Hell on Keels
by Michael Valenti

Howard Arneson is the fastest 78-year-old on water at the wheel of the 46-foot Skater catamaran he designed. The craft is capable of reaching 175 miles per hour. The key to the Skater's performance is a customized Arneson drive using a propeller shaft made of a specialty alloy developed by Carpenter Technology Corp. of Reading, Pa.

The Skater catamaran relies on a propeller shaft made of high-performance alloy and a 4,500-horsepower gas turbine to cleave the waves at 175 miles per hour.

Arneson, whose boat works is based in San Rafael, Calif., pioneered the use of turbine engines on pleasure boats. He also invented the Arneson surface drive propulsion system that is made under license by Twin Disc, a transmission manufacturer based in Racine, Wis. This system runs with the propeller partly out of the water, and is widely used by racing boats, cruisers, patrol boats, and yachts. Arneson had built 16 gas turbine-powered racing boats prior to the Skater.

The inventor selected the 4,500-horsepower Lycoming gas turbine for his latest catamaran. This power plant is similar to the engines that lift the U.S. Army's Chinook helicopters. Arneson was determined to get the best performance out of the Lycoming engine by harnessing its horsepower to a single propeller shaft.

"We were applying three times the power load that's normal to one propeller shaft of this size. I guess, in a way, we were asking for trouble," said Arneson. Indeed, propelling the five-ton catamaran, laden with 1,000 gallons of fuel, out of the water at high speed put tremendous strain on its drive system.

Arneson approached Zeiger Industries, a Canton, Ohio, manufacturer of high-performance marine components, to make a durable propeller shaft for the Skater out of 17 chromium 4 nickel precipitation-hardening stain-less steel. This alloy combines high strength, hardness, and corrosion resistance. Zeiger crafted a finished shaft that measured 40 inches long by 21Ú2 inches in diameter in the center, tapering down to 17Ú8 inches at both ends.

The shaft was installed on the catamaran using a double cardon joint with a front-end drive, with the propeller located at the opposite end, and bearings at both shaft ends. After cruising for 50 hours at speeds of more than 100 mph, the shaft broke. It failed before being subjected to the shear forces of severe acceleration and the sustained record-setting high speeds that Arneson wanted to achieve with the Skater.

Don Zeiger, president of the company that made the propeller shaft, suggested that a new shaft be made from Custom 465 stainless steel, a premium-melted, martensitic (ferromagnetic) age-hardenable alloy developed by Carpenter Technology. The alloy is designed to reach a 260 ksi ultimate tensile strength when peak aged—that is, heated long enough to achieve the optimum hardness.

Carpenter supplied Zeiger with custom 465 stainless bar stock with a ground finish. The stock was solution annealed and cold treated, so it could be hardened in a single step.

Zeiger chose condition H1050 from Carpenter's heat treating schedule to provide the propeller shaft with the appropriate degree of hardness, strength, and corrosion resistance for powering the Skater through the waves.

Metal workers at Zeiger performed a series of turning operations to cut profiles on both ends of the shaft, threaded the propeller end and cut a spline on the other end to fit the transmission drive line. Zeiger's staff then ground the outer diameter of the shaft and shipped it to Arneson Research in San Rafael to be incorporated into the Skater.

Arneson refitted the propeller shaft and took his catamaran out on the ocean in December 1998. At first, the pilot idled the engine, then opened the throttle to accelerate to 100 mph in 12 seconds. Arneson gradually fed more horsepower to the catamaran, reaching 175 mph. For the next four months, he raced the Skater at high speeds without experiencing any problems.

After more than a year of service, Arneson examined the shaft, paying particular attention to where it engages the propeller spline. Unlike the previous shaft of 17-4 stainless steel, which bore marks indicating twisting due to the powerful torquing action, the custom 465 exhibited no marks at all.

"The spline was smooth," recalled Arneson. "It looked like it was never used. That gave me the assurance that I could run at high speeds for a long time without fear of the shaft breaking."

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