If your engine is over revving, consider a propeller with more pitch. Elevation: Many small, trailered boats are used at vastly different elevations, such as high mountain lakes and bays at sea level. Reduced concentrations of oxygen at high altitude cause engines to produce less power about 20 percent less at '. You can partially compensate for this decrease in performance by carrying a second prop with reduced pitch, making it easier for the engine to achieve the correct rpm at WOT.
If you change configurations, sometimes running light and other times loaded with camping equipment, two props with different pitches make sense.
Ventilation results from excessively tight turns, a motor that is mounted too high on the transom, or an engine that is over trimmed. Ventilation can also occur from prop designs that are not matched to the application, poorly designed props, props with little or no cup, or props that are worn or have damaged edges or cup profiles. Causes of cavitation include incorrect engine height outboards , dings or sharp corners in the leading edge, poor polishing, too much cup or crummy blade design.
Cavitation can also occur from thru-hulls, sensors, or other turbulence-producing protrusions under the boat forward of the prop. We stock propellers to fit most outboards and sterndrives. Choices include propellers and hubs made by Mercury Quicksilver and Turning Point. Regardless of the brand you prefer, you will need to gather as much information as possible see below to make the best selection. After processing this information, you can make a better-informed decision.
Hubs are purchased separately from props. You will find an explanation of modular hub systems at the end of this article. Mercury also continues to offer one-piece, traditional props. Propeller size is expressed with two numbers, diameter and pitch, with diameter always stated first. Diameter is two times the distance from the center of the hub to the tip of any blade. Smaller prop diameters generally go with smaller engines, or with fast high performing boats.
Pitch is the theoretical forward distance, in inches, that a propeller travels during one revolution. Turning Point Propellers use a squeeze casting process to create thinner blades. They boast stainless performance at aluminum prices.
Rake is the degree that the blades slant forward or backward in relation to the hub. Rake can affect how water flows through the propeller, which can make a difference regarding boat performance.
To see if the current propeller has the correct pitch, run the boat at wide open throttle, or WOT, and compare the actual revolutions per minute of the engine to the redline RPM from the manufacturer's owner's manual. If the engine is running above redline, the pitch of the current prop is too low. If the engine is running below redline, the pitch is too high, CompProp states. Peter Hall graduated from the University of Delaware with a Bachelor of Arts in history and journalism in He has been working and writing in the information technology field since Related How to Measure a Boat Propeller.
Numbers Stamped on the Propeller. Diameter The diameter is the size of the circle that the propeller occupies in the water. Pitch The pitch of a propeller is how far the blade would move forward in the water during one complete rotation, BoatFix.
Correct Sizing of the Prop The propeller acts as a one--speed transmission for your boat, so it is important to match it to the engine, CompProp states. Search forums. Log in. Install the app. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly. You should upgrade or use an alternative browser. What do the numbers on the prop mean? Thread starter Caveman Charlie Start date Dec 4, Caveman Charlie Chief Petty Officer.
Joined Oct 31, Messages I have a 3 blade aluminum prop with the fallowing numbers on it. On the hub is stamped And then there is a symbol. I can't tell what the symbol is. Lets say the other numbers should be read with the prop on the boat.
If so then horizontally there are numbers in large print that read: 9 vertically above them it says 1 and then 3.
Around the other side of the prop in horizontal small numbers it says: A4 and then is says 19P. What does all this mean? Is 19p a 19 pitch prop? The prop came on my pound boat powered by a stern drive Mercrusier I won't be able to get the boat in the water until next summer. And, I did not get it running right yet this last summer after I bought it.
But, it seemed to me to only go about RPM. The book recommends RPM for a But, the engine is old. Maybe it's only making Hp instead of The book that came with the boat recommends about a 15 inch diameter 23 pitch prop.
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