Jargon Pertaining To Marine Props

Posted by adairsawyer on March 1st, 2014

For a sea-going vessel to be able to perform to its optimum limit and serve its user over the years a sturdy and appropriate propeller is a must and this is the point wherein the importance of marine props creeps in. Nothing can prove this point more than an individual who has chosen a wrong propeller for his vessel out of ignorance or may be other reasons and is now suffering from engine trouble as also lack of performance of his vessel. An unspoken rule in case of boat props states that the vessel, engine and propeller are three points of a triangle wherein even a bit of impact on one renders the entire equation out of gear.

Education pertaining to marine props commences with understanding the jargon associated with it namely blade, slip, pitch, diameter, rake and cupping. While these are relatively easy to grasp something that most boat owners struggle to understand are cavitation and ventilation. When the surface of the propeller is dotted with pits which can eventually cause erosion to the point of causing the blades to snap, the phenomenon is referred to as cavitation. Likewise ventilation is said to occur when boat props either get caught in a pocket of air or suck air from above the surface of water. 

Occurrence of cavitation in marine props can be attributed to several reasons, the foremost amongst which is turbulence in the water surrounding the propeller. There are times when the propeller is over-loaded and this causes its blades to be covered with vapor bubbles in such a thick coating that it loses its contact with water and begins to revolve at very high speed. Formation of high and low pressure pockets also causes cavitation in boat props as does an uneven or improperly made hull surface or sudden appearance of a sharp object somewhere close to the engine. The outcome may be as mild as a pit or as drastic as causing the blade to fall of completely.

At times marine props spin within an air pocket instead of pushing water and causing the vessel to move on and when this happens ventilation is said to occur. High-mounted motor or sucking in the emitted exhaust gases are some of the reasons that cause ventilation to occur by forming an air pocket around the propeller. There are several ways of rectifying the situation and the one used most often by sea-men entails destruction of air pocket by reducing the speed of rotation and waiting for a couple of minutes. In bigger ships ventilation plate is provided to prevent the formation of air pocket so that boat props can function smoothly.

Given the importance of diameter-and-pitch combination of marine props, there are certain steps that are universally followed in order to figure out the perfect match and the process starts with determining the WOT, an acronym for wide open throttle. Next the vessel is made to run on calm water wherein its rpm is measured at maximum speed.  Accordingly, the pitch of the boat props can be raised or lowered till the optimum combination is reached. After having researched well on these subjects and gained awareness of jargon that marine equipment manufacturers use, you will be in a better position to understand propellers as they are.

Cavitation is an important part of terminology surrounding marine props because it impacts the life-span of the propeller and performance of the boat significantly. Another commonly used jargon concerning boat props is that of ventilation and knowing about it can enable boat manufacturers to be prepared for handling it when it happens.

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adairsawyer

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adairsawyer
Joined: April 9th, 2011
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