The Prop Shop

  • About Props
  • Prop Sizing
  • Prop Quotation Form
  • Prop Repair Pricing
  • Skeg Repair Pricing
 Contact Us

Rayplex Limited,
341 Durham Crt.,
Oshawa, Ontario,
Canada L1J 1W8
PH: (905)579-1433
FX: (905) 579-1431
info@fibreglass.com

Update Dec - 2002

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

     
 

About Props

 
 

Blade Back
Suction Side. Forward side of the blade (surface facing the bow).

 

Blade Face
Pressure Side, Pitch Side. Aft side of the blade (surface facing the stern).

 

Blade Number
Equal to the number of blades on the propeller.

 

Blade Root
Fillet area. The region of transition from the blade surfaces and edges to the hub periphery. The area where the blade attaches to the hub.

 
  Blade Tip
Maximum reach of the blade from the center of the hub. Separates the leading and trailing edges.

 
  Cavitation
Cavitation, (which is often confused with ventilation), is a phenoma of water vaporizing or "boiling" due to the extreme reduction of pressure on the back of the propeller blade. Many propellers partially cavitate during normal operation, but excessive cavitation can result in physical damage to the propeller's blade surface due to the collapse of microscopic bubbles on the blade.
There may be numerous causes of cavitation such as incorrect matching of propeller style to application, incorrect pitch, physical damage to the blade edges, etc...
 
  Cup
Small radius of curvature located on the trailing edge of the blade. This curved lip on the propeller allows it to get a better bite on the water. This results in reduced ventilation, slipping, and allows for a better hole shot in many cases.

 
  Diameter
Diameter is two times the distance from the center of the hub to the tip of the blade. It can also be looked at as the distance across the circle that the propeller would make when rotating. It is the first number listed when describing a propeller

 
  Hub
Solid cylinder located at the center of the propeller. Bored to accommodate the engine shaft. Hub shapes include cylindrical, conical, radius, & barreled.

 
  Leading Edge
The edge of the propeller blade adjacent to the forward end of the hub. When viewing the propeller from astern, this edge is furthest away. The leading edge leads into the flow when providing forward thrust.

 
  Pitch
Pitch is defined as the theoretical forward movement of a propeller during one revolution assuming there is no "slippage" between the propeller blade and the water. Pitch is the second number listed in the propeller description.

 
  Radius
The distance from the axis of rotation to the blade tip. The radius multiplied by two is equal to the diameter.

 
  Rake
Rake is the degree that the blades slant forward or backwards in relation to the hub. Rake can affect the flow of water through the propeller,
and as implications with respect to boat performance.

Aft Rake helps to trim the bow of the boat upward, which often results in less wetted surface area and therefore higher top end speed.
Forward, or negative rake, helps hold the bow of the boat down. This is more common in workboat type applications.

 
  Rotation
When viewed from the stern (facing forward): Right-hand propellers rotate clockwise to provide forward thrust. Left-hand propellers rotate counter-clockwise to provide forward thrust.

 
  Skew
The transverse sweeping of a blade such that viewing the blades from fore or aft shows an asymmetrical shape.
Aft Skew: Positive skew. Blade sweep in direction opposite of rotation.
Forward Skew: Negative skew. Blade sweep
in same direction as rotation.

 
  Slip
Slip is the difference between actual and theoretical travel of the propeller blades through water. A properly matched propeller will actually move forward about 80 to 90 percent of the theoretical pitch.

 
  Trailing Edge
The edge of the propeller adjacent to the aft end of the hub. When viewing the propeller from astern, this edge is closest. The trailing edge retreats from the flow when providing forward thrust.

 
  Track
The absolute difference of the actual individual blade rake distributions to the other blade rake distributions. Always a positive value and represents the spread between individual blade rake distributions.

 
  Ventilation
Ventilation is a situation where surface air or exhaust gasses are drawn into the propeller blades. When this situation occurs, boat speed is lost and engine RPM climbs rapidly. This can result from excessively tight cornering, a motor that is mounted very high on the transom, or by over-trimming the engine.
 
 

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