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Prop Change?

Old 07-07-2020, 03:37 PM
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Ok all you boating gurus. I have a Bennington S20 pontoon boat with a Yamaha T50 outboard. WOT with just two people on board is around 4400 rpm. Reading the owners manual and information from other forums states this engine should be around 6000 rpm WOT. I had the dealer come out and check the engine and they found nothing wrong and said that 4400 is right. Pulling a couple of my grandkids in a tube the RPM drops to 4000. The prop is an Solas Rubex 3 Blade 14 X 11P Propeller 9411-140-11. Would a prop change give me more RPM and possibly a higher speed? If so, what are your recommendations.

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Old 07-07-2020, 05:29 PM
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How fast is the pontoon going at 4400 RPM?
Old 07-07-2020, 06:35 PM
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Thanks for replying, I'll have to get back to you on that.
Old 07-08-2020, 04:13 PM
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Originally Posted by Tom W Clark View Post
How fast is the pontoon going at 4400 RPM?
17 MPH with two persons on board and 3/4 tank of fuel. I used two different GPS apps for the speed.
Old 07-09-2020, 05:57 AM
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Originally Posted by 2young2retire View Post
Ok all you boating gurus. I have a Bennington S20 pontoon boat with a Yamaha T50 outboard. WOT with just two people on board is around 4400 rpm. Reading the owners manual and information from other forums states this engine should be around 6000 rpm WOT. I had the dealer come out and check the engine and they found nothing wrong and said that 4400 is right. Pulling a couple of my grandkids in a tube the RPM drops to 4000. The prop is an Solas Rubex 3 Blade 14 X 11P Propeller 9411-140-11. Would a prop change give me more RPM and possibly a higher speed? If so, what are your recommendations.

Thanks
From all research you should be 5500 RPM +/-. Your prop diameter may be the culprit and/or how deep the motor is mounted.
Old 07-09-2020, 06:05 AM
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Originally Posted by davepjr71 View Post
From all research you should be 5500 RPM +/-. Your prop diameter may be the culprit and/or how deep the motor is mounted.
The Yamaha T50 is the high-thrust model so that's why the prop diameter is large.

I agree though that the motor should be turning up around 5500RPM at WOT
Old 07-09-2020, 07:53 AM
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You are w a y overpropped. The dealer should never have signed off on an 11” pitch prop.

I bet this boat should be good for 18-19 MPH and a 9” pitch prop would be appropriate.

I recommend the 14” x 9” Yamaha Pontoon SDS
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Old 07-12-2020, 05:40 AM
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Originally Posted by Tom W Clark View Post
You are w a y overpropped. The dealer should never have signed off on an 11” pitch prop.

I bet this boat should be good for 18-19 MPH and a 9” pitch prop would be appropriate.

I recommend the 14” x 9” Yamaha Pontoon SDS
Thanks for all the input. Looks like a different prop is in my future. I'll post after the change and update everyone.
Old 07-15-2020, 02:34 PM
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14X9 installed, RPM increased to 5800 and top speed remained the same. Still don't know how it will do with the kids on the tube but I expect good things. More to come.
Old 07-15-2020, 06:02 PM
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Originally Posted by 2young2retire View Post
14X9 installed, RPM increased to 5800 and top speed remained the same. Still don't know how it will do with the kids on the tube but I expect good things. More to come.
Motor will thank you for that prop change in longevity.
Old 07-29-2020, 07:59 AM
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Things worked out well. Was able to almost maintain the RPM's while pulling the kids, they enjoyed the extra speed. Thanks all for the input and the recommended prop size. This is what it is all about, people with knowledge helping those who are not so boat smart. Thanks again all.

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