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Old 25 August 2009, 08:58   #11
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or you could try a 21 inch aluminium as i originally suggested, should be in the same ballpark as a 20 inch SS rpm wise.cheaper and wont cause as much damage if you hit anything.
I thought going from 4 to 3 blades would reduce the drag a bit!
Nos swears by Mitchegan props think its a match he uses(with a yam)
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Old 25 August 2009, 19:45   #12
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Nos swears by Mitchegan props think its a match he uses(with a yam)
It is, but the damn thing spun the hub while we were on holiday
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Old 26 August 2009, 05:40   #13
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Thanks for all the info, excellent forum.

Ill continue to experiment with props, the top speed is all academic really, its just for my own curiosity to see how much I can get out of it!
I was out on Monday in Cork Harbour & the swell was such that I couldnt make good more than 20kn anyway.
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Old 01 September 2009, 11:41   #14
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avon searider prop

Yamaha 90 hp 2 stroke, 13 3/4" x 17" aluminium prop 38 knots @ 5500 rpm one on board with 91 litres fuel, 36 knots with two on board @5300 rpm same fuel load. When I fit yamaha ss prop same size top speed drops to 30 knots @ 4800. SS props are more aggressive so need to drop the pitch to 15" to get rpm 5200. If your engine is goes to 6000 rpm with 19" aluminium prop you should increase the pitch to 21" and rpm should come down to 5600. If you use ss prop 19" to 20" should be ok. Usually 1" of pitch = 200 rpm, go up in pitch to bring rpm down.
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Old 02 September 2009, 09:30   #15
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What is the gear ratio on the Yamaha?
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Old 02 September 2009, 10:33   #16
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Yamaha 90 hp 2 stroke, 13 3/4" x 17" aluminium prop 38 knots @ 5500 rpm one on board with 91 litres fuel, 36 knots with two on board @5300 rpm same fuel load. When I fit yamaha ss prop same size top speed drops to 30 knots @ 4800. SS props are more aggressive so need to drop the pitch to 15" to get rpm 5200. If your engine is goes to 6000 rpm with 19" aluminium prop you should increase the pitch to 21" and rpm should come down to 5600. If you use ss prop 19" to 20" should be ok. Usually 1" of pitch = 200 rpm, go up in pitch to bring rpm down.
Sure thats not a 19" rather than a 17"to get 38knots @5500rpm?

If not thats strange because my yam 80 went over 5700rpm @ 35knots with a 17" is it a K series?
I thought MattH tried 17K and 19K series too and found the 17 overrevved?
I currently run a 19 with the 80 and cant quite get 5500 rpm but i guess it would be around 38knots
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Old 02 September 2009, 10:45   #17
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What is the gear ratio on the Yamaha?
i believe its 26-13 ie 2-1.
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Old 07 September 2009, 10:35   #18
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Got a loan of a 13 x 21" prop over the weekend, RPM down from 6000 rpm to 5750 rpm & speed up to 39.5 knots with one person on board & 65l of fuel.
Im going to try to get my hands on a 20" SS Laser II as recommended here (hopefully second hand), that should reduce the rpm by a couple of hundred, add a little more speed & problem solved!

Thanks for all advice received...
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Old 08 September 2009, 05:49   #19
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Sure thats not a 19" rather than a 17"to get 38knots @5500rpm?

If not thats strange because my yam 80 went over 5700rpm @ 35knots with a 17" is it a K series?
I thought MattH tried 17K and 19K series too and found the 17 overrevved?
I currently run a 19 with the 80 and cant quite get 5500 rpm but i guess it would be around 38knots
It's the 17k that came with engine as standard fit, also tried Yam ss pro 19" pitch, engine would only go to 4500 rpm.I keep trying different props, but always end up going back to the standard alu prop
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Old 08 September 2009, 07:09   #20
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Originally Posted by Turbodiesel View Post
5.4m Seariders with Mercury 90's always get fitted with Laser 2 Props, 20" pitch.
should do about 38knts at about 5400-5600rpm.
That's what i had fitted to mine. 39.7knots was the best we got. can't remember at what RPM

90hp 2 stroke Mariner - same as Merc.
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