07.10.2016

Retractable windsail for tower cranes

UK rental company Select Plant Hire and Industrial Design Consultancy (IDC) have co-operated to develop a new retractable windsail for luffing jib cranes working in tight urban locations.

The new windsail, which is rather like a curtain that stows in a rigid cassette and extends when required, allows cranes to achieve a smaller out of service radius while maintaining full weathervaning effectiveness. With the advantage that it does not compromise the crane’s performance when operating within raised- but allowable - wind speeds.

With a smaller out of service radius, contractors can also install more cranes on a single site, possibly equip cranes with longer jibs or locate them closer to boundaries.

Select approached IDC to find a solution, the two companies brainstormed possible concepts, before IDC went off to develop a number of ideas, the most promising of which were subjected to a full risk analysis and to understand how they would react at varying wind speeds and loadings. Once a concept was selected, the engineering team produced detailed CAD models, selected materials and undertook finite element analysis to understand the stress resistance of the design and ensure the system was able to withstand large forces.

Finally a working model was produced with the help of 3D printing. The production engineers then manufactured and assembled ‘windsail kits’ - each comprising around 3,000 components, including electronic controls and aluminium extrusions of up to 8.6 metres in length. The prototypes were then installed on a crane at Select’s depot in St Neots, Cambridgeshire, and tested in real wind speeds exceeding 100kph.
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Another view of a luffing jib with two windsails fitted but retracted

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The luffing jib with the two windsails deployed

Select engineering leader Steve Bradby said: "It's common in the UK that cranes aren't allowed into the air space above an adjacent property, an issue especially prevalent in city centres and next to high-rise urban developments where space is tight. In these instances, luffing jib cranes are often the only solution, as they have jibs that can be raised and lowered enabling them to manoeuvre within a site boundary or around nearby obstacles such as buildings or other cranes etc. When the crane is not being used, it is critical, in order to limit the stresses on its structure and achieve increased heights, that the upper part can rotate freely – to ‘weather vane’.

The windsail is essential to generate the force required for the crane to weather vane correctly when the jib is parked at a steeper angle and ensure the crane is left safely overnight. Until now, luffing crane windsails have been made from rigid materials such as steel. Unfortunately a large fixed sail can make the crane difficult to manoeuvre in windy conditions and we recognised that if these windsails were made retractable, the cranes would have much greater productivity."

The following video demonstrates it perfectly

IDC director Ryan Fenton added: “We are delighted to have developed a product which has such a powerful impact on the productivity of cranes. This project relied on expertise across the whole of IDC and demonstrates how diverse our capabilities are, from design and engineering, right through to prototyping, testing and production. The new product has already been shortlisted for a British Engineering Excellence Award and we look forward to seeing further success commercially.”

The new windsails have already been used in Manchester and are currently fitted to cranes in London. At one particularly compact site on the capital’s south bank, 21 cranes are in use, with 17 of them requiring retractable windsails. IDC has manufactured 32 individual windsails to date for four different Terex tower crane models.