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Old 30 December 2014, 04:19   #1
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Upped the pitch and Baffled by the results

So I've got a small rib/tender 3.2mtr alloy hull, with a 25hp rude....it goes pretty good 26knots.... But the the prop was pretty shaggy so I tidied it up with I metal file then wet and dry sand but thought I would get another prop to have as a spare

The original prop was oem 10/13p the prop I purchased cheap second hand but good condition is 10/15p also oem

My expected results were to lose some bottom end but gain up top so I held off using this prop for a couple of weeks while I've been pulling the kids around on toys and playing in the surf. I have now changed to the 15p,prop and am super surprised that I've gained a nice pace at idle, a better smother speed at cruze, faster pop out of the hole and way more usable power low and mid range, it seems I've actually lost a bit of top end but I am not at all fased, but totally confused.. The 15p prop is now staying put intill I can figure which the best setup for me will be???

I am thinking a new 13p with some cup to have as a spare and surf prop?? Any advice would be appreciated
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Old 30 December 2014, 05:38   #2
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By using a more aggressive pitch the outboard will be revving less at WOT (wide open throttle) and thus you probably wont be in the ideal rev range for the outboard. The result of that would mean that there's not enough grunt from the outboard to push you to a higher top speed.

With regard the better hole shot from the 15" prop. Well all I can say is that your older prop which has obviously sustained some damage in the past is past it's best. This probably explains why your 15" prop is outperforming it.

A 2" pitch change on a 25hp outboard is a massive change, I would recommend looking for another 13" prop which should claw back your top speed and reveal a better hole shot to boot.
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Old 30 December 2014, 23:21   #3
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Yea I totally agree with the advice thankyou, I will be getting another 13 in the near future and will continue to try and the ultimate setup so wether it's a slightly cupped 12 or 13 I'm not yet sure. Hopefully I will be able to track down a outboard wreaker with the stash a stash of cheap props. Stoked on the 15p and its performance for now
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Old 31 December 2014, 01:11   #4
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Agree with Hightower. You really need a tach to see what's happening. Even a temporary clip-on auto tuning type would do, as you only need readings at wide open throttle.

jky
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Old 31 December 2014, 02:42   #5
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Tiny tachometer ordered and payed for....will be interesting to see how well my ear is tuned to my motor
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Old 31 December 2014, 08:11   #6
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Hi Guys , What are the indications of a too low pitched prop . My prop pitch is 9x11 on a 12 ft with 15hp johnson . My rib seems to take of rapid and revs out a roughly half throttle !
Thanks
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Old 31 December 2014, 11:45   #7
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Originally Posted by tuskar View Post
Hi Guys , What are the indications of a too low pitched prop . My prop pitch is 9x11 on a 12 ft with 15hp johnson . My rib seems to take of rapid and revs out a roughly half throttle !
Thanks
That sounds like you might have a spun hub. How fast is it going?
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Old 31 December 2014, 12:21   #8
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Hi
Dont think so, can go 18mph with two large adults 80kg each . just feels like I could pitch it up 1 degree and maybe reduce noise level and revs ? Any advice welcome.
Thanks bud.
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Old 31 December 2014, 14:04   #9
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Tuskar, you might be rite the only way to know is properly read you rev range with a thacho.. I know with my setup I was at over rev with my old prop still having a bit of throttle left on the twist grip and sound of the engine reaching a point where I would back off. My new prop is much quieter and smoother thru the rev range and now am reaching full throttle on the wrist without the engine screaming...
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Old 31 December 2014, 15:39   #10
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