Learn about propeller terms for your repairs from CompuProp's experts
Learn about propeller terminology for your repair
Improve your boat's performance and maximize its fuel efficiency with propeller repairs from CompuProp in Fort Walton Beach. Read about all the aspects that can affect your propeller. We've served the marine industry since 2003.
Fuel efficiency
We know that everybody wants to go further on less fuel, however, there are limits. In order to minimize the amount of fuel you use, and maximize your vessels' performance, there are two main factors: propeller efficiency, and engine load. If the propeller is not tuned and running efficiently, your fuel burn will be directly related.
Also, if your engine is overloaded (not reaching engine manufacturer's rated Wide Open Throttle RPM’s) you will also burn more fuel. We tune propellers to customer’s requests depending on what is most important to them: fuel burn, WOT speed, cruise speed, towing or heavy load applications, etc.
Propeller pitch, efficiency, and slip
Propeller pitch is how far the propeller tries to travel through the water in a single rotation. This means that if you have a 20 pitch propeller, theoretically at 100% efficiency it will travel 20 inches forward through the water in one full rotation. The actual distance traveled divided by the theoretical distance is known as propeller efficiency. The distance that was not traveled is known as the propeller slip.
Another factor to propeller efficiency is the blade shape. A propeller can look new and run smooth but still have an inefficient blade shape. With the help of Prop Scan equipment, we can check your propeller's blade shapes and tune them to make them more efficient.
Propeller vibration
The propeller is the first place you should check if you are experiencing vibration. There are many different possible causes for vibration: engine alignment, worn out bearings, bent propeller shaft, poorly seated taper, improperly installed nuts and keys, etc., but the propellers are normally the cause.
Propeller vibration could cause premature failure of bearings, unnecessary wear on electrical wiring, and overall irritation for you. Propeller vibration comes from blade pitch, blade shape, or propeller weight balance being out of tolerance.
View our propeller vibration repair photos .
Ventilation and propeller cavitation
Propeller cavitation burns from when the propeller is operating at high rotational speeds or under heavy load. The pressure on the upstream surface of the blade (the "suction side") can drop below the vapor pressure of the water, resulting in the formation of a pocket of vapor. Under such conditions, the change in pressure between the downstream surface of the blade (the "pressure side") and the suction side is limited, and eventually reduced as the extent of cavitation is increased.
Operating the propeller under these conditions wastes energy, generates considerable noise, and as the vapor bubbles collapse it rapidly erodes the propeller due to localized shock waves against the blade surface. This is most common near the blade root and we can repair this erosion.
A similar, but separate issue is ventilation, which occurs when a propeller operating near the surface draws air into the blades, causing a similar loss of power and shaft vibration, but without the related potential blade surface damage caused by cavitation.
Both effects can be mitigated by increasing the submerged depth of the propeller: cavitation is reduced because the hydrostatic pressure increases the margin to the vapor pressure, and ventilation because it is further from surface waves and other air pockets that might be drawn into the slipstream.
View our ventilation and cavitation repair photos .
Electrolysis in marine environments
alvanic action is the most common cause of electrolysis in the marine environment. Galvanic corrosion is the interaction of two dissimilar metals connected in an electrolyte (salt water). In this situation, the least noble (softer) becomes the anode and corrodes.
The nobler is the cathode, which in extreme cases can actually become coated with the anode metal. Metals can be connected through a bonding system or directly such as bronze prop to a stainless shaft. Thus, by adding a shaft zinc the zinc deteriorates before the prop.
Stray current electrolysis is a type of corrosion is caused by the stray electrical current being introduced most commonly from poor dock wiring. Generally, this is much more aggressive, causing a lot of damage in a relatively short amount of time. Electrolysis affects nibral and bronze propellers differently.
Typically when nickel-aluminum-bronze (Nibral) corrodes the aluminum leaches out of the alloy leaving irregular shallow pitting on the blade surface. In advanced cases, the blade edges become scalloped leaving them chewed up, or the face of the blade can get scaling leaving large depressions sometimes well over an inch in diameter. We can repair this by filling in the pitting, but it is very time-consuming.
Electrolysis causes a manganese bronze propeller to turn copper-red as the zinc leaches out of the alloy. In advanced cases, the blade edges actually begin to peel apart much like the leaves of a book. Prior to this, the propeller will cease to ring and only thud when tapped with a hammer. In copper based alloys once corrosion has set in it becomes almost impossible to weld the propeller. The metal has changed sufficiently that attempting to weld the affected areas only results in creating a larger hole. When the propeller reaches this point there is a good chance of slinging a blade and replacing the propeller is highly recommended.
View our electrolysis repairs photos .
