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What would be the affect of changing out a 10 1/8" x 15" pitch prop to a 12 1/4" x 11" pitch prop ? Just curious how diameter relates to pitch and the overall effect.
If the engine was in the right RPM range it would over rev usally a smaller pitch prop has more dia. to help it hold better as it is being use on a heavyer boat
If your motor requires a 10 1/8" prop a 12 1/4" probably wont fit. Count the splines in both props. <br /><br />Are you trying to gain rpm's? Or what exactly are you trying to change?
Both props are 13 splines. There is plenty of clearance for the larger prop. No real objective, just curious about the result. Will it be better for pulling tubes etc or will I gain more top end etc with the larger prop. Are the two props "equivalent" as far as performance ? Will the larger prop bite better but turn at the same RPM because of the larger dia ? What is the better prop ? I mainly fish and pull tubes, water skiers etc.
A small diameter prop like yours means you probably have a gear case ratio of 1.85:1 or thereabouts. Larger diameter props are usually found on engines with 2:1 or say 2.33:1 ratios. Larger diameter props have more blade area and require either 1) more gear ratio or 2) more engine power. Pitch is the forward distance the prop "theoretically" moves with each turn. Therefore, if all you are looking for is more pulling capability, you want less pitch on a similar diameter prop. For more speed you want more pitch. The down side is you can't have it both ways. You either over rev with less pitch or lug the engine with higher pitch. The trick is to find the sweet spot and then go down 1 for pulling and use the "sweet spot" prop for cruising.
Guess I'll stick to the exiting prop size for now. Not really sure what to use because the iboats prop selector comes up with a 13" dia prop when I input the parameters. Once I get the tach installed I'll have a better idea of where to go. The different diameter thing still puzzles me. There must be a reason such a wide variety of dia vs pitch combinations are available. I'm not even sure if the prop on the motor now is the correct one. It just came with the package.
If I may offer a suggestion...don't worry about the diameter...it changes with pitch, it changes with prop style. It's not likely to be a factor you need to be concerned with on your application.
Where I'm going with this is I want to buy a spare/new prop. I want to get one that is different than the existing one to see performance differences. Maybe I'll look for a shorter pitch that will be better for skiing and tubing as well as lower trolling speeds for fishing. Not that interested in going fast.
The next step down is 10-1/4X14, and then 10-3/8X13....I believe I would go with the 13 for pulling anything. If you don't have a tach, just don't run WOT consistantly for long periods of time with the 13.
