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I can imagine how it works...explain it in 25 words or less er...no. I'm thinking that it is an interaction of prop walk/torque that does it.
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Still waiting for my boat to come in.it came in
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I could see how the direction of rotation of the thrust cones would have an impact on transom/bow lift. Here's what I have in the works:A nation of sheep breeds a government of wolvesComment
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It's a simple explanation, the actual mechanics of it are quite in depth, but spinning inwards gets more clean water to the prop.
That's why it's important to mount your drives as close to the inside of the tunnel as possible.
On the fastest european cats, the drive mounts are usually modified a bit to shift them as close as practically possible to the tunnel.Comment
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Well I don't know for technical but in my simple mind this is what I see!
When they rotate inward the props pull the transom down in the water ... so the bow lift & runs drier!
When they rotate outward the props would have a tendency to lift the transom and make the hull run wetter!
Don't know if I'm right but...............We did it with a Bang!
Cats Are Where It's At!Comment
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There seems to be unanimous info that spinning inwards is faster, but I still can't figure out why this would be so.
If you have studied the water flow at the rear of a cat hull you will see that at slow to medium speeds there is a rectangular wall of water exiting the tunnel and on either side there is a depression from the water flowing under the sponsons.
If the props are mounted as close as possible to the inner edges of the sponsons it seems to me that the inner arc of each will be in contact with some of the wall of water from the tunnel, and if they are spinning inwards they will tend to climb this wall , ie prop walking upwards, which will lift the transom.
However the opposite seems to be happening !!!!!
To confuse things even further, at high speed as the hull lifts out of the water, the wake tend to flatten down and the central wall of water almost disappears, so the props are running in almost flat water with only the lower arc submerged.
At this point I cant see how spinning inwards or outwards would make any difference , but we know it does.
I need to have a cuppa tea and a lie down
Graham.Comment
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Well, I decided to swap around to the "rotating inward" arrangement for the first outing. After I get it working right (maybe "if" would be better
), I can reverse it and see what happens. 
A nation of sheep breeds a government of wolvesComment
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AMEN BROTHA!There seems to be unanimous info that spinning inwards is faster, but I still can't figure out why this would be so.
If you have studied the water flow at the rear of a cat hull you will see that at slow to medium speeds there is a rectangular wall of water exiting the tunnel and on either side there is a depression from the water flowing under the sponsons.
If the props are mounted as close as possible to the inner edges of the sponsons it seems to me that the inner arc of each will be in contact with some of the wall of water from the tunnel, and if they are spinning inwards they will tend to climb this wall , ie prop walking upwards, which will lift the transom.
However the opposite seems to be happening !!!!!
To confuse things even further, at high speed as the hull lifts out of the water, the wake tend to flatten down and the central wall of water almost disappears, so the props are running in almost flat water with only the lower arc submerged.
At this point I cant see how spinning inwards or outwards would make any difference , but we know it does.
I need to have a cuppa tea and a lie down
Graham.
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Inward = bow lift.
outward= transom lift and also turns better with more of the front of the hull In the water.
this has been proven by the big boys many times.
In a full scale hull, you have to trim down to set the boat up for a good turn. If not you slide out more In the turn. Or cat= roll out or over!
In my STV I could stay on the gas and trim down just right and make a sweet hi mph turn on the river.Comment
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I ran the Twin Micro Scat Cat yesterday. Props rotating inward, and all I can say is that the cornering ability of this little cat is amazing!
You want full-speed figure eights in the space of a small swimming pool? No problem. 
The limited selection of counter-rotating props means using less prop that the motor/hull can handle, but run-times are great with the X430s.A nation of sheep breeds a government of wolvesComment
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I'm not saying this hull disproves any theories. What I am saying is Randy's little hull handles well IN SPITE of the twin arrangement, not because of it. I think the "Generous" rudder may have some bearing on handling as well.A nation of sheep breeds a government of wolvesComment
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Hmm, isnt this a european cat? http://www.offshoreelectrics.com/pro...=tp-jolly-twin
Oh and look how far up they are mounted.. Kinda disproves the whole "if you dont have them mounted nearest tunnel and down as far as possible it will just cavitate"Comment
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When you place the outdrives behind the sponsons there Is alot less stess on the outdrives and less drag while getting on plane. IMHO... The best place for the would be allmost Inline with the edge of the Inner side of the sponsons when running two drives.
There Is alot of stress on the outdrive of a cat.
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I run mine inward on my cat. I do get some torque roll at launching but once planed off she runs great and handles well...Twin cat 9xl,... 29 titan 8xl,....37 in mono kb48 8xl.... 42 in twin elc cat project... 42 in gasser cat 260 modded zenoh''' planes and trucks....Comment
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Thats sweet, So by the looks of the jolly, and even lonewolfs placement I should be ok with mine. I was worried for a min.Comment
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