Counter rotating props on twin Jolly cat.

[G Doggett]

Has any research been done, or does anyone have first hand experience, regarding counter rotating props spinning inwards or outwards on model cats ?
Is one way better than the other for top speed , cornering , or stability?
Forget about full size offshore cats because the throttle man is working flat out constantly adjusting the throttles and trim to keep the boat stable.
I have this totally unproven theory that the props should spin inwards ( l/h prop clockwise and r/h prop antclockwise ) based on the following -
If the boat hits some rough water and say the l/h prop comes partly out of the water the r/h prop will push the bow to the left because the thrust is now off centre.
However if in this situation the r/h prop is spinning anticlockwise it will also try to propwalk the stern to the left which should partly offset the off centre thrust.
Is this theory correct, probable, possible, or a load of cobblers ?
Interested to hear from you twin cat guys.
Regards
Graham.

[Steven Vaccaro]

I have not had experience with a cat. But with a mono. The mono ran faster with the left spinning cw and right spinning ccw. It handled better when I ran opposite that setup. I think because it ran wetter.

[ReddyWatts]

I saw robby76 try it on a cat both ways and agree with Steven on the results. L-CW R-CCW it was about 5 mph faster and L-CCW R-CW it turned a lot easier.

This is a video of the problem he was having turning it on the first time out. We first thought he had hit something in a turn, but looking at the video we could see that it was from the prop rotation in the faster L-CW R-CCW setup. I think the batteries (32 cells) mounted in the middle of the hull, raising the COG, also contributed to this. After he got it dialed in, I did not see it happen again, but still looked like it is fighting the turns.

http://www.rcflix.com/photopost/showphoto.php?photo=2853&cat=500&ppuser=3055

[robby76]

I have not had experience with a cat. But with a mono. The mono ran faster with the left spinning cw and right spinning ccw. It handled better when I ran opposite that setup. I think because it ran wetter.

true .
on my 42inch cat with the inward running props, it is said to hypothetically move the CG towards the center of the hull. outward rotating props move it out forward of the front to the hull (not good) which is what causes a decrease in speed.
if you run course CW then the inside strutt/stinger needs to be a tad higher than the outside strut as the hulls centrifical force raises that side off the water. if both are level, a roll over in the turns is possible.
just my obervations.

[SJFE]

If I can stry off topic for a second..On tripple outboard offshore boats...How do they set rotation on the props?

[FE_Chris]

Very Very carfully!!!! :D


I ran my villian stock, the props turn out stock.......it handled OK. When I re-wired it and made the props turn in, the boat was a little faster but handled like crap....even at 15MPH LOL

If I can stry off topic for a second..On tripple outboard offshore boats...How do they set rotation on the props?

[Eyekandyboats]

If I can stry off topic for a second..On tripple outboard offshore boats...How do they set rotation on the props?

I know on the full size boats, both out side are counter rotating and the middle ones goes in either direction.
Because of prop lift and sponsons the props will rotate inwards or outwards to lift the stern or lift the bow. The middle one will not have much effect because it has no sponsor to direct water
at least that is how we do it on the real boats

[G Doggett]

I'm having porpoising problems with my twin Jolly.
From your experience with full size cats, will rotating inwards ( l/h clockwise and r/h anticlockwise) lift the stern or bow ?
Graham.

[Eyekandyboats]

[ReddyWatts]

From watching the robby76 cat, it looks like the inward rotation lifts the bow more. Outward rotation made it run wet. He was also going 5 mph faster with inward rotation. Might need to move your weight forward or trim down your struts? Which props are you using? also try to keep your speed up in the corners.

[G Doggett]

Thanks for the reply and info.
I will set my Jolly up for outward rotation and cross my fingers for next weekend.
Can you explain the theory or reason for this reaction ?
Graham.

[Eyekandyboats]

Yes i can.
I will later on. but now i must leave.
Having the bow up and transom sucked down is great for acceleration.
We trimmed a 32 foot skater to be fast out of the hole and this is what we did.
it go to 100mph in 12 seconds but only toped out at 140.

[G Doggett]

Reddy
I am running Graupner K40 props with Feigao 8XLs on 12 cells each.
The surface drives are parallel with running surfaces and the c/g is 33%.
She flattens out and runs fine at full speed so I dont want to mess too much with the c/g. Besides if I move the batteries any more forward they will be under the deck.
Graham.

[robby76]

~~~~~_______%%%%%

[G Doggett]

What ???? !!!!