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Old 20 May 2010, 19:38   #1
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Country: Ireland
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Tornado 7.4 spec

Hi lads,
I'm looking for late 90' Tornado 7.4 spec ( specialy weight and max twin outboards power)

Maybe someone can advice me with prop. Currently I had 200hp Merc Optimax year 2000 with prop from twin and it's to big. WOT is 4850rpm 35 knots. Prop is Laser II 21p 14. I thing it's should be 17p but it's only my amateur calculation.
)

thanx

Mat
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Old 20 May 2010, 20:00   #2
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I reckon you're about right with a 17", but you may find an 18 would be better as you're probably not hitting anywhere near peak horsepower at 4850 rpm.
According to Mercury you should be between 5000 and 5750 rpm. Personally I'd head for around 5400-5500 if you're running lightly loaded so you won't be massively overpropped if you load the boat right up. That's based on you using the same prop type but a different pitch.

It's a shame the power/torque graphs aren't online as it'd make prop selection a bit easier.
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Old 20 May 2010, 21:09   #3
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hi mat, i've a 13 3/4 by 19 that you could try ? its reving out on me, ive 7.8 with 250 yam , where you in ireland?
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Old 20 May 2010, 22:39   #4
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Country: Ireland
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Quote:
Originally Posted by ribdraft View Post
hi mat, i've a 13 3/4 by 19 that you could try ? its reving out on me, ive 7.8 with 250 yam , where you in ireland?
I'm in Co Wexford, on Sunday we will be in Kilmore Quey
it will be good to try prop like yours

thanx
m
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Old 20 May 2010, 22:46   #5
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Country: Ireland
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Quote:
Originally Posted by Nos4r2 View Post
Welcome to Ribnet

I reckon you're about right with a 17", but you may find an 18 would be better as you're probably not hitting anywhere near peak horsepower at 4850 rpm.
According to Mercury you should be between 5000 and 5750 rpm. Personally I'd head for around 5400-5500 if you're running lightly loaded so you won't be massively overpropped if you load the boat right up. That's based on you using the same prop type but a different pitch.

It's a shame the power/torque graphs aren't online as it'd make prop selection a bit easier.
Thanx for info, you right about graph but also I don't understand why shops ( or even main dealers only) don't have a prop test sets. I heard that Mercury is doing that from time to time
thanx a lot for ur respons.
Cheers
mat
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Old 21 May 2010, 04:38   #6
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Country: Ireland
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Engine: Mercury Opti 200Hp
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Quote:
Originally Posted by Matmagic View Post
I'm in Co Wexford, on Sunday we will be in Kilmore Quey
it will be good to try prop like yours

thanx
m
Was late and I forgot to mention that our engine was working before on different boat in twin and it's left prop...

Cheers
mat
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