertical lift mean? And which is right for your application?
Single-Reeved and Double-Reeved Hoists
Single-reeved hoists have one wire rope, which is attached to the hoist drum. To lift the load, the rope wraps around the drum as it lifts toward the high hook position. Single-reeved hoists cannot provide true vertical lift because of the horizontal movement (called hook drift) caused by the rope wrapping onto or off the drum as the hook moves up and down. However, the amount of hook drift associated with the drum depends on the diameter and length of the drum – for example, our Spacemaster SX® features one of the industry’s largest diameter drums, meaning we can achieve a longer lift with a shorter drum length. This reduces hook drift to just 1/8th of an inch for every vertical foot of lift.
Double-reeved hoists use two wire ropes on one drum, wrapping and unwrapping from the drum at the same time. Because the double-reeved hoist has two wire ropes that move toward or away from the center of the drum at the same rate, the hook stays centered on the drum and associated horizontal hook drift is eliminated. This allows for true vertical lift. True vertical lift is a hoist’s ability to pick up and place an object straight up and down, with no hook drift. In most cases, double-reeve hoists are ideal for either high capacity lifts or loads where exact precision is important.
Capacities
Single-reeved hoists: From 1/2 ton to 40 tons capacity
Double-reeved hoists: From 4 tons to 80 tons capacity
*SXL and DXW are only available as double-reeved hoists
Given these capacities, there are some lower capacity applications (under 40 tons) that could use a single-reeved hoist instead of a double-reeved hoist. Product features like large diameter hoist drums that significantly reduce hook drift can offset the need for a double-reeved solution, while still providing precision. If so, not only do you benefit from the lower initial cost of the single-reeved hoist, but this hoist is more compact, improving potential hook coverage.
Upfront and Recurring Costs
In addition to providing additional possible headroom, single-reeved hoists require half the rope that double-reeved hoists do. If you have a double-reeved hoist, rope replacement cost is doubled; instead of 43 meters of rope, you’d need 86 meters. Because rope is replaced every couple of years – or even more for frequently higher duty cycle – this can add to overall lifetime costs.
While many tend to associate single-reeved hoists with lower capacity, our large drum diameter design makes it an economical choice for capacities over 10 tons as well. For loads between 10 and 40 tons, hook drift of only 1/8th of an inch per vertical foot may be a safe and practical choice, especially if you have the ability to slow down and maneuver the load into place in the final inches of the lift. In this case, this means only millimeters of hook drift.
Precision Possible with Single-Reeved and Double-Reeved Hoists
To further illustrate the precision possibilities of the single-reeved hoist, let’s consider the Spacemaster SX's ability to reduce hook drift to just 1/8th inch of drift per vertical foot. Because this is relevant only to your lifting range, you are measuring drift in terms of the working low hook position to high hook position. This means that if your working range is just a matter of 3-5 feet off of the ground, there is still less than a half inch of working hook drift. For many applications, especially in lower capacity lifts where operators can move the load into the right position, this small amount of hook drift doesn’t inhibit any part of daily operations.
When could I use a single-reeved hoist? With a nearly imperceptible amount of hook drift, there are many applications in which a single-reeved hoist with a large diameter drum can safely perform your facility’s tasks, achieving near true vertical lift. If you have a lower capacity lift up to 40 tons, consider the benefits of a single-reeved hoist for your next project. With ongoing savings and a lower initial cost, plus a more compact design, it can be a very efficient solution.
When would I need a double-reeved hoist? The biggest case for a double-reeved hoist is when you need lifting capacity over 40 tons or if exact precision is key to your lifting operations. And in the case of very precise control needs, there are several other features to consider to improve your precision, including intelligent inverter controls that feature micro speed & inching.
Have an upcoming project and deciding whether a single-reeved or double-reeved hoist is the best solution for your lifting needs? Call us at 800-955-9967 to speak with an expert about your specific application, or contact us online to find a local distributor to help you.