# Trim tabs and highly-cupped prop



## Smackdaddy53 (Dec 31, 2012)

The prop rotation is causing that. What hull/outboard is it on?


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## Vertigo (Jun 3, 2012)

Helm pulling one way or another and/or listing can be caused when blades of the propeller are unevenly loaded by the axis of rotation being nonparallel with the flow of water about it. A highly cupped prop makes the situation worse. One fix for this is to make sure your thrust axis is parallel to the direction of travel. In English, that means fiddle with tilt/trim and see if that helps. Raising the motor can also help the problem since you're reducing the lever arm of the prop. Another possible fix is the trim tab on the motor and, of course the final fix is trim tabs. Many times with hydraulic steering or a no-feedback helm it's hard to feel the uneven load that the motor is exerting on the helm. Just balancing things out by experimentation with tilt/trim, motor height, and motor trim tab could solve your problem.


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## devrep (Feb 22, 2009)

wow that's a huge issue.


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## CKEAT (Aug 26, 2015)

I don’t have this issue, I have cav plate, foreman prop, lower unit trim tab is slanted all the way to starboard side.

also mounted pretty high and I run with plate all the way up.


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## EdK13 (Oct 3, 2013)

HPXS only come with a 70 4 stroke Yamaha. There a small fin on the lower unit above the prop. It is also known as the sacrificial anode.. There is a bolt that when loosened allows the fin to rotate. It's angle can be adjusted to compensate for prop torque, not something that outboard is known for btw. Changes can make profound differences. If that does work I would copy the prior posters setup.


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## CKEAT (Aug 26, 2015)

Here is where mine is and it runs very level.


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## efi2712micro (Sep 17, 2015)

Smackdaddy53 said:


> The prop rotation is causing that. What hull/outboard is it on?


Hi Mack - Yamaha F70!


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## efi2712micro (Sep 17, 2015)

Vertigo said:


> Helm pulling one way or another and/or listing can be caused when blades of the propeller are unevenly loaded by the axis of rotation being nonparallel with the flow of water about it. A highly cupped prop makes the situation worse. One fix for this is to make sure your thrust axis is parallel to the direction of travel. In English, that means fiddle with tilt/trim and see if that helps. Raising the motor can also help the problem since you're reducing the lever arm of the prop. Another possible fix is the trim tab on the motor and, of course the final fix is trim tabs. Many times with hydraulic steering or a no-feedback helm it's hard to feel the uneven load that the motor is exerting on the helm. Just balancing things out by experimentation with tilt/trim, motor height, and motor trim tab could solve your problem.


Thanks for the detailed feedback! Been playing with different scenarios with the engine all the way up, trimming at different stages and running it. Problem still manifests itself. I will give another shot though and report out


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## efi2712micro (Sep 17, 2015)

EdK13 said:


> HPXS only come with a 70 4 stroke Yamaha. There a small fin on the lower unit above the prop. It is also known as the sacrificial anode.. There is a bolt that when loosened allows the fin to rotate. It's angle can be adjusted to compensate for prop torque, not something that outboard is known for btw. Changes can make profound differences. If that does work I would copy the prior posters setup.


interesting! When I was at jack’s shop to fit the prop, he had me tighten that small fin and prevent it from moving. It might be off axis. Could it be? Definitely try to loosen it. Is it supposed to be lose to adjust with the engine axis or tight?


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## CKEAT (Aug 26, 2015)

The engine tab/anode should be tightened down. Just tweak the angle and try it.

Take a pic and post, most likely you need to turn it to starboard side, just guessing.


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## BassFlats (Nov 26, 2018)

The engine tab/anode is adjusted for torque steer. I don't think it is related to the leveling problem the op is having.


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## NativeBone (Aug 16, 2017)

BassFlats said:


> The engine tab/anode is adjusted for torque steer. I don't think it is related to the leveling problem the op is having.


^CORRECT!


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## commtrd (Aug 1, 2015)

Could put the original wheel back on and run it to see if the problem persists. If the problem goes away, there is your problem. If problem still evident, keep on looking for a solution. Seems strange since the F70 is not a super torque-y motor.


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## CKEAT (Aug 26, 2015)

BassFlats said:


> The engine tab/anode is adjusted for torque steer. I don't think it is related to the leveling problem the op is having.


So the engine attempting to torque starboard will not have an impact on Tim tab function? That will impact running level, no?


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## efi2712micro (Sep 17, 2015)

commtrd said:


> Could put the original wheel back on and run it to see if the problem persists. If the problem goes away, there is your problem. If problem still evident, keep on looking for a solution. Seems strange since the F70 is not a super torque-y motor.


Planning on trying that as well this week end!


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## efi2712micro (Sep 17, 2015)

CKEAT said:


> So the engine attempting to torque starboard will not have an impact on Tim tab function? That will impact running level, no?


i would assume it depends on the hull profile and this one being a flatter, likely less of an impact than more Of a v profile.


