Trim tab not suffice to counter-act prop torque - steering too loose?

Fed

Commander
Joined
Apr 1, 2010
Messages
2,457
It's actually the imbalance caused between the attack angle of the down sweeping prop blade on the starboard side compared to the attack angle of the up sweeping prop blade on the port side when the outboard is in negative trim compared to the water surface. The starboard blade is more heavily loaded, trim out and the reverse happens.

To observe this trim the motor well out on the trailer and look at the angle of a blade on the starboard side in the 3 o'clock position then walk around to the port side and move a blade to the 9 o'clock position and note the huge angle difference.

Of course you are suffering from the opposite, too much negative trim.
 

Dukedog

Captain
Joined
Oct 6, 2009
Messages
3,235
You never said motor / boat? Figure OMC of some type from other posts?

A torque-tab should help. You might do a search for them and see if it works. I fabricated one out of a "discus-shaped" zinc anode, for my speedboat. It works very well, but took some trial and error to get the right size and thickness.

If you have "plain jane" mech. cable steering the above is only choice but it will not completely eliminate it. It just helps. Tha little tab above tha prop has little ta no effect at speed. Motor height, offset, prop type and trim angles when running will make some difference.........

Tha only things that will pretty much make it go away would be tha NFB or hydraulic steerin' system................
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Duke, I don't agree with your statement in the post above. I had a very hard pull to starboard on my speedboat, with the zinc anode (Mercury OB) turned all the way to compensate. A NFB steering setup kept the steering wheel set where I had it, but to turn to port I still had to overcome the hard pull to starboard.

I installed a torque-tab on the skeg and that just about eliminated any pulling. Of course it took some trial and error to get the torque tab to the right shape and size, but it works well.
 

Dukedog

Captain
Joined
Oct 6, 2009
Messages
3,235
Think we're sayin' say thing just in different ways. I've found tha "trim tab" takes out very little torque at speed compared to tha "torque tab" when motor set up is at is best..........We actually weld a tab ('bout 4" long) on tha trailing edge of tha skeg. It can then be "adjusted" with a leather or rubber mallet.....

Get from Bob's. Called "torque tamer"...Picture will show three. Bottom 2 in tha picture are trailing edge weld on. Top 1 is rivet or weld on "side" of skeg....

LINK......mght/might not show up! http://www.bobsmachine.com/Torque-Tamer-Hi-Perf-Weld-On-409-100000.htm?categoryId=-1
 
Last edited:

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,036
Duke, I agree with your last post. The OP should know that a NFB steering system will not eliminate his issue. He will need to address the pull by using the fin above his prop, or by installing a torque tab on the skeg.

I am still surprised that he has this issue with his boat/motor combo. I had thought it would have been restricted to boat/motors capable of high speed, with high-on the transom-mounted motors, which I did not think he had.
 

redneck joe

Supreme Mariner
Joined
Mar 18, 2009
Messages
10,201
I've had it with I/O's and this, adjusted, worked


22025_0_2.jpg
 
Last edited:

frantically relaxing

Senior Chief Petty Officer
Joined
Nov 19, 2011
Messages
699
"drive" trim tabs--- these things--

ttab.jpg


Work great, if set correctly. Some people don't set them correctly, I was one of them. Years ago I was under the wrong impression these things corrected boat pulling by steering the BOAT. But what they're intended to steer is the OUTDRIVE. Aiming the tab to steer the boat just makes it worse. So, if your boat is pulling to the right, this means the tail of the outdrive is wanting to go to the right. This means you must turn the tail of the trim tab to the right so it will push the tail of the outdrive to the left. And unless there's a serious problem with your drive, the faster you go, the more 'push' the tail will exert on the drive. Sometimes it takes a few adjustments, but when you're dialed in, you'll likely be able to drive the boat for miles at any planing speed without ever touching the steering wheel...
 

muncedog

Seaman
Joined
Nov 13, 2014
Messages
67
No Title

Hi guys,

Thanks all for your help. I had set the trim tab (photo post above) correctly (actually fully tail to the starboard). I think the issue was as someone said the trim position. Trimming up slightly appears to help although still a slight pull starboard.

I am considering moving my trim stop rod to a higher slot - anyone know how to move one of these (Shown in position 1 in the photo stolen from google)
 

Attachments

  • photo217698.jpg
    photo217698.jpg
    42.4 KB · Views: 0
Top