TOPIC: Torque trim tab

I have a 16.5 1970 Las Vegas Boat Co. Tri-hull that I just installed motor and out drive in. It is a mercruiser 165hp I6 with a 15" 17p prop @ 5400' asl. I have no clue what way or how much I need to set the trim tab on the out drive. It would be helpful to describe it like "move 4 degrees counter clockwise looking from top from center." Also, I plan on putting it in the water first thing in the morning. Thank you for your help!

You set these up by setting the tab so it is pointing straight forward to start with. Take it out on the lake and see how it runs at different speeds andin which direction it is hard to turn. Ie. if the boat is hard to turn turn to port turn the tab to starboard. If it is hard to turn to starboard turn the tab to port. You will be able to feel if the steering is hard to turn one way or another the faster you go. You will not have to turn the tab very much. It is more of a trial and error prosess. Skip.

I can't say how much, but I can offer this. On my 1979 Evinrude 55, I had to turn it much farther than I though I would have to. I'm at least 10 degrees off center and maybe as far as 15. The motor is on a boat with cable and pulley steering, so it was easy to tell when I had a good setting vs a bad one. My trim fin is cupped on one side. I turned it toward the cupped side.

Ok. I set it straight. From what I can visualize, the torque should make the boat want to go left. If it does this, what direction(clockwise or counter looking from above) do I turn the tab?

The torque trim tab is not for runing in a straight line . It is only to help you in a turn. It is to make turning easyer. if your steering is hard say to the left than it is to the right then you need to turn the trim tab to the right. Only turn it a small amount and then take it out on the lake and try a couple of high speed turns to see if your turning to the left is easyer. It will take a couple of trys to get it just right.This setting will also depend on what type of steering you have. Cable and pulley steering and a telflex system will give a different feedback.

Like so many things about our hobby/passion/obsession, I guess everybody has their own preferred way of doing things Nitro. Although my experience is with outboards only, I think the same would apply to I/O's.

Starting with the tab at 0 degrees to establish your baseline as stated, and see if the boat pulls to one side or another at your regular cruising speed (in a straight line). If it pulls to the port (Left), move the tab a few degrees to the port and try again. If it pulls starboard (right), move the tab a few degrees starboard.

The amount of motor (or outdrive) trim angle (up and down) and throttle (ie: boat speed) will have an effect on the torque steer as well, but shoot for a happy medium with your most frequently used settings. Just keep the wrench handy until you get it tweaked or dialed in, you'll get the hang of it in no time.

Just my humble two cents worth, submitted respectfully.

Thanks Mark. This is what I thought the tab was for. What I am still confused about is its effect. Does it trim the out drive in the direction that it is turned or does it move the stern of the boat in the direction it is pointed. The effects of these are reverse of each other. I do a lot of rc airplanes where torque is a big deal. We will angle the motor to the right to counteract the effect instead of adding rudder. The torque tab just seems backward or something to me. Tanks guys!

The trim tab is a airfoil (hydrofoil). It creates a low pressure area on one side or the other, thus causing the drive to want to pull to the low pressure side.

Typically on a MerCruiser, the tab will end up being set with the trailing edge to the port side. As Mark said above, start with your typical cruising speed & trim setting. Then adjust the aft end of the tab towards the direction the steering wants to pull to.

Assuming the steering pulls left (is harder to turn right), adjust the trailing edge left. This will create the low pressure area on the right hand side, thus trying to pull the outdrive to the right & counteracting the torque.

Expect pretty heavy torque at high trim angle/high speed operation regardless of what you do.

Jim

OK, so the re maiden went fairly well. I ended up setting the trim tab around 3 degrees to the left. It pulls very slightly at top speed but is just right at cruising speeds. Thanks for all your help!