Metlab, Wyndmoor, Pa., has provided heat-treated propeller blades for a hydroplane racing team located in Cinnaminson, N.J. The treatment was subject to the H-900 condition (900\u00b0F\/ hours at heat) and was age hardened in a vacuum furnace to ensure that the parts were free of scale.<\/p>\n
A modern unlimited hydroplane is the world\u2019s fastest racing boat, capable of speeds greater than 200 mph. A typical unlimited hydroplane can weigh a minimum of 6750 pounds. All unlimited hydroplanes are a \u201cthree-point\u201d design, meaning they are designed only to touch the water at three points when racing \u2013 at the rear of the two front sponsons (the projections of the hull in front of the driver cockpit) and the propeller at the rear of the boat. Most of the unlimited class boats are powered by Chinook helicopter Lycoming T55 L7 turboprop engines, generating up to 3000 HP.<\/p>\n
The propellers must meet strict design criteria imposed by the Union Internationale Motonautique (or \u201cUIM,\u201d headquartered in Europe), not only for propellers but for the entire boat design. The propellers are typically 16\u2033 in diameter and have three blades. Different pitch propellers are chosen for use based on course length, conditions, and starting position. It is not uncommon for a racing propeller to cost more than $15,000.<\/p>\n
The high tensile strength (200 KSI) produced by the heat treatment keeps the blades from shearing apart; the excellent ductility associated with the heat-treated material allows the propellers to withstand the RPM and torque conditions without failing. And hardness of HRC 40 protects the blades from impact with potential debris in the water. 17-4 PH stainless steel properly heat treated also benefits from increasing torsional fatigue strength, a common cause of propeller failure.<\/p>\n