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Old 14 April 2008, 15:35   #1
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Country: UK - England
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Prop selection

ok, after a run to teignmouth this weekend to try out the new prop ,findings were as follows.

Yamaha 90 2 stroke, peak rpm 5500.... 60 Litres of fuel and one person,( still could not acheive 40 knts even on 20 litres of fuel left) i did speak to prop developments and they recommended a 13.25 x 17 s/s prop!!! is this right ???

13x19 ally 5300 rpm and 39 kts
13x19 S/s 4700 rpm 33.5 kts
13x17 ally 5500 rpm 33 kts,

really would like to reach 41 kts, IS THIS DO-ABLE???

(cos chris's boat is still faster than mine)
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Old 14 April 2008, 16:07   #2
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What boat is it?
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Old 14 April 2008, 16:08   #3
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Country: UK - Wales
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Boat name: doggypaddle
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matts boat is an avon searider 5.4m with a heavier than standard console.
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Old 14 April 2008, 16:24   #4
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Country: UK - England
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Only ever managed 39.7 knots in my 5.4 Searider. Outhill console. 2 persons. 100 litres fuel.

90hp 2 stroke Mariner 20" Laser II.

Reckon it might have gone a bit quicker if the engine was lifted an inch or so but sold it before I had an opportunity to try it.
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Old 14 April 2008, 16:29   #5
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Quote:
Originally Posted by matt h View Post
ok, after a run to teignmouth this weekend to try out the new prop ,findings were as follows.

Yamaha 90 2 stroke, peak rpm 5500.... 60 Litres of fuel and one person,( still could not acheive 40 knts even on 20 litres of fuel left) i did speak to prop developments and they recommended a 13.25 x 17 s/s prop!!! is this right ???

13x19 ally 5300 rpm and 39 kts
13x19 S/s 4700 rpm 33.5 kts
13x17 ally 5500 rpm 33 kts,

really would like to reach 41 kts, IS THIS DO-ABLE???

(cos chris's boat is still faster than mine)

They do say that a stainless prop normally needs to be a couple of inches less pitch than the equivalent Ally prop so I would say your next trial should be a 17" stainless prop, I reckon that will get you pretty close to your perfect set up and if it needs tweaking then send it to steel developments to get it perfect.

Interestingly enough great minds must think alike cause I have been doing some investigation into how I can get a couple more knots out of my set up and I spoke to Ralph the Outboard Wizard (in the US) about options.... he suggested that I should try the new BRP Rogue four bladed prop and that I should run the engine as high as poss on the transom.

Good for 45 knots I reckon
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Old 14 April 2008, 16:46   #6
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Hi matt

where did you get all those props??

go with the steel developments recommendation, 13x17 titan stainless steel, ive seen 40kts @ 5100 revs approx 20ltrs fuel.

im suprised you only got 33knts with 13x17 alloy, i gone back on my standard prop while mines still a bit damaged and im seeing 35knts @ 5500 with plenty of fuel.

is it worth trying a second satnav unit to calibrate your speed
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Old 14 April 2008, 18:18   #7
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When using a stainless steel prop, try to lift the engine as high as possible without causing excessive cavitation or too low water-pressure, it will give you more RPM's and thus more speed.
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Old 16 April 2008, 14:57   #8
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Hi Matt,
with a transmission of 2:1 , or 26:13, normally 1 inch of pitch means 500 1/min more ore less.
Mike
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Old 16 April 2008, 17:30   #9
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thanks for the input guys, really appreciate it, going to Nick chris's prop while he's adjusting something or other!!

More Speed egor!!
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Old 19 June 2008, 00:02   #10
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what shaft length are your motors? 20" or 25"?
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