right turn under speed

[cassidyta]

I noticed today that when under full power, my boat wants to turn right. It acts like a car with a bad alignment. I thought that this may be caused because of my weight, but it happened even when I sat on the opposite side.
I have a 75 HP merc with a jet propulsion.
Is this normal, what would cause it, and should I be concerned.

[carolina-rig-01]

Well I have no idea with a jet motor, so I won't be any help at all. However a lot of boats have this going on with regular outboards and it is pretty much normal.

[bamabassman]

mine does that too cass. there is a little flap in back that you are supposed to be able to adjust. send me your cell number and i'll send you a pic from mine of what i am talking about.

[bassboogieman]

Torque from prop rotation is the cause. Not much of an issue w/hydralic steering, much more noticable w/cable steering. There should be a torque tab above your prop that (as 'bama said) can be adjusted to give you some compensation. It's also a sacrificial anode and will corrode a bit, but they last many years. Boats w/hydralic steering may have a flat anode in place of the torque tab, or a tab. Should look like this and be above the prop.

[nofearengineer]

Remember guys.....he doesn't have a prop, so it can't be prop torque. His problem almost certainly has to be hull-based. He might still be able to fix it (or at least counteract it a little) with a toque-tab, though. Sounds like one for Laser Man.

[walkeraviator]

The prop is not what causes the torque. It is the engine itself sitting vertically. So no matter if you have a prop or a jet , you still suffer the same consequences of Newtons Third Law. The torque tab is in deed designed to counteract this problem. But dont expect it to ever go away comletely, because that torque tab has a certain angle of attack that will only produce the exact same force in teh opposite direction of force at a certain speed. As speed increases, so too does teh force (similar to lift in an airplane only sideways) the tab makes. There is a certain magic speed and RPM somewhere, that tab will be 100% effective, but get away from those norms and a small force will still be felt.

Sorry to get too in depth. As a flight instructor, I tend to get way to into stuff...especially when it involves physics. And Hydrodynamics are VERY similar to Aerodynamics.

[Captmikestarrett]

The jet gate has an offsett on the cable side that allows you to adjust the jet direction slightly. Perhaps it has come loose or the bushings in the gate pivot arms are gone.

http://168.143.27.144/catalog/2008/M...RSE%20GATE.pdf

Capt Mike

[cassidyta]

Thanks for all the input.
I am not sure that I made myself clear. The motor and steering wheel actually turn. I have been looking at the back to see if there is some sort of water resistance that is causing this.
Perhaps it is just caused by the gyro of the motor.
At the end of the day it is not a big deal I was just curious if it was something to be worried about.

[nofearengineer]

Originally Posted by walkeraviator

The prop is not what causes the torque. It is the engine itself sitting vertically. So no matter if you have a prop or a jet , you still suffer the same consequences of Newtons Third Law. The torque tab is in deed designed to counteract this problem. But dont expect it to ever go away comletely, because that torque tab has a certain angle of attack that will only produce the exact same force in teh opposite direction of force at a certain speed. As speed increases, so too does teh force (similar to lift in an airplane only sideways) the tab makes. There is a certain magic speed and RPM somewhere, that tab will be 100% effective, but get away from those norms and a small force will still be felt.

Sorry to get too in depth. As a flight instructor, I tend to get way to into stuff...especially when it involves physics. And Hydrodynamics are VERY similar to Aerodynamics.

Walker, you're misunderstanding torque steering of boats. It is indeed a prop problem. what happens is at full trim, the water/air mixture above the prop is more air than the water/air mixture below the prop. So the prop has more "bite" on its bottom. Depending on the direction of prop rotation, the prop wants to "roll" to one side or the other. This makes the engine want to turn left or right, making the boat want to steer off line.

What you're describing is the response torque to the engine crankshaft accelerating (not simply rotating) about its vertical axis. However, except for very a very small torque due to frictional losses, the only time this applies is during acceleration. Constant speed = no torque. It's like a dragster picking up its left front tire on launch. It doesn't happen at speed. Cassidy is talking about that constant slight pull to the right that we all are familiar with.

But you are right about the torque tab being optimized for only one speed. It is a "bang for your buck" fix. It takes care of 90% of the problem, with very little expense or performance hit.

However, as was stated earlier, Cass doesn't have a prop. He has an impeller, which obviously doesn't suffer torque steer like a prop, since its immersion level doesn't vary with trim (hopefully!!).