A tight squeeze
In very narrow aisles, the right fit is what matters most in a lift truck.
By TOM FEARE -- Modern Materials Handling, 11/1/1999
While counterbalanced forklifts are the workhorses of many warehouses, those facilities where space is at a real premium often rely on a different class of trucks--very narrow aisle (VNA) lift trucks. They're the trucks for tight spaces.VNA refers to the dimension of the storage system aisle in which these trucks operate. Roughly, a VNA aisle is only 5 ft 6 in. to 6 ft wide. In more conventional rack systems with counterbalanced forklifts, there are typically 12-ft-wide aisles, which the workhorse requires for full maneuverability.
And just as VNA and counterbalanced models differ, not all VNAs are alike. In fact, there are four basic types of VNA trucks: turret models, which come in two flavors, man-up or man-down configurations; sideloaders; and moving-mast, counterbalanced trucks. Selection of one specific VNA truck model over another is part of a total system choice that involves vehicle performance and cost factors along with storage system parameters, and vehicle guidance issues.
Demanding cube utilization requirements often figure prominently in the selection of VNA trucks. For instance, when large numbers of pallets need to be packed into a confined area, easy access to these pallets is expected. That's a perfect opportunity for VNA trucks.
But there is more to VNA equipment selection than deciding that rack aisles will only be 66 in. wide and the distance between pallet pick faces will be minimal. It should be looked on as a system purchase. "There needs to be proper integration of rack and trucks," as one product manager for VNA vehicles says. And he includes guidance technology and floor surfaces into the trucks' component.
Depending upon how high can be "high" for your specific application, the system may require that the vehicles pulling and putting away those pallets be rail--or wire-guided for safety and insurance coverage purposes.
And some of these systems may function well only with very, very flat floors. Flatness will be measured in a variation of only 1/8th inch or so over a span of 48 in.
Often, VNA applications are in refrigerated or frozen storage where costs per cubic foot already run high because of the need for low temperatures. Here, maximum cubic capacity minimizes cooling expenses. High-rise storage may also offer product security benefits by making access to inventory difficult to all except authorized personnel.
It's worth pointing out that VNA systems aren't just for pallets. Or frozen foods.
Long loads such as pipe, lumber, and carpet rolls are candidates too. Metal handling and steel service center applications where tube, bar stock, coils, and similar goods are stored (see sidebar) are further examples of warehousing where VNA technology pays off. In these applications, VNA racking need not soar to dizzying heights to be cost effective.
Whether it's pipe or pallets to be stored, the technology, as one manufacturer's VNA product manager says, "isn't a one-size fits all proposition. Not every man wears a size 17-35 shirt."
There are a variety of solutions and trucks to consider, even within the purely pallet handling systems. Turret trucks and counterbalanced trucks with masts that swing or pivot will be among the choices confronting you. Turret vehicles, in particular the higher-rise, man-up trucks, may need to be teamed with more conventional forklifts for maximum productivity, moreover.
How high is high enough?
In conventional rack storage systems, roughly 60% of the space used will go to the aisles (around 12+ ft). In narrow-aisle systems (8+ ft) that percentage drops to around 48%. And in VNA systems (5 ft 6 in. to 6 ft) it's about 39%. Then, depending upon how high up the system goes, there's increasingly greater cube utilization with racking for VNA compared to conventional storage.
So one focus of VNA systems has been on those systems where "high" translates into storage at 6, 7, or 8 pallet positions up. That height compares to racking served by the more traditional counterbalanced forklifts where a height of 4 pallet positions "high" is about tops.
(Some VNA systems will go 12 or 13 pallet positions high, but specialized trucks or hybrid vehicles more like storage/retrieval cranes are necessary under these conditions.)
How high up your system can go also may be dictated by your property damage insurance company, as one VNA truck specialist notes. "Development of early suppression, fast response fire sprinkler technology has made life easier, however," he adds. With ESFR sprinklers protecting the goods below them, it's often possible to go higher, he explains, than with conventional fire sprinklers.
Check with local officials, however, who interpret building and fire codes. The codes vary, city to city, state to state, on what's legally feasible, what's not. Be aware that the stored product's potential to catch fire is a factor setting height limits as well.
Turret trucks up top
The most widely used of all VNA models is the turret truck. It features a fork mechanism that rotates 180 degrees, right or left, to work either side of the very-narrow aisle. The rotating mechanism is what gives the truck its VNA capability. Rather than having to maneuver the truck up to the pallet pick face as in a conventional counterbalanced vehicle, the forks rotate. Man-down and man-up turret truck models are offered.
