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Old 19 July 2011, 19:17   #1
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What prop?

Hi guys,
Really appreciate any input you fellas might have to this situation.
I have upgraded from a 2 stroke 150 to a f150 on my 7m crompton. Currently running the original 3blade ss 13.75 dia. x 19 pitch from my last engine. This produces 35 knots gps at 5200 rpm with a light load.
The boat is operated comercially and coded for eight so it is more important to be able to cruise with economy that outright speed. I have it on good authority that for best economy with this motor you should prop it to run as close to max rpm as possible.
I was thinking 13.75 x 17 in 3 blade ss. ?
Any ideas or suggestions appreciated.
Cheers Aaron.
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Old 20 July 2011, 08:05   #2
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According to Yamaha, the F150 max rpm is 5000-6000 which is a bit vague.

If you went down to a 17" you should make 5400-5500 under your light load conditions.

But with 8+1 on board you should find the motor will still be really struggling, a 15" will be much better.

Also, not true re propping for max rpm to get best economy. I had 19" on my boat which gave correct max rpm. I changed to 17" and although I could over rev the motors at WOT under most conditions, at a given cruising speed I was burning less fuel even though the revs were higher than with the 19". Less load on the motors.

Your boat is well under powered with 150hp, when the yammy goes bang stick at least 225 on there
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Old 20 July 2011, 08:29   #3
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when the yammy goes bang stick at least 225 on there
Just not an Opti though
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Old 20 July 2011, 09:03   #4
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Just not an Opti though
Absolutely
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Old 20 July 2011, 09:17   #5
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Cue Gotchi, the caped etec crusader!

ee lad, tha can't educate pork
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Old 20 July 2011, 14:15   #6
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15" pitch sounds good to me, When you're fully loaded you'll really struggle with the 19"er. How about getting two props, a 15" and a 17"er. Just swap em over to get the max out the set-up depending on loading/sea conditions? The one you don't run will make a terriffic spare.
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Old 20 July 2011, 14:21   #7
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BTW aren't Mercury, Yam, Honda 15 spline props interchangable?
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Old 20 July 2011, 18:34   #8
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Thanks guys.
Martini I would love a 225 but to tell you the truth for our needs the 150 is ample.
I had an option of an optimax but in this neck of the woods yamaha is the only way to go. I will look at getting hold of a 15 so. Almost swallowed my tongue earlier when I was quoted 550 +Vat for a black yamaha stainless 13.75 X 17.
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Old 20 July 2011, 18:42   #9
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Mercury have the best range of props, you just need the correct flo-torq hub. Lots on ebay USA, mirage plus if you want 3 blade or revolution 4 if you want 4 blades (you'll need a 13" Rev4 though, not sure if they go down that small)
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Old 22 July 2011, 09:54   #10
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Ok have ordered a 14.5 X 15 3 Blade SS from the US fingers crossed it does the job.
The extra diameter will mitigate the reduction in pitch I'm sure but it is impossible to know for sure until I get it in the water
Will post the results.
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