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Old 27 May 2014, 06:16   #1
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Country: UK - England
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Prop size for a zodiac 4.2 with a yammy 50

Hi all,

Zodiac 4.2m rib with a yamaha 1990 50hp 2 stroke long shaft.

Need to change the prop, really want overall good performance rather than acceleration, top speed etc.

Boat will be used for beach hopping, coastal trips, and a bit of wakeboarding, mainly 2 or 3 up maximum.

Advice required on prop size, pitch etc

many thanks
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Old 27 May 2014, 06:30   #2
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What have you got on at the moment ? What does it do well and what part do you want to improve ?
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Old 27 May 2014, 06:43   #3
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hi, only done one sea trial so info lacking. Seemed to perform very well 2 up, the issue is the prop is bent and needs replacing, presuming its the original but not sure what size it is.
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Old 27 May 2014, 09:10   #4
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You will need the original size as a starting point, it avoids expensive guesses Number will be stamped on the prop in the form of (Number) x (Number), this gives you the diameter and pitch. It will be something like 13 x 15 etc.

Props can be fixed easily and cheaply if you are happy with the size of the current one, send it Steel Developments, costs about 40 and it will come back like new. They also sell new props as well, buying a spare prop is a good idea and it reduces postage if you buy at the same time as a repair.

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Old 28 May 2014, 04:48   #5
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Depending on what weight the boat and crew usually are, the yamaha 50's on zapcats use 11x15p for all round props. Maybe for a heavier boat you want 13 or 14p.
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Old 28 May 2014, 10:46   #6
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You need to put a tach on the motor to see what max RPM is.
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Old 28 May 2014, 11:16   #7
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more info

max RPM for engine is 5,500, I have measured the existing prop and as far as i can calculate it comes out at 10 x 17, I think the closest yamaha prop is 10 3/4 x 17?

As I said I am happy with the performance but the prop is bent and needs replacing.

Many thanks
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Old 28 May 2014, 13:14   #8
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Quote:
Originally Posted by dij66 View Post

As I said I am happy with the performance but the prop is bent and needs replacing.

Many thanks

It doesnt matter how bent it is, or how many blades are completely missing, Steel developments will sort it.
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Old 29 May 2014, 21:57   #9
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Standard factory delivered props are medium ptched, on a rib that size will work perfectly well. If wanting to know if revs up to 5500 rpm must install an induction tach to check wot numbers with you alone and lightly loaded sib..

That 420 with 50 HP should fly as in Back to the Future. My 430 rib with just a 18 HP and lightly loaded, is extremely fast...

If happy with current combo performance buy a new one with same pitch.

Happy Boating
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