Rudder off center on Supra

[FoiltechLaunch21V]

Just wondering why the rudder on the Supra boats is off center to the right. I'm sure there is a reason, just curious.

[DKJBama92Mariah]

Just wondering why the rudder on the Supra boats is off center to the right. I'm sure there is a reason, just curious.

I'm not precisely sure on that one. There are two reasons that pop out to me though.
1) So you can pull the shaft without removing the rudder

2) To somehow counteract prop torque (not real sure on that one though)

[Water Dog]

I'm no engineer, but I play one on tv.
I'm going to go with prop torque here, just seems logical when thinking about the null in the center of the prop under load and the direction of prop rotation. I know too many engineers, they always look at performance vs. being easy on the mechanic, but I do like the pulling the shaft idea, but I think that was just a random lucky draw...

[rludtke]

Yep, the rudder is off-set to counteract torque and what aerodynamicists refer to as P-factor (as an aero guy, I am unaware of the term for the hydronamic equivelant). P-factor is the result of the spiral airstream off of the propellor, and it's effects upon the airframe. Essentially, P-factor amplifies tourque effects. Designers off-set the vertical stabilizers on single engine propellor driven ariplanes for the same reason.

Have you aver noticed how when you are accelerating, you need to maintain pressure on the steering wheel to keep the boat strait? If left to it's own devices (at least this is true with my 1987 Ts6m, modern boats may have designed this tendancy out) the rudder wants to deflect and the boat wants to turn. This is illustrates the tourque/P-factor effects remaining even after off-setting the rudder.

[cocheese]

I wouldn't be able to pull the prop off if the rudder were directly inline with the prop. I think the answer is simple and is a service requirement.

[kingwoodlee]

I've always been told it was so you can remove the drive shaft without removing the rudder. That's my 2c.

[DKJBama92Mariah]

Personally I lean towards the ease of service angle, but I freely admit that I don't know enough to say for sure either way.

rludtke,
Welcome to the forum! If I am not mistaken, the laws of fluid dynamics are the same with either a gas or liquid. The only variable between the two being that the liquid obviously has a much higher density.

Just a note, older ski boats are built to pull to one side to make it easier for the driver to drive a straight line through a slalom course. If the rudder was completely neutral, the boat would wander all over the place going down the slalom course. This "pull" can be lessened, neutralized, or reversed by grinding either one side or the other of the trailing edge of the rudder. Much like your rudder trim on a plane; just a little more permanent.

[DKJBama92Mariah]

Come to think of it, your idea makes sense as well. Perhaps ease of servicing could be just a good side-effect of your theory. Guess we'll never know until someone googles it.

[rludtke]

Thank you DKJBama92Mariah! I only recently discovered this forum. I purchased my '87 TS6m two Februarys ago, and have been searching for documentation, and advice ever since. I like what I see here.

I have some pictures of my boat in my profile area, check her out!

My boat is not the sharpest Comp by far, but she is in good mechanical condition. The engine was 49 hours into an overhaul when I purchased her, and featured MSD electronic ignition. I have been chasing the little things, such as corroded electrical connections, intermittent carburator issues, leaky transom drain tube, etc. It took several months of following someone elses bugs, but she has become a very dependable user.

I am old school, and only knew how to slalom when I purchased her, which is more or less why I wanted a tournament boat to begin with. But recently I have started playing with the permanant surf behind the boat, and having a lot of fun doing it. So now I am considering adding ballast, or a ballast system of some type. Not permanant ballast mind you, as I am very old school, but I wonder if lead weights wouldn't be a bad way to go. For one thing, it is very quick and easy to remove the weights when you want to switch back to the stick, the weights can be transferred from one side to the other quickly, and they won't take up as much room in the boat.

Well, i've kicked this thread way off topic, sorry about that!

[FoiltechLaunch21V]

I wouldn't be able to pull the prop off if the rudder were directly inline with the prop. I think the answer is simple and is a service requirement.

There is plenty of room to remove the prop whether inline or not. Some inboards are inline some are to the left some to the right with the same rotation seems strange. The funny thing is if you go to the dealerships and ask, most of them have never noticed. So obviously they don't have the answer either.

[tazz3069]

I asked the same question. Even though I do not have a supra, my Moomba is almost the same. The Rudder is off centerbecause of the way the prop turns. Ours, if looking from the rear, is off to the right. We use Land Hand turn props. Other boats, with right hand turn props, the rudder is favored to the left.
Tazz

[DKJBama92Mariah]

Weird. My prop is RH b/c of my reduction tranny and i'm almost certain that mine is offset to the right. I'll take a look to be sure next time I'm out that way.

[DKJBama92Mariah]

I checked today and my rudder is indeed offset to the right. Go figure. The mystery continues...