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Thread: Prop help please
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12-09-2024, 08:01 PM #1
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Prop help please
I have a 21 ft cobia center console that I have just redone the floor and transom and I'm just getting it on the water , with that said I have a 1990 Johnson 125 25" shaft and when on plane if I give it all the throttle , it will hit 6700 - 6800 rpm quickly .
I feel this is too much and the prop is a 13 3/8 X 17. Is this close to the right prop ? There is evidence of the rubber hub slipping some but I don't want to pay to have it re worked just to figure out it's the wrong one anyways .
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12-09-2024, 09:16 PM #2
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How fast does the boat go? Is 6700 a transient rpm while planing or the rpm at top speed?
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12-09-2024, 09:21 PM #3
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According to gps and fish finder around 34-35 mph if I remember correctly .
6700 is all the rpm at top speed . The boat itself comes up on plane easy and quick , just worried about the excessive rpm .
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12-10-2024, 11:55 AM #4
If the hub is slipping it is a real problem. From what you have posted I would really think about going to a 19" pitch prop. That should lower your RPMs by about 200 RPM. A four blade prop will also give you better control in rough water and less propeller slip.
Best wishes, Carter Powell
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12-23-2024, 08:15 PM #5
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you can check your hub, put a 2x4 in so the prop wont turn, engine at idle, shift in to foward. engine should stall immediately. have someone look at a safe distance. worked for me.
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