Getting the full benefit of warehouses and DCs with narrow aisles and reach-for-the-sky racks requires equipment that's specifically designed for that environment. Examples include reach and stacker trucks, which keep the operator on the ground while the forks and mast rise to the required height for pallet putaway and retrieval; order pickers and turret trucks, which lift the operator into the racks for case or piece picking; and articulated very-narrow-aisle (VNA) trucks, which have front steering assemblies that pivot in either direction.
How high this equipment can go depends on the type of truck and the application, but the lift truck makers we spoke with for this story offer forklifts with mast heights ranging from 17.5 feet to 59 feet. Several said that customers are asking them to design trucks that can reach even higher.
Height has a big impact on lift trucks' design and performance, of course. Accordingly, there are several considerations warehouse and DC operators should be aware of if they want to get the most productivity from their tall trucks.VISIBILITY
When forks and pallets are 30 feet or more—often much more—in the air, it's difficult for an operator on the ground to discern exactly what's happening up there. The result is a slower operation; an operator who isn't 100 percent sure of fork positions will be cautious and may need a couple of tries to get it right. Poor visibility can also cause mistakes that result in damage to the racks, the pallet, or the product, which introduces more delays.
There are several ways to give operators on the ground an "eye in the sky." One popular solution is a camera mounted on the fork carriage paired with a video screen in the operator's compartment. This provides an eye-level view of the forks' position and angle, allowing operators to adjust and guide them like a doctor conducting laparoscopic surgery. They're especially useful when minimizing damage is a high priority, says Tim Forlow, senior product marketing manager at Crown Equipment Corp. He considers them essential for applications with double-deep racks. "Now you can see something you normally couldn't see while down on the floor," he says.
Camera systems are so beneficial, says Bruce Dickey, vice president sales for Narrow Aisle Inc., that his company has made them a standard feature on its high-lift trucks.
Another visibility-enhancing option is a laser-line projector mounted on the fork carriage. "The laser line shoots right into where the fork goes into the pallet opening, so the operator can see that more easily," explains Susan Comfort, product manager, narrow-aisle products for The Raymond Corp. A third option is a programmable shelf-height selector that automatically stops the forks at preselected heights instead of depending on the operator to visually assess when the forks have reached the right spot. Using all three of these tools together can significantly reduce the time required to pick or place loads.
Because a high-lift mast's components can obscure the operator's view of an elevated load, a mast design that tucks them out of the way is beneficial, notes Matt Barrow, product manager, warehouse solutions at Yale Materials Handling Corp. "Reducing wiring and electrical connections is not only good for reliability but also improves visibility, as does housing the cylinders and chains behind mast channels," he says.
Yale and several other lift truck makers have gone out of their way to address that concern in their narrow-aisle models. One example is Crown's MonoLift mast. The single-column design provides greater visibility than traditional two-column masts because operators don't have to look in between columns, Forlow says. In addition, positioning the mast to the side rather than in the center of the truck allows the operator to look past the mast rather than through it, providing a clear view at all heights, he says.SPEED
Operating cycle times (the total time it takes for the vehicle to travel to the correct spot and store or retrieve a load) for high-lift trucks are somewhat longer than those for conventional sit-down trucks. How big a difference is there? Dickey of Narrow Aisle points to this comparison of average cycle times for Class II narrow-aisle trucks with Class I electric rider trucks, calculated by the European Materials Handling Federation:
One factor behind this difference is the lengthy round trip the mast must complete as it's raised and lowered. Lift and lower speeds vary with the manufacturer and individual model, but man-up models typically go slower for safety. Furthermore, because an on-the-ground operator's sight line is restricted and tall masts sway a little while in motion, operators must wait for the mast to stop moving before they can pull or put away a pallet, adding more time to the cycle, says Perry Ardito, general manager for Jungheinrich's warehouse products group, North America.
Horizontal travel times are slower, too. A typical reach truck, for example, won't travel as fast as a counterbalanced truck will because it's specifically designed (right down to the tires) for moving up and down aisles, as opposed to long-distance transportation, says Tony Kordes, product manager for UniCarriers. "But what you lose in speed you make up in maneuverability in narrow aisles ... [so] it may take less time to reposition a pallet," he adds.
