Reverse Engineering an Anchor Handling System on the USS Harpers Ferry

摘要

This paper describes the process of reverse engineering a malfunctioning anchor handling system on the USS Harpers Ferry (LSD 49). There are two anchor handling systems at the bow of the ship, one on the port side and the other on starboard. The starboard system worked properly, but the port system didn't. Instead of seating properly into the pockets of the port wildcat, the anchor chain began to ride-up on the wildcat whelps after six shots of chain had been paid out. Once this had occurred, the chain could not be let out any further because of the danger that the anchor and chain would fall uncontrollably. Several changes were made over the years to the system in an attempt to fix the ride-up problem. However, these changes made little or no improvement in the operation of the system, and in some cases made it worse. Two approaches were used to analyze the problem. One approach used empirical evidence to determine the cause of the problem and recommend a solution. The other method was to reverse engineer the system using 3-D CAD and Mechanical System Simulation software. Due to the complex geometry of the wildcat, its surfaces were mapped using a 3-D digitizer to obtain accurate dimensions. The data was then used to create 3-D CAD surfaces that could be easily measured and compared to the wildcat specifications. Dynamics models that recreated the ride-up phenomenon as seen on the port wildcat and proper operation as seen on the starboard system were constructed. The dynamics model was used to analyze the cause of ride-up and evaluate different approaches for eliminating it. This model also gives insight to the nature of ride-up and is a tool that can be further developed in the future to model other anchor handling systems.