Man-down turret trucks function more like their counterbalanced cousins. There are stability and safety issues to weigh here in the truck selection process when comparing man-down to man-up vehicles. With man-down operation, there's inherently greater vehicle stability, of course. But man-down operators may need load-positioning, shelf-height-indicating sensors, or special racking to assist them in load movements in pallet bays above the fourth or fifth level. Visibility to the top of the rack becomes a potential concern.
Man-down turret trucks do have a distinct advantage compared to some specialized counterbalanced, moving-mast VNA vehicles. The man-down turret truck models will work both sides of the aisle due to the turret attachment's 180 degree, side-to-side capability.
Riding up to the load level in a man-up truck and working some 40 ft above the floor presents some risks. The operator is tethered to the vehicle, to be sure, with a safety harness. Man-up operation offers certain advantages, however. The operator gets a bird's eye view (sidebar). Less damage to product, pallet, and racking is one benefit, product managers maintain. As man-up vehicles, the trucks can be pallet handler or case picker -- or both in a single model with some manufacturer's lines.
Indeed, the U.S. market for applications has been turning towards far more users opting for man-up turret trucks, manufacturers say, than man-down. And it's been a growing business as well.
Costs for man-up vehicles have decreased over the past ten years, attracting more potential users, says one manufacturer. A type of turret truck that sold for $100,000 in the late 1980s now has a price tag closer to the $60,000 to $70,000 range. "The business has grown four to five times what it was at the start of the 1990s," adds one company executive.
Yet cost savings these days in the man-up turret truck investment must be weighed against the expenses of guidance system technology along with the extra dollars to be spent if the vehicles will need to operate on super flat floors. VNA guidance of some sort and VNA flat floor operation tend to go hand in hand, particularly for higher rise, heavier load operation. Not all higher rise systems will need them, however; check with your potential truck suppliers.
A wire guidance package might add some $8,000 to $10,000 in costs per vehicle to the turret truck investment. Installing the wire in the center of the aisle floor may run $3 to $5 a foot. And putting in a class 200, super flat floor may add some $2 to $3 per square foot to building costs for the VNA warehouse.
It is also worth pointing out that turret trucks perform most productively within the aisle. Once the truck moves outside the aisles, however, you may want to have pickup stations for load transfers to handling by counterbalanced trucks, to conveyor, or to other delivery and takeaway methods.
Why transfer? Consider the basic cost/benefit issue here. In all likelihood, you'll have some $60,000 to $70,000 invested per high-rise turret truck. It doesn't make much economic sense to have that vehicle and its operator doing work outside the VNA racking that could be done by a counterbalanced truck at a capital cost of $20,000 per vehicle.
Multipurpose VNA vehicles
Vendors of two types of specialized vehicles with moving masts suggest that you weigh the multipurpose nature of their counterbalanced VNA trucks against the diminished versatility of turret trucks operating outside of the VNA aisle. Indeed, these vendors pose another question: will the turret truck application require an intersecting aisle 14 ft to 18 ft wide so the turret vehicle can make the transition from one VNA aisle to another?
There's little challenge to the argument that moving-mast vehicles are more versatile, more multipurpose. They pull and pick loads in VNA aisles, then can go to the dock and inside trailers.
But these vehicles are height limited in their operations. In general, they work with racks rising up only to 30 ft or so, sometimes less, depending upon model and load capacity.
Finally, the vehicles have one limiting feature: Their pivoting or swinging motion is only 90 degrees, and to the right of the direction of forward travel. Thus, to work both sides of the aisle they must make all the right-side picks or pulls, then reverse direction outside of the end of the aisle, and return to the aisle to work the remaining side or they back down an aisle.
This operational limit and tradeoff must be factored into your cost/benefit considerations. At a $53,000 to $60,000 purchase cost per moving-mast vehicle or swing-mast truck, initial investment is less of an issue in comparisons.
Finally, you will want to examine different models of turret trucks, sideloaders, and these special counterbalanced vehicles for a range of factors common to most forklifts. Included are cab ergonomics, operator controls, ease of battery charging and changeouts and maintenance/repair factors, and all the many other features, load capacities, and specifications that you would check into before selecting any forklift for your fleet.
Sideloading VNA trucks lift long loads
Metal distribution centers, lumber yards, plastics production, and other operations where the loads are long and/or bulky, and not necessarily palletized, are all candidates for rack storage using sideloading, very-narrow-aisle trucks. Coiled steel products in loads weighing up to 10,000 lb each are readily handled in the VNA application at a Midwestern steel service center, shown on page 48. Generally, rail- or wire-guidance will be required to keep the sideloading VNA vehicle on the straight and narrow path down the aisle. Rail-guidance tends to be more traditionally used in sideloaders compared to wire-guided turret trucks in high-bay systems. Operator-aboard sideloaders are the norm among the industry's manufacturers. Maximum rack system heights range up to about 30 ft, depending upon load capabilities of the specific VNA vehicle chosen.
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