![]() ![]() The reason is that both are much softer than stainless steel, so function as the point of failure on a hard prop strike, protecting the much more expensive transmission and gearing from damage that might result with a stainless-prop strike.The 630 Super Sun Sport and her sistership, the 630 Sundancerset American sport yacht standards in their day for size and luxury. Nibral is stronger than bronze so the propellers blades can be made thinner and more efficient, somewhat like comparing a stainless steel propeller to an aluminum propeller on an outboard or sterndrive.īronze and nibral props are the province of larger yachts and offshore sportfishing boats, as well as inboard watersports tow and wake boats. The purchase cost of a nibral inboard propeller will be higher than bronze, as will repair work you may need done in the future. While nibral and bronze props look much alike, nibral is harder, stronger and more corrosion resistant. Nibral is an alloy of nickel, bronze, and aluminum. The Michigan Wheel DynaQuad prop for inboards is cast of bronze, relatively affordable and a softer material than nibral. A lower pitch or fewer blades means the prop’s diameter can be larger for a given power package. In general, adding pitch or blades means decreasing the diameter of a prop to allow a given engine to reach its recommended maximum rpm. For example, 16RH x 18 designates a 16” (40.64 cm) diameter right-hand propeller with an 18” (45.72 cm) pitch. These numbers are usually embossed into the barrel of the prop, with the diameter first, followed by the rotation direction and then the pitch. Twin-engine boats typically have counter-rotating props with the wheels turning toward the outside of the boat for each engine. Most props for single-engine boats are right-hand rotation. ![]() Rotation is the direction the prop is designed to turn, viewed from behind the boat. In this slip graphic from Mercury Marine, the dotted line shows the distance the prop would travel forward on each rotation if there were no slip, and the solid line shows the distance it actually travels due to slip. Conversely, a 2” (5.08 cm) decrease in pitch will result in a 300- to 400-rpm increase. In general, for outboard and sterndrive powered boats, a 2” (5.08 cm) increase in pitch will reduce engine rpm by 300 to 400. Higher-pitch propellers can push a boat faster provided the horsepower is matched to the prop so the engine can reach maximum recommended rpm. Pitch is the theoretical distance the prop would travel forward in one rotation if there were no slip. In other words, the larger the better on inboard displacement boats Pitch Propeller engineers tell us that it’s the most significant factor in propeller performance for boats running anywhere from idle speed to about 35 knots.Ī larger-diameter prop is more effective at controlling low-speed operation like docking where you need to stop, back up and kick the stern to one side or the other. The diameter of a propeller is twice the radius from the center of the prop to the tip of one of the blades. ![]() In general, the added blades also deliver smoother operation. (Mercury Marine)įive-blade up to eight-blade props are the province of larger yachts and work boats, designed to push very heavy displacement boats in rough conditions as well as to improve handling in the harbor. A high-performance 5-blade prop like this cleaver design is engineered to deliver impressive top speeds. ![]()
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