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Old 27 June 2013, 13:23   #11
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Boat name: Zodiac
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I have a GPS. I referred above to only one event when my batteries died.
Speed is constant, not fluctuating. If ventilating i would hear revs increase as it ventilates, and speed would drop.
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Old 27 June 2013, 13:27   #12
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Is that a standard prop factory delivered ? If not, better ask Evinrude which of their brand props, size/pitch would recommend for that engine mounted on a light weight boat ? Then going from there to a +,- pitch for best top sib/engine rpm optimization if needed. Much better than making other brands props costly purchase guessing...

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Old 27 June 2013, 13:39   #13
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Yes, OEM prop as recommended in consultation with the dealer and the supplier. First tried 17 pitch, then 15 to get more rpm.
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Old 27 June 2013, 14:03   #14
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Very strange indeed, and that's not a heavy sib, with a 50 should fly to US border. That's a center console sib/engine combo, with small speed tubes under main ones, right ? Ask dealer/supplier which top speed are you supposed to achieve with both recommended props ?

With a 30 HP OEM standard prop, my 430 rib achieves 31 knots at wot. Original delivered OEM props used on light sib/rib inflatables performs top best as personally have rpm tach & gps tested.


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Old 27 June 2013, 14:05   #15
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I had the old Futura Sport (Small speed tubes) with a Yamaha 50hp 2 stroke. Stunningly fast sib which hit just over 50mph when propped and trimmed up.

So on the face of it 25mph for yours does seem slow, however the new bigger speed tubes do make a difference and Zodiac only quote a maximum speed of 37mph with a 60hp engine.

Did you try it with the original Evinrude prop ? I'm a sucker for shiny new props but I have realised over time that the original prop can often be the best one to use.
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Old 27 June 2013, 14:27   #16
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Quote:
Originally Posted by Northern Pike View Post
Yes, OEM prop as recommended in consultation with the dealer and the supplier. First tried 17 pitch, then 15 to get more rpm.
The SS viper is NOT the standard prop for that engine. Its made for V4 engines in the 75-140hp range. For much heavier ~24ft cruising boats to run in the 25 mph range.
# 389949 V4 SST II 13.75 x 15. For 22-26 ft. Cruisers

I'm surprised its working for you on a 50hp Etec at all.

I would go back to a standard 3 blade ali prop, no cup, no rake, and figure out performance at that baseline before messing with alternatives. You are overpropped, but its not a question of pitch which is roughly correct. The incorrect blade shape is screwing you up and slowing you down.
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Old 27 June 2013, 15:15   #17
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Quote:
Originally Posted by Locozodiac View Post
That's a center console sib/engine combo, with small speed tubes under main ones, right ? Ask dealer/supplier which top speed are you supposed to achieve with both recommended props ?
Its a tiller, no console. Yes, Zodiac Futura Mk 3 has speed tubes. Dealers no nothing about inflatable boats.
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Old 27 June 2013, 15:31   #18
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Originally Posted by Landlockedpirate View Post

So on the face of it 25mph for yours does seem slow, however the new bigger speed tubes do make a difference and Zodiac only quote a maximum speed of 37mph with a 60hp engine.

Did you try it with the original Evinrude prop ? I'm a sucker for shiny new props but I have realised over time that the original prop can often be the best one to use.
Yes, Zodiac spec.s 37 mph max. for this hull. I should be able to come closer than half with max. recommended HP (50) don't you think?
60 is max. allowed.

This is a brand new motor and prop. I started with a best guess according to dealer, factory rep., and my experience. I think we are in the ballpark when it comes to pitch, but I think the larger diameter is my problem.
This motor has the same large gearcase as the bigger ones mentioned by capnjack, so available props seem to be a little large when it comes to diameter.
A stainless prop was included as part of a promotion. I thought that was a great bonus but so far the first 2 I've tried haven't worked as well as I had hoped.
I've been thinking about aluminum too lately, but since I've got a stainless one coming to me, I had better settle on one of them first. I can always sell it and buy 2 aluminums.
Thanks for your help guys.
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Old 27 June 2013, 16:05   #19
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Originally Posted by Northern Pike View Post
Yes, Zodiac spec.s 37 mph max. for this hull. I should be able to come closer than half with max. recommended HP (50) don't you think?
60 is max. allowed.

.
Yep, you should be getting a bit more, 33-34mph ?

I love the Etec, we had a 90hp on a centre console and it was fantastic. As everyone has pointed out the SS props you are running are way too big, look for a prop with a 11-12" diameter and stick with the 17" pitch. Propping boats is a bit of a black art but I would find out what the standard ali prop supplied on the engine is and get one of those.

Its not perfect and you have to use a rib rather than a sib but I always start with this prop calculator:

Prop Selector | Mercury Marine

Have just run it making some assumptions for your boat and it suggests 33mph with a 11x17 3 blade aluminum, I guess I wasn't too far off
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Old 27 June 2013, 16:27   #20
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Have just run it making some assumptions for your boat and it suggests 33mph with a 11x17 3 blade aluminum, I guess I wasn't too far off
^^^^^^
Ding!!! Diameter and blade shape/area/size are just not right for this motor.

There might be another SS prop that works well, but its not going to be in the viper product line.
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