Weathervaning Explained: Why Cranes Spin in Storms

In almost every city across North America police receive calls about spinning tower cranes during storms and windy days. For many civilians, seeing a tower crane spinning around is really scary. Tower cranes already seem to defy some laws of gravity, standing so tall with seemingly no support system. Believe it or not, but this phenomenon is absolutely completely safe and normal. In fact, there’s even a name for it: Weathervaning. 

What Is Weathervaning for Cranes?

Weathervaning or “free slewing” is the practice of releasing the slew brake or parking brake on a crane. This allows the crane to rotate it’s full 360 degrees with the natural direction of the wind. This is actually used in other industries as well. Planes, windmills and boats all use the concept of weathervaning to move with the wind instead of fighting against it.

What Is the Purpose of Weathervaning?

The purpose of weathervaning is to prevent any damage that could be caused by the force of the wind. By allowing the tower – or plane, boat, etc – to move with the wind it removes the pressure and force that would otherwise cause excessive pressure on the structure, potentially even toppling it over.

Is It Common for Cranes to Fall Over?

Is it not common for cranes to fall over. When they do, it is almost always related to improper use, incorrect assembly or a bigger issue with the structure or foundation.  About 10% of crane accidents happen because of mother nature. 

Most of the time accidents related to cranes happen during set up or tear down of the equipment. Between 2011 and 2017 there were 297 crane-related deaths in the USA, over half of these caused by a “struck by” accident involving other objects or equipment. Falling debris, improper use of a crane, and improper setup are most common causes of accidents related to cranes.

Why Are Cranes Weathervaned?

Have you ever tried to open your car door against the wind? That feeling that happens when the wind catches your door and flings it open is exactly what weathervaning is hoping to prevent. Such intense pressure on a tall object could be dangerous and cause the tower to fall over. It all comes back to safety. 

How Do You Weathervane A Crane?

Cranes are weathervaned by removing the slew brake or parking brake when high winds or a storm is expected. The front jib is longer and heavier, meaning that it will move in the direction of the wind, helping to reduce the pressure put on the tower. 

Perhaps the most important step in weathervaning is surveying the surrounding area for debris that could be hit by a spinning crane. If high winds are expected, powerlines, signs and other types of debris could move into a contact zone of the tower. Being proactive in addressing these possible hazards is an important part of safe weathervaning.

Calling the Police Because of a Spinning Crane Tower

Every year, police across North America respond to calls about spinning tower cranes. While it is important to be aware of your community and report safety hazards, public education about what weathervaning is and why it matters can help reduce these calls. When a call is made to report a spinning crane, it involves both police and the contracting company to visit the site and respond to the call. 

If the crane operator is following proper procedure, then the crane will spin with the wind and do so safely.

Weathervaning or Free-Slewing Cranes

Whether it’s a spring storm or a windy fall night, a spinning tower crane should not cause any concern for contractors or the public. The process of weathervaning highlights the importance that all operators have on following proper procedures. This is especially true with cranes because incorrect use could not only injure contractors on site but the public as well. 

At the end of the day, knowing your equipment is key to keeping yourself and those around you safe – whatever the weather.