ZF: Getting to the Root (Burn) of the Problem
ZF's work in helping Catalina Express solve its root burn issue helps to exemplify the company's evolution to that as a system supplier and performance as a solution partner. San Pedro, Calif.-based Catalina Express is a long-time ZF customer. The company's vessels provide yearround, daily scheduled passenger service to Avalon and Two Harbors on Catalina Island from San Pedro, Long Beach and Dana Point. Greg Bombard, President and CEO, Catalina Express, takes obvious pride in operating the self-proclaimed "greenest fleet in the United States," a claim made based on his investment in repowering the entire fleet starting late in 2000. The company takes great pride in its boats, specifically investing in the technologies, designs and equipment that are proven to increase passenger comfort and reduce downtime and fuel consumption. "The comfort factor is a key to Catalina Express," he explained, noting that each of the vessels has an active ride control system. Also key is keeping the boats running: "You never want to be tied to the dock," he said. A few years ago Catalina Express approached ZF Marine to help it solve an ongoing, severe root burn issue with two of its propeller-driven vessels. Root Burn is an erosion of the material at the base of the propeller blade due to poor hydrodynamic effects around the propeller, and the ferry operator had little luck in solving the issue. Enter ZF's in-house naval architect staff, which embarked on the process to help fit the four propeller-driven Catalina Express boats with propellers to aid propulsion efficiency and eliminate the root burn issue. ZF Marine supplied two sets of propellers for Catalina Express to evaluate. The ZF propellers, were smooth, increased speed and improved fuel economy; however, the propellers still had root burn, though to a lesser degree. Standard prediction methods for propeller loading did not indicate the presence of root burn and the occurrence remained somewhat of a mystery. An opportunity arose during a scheduled drydocking that allowed ZF personnel to inspect the hull bottom for other sources of root burn besides propeller design. The inspection revealed some hull issues that could contribute to the problem. ZF Marine suggested some hull modifications that were then implemented on one of the vessels. After a year in service the operator found the
November 2008
root burn issue was greatly reduced and the modification was made to the sister ship. During that year ZF Marine continued to investigate the root burn issue and developed new "in-house" theoreti-
cal methods to aid in the design of propellers resistant to root burn. "For over 25 years we have put serious performance demands on our vessels," said Bombard. "ZF Marine has been
with us all the way, always willing to work with us - right up to the engineering department at the factory, to maximize the performance and reliability of the propulsion systems in our fleet."
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