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## efi2712micro (Sep 17, 2015)

BassFlats said:


> The engine tab/anode is adjusted for torque steer. I don't think it is related to the leveling problem the op is having.


Come to think about it, the way I run the engine high, the anode is out of the water at high speed


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## NativeBone (Aug 16, 2017)

CKEAT said:


> So the engine attempting to torque starboard will not have an impact on Tim tab function? That will impact running level, no?


No


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## crboggs (Mar 30, 2015)

1) Welcome to the world of prop torque. 
2) It shouldn't cause your skiff to run off kilter...even when I'm feeling torque on my tiller my skiff runs flat and level with only minor tab adjustments.


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## NativeBone (Aug 16, 2017)

Look forward hearing some info from others as well. I run a copperhead w/ a 70hp 3cyl. 2s. rigged with a SS 19p prop. I notice under power, I have to trim down port side a little to level out. I beleive what I am is is prop torque.


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## sjrobin (Jul 13, 2015)

The starboard tab could be mounted closer or further from the outside edge of the transom. One of the tabs will be used more or less if the mounting distance is not perfect. Weight distribution will always be a factor for trim tab use. Some tabs have adjustable full up settings. The larger the tab, the more differences in positions.


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## Smackdaddy53 (Dec 31, 2012)

Another member (Blackdog I think) cut his off with no ill effects. I cut my anode fin off completely, they are of no use when running jacked up and that’s how I run 90% of the time. My prop was too close to hitting it and I figured I’d lose some drag...
Your hull may have some hook to it...


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## NativeBone (Aug 16, 2017)

Smackdaddy53 said:


> Another member (Blackdog I think) cut his off with no ill effects. I cut my anode fin off completely, they are of no use when running jacked up and that’s how I run 90% of the time. My prop was too close to hitting it and I figured I’d lose some drag...
> Your hull may have some hook to it...


^same
I have hydraulic steering. 
I cut the fin off


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## not2shabby (Sep 14, 2016)

Have you called Jack?


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## jay.bush1434 (Dec 27, 2014)

Prop torque. My buddy's Panga does the same thing. At a comfortable cruising rpm of about 3800-4000, the boat runs level with no tab input, assuming the weight is evenly balanced side to side. Once you punch it up to 4500 and higher, the boat starts to roll and requires tab input to level out. Raising the jackplate some will likely reduce this roll because the prop will be slipping a little more, lower the jackplate all the way down and you'll notice the roll increase. You might gain some speed but that will be from the reduction of drag from the lower unit moving through the water. At some point, you will jack up enough that your speed will go down and the roll will reduce as well. This is where you need to watch your speed as you make trim, jack, tab and throttle adjustments to find the happy spot. My GPS is NMEA'd to the motor's computer so I get fuel burn going to the injectors. This allows the GPS to calculate instantaneous MPG, letting me know when I've got the boat set up at the most efficient setting. That being said, if you want hair on fire top speed, give up the hole shot and get a different prop, but you already know that...


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## NativeBone (Aug 16, 2017)

jay.bush1434 said:


> Prop torque. My buddy's Panga does the same thing. At a comfortable cruising rpm of about 3800-4000, the boat runs level with no tab input, assuming the weight is evenly balanced side to side. Once you punch it up to 4500 and higher, the boat starts to roll and requires tab input to level out. Raising the jackplate some will likely reduce this roll because the prop will be slipping a little more, lower the jackplate all the way down and you'll notice the roll increase. You might gain some speed but that will be from the reduction of drag from the lower unit moving through the water. At some point, you will jack up enough that your speed will go down and the roll will reduce as well. This is where you need to watch your speed as you make trim, jack, tab and throttle adjustments to find the happy spot. My GPS is NMEA'd to the motor's computer so I get fuel burn going to the injectors. This allows the GPS to calculate instantaneous MPG, letting me know when I've got the boat set up at the most efficient setting. That being said, if you want hair on fire top speed, give up the hole shot and get a different prop, but you already know that...


Yelp, bout the same. Good amd level around 3500ish, punch it and the boat leans to port.


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## Smackdaddy53 (Dec 31, 2012)

It’s the same prop I have, I spoke to the OP yesterday. There’s no way the prop is causing that much torque to need just one tab down all the way to level his skiff. I use both tabs equally, never have to use one tab more than the other to keep her flat. It could be causing some of the issue but not all. He said he had a trim tab issue before so I think that’s where we will start.


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## SeaDrifter (Apr 4, 2018)

Silly question but, is your load level? If you have your batteries off to one side just a bit (esp if stored at the bow) it will cause the vessel to favor that side. I had to play with where things were stored to get the maximum performance out of her.



Michael


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## No Bait / Lures Only (Apr 10, 2011)

efi2712micro said:


> Come to think about it, the way I run the engine high, the anode is out of the water at high speed


High engine height more steering torque with tab outa d water


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