Curtain sider: The best of two worlds

It is safe to say that the concept of swapping a static sidewall for a flexible curtain originated in Great Britain in 1969. Congleton based company Boalloy turned the local market’s eyes to the new concept with the patenting of the “strap in a sheath” design, which added both strength and durability to the curtain sided lorry design used before.

At the time, PVC fabric was only available in a width of 1500mm, and the sheath or pocket created by welding vertical overlapping panels was Boalloy’s way to hide joins inside the curtain. Nonetheless, the market was slow to accept and understand the new configuration, although the benefit soon became obvious. Due to the movable curtain, it was now possible to unload freight from each side of the trailer. In addition, operators did not need to cover exposed freight anymore, reducing the risk of damaged cargo and injury.

The clientele, on the other hand, was now able to send freight in a safe and sound way, delivering an undamaged, clean and dry product. It is no surprise that the new level of versatility and increased utilization generated a huge economic gain, so demand continued to grow – and Boalloy began to offer the concept worldwide, calling it Tautliner.

In England, the concept was soon adopted by Eddie Stobart, a large multimodal logistics company with operations in the United Kingdom and across Europe. The influential company helped making the curtain sided solution acceptable in the industry, and it still uses it today.

Looking back, the curtain sider was the last all new design to enter the global stage. In a market that only knew either platform or van, it was a logical evolution as there was no solution for those who needed to perform both side loading and end loading. It is needless to say that the opposition was eager to implement the new technology.

In the late 1980s, Boalloy’s patent expired, and non-licensed manufacturers jumped at the chance to add the new design to their product range. In fact, there was a notable leap in curtain sider development as the industry began to fight for market share. New technology evolved, changing the fabrication process of curtains, buckles, front wind deflectors, roof constructions and curtain coatings.

Today, the curtain sider is a common sight. In sparsely populated regions with a small freight volume, it can operate with the versatility of a platform trailer and the efficiency and freight protection of a van. In addition, it does not demand any additional infrastructure such as loading docks, and there is a vast potential to tailor a highly specialised unicum.

Since the early Boalloy model, the design of the curtain has progressed from a load bearing, high deflection system to a high load, low deflection system. Current thinking is that load weighing on the curtain will destabilize the entire trailer, and that the load will intrude into oncoming traffic. Therefore, we now see curtains with steel, Kevlar, glass fibre and wire straps replacing the original, relatively stretchy seat belt webbing in order to reduce deflection and provide load restraint. In Australia, for instance, deflection has been reduced to 100mm at 0.8g, requiring a stronger roof and near zero elongation in the curtain straps.

As a matter of fact, the original buckle is facing extinction as well. It started off as a simple wire loop with an internal bar that would tighten the strap by folding it down. In the past decade, though, engineers have recognised customer frustration with the laborious task of buckling up curtains, and produced numerous systems to automate the process.

In the future, the curtain will be nothing but a flat panel with no hardware on the outside and no pillars on the inside. British trailer manufacturer Lawrence David, for instance, was just certified to the highest standard for a pillarless curtain sider trailer in accordance to European Union guidelines.

In order to meet the standards, the curtain sider had to undergo stringent stability tests, as well as load resistance tests to front, rear and side walls, conducted by the German TÜV authority. David’s new trailer uses standard load-bearing curtains with enhanced webbing, rollers and buckles, and a load restraining system named StrapSafe in combination and a new netting system called Scrimcloth.

Tech fact

The idea of a curtain that can combine weather resistance and load restraint is not new. Even Boalloy’s early version did restrain the load in case it bore down the curtain, but only to a certain extent. Interestingly, though, Boalloy already used double straps in the curtain sided containers they manufactured in the late 1980s, providing the basis for the all-in-one load restraint curtain as we know it today.

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