Warehouse and distribution centre bosses are under constant pressure to make maximum use of all available storage space within their facilities. But extra pallet locations account for very little if aisle widths have to be reduced to the extent that forklift truck travel speeds and, therefore, efficient throughputs are sacrificed, says John Maguire , sales and marketing director of Narrow Aisle Flexi
With warehouse and distribution centre bosses under constant pressure to make maximum use of all available storage space within their facilities, it has become seen to be essential that the width of the aisles along which materials handling equipment and order picking staff travel around the store is kept to an absolute minimum.
Traditionally, the narrowest aisle widths were achieved by using VNA forklifts. VNA machines can – depending on load sizes – work in aisles as narrow as 1.4 metres wide because they turn only the load while other forklifts turn the entire vehicle in the aisle.
However, with the arrival in the early 1990s of the articulated truck – which also only turns the load in the aisleway – specifiers could obtain a forklift capable of working in narrow aisles but with the added capability of being suitable for use outside to load and unload lorries.
"When articulated forklifts were first introduced they were offered to the market as an effective alternative to VNA trucks," says John Maguire, sales and marketing director of Narrow Aisle Flexi – whose G4 electric VNA counterbalance truck is the most popular articulated forklift in Europe.
But, John Maguire believes that modern warehouse designers and some forklift truck manufacturers now place too much emphasis on achieving the narrowest aisleways and, as a result, safety and productivity can be compromised.
"Although I would be the first to acknowledge that the accepted wisdom when it comes to restricting aisle widths has certainly benefited articulated forklift truck sales, narrowing the aisles has become something of an obsession," he says. "Of course, companies like my own must take some of the responsibility for this; after all, we’ve been stressing the benefits of keeping aisle widths to a minimum for many years.
"In attempting to squeeze the highest number of racking runs into any given storage cube many companies are in danger of adversely affecting the efficiency and productivity of their forklift fleet.
John Maguire continues: "Quite simply, narrowing the aisleways restricts the speeds at which a forklift can travel between picking locations. When using an articulated forklift truck it might be technically feasible to pick up and turn pallets in aisles as narrow as 1.8 metres, but in applications where high throughputs need to be achieved, faster travel speeds are required. If there is insufficient clearance in the aisleway, then the speed at which the truck can be safely operated will be reduced.
"I recently visited a site where the articulated trucks in operation have no choice but to travel at less than half of their top speed within the aisles because the aisle widths are so narrow that there is very little margin for error on either side of the truck. This is clearly counter productive to any benefits the user may have derived by being able to add extra pallet positions by cutting the aisle dimensions."
Some years ago the British Industrial Truck Association (Bita) introduced Guidance Note 9 (GN9) – a guide that allows the minimum aisle width to be quickly and easily determined based on the type and combination of fork trucks being used.
GN9 has been adopted by all of the main forklift truck suppliers as the most straightforward and reliable method of configuring warehouse design and today the document is regularly consulted throughout the warehouse planning process.
Historically, the guidance laid down in GN9 has been endorsed for sites where traditional counterbalanced and reach trucks are in operation but, for facilities where articulated forklift trucks are working, the rules of GN9 haven’t always been applied.
In simple terms, GN9 outlines the ideal aisle width where a truck and a pallet can turn safely. For reach trucks, this measurement has always been calculated on the assumption that the pallet is at ground level when it is picked up and turned at 90 degrees in the aisleway before the load is raised.
Because articulated forklift trucks enter an aisle with the palletised load to the front (like a traditional counterbalanced machine) then articulate before turning the pallet through 90 degrees to put it away, they are able to operate in aisles far narrower than conventional reach and counterbalanced trucks.
"However," says John Maguire, "the most important dimensions when assessing the ideal aisle width for any operation involving articulated trucks to conform to GN9 is the distance diagonally across the pallet, ie, from one corner to another when a pallet is being rotated in the aisle. Safety clearance of 100mm either side (200mm in total) of a typical pallet will need to be added to ensure safe pallet put-away and retrieval. Flexi articulated trucks can operate in aisles as narrow as 1.8 metres, but in applications where a high throughput is required and where 1200mm deep Euro pallets are being stored, I would always say that the optimum aisle width is two metres. It is certainly worth remembering when designing any storage system that the use of Euro pallets is growing in the UK and increasingly companies need to plan for handling them as well as a traditional pallets."
John Maguire continues: "The regulation width for reach truck aisles is 2.7 metres wide but noone would design a storage system around 2.7 metre wide aisles because the trucks would be forced to operate too slowly. That’s why the majority of aisles where reach trucks are in operation – including most of the major supermarket RDCs – tend be 3 or 3.1 metres wide.
"Just because it is physically possible for an articulated truck to turn a pallet in a 1.8 metre wide aisle, doesn’t necessarily mean that it makes sense to set the aisles 1.8 metres wide."
"Of course, even by going to 2 metre wide aisles, an articulated truck is still far more space efficient than a reach truck. Articulated trucks are also faster than reach trucks and remove the need for double handling inside and outside the store."
"These are all reasons why the articulated truck concept has – and is continuing to have – a significant impact on reach trucks sales both in the UK and overseas. In fact, although articulated trucks were first introduced as an alternative to established VNA technology, the articulated truck concept is now regarded a highly credible alternative to reach trucks in more and more applications.
"Narrow Aisle is winning business by supplying solutions that allow maximum storage density as well as fast throughputs to be achieved. Our message is creating extra storage space is important, but it accounts for very little if truck travel speeds and efficient throughput have to be sacrificed in the process."