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Old 13 October 2013, 13:23   #1
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Pitch on yamaha K series propellers

On my SR 5.4 (90 YAM) a yamaha K series 19 inch ali have so far worked OK.
The sweet spot has been in calm seas abt 4200 rpm, speeed 28+ knots and according to fuel flow abt 22-23 l/h. Handling ok, but grip is not always perfect and need to be trimmed out pretty much.

Today tested a black max ali prop, also 19. got approximately same speed and consumption with 3800 rpm, prop seams a bit too high pitched for my usage, and struggled to go over 4600 rpm. So it seams like there is a significant difference in the actual pitch on either the Yam or Mercury prop. Wa

It was choppy seas so did not get a clear picture but by the feel, seams like there is slightly more bow lift on the black max, less need for trimming out.

Anyone else noted similar pitch "errors" on the K series props?
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Old 13 October 2013, 15:56   #2
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Check diameter

Hi,

what is the diameter for both props ? There could be an explanatory difference ?
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Old 13 October 2013, 16:18   #3
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There is a lot more to a prop than just the pitch and diameter. Shape of blade, the amount of cup, the length of the hub etc etc.

I would use the prop you feel suits you best.
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Old 14 October 2013, 00:52   #4
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They are both 13X19. For sure there is a lot of differences but 400 rpm is unusual much as both are standard ali propellers. In the Black Max range guess the 13 x 17 would be better for my needs, the K19 is not bad either.
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Old 14 October 2013, 02:59   #5
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A tiny difference in diameter will easily manifest as 400 rpm difference. Despite all the talk here about pitch, for my prop selections over the years, diameter ends up being a far more critical variable.
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Old 14 October 2013, 07:22   #6
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Quote:
Originally Posted by captnjack View Post
A tiny difference in diameter will easily manifest as 400 rpm difference. Despite all the talk here about pitch, for my prop selections over the years, diameter ends up being a far more critical variable.
That is probably the case. Then will give it a kiss with the angel grinder, style" ballistic" to sort the diameter...No, only joking In fact I have 17 ballistic that will try out when having the time, interesting to see how that will perform.
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Old 14 October 2013, 08:27   #7
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+1 for the diameter.

Also rolled in there is the engine's top end torque......
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Old 14 October 2013, 12:46   #8
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And the thickness of the leading edge of the blade.

I've been using Michigan Wheel Match props on my Yam for a few years. They've got a sharper leading edge than standard Yam props, and they pick up a bit better.
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Old 14 October 2013, 14:00   #9
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Hi,

searching for the right propeller seems to be really difficult. My boat came with an old scuffy Yamaha 12 5/8 x 21 with a topspeed of 42 - 43 knots but reaching only 5300 rpm at WOT and offcourse some chine-walk. So trial and error began, with a 13 3/8 x 19 Ballistic I lost a few knots topspeed but gained a faster hole shot leaving WOT at only 5100 rpm. Then we checked the 21s diameter and discovered that it was some kind of special propeller for light boats. My SR 4.7 weighs 250 kg + 122 kg for the Yamaha 90 and then some fuel etc leaves me at 400 kg ? which I guess is a light boat .
Next a friend borrowed a 20 inch Laser II, which behaved a little odd. Back in the harbour I found the explanation: the propeller was 22 inches.
The 4-blade Solas was really fun to drive, but topspeed left a little to desire, 38,5 - 39,5 (downwind)... So the search goes on, next in line two steelpropellers, 17 & 18 inches.
Any suggestions for propellers or do I have to accept that a 21 inch aluprop is the best for my boat ? I am trying to reach 5600 - 5800 rpm at WOT and a good grip + topspeed. I havent started to play with the engne hight yet. The cavitation plate is about level with the bottom, so it could be higer ?

Test table:

Alu Steel Steel Steel
Yamaha Solas Laser 2 Ballistic
RPM 12 5/8 x 21 4 x 13 x 17 13 x 22 13 3/8 x19
2000 14,7
2500 15
3000 20 19
3500 25,7 25
4000 30,5 28,7 36
4500 35,3 32,5
5000 39,3 36
WOT 42 - 43 38,4 - 39,3 39,7 41,3
RPM 52- 5300 53- 5400 4400 5100
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Old 16 October 2013, 04:57   #10
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Had a similarly frustrating experience this summer myself after my yam 70 had an argument with something solid and made an interesting shape of 2 of the blades.. Prop was a yam k 13 1/4 x15 and totally unmarked...wot with my normal load was 5500..right in the middle of the rec 5-6k only replacement i could get at short notice was a Michigan wheel..quoted at same size and pitch but when fitted wot way down at 4800 and acceleration none existent..was convinced i had lost 20hp somewhere! Had the original yam prop rebuilt and put that back on and wot 5500 again with driveability 100% better...slight difference in blade shape/area seems to have had the same effect as 3 inches more pitch! Slightly annoying when sold as an equivalent replacement for the original Yam K series! Still...its back in the box as a spare, and i haven't got to go looking for my missing power!
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