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Old 27 June 2013, 09:38   #1
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Country: Canada
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Boat name: Zodiac
Make: Zodiac Futura MkIII
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Engine: 50 HP ETec Tiller
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Futura Mk3 owners: What prop/max. speed?

Trying a new motor and I don't think I've found the right prop yet. E-Tec 50 with tiller handle.
Started with a Viper stainless 13 7/8 X 17. max rpm was 5250: not high enough. Dropped to same prop, lower pitch 13 7/8 X 15. rpm.s are now higher and close to optimal. But max. speed is lower than I had hoped for, at only 26-27 m.p.h. with a light load.
What props/HP are you guys using and what speeds are you getting?
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Old 27 June 2013, 11:09   #2
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Is that sib well inflated to it's max factory recommended working pressure, well load ballanced, well trimmed and engine sits at opt transom height ? The final top speed will depend on the engine brand use and different pitch/size prop availability for that brand HP.

Which was your wot speed with standard delivered prop when at 5,250 rvs ? 27 MPH at near max wot rpm is definitely low for a 50 horse. My 430 Mt rib with a 18 HP it's doing near 22 Knots with me alone at wot.

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Old 27 June 2013, 11:26   #3
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Yes, inflated, balanced. GPS wasn't working that day but it was around 25-26 I estimate. I'm up one hole. Might try coming up one more, but with previous motor up 2 holes I got occasional ventilation.
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Old 27 June 2013, 11:35   #4
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Float sib alone, trim engine to be perpendicular to boat, anticav plate must ride paralell to water surface when boat is on plane. Probaby engine sits too high on transom, prop is not biting water properly as it should at wot.

Place a mate up front, sit on tube next to transom, full throttle, once on plane pull your head out and check water flow passing through leg, do you have water splashes over or out transom ? If not. Check if water flow passes near lower anticav plate or under small upper deflector plate so to know which transom height that engine sits on.

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Old 27 June 2013, 11:42   #5
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Done that. Water passes under but close to upper small deflector.
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Old 27 June 2013, 11:55   #6
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How close ? Is water flow flowing paralell to upper small def plate as in pic ? Are you testing wot on flat, no wind water conditions ? Are U using a pressure gauge to inflate sib's tubes & small speedtubes if having so ? Do you have a center cosole, or it's a plain open sib ?

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Old 27 June 2013, 12:25   #7
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Yes. Flows nicer than in pic. Not so splashy.
I can see anti vent. plate somewhat.
Yes, yes, yes and yes.
I have power trim adjustability.
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Old 27 June 2013, 12:51   #8
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Water seen on posted pic is no splashy at all, it's flat churning water from slightly choppy sea when that sib/engine combo was tested. You should not be able to see anticav plate whatsoeever if water flow passes slightly under small upper plate. Would you say something like this...

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Old 27 June 2013, 12:57   #9
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More like that than the first pic. Thanks!
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Old 27 June 2013, 13:10   #10
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While the Viper is made for V4 and V6 engines...
Try going back to the 17" pitch, but trimming the motor up more.

You need a GPS and current free water, minimal wind. Don't "estimate" speed, measure.

I suspect you are overpropped but getting ventilation and its ventilation which is confusing your rpm changes not actual changes in speed.
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