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A  Selecting the right propeller is an important factor in maximizing your boat's performance, while allowing it to operate in the recommended rpm range.  Determining the correct size and style of prop will keep the engine from over-revving, while allowing it to achieve the maximum horsepower at the lowest rpm's. 

NOT ALL PROPS ARE THE SAME!

Size - Props are described by referring to diameter and pitch.  Diameter is twice the distance from the center of the hub to the tip of any blade.  Generally smaller diameter props correspond with smaller engines and boats or higher speeds.  Larger diameter props correspond with larger engines and boats or slower speeds.  Pitch is the forward movement of a propeller through one complete revolution.  Pitch can be thought of as speed.  The higher pitch prop the engine can turn, the faster the boat will usually go. 

Number of Blades - Sufficient blade area is needed to properly distribute engine power across blade surface.  Too little blade area causes high "blade loading", which means the prop can't absorb all the power transferred by the engine.  With increased blade are you can decrease the blade diameter, but often with less efficiency at higher speeds.  A 3-blade prop is considered the best combination of blade area and low blade loading.  When the number of blades is changed, diameter and pitch may require a minimal adjustment to remain in the safe blade loading range.  For most purposes 3 and 4-blade props can be used interchangeably on outboards and sterndrives (I/O) without much of a change in performance. 

Material - Propellers are made of either composite, aluminum, or stainless steel.  Composite props are good, durable, and inexpensive.  Aluminum props are the most common.  They are suitable for the widest range of applications.  Stainless steel props offer higher performance and better durability. 

Cupped Propellers - Special curved trailing edges enable the prop to cut through the water better.  Cupped props allow most boats to achieve a higher top-end speed or at least the same speed at a lower engine rpm.  They also promote more efficient fuel consumption. 

Wide Open Throttle (WOT) rpm Range - When selecting a prop, the goal is to choose one that allows the engine to reach its optimal WOT.  This is generally between 5000 and 5500 rpm, depending on engine type.  This information is usually included in the owner's manual of a new boat or engine. 

If your current prop's performance is within manufacturer's WOT guidelines, choose a replacement prop which duplicates the diameter and pitch of your current prop. You might consider upgrading to a different material such as stainless steel. 

If your current prop is unsatisfactory - What if your engine operates at the wrong rpm at WOT?  Pitch and rpm have an inverse relationship.  Increasing pitch reduces rpm and reducing pitch increases rpm.  A 1" change in pitch will result in a 200 rpm change in engine speed.  Therefore, if your engine operates below the proper rpm, consider a propeller with less pitch.  If your engine over-revs, consider increasing the pitch. 
You might also consider changing the propeller size to affect a specific performance attribute. A lower-pitch power prop makes it easier to pop skiers out of the water.  Tournament bass boats may need more top end speed and should use a prop with a higher pitch.  Houseboats and cruisers care more about efficiency at displacement speeds, therefore they require a lower pitch to achieve low-end power and the largest diameter their lower unit can handle. 

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3 or 4 Blades?
A 3-blade propeller usually offers top speed performance while a 4-blade propeller provides maximum thrust and smooth cruising operation.
 
 
 
Diameter:
Diameter is the distance across the propeller from blade tip to blade tip. Calculate the diameter of the propeller by measuring from the center of the shaft hole to the tip of a blade and then multiply by 2. (Example: a Propeller measures 7 1/4 inches from the center of the shaft to the outermost tip of one of its blades. The diameter = 7 1/4 X 2 = 14 1/2 inches)
 
Pitch:
Pitch is the distance a propeller will move through the water for each revolution. For example, a 21" pitch propeller should move a boat forward 21" each time it rotates, assuming there is no slippage.
 

Right Hand or Left Hand Rotation:
This refers to whether the propeller rotates clockwise or counter-clockwise. In most cases, right hand propellers are used for single engine applications, and both a right hand and a left hand propeller are used for twin engine application to achieve better steering control.
 
Cupped Blades:
This is a technique used to enhance the performance of propellers under certain conditions: a cupped propeller will exhibit very high efficiency at high speeds as well as minimize cavitation under heavy loads. To determine if you have cupped blades, feel the blade tips of your prop. They should curve upward on the edges.
 
Rake:
Rake is a special design feature. Positive rake benefits from normal bow lift to permit the use of a larger diameter propeller, while negative rake can provide extra blade strength for use in very high speed application. A propeller with 20 degree rake has blades that meet the propeller shaft at an upward 20 degree angle
 
Quality boat propellers
 
Additional propeller replacement considerations:
Year, brand, model and horsepower of your exisiting motor.
 
What is the current propeller's diameter? (see Diameter heading)
 
Aluminum or Stainless Steel?  
 
Type of boat do you have? Cruiser, Ski, runabout, bass, pontoon...
 
Choosing the right propeller for your boat can be one of the most important choices for a boat owner.  There are manufacturer websites available designed to help you determine the best propeller for your boating application based on specific information, but it is always a good idea for you to check with Captain and your local dealer.

A All you need to do is have the right tools, some help from a few friends and you will soon be sailing and having fun.
What You Will Need: New Propeller,Ratchet Set,Gloves,Socket Wrench,Prop Puller,Marker or Pencil
 
Step 1 – Buy a New Propeller
Take a trip to the local boat supply store and buy a propeller for your boat. There are two types of propellers; steel and aluminum. It is better to choose the steel propeller as it will last longer than the aluminum propeller. Though it is a bit more expensive, it is worth the investment.
 
Step 2 – Buy a Prop Puller
Pick up a good prop puller at the supply store as you will need this to remove the old propeller easily. A prop puller can save you more than half the time if you try to remove the propeller with your hands.
 
Step 3 – Mark the Position of the Old Propeller
Take a marker or pencil and mark the position of the old propeller before you take it off. This will help you know the correct position to install the new propeller.
 
Step 4 – Mark the Location on the Propeller Shaft
Mark the position of the old propeller on the shaft so that you will know how far the new propeller should go on the shaft.
 
Step 5 – Loosen the Nut
Begin to loosen the retaining nut to remove the old propeller. Use the ratchet and turn one blade at a time. Remember not to loosen the nut completely. In case the propellers get stuck, you can use the prop puller to remove the blades. This will make the job easier.
 
Step 6 – Remove the Propeller
Once you have loosened the retaining nut and the propeller is loose, remove the old propeller from the shaft by pulling it off.
 
Step 7 – Check for Damages
After removing the old propeller, check the shaft for any damages.
 
Step 8 – Check the Key Way
Check the key way for any damages before installing the new propeller.
 
Step 9 – Unpack the New Propeller
Unpack the new propeller from its package and keep the nuts ready.
 
Step 10 – Install the New Propeller
Slide your new propeller onto the shaft taking note of the course of the key way.
 
Step 11 – Position the Propeller
Use the markings you made earlier in step 3 to align the new propeller. Make sure your new propeller is in the right position and the right place on the shaft.
 
Step 12 – Fix the Nut
 
Once the new propeller is in the right place, use a wrench to tighten the nut onto the shaft. Make sure the nut is tightened well. That’s all that you need to do to get your new propeller fixed on your boat. Happy Sailing!

 

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