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Old 12 April 2014, 13:31   #31
Landlockedpirate's Avatar
Country: UK - England
Town: St Helens
Boat name: Wine Down
Make: Maxum
Length: 8m +
Engine: Inboard
Join Date: Apr 2012
Posts: 934
Originally Posted by Bos suzi View Post
@ rik_elliott i cant find any semicleaver or cleaver prop for 15 hp, in other words, 10 inch or 9inch pitch

I doubt you will, a 15hp on a boat of your size/weight simply doesnt have the torque or power to spin anything other than a standard or high thrust prop efficiently.

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Old 12 April 2014, 16:33   #32
Country: Australia
Length: 4m +
Join Date: Apr 2014
Posts: 2
From what I can see your motor is way too deep. About 6 inches. At speed the motor should lift right out so that the top of the prop is almost coming out of the water. Your intake should be just above the gearbox between the hump and lower plate. You might be looking at the wrong grill

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Old 26 April 2014, 03:05   #33
Roflhat's Avatar
Country: UK - Scotland
Town: Isle of Lewis
Make: Ceasar Thundercat
Length: 4m +
Engine: Yamaha 70ces
Join Date: Jul 2010
Posts: 705
Hi mate,
replied to you on another forum.
If you're after a semi cleaver or cleaver for that engine give Ron Hill a shout, he can make you what you need (if he doesn't already have it) and they're pretty cheap too.

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Old 22 May 2014, 05:58   #34
Country: Norway
Town: OSLO
Boat name: Futura 470S mk3
Make: Zodiac
Length: 4m +
Engine: outboard 55Hp
Join Date: May 2014
Posts: 1
This looks wery like the original Futura solution of Zodiac. but what you are describing about handling is in slow speeds yes?
I guess that your problem lies in the fact that you have added bouyancy to your boat and thereby disrupted your steering stability in slow speeds. the added tubes will in fact not give you less handlingstability at higher speeds because of now you have in fact two keels and the boat now is an catamaran.
The main issue is rigth pressure in all the tubes on your boat and that is usually a lot higher than you imagine.
I myself was amazaed when I started measuring this.
the result is a mutch more rigid body and the boat less influeced by the surroundings.
I own a Zodiac Futura MKIII 470S, engine of 55Hp the top speed is approx 45 knots (ticked on GPS).
On this rig I used a ProPulse adjustable composite proeller this gave me the speed of 45 knots in ahead fair breeze.
But since the boat weigths just 90kg and the engine likewise, the rig is wery tikly in windy conditions in highspeeds.
A SIB is allways more influented by the enviroments like wind and so, due to the fact that it has a smaller portion of the body in the water and there by a huger body in the wind.
It's like a ball on the water. you can newer sink it but you can capzize it.
(bare with my bad English, I am Norwegian by birth).
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Old 22 May 2014, 12:23   #35
dave3235's Avatar
Country: UK - England
Town: Bristol
Boat name: Salty Cheeks
Make: Honwave
Length: 3m +
Engine: 20hp 2stroke Mariner
Join Date: Mar 2014
Posts: 453
Originally Posted by Bos suzi View Post
Hi guys.

I am new to this forum and would really like some help from experienced inflatable boaters.

I have 3.3 m fully infalable with a 15 hp 2 stroke,

I recently installed small pontoons underneath (high jackers ) to create a tunnel hull, this was done professionally by one of the companies that specialize in tunnel hulls for racing.

I currently am strugling with handling issues,

It is realy difficult to to steer and have directional stability. If i am on the dam , it is realy hard to drive underneath a bridge as the boat flanks left and right and is extremely sensitive to any movement on the throttle in terms of steering.

My highjackers was around 0.8 bar, should it be pumped harder?

Should i avoid sitting on the oversized pontoons?

Should i try lowering the engine deeper in the water?

I am really worried , and would love just to have directional stability,

Can this be caused by running a trim which is too negative !?

It feels as if when i am on the plane, that the tunnel hull suddenly bites on the water trying to then change to direction of the boat.

Please help ,

Thank you.
Hi if you don't mind me asking, where did you get the tubes fitted and how much in sterling

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