Skidder Mounted Logging Grapple

Hydraulic System Design

Skidder Mounted Logging Grapple

The skidder-mounted logging grapple is used in the forest products industry for bunching and retrieving harvested timber. The logging grapple, including both a rotary axis and double acting cylinders, is operated using the hydraulic system on the skidder tractor. The application includes very high and repeated shock loads and the operating environment is dirty and abrasive with large temperature variations.


Our challenge was to redesign a mature product that had been a standard in the industry but was too costly to manufacture and had new competition in the market. The requirements included reducing the cost of manufacturing by 20%, reducing the weight by 20%, improving performance with faster tong actuation speed and better log bundling ability, and addressing fatigue failures occurring after several hundred hours of service.

We redesigned the main housing to reduce stresses in the weldments while maintaining the essential operating geometry. We also reviewed the material properties of the steel in the original design and re-specified materials based on the stress calculations, redesigned pin joints and attachment methods, redesigned hydraulic cylinders to reduce size based on new operating geometry, and we interfaced with manufacturing team to ensure transfer of engineering intent.


This project was on time and on budget supporting our customer’s requirement to offer a refined version of an existing product.


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