Get to know YOUR Propeller...
Propeller BASICS
1. 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.
2. Diameter
Diameter is the distance across a circle encompassing all of the propeller blades.(see Original Equipment Considerations item 2 below).
3. Pitch
Pitch is the theoretical distance a propeller will move through the water for each revolution (i.e., a 21 "pitch propeller should move a boat forward 21" for each revolution, assuming there is no slippage).
4. Right hand or Left hand Rotation?
In most cases, right hand propellers are used for single engine applications and one left hand propellers are used for twin engine applications to achieve better steering control.
5. 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.
6. 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 applications.
3 or 4 blade? Aluminum-Brass-NiBrAL-Stainless?
How does your prop perform?
Finding the right propeller can be tricky
The proper propeller size for your boat and engine is based on the wide open throttle (WOT) operating range for your engine (see your owner's manual). This will be expressed in terms of horsepower (HP) at a certain RPM (Revolutions/Revs Per Minute).
The goal in propeller selection is to determine which propeller will maximize the overall performance for your boat, while allowing your engine to operate in the recommended RPM range.
The correct propeller will prevent the engine from over-revving, yet allow it to reach the MINIMUM RPM (where maximum horsepower is produced).
TEST YOUR PROPELLER:
- What is the MAXIMUM RPM you are able to obtain?
- If, during this test, you begin to EXCEED the maximum rated RPM of the engine, then REDUCE the throttle setting to a position where the maximum RPM is NOT exceeded.
- If your test results in you being able to OVER-rev the engine, then you need to increase the pitch of the propeller. Increasing the pitch increment by 2" will result in approximately a 300-400 RPM drop.
- However, if your test shows that you can only obtain a LOWER RPM than the maximum rating given by your engine manufacturer, you would need to decrease the pitch of your propeller. Decreasing pitch would increase your RPM accordingly.
Switching from an un-cupped to a cupped propeller will also REDUCE your RPM.
The cupped propeller of the same pitch and diameter will typically reduce your RPM by approximately 200.
Once your wide open throttle RPM falls within the recommended range of the engine manufacturer, you have a propeller that is suited correctly for your boat with respect to RPM!
Performance Considerations
1. Type of boat (cruiser, ski, runabout, bass, pontoon) ?
2. Prop on boat now (brand, model, diameter, pitch, cupping) ?
3. Engine RPM at wide open throttle (WOT) ?
4. Speed of boat over water at WOT ?
5. Normal operating altitude (motors lose 3% of power per 1000 ft. of altitude)?
Type of boats and propellers vary. Do you have the right prop on your boat?
Original Equipment Considerations
- Determine the year, brand, model and horsepower (HP) of your motor.
- Calculate the diameter of the OEM propeller by measuring from the center of the shaft hole to the longest tip of a blade, x 2 (e.g. a measurement of 7 ¼ inches = a diameter of 14 ½ inches).
- What type of metal is it? Aluminum, NiBrAL, or stainless steel?
A SPARE PROPELLER IS LIKE A SPARE TIRE...
Do you have a spare PROP on board?
At all times you should have a spare propeller with you in the boat.
Boating without a spare prop is like driving a car without having a spare tire. If your working propeller is damaged, you may be out of luck without having a spare propeller along!
Prop Finder
To assist you in your endeavor to find a propeller, while you've got a few minutes to spare, click button below BELOW:
