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General Rules to Follow:
A 1 inch reduction in propeller pitch will result an an increase of 150 to 200 RPM at full throttle.
If at full throttle, the engine RPM is too high, you will need to try a propeller with either a higher pitch or larger diameter.
Conversely, if the engine RPM is too low at full throttle, try a propeller with a lower pitch or smaller diameter.
Due to the differences in hull designs, engines, and weight (and weight distribution) from one boat to another, finding the correct propeller for each boat will vary.
Finding the best propeller can only be accomplished by trial and error after determining what is most important to you (speed, handling, etc.) under specific water conditions (lake, ocean, rough seas, etc.)
Brands and Styles of Propellers
First, we must say we recommend genuine OMC BRP propellers for your Johnson and Evinrude outboard engine...
We have in stock ALL of the propellers listed in the OMC BRP genuine parts and accessories catalog.
Propellers are also made and manufactured by Michigan, Aqua Power, Stelitto, and others.
OMC models include
Aluminum, Stainless Steel, SST = Stainless Steel Tough, SST II, The New Rebel polished stainless steel propeller, Viper, Raker, Renegade Bass, Renegade Offshore,
Electric, Weedless, SRX, Weedless Plastic, Plastic
Stern Drive Models: Cobra, OMC Sea Drive & Sail Drive, Volvo Penta DuoProp,
...and a few more.
There are some minor and major differences between the different models.
A few details on some of our favorites...
REBEL Prop: Designed and engineered to deliver even greater fuel economy plus improved midrange and top-end performance;
Plus best hole shot and take-off and out of the hole performance!
SST (Stainless Steel Tough)Propeller
:
The SST propeller is 5 times stronger than an ordinary aluminum prop. That means we can cast the blades thinner for a cleaner bite to achieve higher top end speed.
The SST is a fast planing prop with thru-hub exhaust and cupped blades.
With it's outstanding durability and high performance feauture, the SST is unmatched as the
best value in a stainless steel prop. More expensive than aluminum, but highly recommended for
the serious boater.
OMC VIPER Propeller: Heat Treated Stainless Steel that provides protection from minor dents and dings; Swept-Blade that has a longer tip and larger diameter creating a better grip on the water; Optimum blade thickness.
RENEGADE OFFSHORE PROP:Four blade design, Left hand and right hand V6 sizes; Superior acceleration;Stays hooked up in rough water and is stable in all water conditions; Superior top end speed; Stays solidly on plane when running at minimum RPM
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The Size: Diameter and Pitch
The diameter and the pitch (in inches) is very important information in choosing the correct propeller.
The correct propeller size (diameter and pitch), and material (stainless steel, aluminum etc.) will allow your boat's engine to operate at the engine manufacturer's maximum recommended engine RPM at full-throttle.
Diameter is the distance measured across the propeller hub line from the outer edge of the circle that is made by the propeller's blades during rotation. Pitch is the distance, theoretically, that a boat will travel for each revolution without any slippage. (The actual distance the boat moves forward for each propeller revolution is somewhat less, depending on the amount of propeller slip.) The diameter is listed first and the pitch is second. Therefore, a 14" x 21" propeller would have a 14-inch diameter and a 21-inch blade pitch.
A higher pitch prop will increase your top-end speed but reduce your acceleration (reduce your "hole-shot" power). Decreasing the pitch will increase your hole-shot but sacrifice some of your top-end speed. If the hole-shot speed is important to you, (Eg. water skiing) then you would want to go with a lower pitch prop and sacrifice some of your top-end speed but increase your hole-shot speed to get the skiers up faster.
If your propeller is either too large in diameter or too high in pitch (or both), your engine will not be able to reach the maximum recommended RPM at full throttle, (assuming your engine is in otherwise excellent running condition). This condition will cause strain on the engine and cause poor performance . If, on the other hand, the propeller is too small, either in diameter or pitch, the engine can be damaged by excessive strain.
What is your engine's recommended propeller diameter and pitch ?
Look at the inside of the hub of the propeller for either a serial number or the propeller size stamped into the hub. Consult your owner's manual. Review our OMC Catalog Propeller information chart. (For recommended boat size, speed, HP, etc.)
Material: Aluminum or Stainless Steel ?
Aluminum is good for general all-purpose recreational use engines. It is cheaper and less durable than stainless steel. Most pleasure boats are factory equipped with aluminum propellers. A good quality aluminum propeller will provide satisfactory performance for most family and fishing boats. For ultimate top speed or better acceleration, a stainless steel propeller will probably be required. Stainless steel is much stronger than aluminum, and can endure far more abuse.
If you can afford the higher price of stainless steel with the desire for top speed and acceleration, I would recommend stainless steel as the best choice overall.
For electric and selected small outboards (small fishing boats),OMC propellers are also available in weedless plastic.
Test for Maximum RPM:
Find the manufacturer's recommended RPM range in the owner's manual or ask your dealer.
Using the existing propeller or a new propeller, make test runs to determine the maximum RPM and boat speed. This is known as "wide open throttle" (WOT). Vary the trim angle for optimum performance. If possible test different types of propellers. Test the propeller in a variety of water conditions, at a variety of speeds, under the conditions you will primarily use your boat (calm water fishing, rough seas, water skiing, racing, cruising, etc.).
Running your engine at the wrong rpms can cause severe strain and lead to engine damage. An engine that revs past the manufacturer's recommended RPM will have higher than normal wear and tear.
3-blade or 4-blade Propeller?
Basically the difference between using a 3 blade or 4 blade propeller can be seen in the boat's handling and performance.
Three-blade propellers are the most popular and are good for general, all-purpose use. They provide good acceleration and control, and excellent top speed performance. Please note: Aluminum propellers are ONLY available in a 3 blade design.
The 4 blade design (stainless steel)is popular with boaters who are looking for a good hole shot, better acceleration, and better bow lift (higher trim angle) to reduce boat drag (too much of boat in water- reducing top end speed).
Important: 4 blade designs allow your boat to stay on plane at a lower rpm - Producing a slower cruising speed without loss of plane of the boat in rough seas and conditions. Renegade props (4 blade) are of an excellent design -allowing better top end, speed, with minimal drag.
Boating Activity (Cruising, Fishing, Racing, Skiing...) The type of activities you do with your boat are important in determining what type of propeller you will need.
You may need to have more than one propeller if you use your boat for different types of activities.
The Truth: No single propeller will be able to give you top speed and handling under all conditions. The propeller that provides the best hole shot will probably not provide the best top speed for your boat. A propeller that will give you absolute top speed, will probably provide uncomfortable midrange handling or ride.
If you use your boat often under a variety of conditions, you will probably decide that you need more than one propeller. Eg. one for cruising, one for speed and one for pulling skiers... of course, if your budget only allows one good quality propeller, you will need to select the propeller that provides the best compromise between the characteristics you are looking for.
Coming Soon: Part 2 Propeller Ventilation, Cavitation, and more...
This article cannot be reproduced or copied without prior permission from the author. Thank you :)
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Too confusing...Too many choices ? Call the Outboard Wizard, Ralph at Lindenhurst Outboard Inc. He will be glad to recommend the best choice of propellers for your particular boat, engine, conditions, usage and budget.
The Outboard Wizard
Lindenhurst Outboard Inc.(631) 225-0077 (10:00 AM - 5:00 PM Eastern Time). Happy Boating !
All products from the 2005 OMC Parts and Accessories Catalog are available at 10-20% off retail.
Email The Outboard Wizard:
For assistance in choosing the correct propeller.
Call The Wizard's Technical Advice Hotline:
(631)
514-1525
For Propeller Prices and Ordering:
(631) 991-4491
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Evinrude-Parts Outboard Wizard Marine Shop & Service
