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Boat Propeller Advice & Tips

A boat propeller is the most 'technical' component of a boat as well as one of the most critical to the overall safety and performance of a boat. Therefore, taking the time to select the right propeller is important and will ensure you get optimal enjoyment out of your boat.

How to Test a Boat Propeller Performance

When you have the right propeller and it is working properly, your boat engine will run within the manufacturer’s designed RPM at Wide Open Throttle (WOT). If that is not the case, you may need a new propeller. Here is how to test your propeller performance:

  1. Make sure your gas tank is full but overall load in your boat is lighter than normal (e.g. do not go out with the maximum number of people on board)

  2. Warm up your boat for at least 5 minutes to ensure your engine is properly warmed up

  3. Find a wide open piece of water with little to no other boat traffic

  4. Give your engine full throttle and get it up to maximum speed

  5. When at maximum speed, note and record your RPM

If the RPM at full throttle and speed is outside of (either below or above) the manufacturer's recommendation, it is time to shop for a new propeller.

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How to Select a Boat Propeller

Are you satisfied with your current prop performance (apart from any damage that may be requiring you to purchase a new prop)?

  • If "yes"... your job is easy - simply order the same propeller again!

    Locate the serial number from your current propeller (it should be engraved on one of the blades of the propeller) and you an look up the prop from tha t

  • If "no"... you need a different type of propeller (maybe for greater speed or more power).

    Use our Boat Propeller Finder to identify your new prop.
If you have...
An Outboard Boat -
You Will Need to Know...
A Sterndrive Boat -
You Will Need to Know...
  • Brand
  • Horsepower
  • Model & Year
  • Brand
  • Horsepower
  • Style

Once you get to the next page, you can narrow the selections by various features. Use the information below to help make your selections

  • Number of blades

The type of boat you have and the performance you want from it will determine the number of blades you choose.

Choose a 3-Blade Prop for: Choose a 4-Blade Prop for:
  • Recreational boats
  • Higher top end speed
  • Slower to plane
  • Greater pitch and style options
  • Lower price
  • High performance boats with high HP outboards or I/Os
  • Faster hole shot
  • Better performance and fuel economy at mid-range RPMs
  • Better holding power in rough water
  • Better low-speed handling

  • Pitch

Pitch is the theoretical distance a propeller travels in one revolution. Pitch affects the performance of a prop more than any other aspect and is measured in inches - as such, you will hear about "high pitch" or "low pitch".

Higher Pitch Characteristics Lower Pitch Characteristics
  • Lower top end RPMs
  • Slower initial hole shot

  • Less acceleration
  • Better top end RPMs
  • Improved hole shot
  • Better acceleration

If your pitch is too high, it will "lug" the engine, reducing both top speed and performance. If your pitch is too low, it will cause the engine to exceed the specified RPMs at the top end. Sustained operation in either of these situations will cause catastrophic damage to the engine.

  • Material

Boat propellers are made of aluminum or steel and both have their advantages and disadvantages. Unlike other prop features, the choice of material is really more a matter of preference (vs. requirements based upon boat style, etc).

Choose Aluminum Blades For:

Choose Stainless Steel Blades For:
  • Lower cost
  • Protective coating
  • Light weight (weighs about 1/2 as much as steel)
  • Satisfactory performance in most situations
  • Less expensive to repair
  • Higher performance
  • Repairs closest to brand new condition
  • Blade strength prevents flexing under pressure; blades remain in optimal condition longer
  • Durability and lower susceptibility to damage from sandy conditions or minor impacts

  • Cup

Cup is the added curved lip on the trailing edge or blade tip. This added curvature will increase pitch when added to the trailing edge and increase rake when added to the tip.

Cupping a propeller will cause a decrease in RPMs. The actual amount of RPM decrease depends on where, how much and the quality of the cupping.

Cupping also tends to decrease ventilation and allows higher trim angles and transom settings. It is typically used on propellers when higher performance if required.

  • Rake

Rake is the measurement of the angle of the tilt of the blade’s tip toward or away from the gearcase. The angle is measured on a line extending from the center of the hub through the center of one blade.

  • Diameter
Diameter is the distance across the circle formed by the blades of the propeller.
The correct diameter of your propeller is determined primarily by the size of your boat.
Choose a Large
Diameter Propeller for:
Choose a Small
Diameter Propeller for:
  • Heavier boat
  • Bigger engines
  • Higher engine mounting height
  • Lighter boat
  • Smaller engines
  • Lower engine mounting height

You can know if your blade diameter is appropriate by a few easy signs:

Too Small Proper Fit Too Large
  • Underpowered and lower speeds
  • RPMs exceed motor guidelines at top end
  • Boat will achieve preferred wide open throttle (WOT) RPM level
  • Maximum efficiency and safety
  • Slow hole shot and top endt
  • Decreased RPMs in all ranges. Top end RPMs are below motor guidelines
  • Rotation

Boat propeller blades can rotate either to the right or to the left. Right-hand rotation is the most standard while left-hand rotation is mainly used for one engine in a dual motor application to balance performance across the two engines.

  • Fixed or removable hub

The hub, as the name implies, is the inner core of the boat propeller. It slides over the propeller shaft and is the point onto which the blades attach. Always be sure that the prop and the hub have identical splines.

A fixed hub is most common and has the hub integrated into the propeller core as one unit. This is the most cost-effective solution for running a single prop.

If you need to change props for different conditions, you will want to consider a removable hub. This allows multiple props to fit onto one hub, reducing the cost of needing multiple props.


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Common Boat Propeller Problems

Being aware of some common problems can also help guide uou in selecting the right propeller for your needs.

  • Ventilation

This occurs when exhaust gas or surface air is drawn into the blades of the boat propeller. This causes the boat to lose speed and RPMs to climb rapidly, leading to excessive slippage. Slippage is essentially the difference from the theoretical pitch to the actual pitch. You will want the minimal amount of slippage for top performance.

  • Cavitation

This occurs when there is an area of low pressure caused by the inability to move through the water and then the water around the boat propeller begins to bubble. The bubbles collapse when they reach an area of higher pressure around the blades. Cavitation and changes in pressure can result in erosion on the face of the boat prop blades, ventilation and/or slippage.

< Severe cavitation damage on a boat propeller

  • Contact with silt or sand

Seemingly soft surfaces can reduce a boat’s fuel economy and overall efficiency. The damage can lead to cavitation and irregular leading edges on the boat prop blades.

  • Use in shallow waters

Boat propellers can become damaged by hitting hard items, such as rocks, in shallow waters.

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Common Boat Propeller Problems

Follow these tips to keep your boat propeller in top shape:

  • Regularly inspect your boat propeller for bent blades, nicks and rolled tips.

  • Replace worn boat prop blades to prevent the engine from accelerating beyond the normal range.

  • Keep the bottom of the boat and the boat props free of marine growth such as moss, grime, lime, aquatic weeds and barnacles. Buildup on a boat can decrease the performance of an engine by up to 50 percent.

  • Avoid using a damaged boat propeller as it leads to cavitation as well as damage to the stern drive and engine.

  • Always carry a backup boat propeller on your boat, just like you have a spare tire in your car.

  • Keep the boat propeller shaft greased with a marine-quality waterproof product. Use the grease before fitting the boat prop and as part of your routine maintenance procedure. If you have an aluminum bat propeller, grease the tosion rods inside the hub as well.

  • Have a professional service your boat propeller and repair it if damaged. A damaged boat propeller compromises the efficiency and performance of your boat, as well as your safety. With proper care and maintenance, you can get the most enjoyment out of your boat and save money as well.

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