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A question about prop rotation on twin engine setups?

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Old 07-15-2003, 08:34 PM
  #21
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If your props are turning in, you should see a gain in speed if your hull can use it. I have tried both ways and there is a big difference in top end performance. However if your boat docks poorly, it will only get worse if you turn the props in. I have never had a problem docking with mine in, but I have had some big crusiers that I have practiced with and it is no problem anyway, unless you have heavy current and high winds, and then good luck to anyone.
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Old 07-15-2003, 10:08 PM
  #22
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Out/In make sure you can park the thing 2 people apart from you will be looking when you go around 2.69 MPH faster on GPS but 200 will be looking at the guy with the hot boat banging into the dock at the local hot spot. I say OUT and park it like a pro without touching the steering, instead of looking like a doughead pinballing your way into a dock space !
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Old 07-15-2003, 11:04 PM
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From the thread, Great Moments in Cat History.
==========================================

My thoughts on "spinning" in..... Simple physics.... Right hand rotation propellers,torque (lean) the boat to the left. Left hand rotation propellers torque the boat to the right. In a twin engine boat spinning outboard or , RH on right side, LH on left, the torque of the propellers tends to return the boat to level when one side or the other leans outward. When props are spun inboard RH on left, LH on right, or counter rotated the torque tends to make the lean worse. This occurs because as a boat(Cat or Vee) leans to one side, the prop on that side buries deeper and exerts more force, while the prop on the other side rises (in some cases out of the water) and exerts less force. So...... If a RH prop is spinning on the right side of a boat leaning to the right, the prop tends to push the hull back over to the left. (spinning Outboard). If, however, the left hand prop is on the right side in a right hand lean , the prop tends to continue to roll the boat over. I submit that this is why there has been such a dramatic increase in barrel rolls (even in straight-aways) in races in recent years. When I flew over races for 16 years, I could always spot the counter rotated boats, because they behaved very differently (and definitely not better)than their properly spun (outboard rotation) competitors.
The reason that many people spin them "backwards" is the fact that on some hulls the boat may gain a mile or two per hour at top speed....or..... the boat has a bottom tune that needs more bow lift. The speed can generally be achieved in other ways without using an unnatural rotation as a "bandaid" (This is particularly problematical on stepped bottom boats that skid first, then catch suddenly, then roll outward......get the picture?)
One can re-tune most bottoms to add rocker to provide bow lift without resorting to ill advised prop rotation changes.

Counter rotation is adviseable on SINGLE engine race boats when the courses change from counter-clockwise to clockwise. LH props like right turns and handle better, RH props like left turns. Since the Bravo drive allows for a simple flick of a lever to reverse rotation, one would expect that Factory 1 racers would have a supply of left and right props depending on the course ....... up until this year most F1 racers don't...... I guess nobody has "invented" this yet.

It's T2x....NOT "Tx2" please
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Old 07-15-2003, 11:27 PM
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I agree with Shawn. On my cat it docks find with the props turning either way. In does provide more bow lift but I can't yet say if in is faster or not
Damm, I hate when I agree with Shawn

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Old 07-16-2003, 10:33 PM
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My stepped 32' Fever had the props spinning in. I couldn't dock worth a chit. Thought it was because I was a twin newby this yr.
I switch to spinning out and docking is now a breeze. World of difference. Never really ran the boat when spinning in, so no idea on top end, but I hit 78 mph easily with them spinning out. Been told 78 is about norm for this boat, so figure I didn't loose any top end. Handleing feels the same, or at least not enough noticable difference that I can tell.
I dock more than run WOT, so docking ability takes precedent. I'm leaving them spinning out.
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Old 07-16-2003, 10:40 PM
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Quote:
Originally posted by US1 Fountain
...I dock more than run WOT, so docking ability takes precedent. I'm leaving them spinning out.
Logic taking over!!! Some people are in trouble!
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Old 07-17-2003, 08:26 AM
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My props have been turning in since I bought my boat in '96. It's my first boat with twins so I learned to dock with it this way, so I guess I wouldn't know what I'm missing. The previous owner did the experimmenting to find that my boat is faster turning in (and it still needs more bow lift). My boat has a notched transom and a decent sized pad.
I'm certianly not going to swap my drives (TRS) to see if my boat goes slower and my docking improves.
But that's just me.
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Old 07-17-2003, 09:28 AM
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Michael, I feel your pain. I hear your boat looks great with the new colors. Are you going to be out this w/e? Can't wait to see how it turned out

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Old 07-17-2003, 01:14 PM
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To experiment with this can't you just change the props and shift the drives the opposite way? This whould really make docking a trick but a easy way to try it out.
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Old 07-17-2003, 01:22 PM
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Quote:
Originally posted by Quiet Storm
To experiment with this can't you just change the props and shift the drives the opposite way? This whould really make docking a trick but a easy way to try it out.
With bravos - Yes
With TRS - Nope, must swap drives.
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