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Old 19 November 2018, 14:01   #1
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Country: UK - Scotland
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Boat name: Vega
Make: Valiant
Length: 4m +
Engine: Mariner 60 Outboard
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Valiant 490 Best prop?

Hi, Just had a great day on the Clyde with the usual weather.



The rib is fitted with a Mariner 60 2 stroke, with an aluminium 3 blade 11*14 prop.


Boat responds exceptionally well off the mark, but going from mid to high revs it literally leaps forward even in rough conditions as though a turbo has come in.


3 X 20l fuel in the bow has helped the handling, along with a Doel Fin which gets it on the plane much quicker.



Top speed unladen on a calm sea is about 32k at 5500rpm.


Just wondering if a slightly higher pitch prop might calm it down a bit??


Any advice or previous experience with this set up would be greatly appreciated.


Cheers


Chris
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Old 19 November 2018, 14:28   #2
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Sounds like you can go up in pitch, will give you lower rpm for the same speed so should save fuel too
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Old 04 December 2018, 08:54   #3
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Country: UK - Scotland
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Boat name: Sula
Make: Ribcraft 4.8m
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Surprised the engine isn't over-revving with a 14 pitch propeller. The lower pitch is perfect for hole shot but going up in pitch should increase overall speed. From memory increasing pitch size reduces 200rpm each time.

I've got a Ribcraft 4.8m with Tohatsu 60hp tweaked to 70hp, that is paired up with a Solas stainless steel 17 pitch propeller at just over 5,200 revs on WOT. I've also got a standard 15 pitch aluminium propeller which is fine for day to day use.
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Old 04 December 2018, 09:01   #4
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Thanks for that info. Just got a 17" stainless from Mich Wheel. It was on offer for black Friday so I got a good deal. It's a Christmas present from the wife, so next month before I can try it. I'll come back with results.


Cheers


Chris
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Old 18 December 2018, 13:44   #5
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Correction to above (couldn't see the edit button) it's 15" prop not 17.
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Old 08 January 2019, 09:20   #6
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Update: Back on the Clyde last Friday, (usual weather).


Prop absolutely brillant. Extra 4 knots.



Improved mid range performance and fuel economy. (1.4miles/litre).


Hoping to get to Ribfest this May!
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Old 08 January 2019, 09:49   #7
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What RPM you spinning?

You want to be close to the max higher number with normal load.
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Old 08 January 2019, 09:59   #8
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Was at 5400 with the 14" prop, dropped to 5200 with the 15" stainless

(think it's 10,1/4*15). Increase in speed and better fuel consumption.



Must have been really underpropped wi the 11*14.



Weight in the front and doel fin helped as well as it used to "rear up" before getting on the plane.
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