adding 1" in diameter

robertsc2

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May 15, 2017
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Will adding 1" in diameter to the prop of my Yamaha 250SHO do anything to increase fuel consumption on my 25' tri-toon? I currently have a 15 pitch-14 1/2 dia. prop. Thanks for any input.
 

Sea Rider

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What about max wot revs achieved as usually loaded on flat water cond ? Without rpm numbers won't dial best fuel consumption rate as won't know if OB revs inside mim-max wot rpm range factory stated.

Happy Boating
 

robertsc2

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May 15, 2017
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Ok, I will get those numbers when I get back to the lake house & reply to this post.
Thank you.
 

ondarvr

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It may go up, or it may go down, there is no solid rule on what a prop will do until you try it. There are tendencies for certain styles, pitch and designs, but each manufacturer has their own twist on what those numbers or designs may mean.
 

H20Rat

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Its a boat..., well, a pontoon with a 250hp motor on it. There is no reasonable prop change in the world that is going to affect your mileage more than a fractional amount. Are you trying to achieve any other goals, and how does your current prop perform?
 

robertsc2

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May 15, 2017
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The only goal is wanting to be able to pass up a marina without filling up. The boat gets used at Lake Travis, so we drive a lot of miles. I should have ordered the boat with the biggest tank possible. The boat performs great otherwise. I believe it turns about 6,000 rpm wide open.
 

Sea Rider

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If not mistaken that OB runs 5000-5000 wot rpm, if assuming running at 6K, OB is over revving + 500 wot revs as loaded. If so, will need to go at least 2 + pitches to lessen wot revs towards max 5500 rpm range. At which amout of throttle do you like tooning with ?

Happy Boating
 

muskyfins

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Jun 7, 2012
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The reduction of the above stated over-revving will help milage. So will running closer to 4500-4800 RPM's. Lose only a MPH or 2, but save 20% on fuel. (personal observation)
 

robertsc2

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May 15, 2017
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I'm guessing about half to 3/4 throttle or 20-25 mph & I'm thinking its about 4500 rpm at around 25 mph. I'll get some more accurate numbers in about a week when I go back to the lake house & will post accurate figures.
Thanks for all the reply's thus far.
 

robertsc2

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May 15, 2017
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Ok, just got back to the computer from the lake. WOT revs fully loaded with fuel & people etc. was 6200 RPM's at 36mph. Any suggestions based on that info?

Thanks
 

Sea Rider

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Are we talking about a 2 or 4 strokes 200 HP Yam ? Is it a 4 in line cylinder displacement ot a V6 one ?

Happy Boating
 
Last edited:

robertsc2

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May 15, 2017
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It's a 2015 Yamaha 250SHO on a 25' Avalon tri-toon. Fully loaded with people & gear with reasonably smooth water it was turning 6200-6250 RPM wide open at about 36 mph.
 

Sea Rider

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OB wot range is 5000-6000 rpm, achieves max horse power at middle 5500 rpm. It's a DOCH, not SOC engine. If already at 6250 wot rpm, OB is over revving + 250 wot rpm while rev limiter isn't kicking in.

Ideal would be for OB to run at middle 5500 wot range or at max 6000 range as loaded. If like going full throttle, over revving will consume more fuel at slight less top end speed than going at middle/max wot range. Try a 16 pitch prop to lower wot rpm towards max wot range or a 17 towards middle wot revs, only checkable on a water tets...

Will depend entirely on what you preffer : better hole shot with slight less top end speed or less hole shot eficiency with slight more top end speed. Can't have the best of both worlds on a single prop...

Happy Boating
 

Sea Rider

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Can't recommend diameter, it's all to prop manufacturer whatever diam wants to add to a 16-17 pitch prop. Unless you can fabricate one with a diam of your prefference LOL!!

Something to have in mind : will you always, most of the time go boating loaded as previously described ? say it's a family oriented combo ?

Happy Boating
 

robertsc2

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May 15, 2017
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I'm sorry I didn't respond to you last post, (I thought I did).
Yes, a typical day on the lake has around 6-10 adults plus a couple of kids on the boat. We do a lot of crusin' with a little of knee boarding & tubing, so the hole shot & top speed are not important. I'd say if I wanted one more it would be the hole shot, because we like to cruse around 25mph so top speed is certainly a non-issue.
Thanks for all your input.
 
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