Trim tab adjustment. Why can't I get my head around it?

[DJ_Allatoona]

Interesting side effect of long-overdue replacement of my control cables is that my steering is now so one-finger buttery smooth that the torque-pull to starboard is very pronounced. And it seems my trim tab/anode is gone. Probably fell off ages ago, but I never noticed. So I bought a new one, it goes on tomorrow.

Thing is, reading about how to adjust it, everyone says if the torque pulls the boat to the RIGHT, you adjust the tab's trailing edge to the RIGHT (looking down at it). That goes against my gut which tells me I should move the trailing edge of the tab to the LEFT...BECAUSE I have it in my head that the tab would introduce a rudder effect to counter the prop torque. Ergo, the tab turned counter-clockwise (looking down) would only magnify the starboard turn.

Someone smarter than me...please explain how these things work. Does the tab act as a rudder to reverse the torque effect, or is there another physics explanation for it. Grazi.

 

[jakedaawg]

By turning the trailing edge to the right it creates a low pressure area on the left. This low pressure area then sucks things back that way equalizing the steering forces when done properly. It all about the low pressure created.

***for those that want to criticize: This is an over simplified explanation. This answer should suffice. I realize some could go much deeper into it.

 

[DJ_Allatoona]

Ahhhhhh....gotcha, That makes a lot more sense than the mini-rudder theory. I didn't think that little tab was able to push the boat around that well, but I'm not very smart and get stuff wrong all the time. Thanks for the explainer.

 

[racerone]

If it pulls to the right you have to swing the trim tab to the right.----As people have clearly stated.-------That pushes the gearcase to the port side thus correcting for the pulling to the right !!

 

[Fed]

You're thinking about it as if the trim tab was mounted on the boat but it's not.

The trim tab steers the motor and then the motor steers the boat.

 

[Fed]

Does the tab act as a rudder to reverse the torque effect, or is there another physics explanation for it. Grazi.

You have that part exactly right.

Looking down from above your flywheel is spinning clockwise but at the same time your engine block (complete motor in this case) is trying to spin counter clockwise and steering the boat to Starboard.

I have a link to an old but very good Mercury publication that shows how propellers interact with boats & steering.
It includes trim settings, engine heights, prop walk, engine torque etc, if I can find the link I'll put it up.

 

[Thesirfin]

You have that part exactly right.

Looking down from above your flywheel is spinning clockwise but at the same time your engine block (complete motor in this case) is trying to spin counter clockwise and steering the boat to Starboard.

I have a link to an old but very good Mercury publication that shows how propellers interact with boats & steering.
It includes trim settings, engine heights, prop walk, engine torque etc, if I can find the link I'll put it up.

Hi Fed. Thanks for this. I had the exact same thoughts as the OP! I don’t suppose you manages to find that mercury publication by any chance? There is Surprisingly little on line about this effect! Cheers.

 

[JimS123]

The owner's manual tells you what to do. Just follow the directions, even if you don't understand them, and you'll be OK.