There are ways to compensate for slower operating speeds. For example, a man-up truck allows operators to pick both sides of an aisle, reducing total travel and raise/lower time, says Toyota Material Handling U.S.A.'s Cesar Jimenez, director, product planning, technical services, and warranty. Another possibility is to put order pickers on rails or guide wires, allowing operators to devote more attention to picking than they could if they had to steer as well. In addition, says Scott Carlin, national product planning manager, slotting fast movers down low and sequencing picks to minimize lifting and lowering can make a noticeable difference.CAPACITY AND STABILITY
Man-up trucks like turret trucks are heavy-duty in design, but the allowable load weights at maximum height can be less than those for a reach truck, Ardito notes. "The difference really is that a man-up truck is lifting the entire operator compartment plus the load. With a reach truck, you're lifting just the forks and the load." Still, he continues, man-up trucks often can be more productive than reach trucks because they don't have to make right-angle turns into racks; the forks themselves turn 180 degrees to pick either side of the aisle, he explains. (Articulating fork trucks also do that.)
Stability is another important factor in productivity, Ardito notes. "If there is any instability, it will affect the operator's confidence, whether that person is in the air or on the floor ... and if the operator lacks confidence in the truck, then it affects the operator's productivity." It's not just the truck itself that affects operators' confidence, he adds. Effective training and retraining play a big role as well.
According to Narrow Aisle Inc.'s Dickey, when it comes to stability, turret and swing-reach trucks have a disadvantage: neither their masts nor their carriages tilt to help compensate for the irregularities commonly found in warehouse floors and to limit the amount of sway in the mast at higher lift heights. As a result, they require perfectly flat, level floors. Because the front end of an articulating VNA forklift pivots, the load remains stable even on rough floors, he says. For his company's Flexi model, tilting masts are used up to around 400 to 420 inches; above that height, fixing the mast vertically and using a tilting carriage instead allows for higher capacity and better stability, he says.
Another productivity factor to keep in mind is energy capacity. It takes about four times more energy to lift a load to today's extraordinary heights than it would to lift the same load a short distance with a conventional electric rider that has a limited reach, according to Comfort. Designing exceptional energy efficiency into high-lift trucks, she says, is one way to avoid having to change the battery prematurely. Yet another approach, says Toyota's Jimenez, is to use equipment with bigger battery compartments that accommodate larger batteries—"It's like having a bigger fuel tank in your car," he says. He also recommends considering other alternative power sources, such as lithium-ion batteries and hydrogen fuel-cell batteries.FACILITY DESIGN
Getting more productivity from high-lift trucks isn't just a matter of how you operate the equipment itself. Warehouse design comes into play as well. To maximize productivity, Jungheinrich's Ardito suggests looking at a warehouse or DC as an integrated material handling solution, where the various components work together and affect each other. For example, racking and lift trucks are both components of that integrated solution, so it's critical for the trucks to have the most effective interface with the racks, he says. Precision is key. "We could be working with a client on a 500,000-square-foot facility to implement an effective lift truck solution, yet it often comes down to a matter of inches, especially with a VNA system involving order pickers and/or turrets," he observes. "Inches do matter for maintaining the integrity and safe use of the system, and for maximizing productivity and minimizing opportunities for unsafe practices."
Comfort agrees, citing the example of a lift truck provider's making sure that a rack provider "buries" the columns so they don't jut into a VNA truck's path. Other concerns include the heights of doorways, mezzanines, and pick modules as well as obstructions like sprinkler fixtures and pallet overhang (which could damage wires on a VNA truck's mast). It's also important to keep in mind that the actual height of the work area will include the height of whatever product is stored on the top tier of racks.
Failing to take these factors into account can be costly. UniCarriers' Kordes once encountered a facility that ordered new lift trucks without considering the height of the outriggers, only to find that they prevented the trucks from fitting into some of the racks. (Outriggers, also known as baselegs, are structural components that extend in front of either side of the mast to improve stability.) Outriggers should also be considered in tandem with aisle width, he says. "As lift trucks go higher, outriggers can go wider, and this can lead to 'aisle contention,' where two trucks can't pass in the same aisle," he explains.
Every operation's situation is different and should be judged individually, our sources agree. But there are some basic principles that can help to maximize the productivity of high-lift trucks of all types. First and foremost is to maintain a relentless focus on safety, including visibility, stability, and operator training. Another is to avoid treating forklifts as an afterthought. "People think that getting the building going and then inviting the lift truck dealer in is OK," says Comfort. "You really want them to go in earlier, before you lay out the racking and aisles, to determine what will work best." And be realistic: Extra time may be required for performing many tasks—a consideration that should be taken into account when measuring driver productivity and calculating throughput requirements.