Prevents cargo movement during transit.
How do chocks work?
Wedge Power
Chocks are designed to be wedged tightly against a wheel or object, providing a strong and stable barrier against movement. The wedge shape allows them to distribute force effectively, preventing even heavy cargo from moving.
Material Matters
Chocks come in a variety of materials, each with its own strengths. Wood is a traditional choice, offering affordability and ease of use. Metal chocks, on the other hand, are sturdier and better suited for heavy loads or uneven surfaces. Depending on the application, rubber or composite materials might also be used for enhanced grip or protection.
Securing Different Cargo
Chocks are versatile tools that can be used to secure a wide range of cargo on various transportation platforms. They’re commonly seen on trucks, trailers, and ships, where they prevent containers from rolling during movement. In construction, chocks might be used to stabilize machinery or lumber.
Blocking and Bracing vs. Chocking
In heavy machinery shipping, chocking is rarely used alone; it is part of a system called Blocking, Bracing, and Chocking. While the chock stops the wheels from rolling, blocking involves nailing heavy lumber (often 4×4 or 6×6 timbers) into the floor of the shipping container or flat rack to prevent sliding.
If you are shipping a 30-ton dump truck on a Flat Rack container, simply putting a wedge under the tire is not enough. The ocean heaving creates massive G-forces. You must nail chocks into the wood floor of the flat rack, often using a doubled-up pattern where one block backs up another for added strength.
Nailing Pattern
For Out-of-Gauge (OOG) cargo, the National Cargo Bureau (NCB) or marine surveyors will inspect the chocking. They look at the nailing pattern. You cannot just drive a few nails straight down. Proper chocking requires nails to be driven at opposing angles to create a grip that resists pulling out. If the wood splits during nailing, the chock is compromised and must be replaced.
Rubber vs. Wood in Ocean Transit
While rubber chocks are great for parked vehicles on land, they are generally avoided for ocean freight unless they are bolted down. Rubber can bounce or slide if the deck gets wet or oily. Hardwood is the industry standard for ocean transport because it can be customized (cut to size) and nailed securely to the container floor.
However, all wood used for international shipping chocks must be heat-treated and stamped with the ISPM-15 mark to prevent the spread of pests. If you use non-treated lumber for chocks, Customs at the destination will reject the entire shipment.