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Old 08 April 2014, 14:20   #11
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Originally Posted by Exe treme View Post

A few thoughts for consideration beyond the engine position, but am I right in thinking the engine needs to be lower because the boat will be much higher in the water when planning?
If the engine were the correct shaft length for the boat in the first place, yes. But it looks to be a long shaft engine on a short height transom.
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Old 08 April 2014, 14:36   #12
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Originally Posted by Exe treme View Post
Hi

A few thoughts for consideration beyond the engine position, but am I right in thinking the engine needs to be lower because the boat will be much higher in the water when planning?

I had a similar factory built set-up on a Lodestar Trimax 3D-V. The two main difference are:
1: The sponsons on the Lodestar are more inboard, so the main tubes still contact the water to provide lateral stability.
2: An inflatable keel runs the length of the hull to the transom, giving a much deeper V. This effectively produces a trimaran, offering better directional stability as the V cuts through the water.

As a comparison, your sponsons are nearer the bottom of the tubes, and your boat is much flatter. Therefore, when planing, the sponsons are the only part of your boat that can have contact with the water. There is no centre V to help directional stability, and there is no lateral stability from the main tubes, if the boat keels over beyond the sponsons.

This is only an idea, but perhaps the sponsons need to be moved further inboard, so the main tubes can help stabilise the lateral movement?

Here are some images of the Lodestar's design, including one showing engine height and tube position.

You might be on to something, the Futura also has the speed tubes more inboard and the keel is the same depth as the sponsons. Maybe sibs of this shape need to run like a trimaran to be stable ?
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Old 08 April 2014, 16:35   #13
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Originally Posted by captnjack View Post

If the engine were the correct shaft length for the boat in the first place, yes. But it looks to be a long shaft engine on a short height transom.
Hi Captnjack

Understand that but there must be an additional 10cm (4") to the cav plate because of the sponsons. Not far of the difference between a short and long shaft?
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Old 08 April 2014, 16:58   #14
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Hi guys, thanx for the imputs,
My engine is a short shaft, and the boat was set up for a shoft shaft, i cutted a groove into the transon because the manufacturer of the hi jackers said to i had to look at it to see if my motor isnt going to be too high,

The engine wasnt at the manufacturer while he was installimg the high jackers,

I agree with it needs something to improve the lateral flex, the guy told me to pump both the oversized really stif and the high jackers to about 1 bar to avoid flex otherwise it wont be as rigid, a inflatable keel might help too but doesnt make sense when trying to create air underneath the deck of the boat right?

I dont think the high jackers should be more inwards, personally i think its in the right position, it is really stable and easy to drive when the bow is lifted.As soon as the bow get lowered then it feels like the steering is exagerated it if steer left then it steers too left and the. I have to steer right and it steers too much to the right , this steering process is so harsh it feels like i get thrown off my balance.

I wonder if the start of the highjacers underneath the bow, is perhaps slightly started to early? Or perhaps nor exaclty straight, look at this comparison.
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Old 08 April 2014, 17:02   #15
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Compare this photo to the one above?

Does my high jackers start perhaphs to easly and have a slight bend inwards ?
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Old 08 April 2014, 17:12   #16
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Hello again

The difference is that one has been designed to work like that, and the other has been coverted to look like that.
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Old 08 April 2014, 18:15   #17
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Is your inflatable deck at full pressure? Zap cats have a steel transom, fibreglass nose and solid deck to stop the pontoons potentially heading off in different directions. If your deck flexes at all the tubes might go slightly toe-in or out leading to directional stability problems?
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Old 09 April 2014, 02:12   #18
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Is your inflatable deck at full pressure? Zap cats have a steel transom, fibreglass nose and solid deck to stop the pontoons potentially heading off in different directions. If your deck flexes at all the tubes might go slightly toe-in or out leading to directional stability problems?
Its a wooden dect consisting of 4 wood pieces conected with aliminium insert pieces.

So it flexes a little bit, thank you for the input.


Trimming of the engine in n negative degrees, in other words the bow it to low so that it throws up alot of water, does that effect the directional stability?
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Old 09 April 2014, 14:48   #19
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It's a costly experimentation, one thing is factory tested and built, other story add-on gadgets glued on standard sibs. Does sib have a central inflatable keeel, are all air chambers inflated o its factory recommended working psi ?

What does installer say about your extremely poor performance combo ? Is him a Pilatus type installer ? that is, sets and takes and washes hands afterwords. Installer should be responsable for his work, let him optimize combo performance for you...

Definitely Unhappy Boating
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Old 09 April 2014, 15:22   #20
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Quote:
Originally Posted by Bos suzi View Post
Hi guys, thanx for the imputs,
My engine is a short shaft, and the boat was set up for a shoft shaft, i cutted a groove into the transon because the manufacturer of the hi jackers said to i had to look at it to see if my motor isnt going to be too high
It still seems a little high but ok.

Quote:
Originally Posted by Bos suzi View Post
I dont think the high jackers should be more inwards, personally i think its in the right position, it is really stable and easy to drive when the bow is lifted.As soon as the bow get lowered then it feels like the steering is exagerated it if steer left then it steers too left and the. I have to steer right and it steers too much to the right , this steering process is so harsh it feels like i get thrown off my balance.
You are bow steering. On a normal SIB this would happen with too much weight in the bow or the engine trimmed down too much. In your case its because of the speed tubes and the fact that you want to travel slow under bridges. You altered the boat so much it doesn't want to go slow. Its meant strictly for racing now with the bow off the water and only the rear portions of those speed tubes in contact with the water as you fly along at full throttle. If you want those (very large for the size and weight of the SIB) speed tubes then you are going to have to drive it much much faster to create the bow lift and give you directional stability. If you want to go slow and stable then cut off the speed tubes. You can't optimize the hull for both at the same time.
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