Correct prop for a Bennington pontoon

rpatton

Petty Officer 1st Class
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Feb 17, 2011
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ok I inherited a 2013 20’ Bennington pontoon boat with a 2013 Yamaha 90 hp 4 stroke in it. It came with a 13 pitch prop. Does that sound correct? It has a great hole shot but not a lot of top end. I can’t go much over half throttle with out the motor over revving or cavitation. I check for a spin prop and it’s good. Any thoughts
 

Sea Rider

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Sep 20, 2008
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To start with, you need to tach currant OB at wot and as usually loaded to know if working safely between min to max wot rpm range as factory stated. Then will know if under or over pitched with current prop.

If prop aerates, ventilates badly when giving throttle, trim, deck weight distribution or OB height could be set incorrecty ?

Happy Boating
 

ahicks

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Sep 16, 2013
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I have a 90 hp Honda on our fairly light 24' boat. It's currently using a 13p prop, turning it right up to max rpm for good (best possible) pulling performance. If it were not for the pulling performance I was looking for, I would likely go to a 15p prop to get the rpms down a little.

Without being able to run at wide open throttle, and being able to see what rpm the engine is turning at that point, coming up with the correct prop for your application will be difficult/impossible. Are you running into this problem with the engine trimmed all the way down?

"Top end" and "pontoon boat" are mutually exclusive terms. Pontoons are not fast, though 25 mph or so with your combo is not out of reason. It's about what ours does.
 

Lightwin 3

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To start with, you need to tach currant OB at wot and as usually loaded to know if working safely between min to max wot rpm range as factory stated. Then will know if under or over pitched with current prop.

If prop aerates, ventilates badly when giving throttle, trim, deck weight distribution or OB height could be set incorrecty ?

Happy Boating

Agree. Tach is needed to find correct pitch. Cavitation is usually another iasue but not unusual on Toons.
 

rpatton

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Feb 17, 2011
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249
Thanks for all the replies. The rpm’s at wot are up at about 6800 grimed .If I’m correct my motor is rated for between 5-6000 rpm
 

Sea Rider

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If max wot is 6 rpm K factory stated, OB is +800 rpm over revving as currently loaded which is bad for the OB. Will plane faster but will lose best top end speed along increasing unnecessarily fuel consumption Will need to go for higher pitch props to decrease wot rpm down towards middle to max wot range to have a better combo performance than with current prop.

Happy Boating
 

ahicks

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Is that 6800 when loaded with your typical load, or very light, maybe with just you on it?

Are you going to be tubing with it regularly, or just cruising?
 

rpatton

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Feb 17, 2011
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Typically it’s just me and my wife and 2 Labradors on board. We’re getting to Old to tube. Am I correct in assuming that each pitch is worth about 200 rpm’s? So I Need to be up around a 16 pitch? I don’t want to be over proper either.
 

Sea Rider

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Having a fixed load is the way to go to prop right an engine whether wanting top hole shot or top end speed. On your particular case will need to increase 4 pitch sizes to lower wot rpm towards max safe 6 K wot rpm range, thst's if the theoretical rule of thumb applies 100% which in most cases doesn't..

Personally wouldn't dare put my hands to the fire going that route. Will start trying + 2 prop pitches to decrease wot revs. How much rpm reduction per pitch will OB gain, impossible to tell, props must be water tested. Each combo and load is a unique water animal.

Could re pitch current prop to a 15 pitch or buy a new 3 blade alum 15 pitch OEM prop, you decide.Be aware that tach must be in excellent working order before venturing playing with props.

Happy Boating
 

rpatton

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Feb 17, 2011
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Thanks for the help. I will take the advice when I’m down by the boat next weekend. I’ll either try the 15 or if I can find a 16
 

Sea Rider

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OK, for the record report max wot rpm achieved whether with a 3 blade 15 or 16 pitch prop. If can dial revving near max wot rpm range as loaded will be excellent.

Happy Boating
 

rpatton

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Feb 17, 2011
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249
one last question guys ? Can anyone tell me the correct size of the prop nut on my 2013 F-90 ? the boat is 3 hours away and I want to make sure I have the right socket along with me when I go to swap props.
 

Silvertip

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Sep 22, 2003
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Do not overlook "pontoon-specific" props in both three blade and four blade varieties. Pontoon props have very big, rounded blades commonly referred to as "elephant ears". These props are designed specifically for hard to push work boats, barges and yes -- pontoons. Without a doubt, 13P is way too little pitch for that combination. You should look for a prop shop in your area and see if they will work with you on a try & buy basis. Marine dealers always have a pile of used props and they may rent a few for you to try, or if they are a "stand up organization" just let you try a few. Then buy from them.
 

rpatton

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Feb 17, 2011
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UPDATE . Ok I was unable to get a 16 pitch prop which was a good thing. I put a 13 1/2 x 15 pitch on and now the rpm are running at 5700 with 2 people on board at plane wot. Much better. The 16 pitch would have been to much of a jump. Thanks for all the help guys.
 
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