Prop Sizes

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wright74012

Cadet
Joined
Jun 23, 2011
Messages
25
What is the proper prop size for a 25' pontoon with a 1999 Johnson 115hp?
 
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natedog337

Petty Officer 2nd Class
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Jul 11, 2011
Messages
107
Re: Increasing RPM

Re: Increasing RPM

Need more info.... What is the proper rpm range for that engine and what prop/pitch are you running now??
 
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wright74012

Cadet
Joined
Jun 23, 2011
Messages
25
Re: Increasing RPM

Re: Increasing RPM

RPM range should be around 5200-5700 i believe. I don't know the size of the prop I am running now. I transferred the motor from a smaller bass boat and now when I run it I only get about 3000 RPM, that is why I was asking about what size I should run.
 
lncoop

lncoop

Vice Admiral
Joined
Apr 18, 2010
Messages
5,147
Re: Increasing RPM

Re: Increasing RPM

Tough to say for sure, but something in the 13-15 pitch range would be a good place to start. Rule of thumb is supposed to be a couple hundred additional RPMs for every 1" drop in pitch, but that's not a steadfast rule. Your best bet is to find a dealer who's willing to take back a prop that doesn't work (most are) so you can experiment a little until you get it dialed in to where you want it. Be sure to replicate typical conditions (water conditions, normal load, etc.) to the best of your ability when performing your tests. Good luck.:cool:
 
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natedog337

Petty Officer 2nd Class
Joined
Jul 11, 2011
Messages
107
Re: Prop Sizes

Im using a solas 4 blade 13 pitch on my 26 ft pontoon with a yamaha f115 on it. Gives me 5800 RPM at WOT and 27 MPH
 
lncoop

lncoop

Vice Admiral
Joined
Apr 18, 2010
Messages
5,147
Re: Prop Sizes

Yeah, that one won't work. Try and sell it on CL or something unless you have another rig you can use it on. You'll likely need something in the thirteen to fifteen range.
 
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EGlideRider

Lieutenant Junior Grade
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Dec 14, 2008
Messages
1,000
Re: Prop Sizes

A 13 will be a good starting size. The 20 is about right for a bass boat, but certainly not for a pontoon boat.
 
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jonnymark

Recruit
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Jul 25, 2011
Messages
5
Re: Prop Sizes

A prop size and pitch is determined by the particular model and desired flying style, with the additional requirement that the maximum rpm should remain reasonable. I prefer to keep the maximum rpm in the 8500 to 9500 range, some people prefer a higher rpm but greater than 10,000 is probably not good. The rpm with a given prop will depend on the fuel used and brand of prop. A larger diameter or pitch can be used with fuel that has more nitro. Also some models fly better with bigger diameter and lower pitch , and other models are better with more pitch and less diameter; you have to experiment to determine what best suits you. Use the max rpm as a guide with values about 8500-9500 being satisfactory. Try these sizes as starting points, all are APC brand. If you use high-nitro content fuel you will probably need to use a larger size prop to limit the maximum rpm to about 9500. (Note: The Saito literature that accompanies most engines states a maximum rpm value that is quite a bit higher than my suggested 9500 rpm maximum value. I guess that the higher rpm numbers quoted by Saito are ?not too exceed values?, and not actual recommended operating rpm).
 
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johnathan777

Recruit
Joined
Jan 29, 2010
Messages
5
Re: Prop Sizes

jonnymark said:
A prop size and pitch is determined by the particular model and desired flying style, with the additional requirement that the maximum rpm should remain reasonable. I prefer to keep the maximum rpm in the 8500 to 9500 range, some people prefer a higher rpm but greater than 10,000 is probably not good. The rpm with a given prop will depend on the fuel used and brand of prop. A larger diameter or pitch can be used with fuel that has more nitro. Also some models fly better with bigger diameter and lower pitch , and other models are better with more pitch and less diameter; you have to experiment to determine what best suits you. Use the max rpm as a guide with values about 8500-9500 being satisfactory. Try these sizes as starting points, all are APC brand. If you use high-nitro content fuel you will probably need to use a larger size prop to limit the maximum rpm to about 9500. (Note: The Saito literature that accompanies most engines states a maximum rpm value that is quite a bit higher than my suggested 9500 rpm maximum value. I guess that the higher rpm numbers quoted by Saito are ?not too exceed values?, and not actual recommended operating rpm).
Click to expand...

Johnny
They are talking boat props not RC model props ?
 
C

clemsonteg

Petty Officer 3rd Class
Joined
Jul 17, 2011
Messages
77
Re: Prop Sizes

If it makes you feel any better I'm having a similar issue. I'm also thinking about going to a 13 1/4 x 13 4 blade prop for my 24 ft with an 85 hp Johnson. I'd prefer an 11 pitch 4 blade bu I may just do the 13 and see what happens
 
Cubbyblue22

Cubbyblue22

Petty Officer 1st Class
Joined
Jul 25, 2010
Messages
220
Re: Prop Sizes

So I have a similar set up but I was wondering, will it affect much getting a 13 pitch x 13.75" vs. 13 pitch x 10.1" ??? Both 3 blade
 
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dwells1234

Seaman Apprentice
Joined
Aug 31, 2011
Messages
44
Re: Prop Sizes

Where do you find the numbers on the prop. I am new to this. Just bought a 88 ski cat pontoon with fiberglass toons. It has a evinrude 150xp. There are three blades on this. It is 24ft.
 
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dwells1234

Seaman Apprentice
Joined
Aug 31, 2011
Messages
44
Re: Prop Sizes

I have a 24ft fiberglass with a 17p prop. !50 evinrude and I get to 30 mph. Tach is inop and trying to figure it out. Would a different size get anymore mph?
 
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