| Adapter Plate | "Adapts” and connects the powerhead of an outboard engine to the center section, and usually incorporates the exhaust tuner. |
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| Aerodynamics | Pertains to the forces generated by flow of air over a surface, used to lift the hull out of the water, also responsible for generating drag, among other things. |
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| Afterplane | A device that is attached to the anti-ventilation plate that increases its working area, thereby increasing its effectiveness. |
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| Anti-Cavitation Plate | See Anti-Ventilation plate. |
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| Anti-Ventilation Plate | The horizontal web or plate above the Lower Unit. It is intended to prevent the Prop from sucking surface air, Ventilating, into it and causing a Cavitation like effect. Useful on a deeply mounted outboard or drive unit. On high-performance or surfacing setups, it is of limited value due to it being out of the water while on plane. |
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| Backing Plate | Any type of plate that lies on the inside of the hull. It helps distribute the load from the fasteners over a wider area than otherwise covered by a washer. |
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| Blowout | Occurs when the ratio of air to water around the propeller gets so high that the propeller is no longer grabbing water, but is trying to propel itself through air (or a relative vacuum). This causes the propeller to lose "bite", and then a chain of events occurs that can range from merely a "loose" steering feeling, to a vicious turn to the right (typically). The speed at which this occurs varies with boat design, gear case design, and propeller design. |
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| Blowover | An inherent dynamic instability in high-speed powerboats, a potentially dangerous tendency to pitch up, when under significant aerodynamic lift. Often seen when they meet a wave or a wind gust they may suddenly flip backwards – or “blow over”. |
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| Blue Print, or Blueprinting | On an engine, it is bringing the specifications to a tighter tolerance range. On a Hull, it is the process of making the bottom straight for the entire running surfaces and bringing any edges to a sharp edge, especially the hull - transom interface. Check with manufacturer before removing hooks and rockers designed into the hull. |
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| Bucket or Bucketing | An effect like swinging a bucket of water over your head. The bucket is the helmet, the water your head, and the handle your neck. In this case, it works in reverse. The helmet tends to put more strain on your neck. See Helmet Restraint. |
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| Bullet | See Nosecone. |
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| Catch Can | Sometimes referred to as a “Puke Can”. Small tank that holds a “buffer” supply of fuel to prevent fuel starvation due to fuel slosh in the main tank. Sometimes used to return fuel for electronic fuel injection (EFI) systems. |
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| Cavitation | The formation of “voids” or air inside the water stream, caused by low pressure near a surface. Encountered when the water separates from the propeller. Also called “ventilation”; causes propeller burn, and can lead to “blow-out”. |
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| Cavitation Burn | Metal erosion on the propeller blades caused by air or gaseous bubbles on the positive side of the propeller blades. Usually caused by excessive ventilation of the propeller. |
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| Cavitation Plate | See Anti-Ventilation plate. |
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| Center of Gravity | The STATIC balance point of the deadweight of entire rig. Fore and aft, starboard and port. One of the most critical aspects of the setup; generally, a lower center of gravity is more desirable. Not the same as, and not as important as, the Dynamic C of G, which accounts for dynamic forces that are in play during all phases of operation. |
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| Center Steer | A hull setup that positions the steering helm (and driver) in the center of the boat, laterally. |
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| Chine Walk | Severe side-to-side rolling of the boat. It actually means to roll from chine to chine but it is also used for less severe rolling, although always severe enough to scare or cause a loss of control. Essentially, this is a characteristic of high speed V-bottom boats, where the boat is balancing on the pad or very bottom, further aggravated by the drag of the lower unit. Chine walking must be compensated for by steering input from the operator. |
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| Chopper Propeller | Also known as a “Round Ear” propeller. A high-rake propeller design utilizing rounded leading and trailing edges. This design is useful for V-bottom and heavier hulls that do not generate their own bow lift. |
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| CLE | “Crescent Leading Edge” lower unit. An older-generation Mercury high-performance lower unit with integral nosecone and low water pickups. There were two designs of the CLE, both offering the same performance. Designed for high-speed surfacing applications, and originally equipped on 2.4 Bridgeport engines. No longer in production. 2.0/2.4/2.5L applications only. |
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| Cleaver Propeller | A stern-lifting propeller design utilizing thin leading edges and square trailing edges, primarily used for stern lift/tunnel boats. |
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| Cone or Nose Cone | The foremost part of the gear case on a Lower Unit. It is also the after market add-on to create a longer aspect ratio out of the gear case. It is the location for the Low Water Pickups. |
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| Crab | The tendency of a high performance single engine boat to track to one side. The cause is surfacing of the propeller causing a paddle wheel effect. Can be noticed on dual engine boats that do not have counter rotating gearcases. |
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| Crossflow | A type of two-stroke technology.. The incoming fuel mixture is deflected by a dam on the piston and is forced up into the combustion chamber. |
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| Cup | Modified area of the trailing edge of the propeller that will and can affect hole shot and bow lift. |
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Powerboat Glossary