2001 Mercury 25 pulling hard right

Paulio91184 · Aug 19, 2020

Hi all. I just got a new (to me) 16ft Starcraft Seafarer 16 with a 25 Mercury tiller outboard on it and took it out for a shakedown run and the motor pulls very hard right. Allow me to explain.

I was steering with my left arm and the tiller pulls hard to port making the boat steer starboard. It happens at all speeds and its bad enough that if I let the tiller go on plane I'm sure I'd be ejected from the boat!

Theres pretty much 0 tension on the pivot tube and the red lever to lock it doesn't work. Any ideas on how to tighten it up. My left arm is gonna be twice the size as my right arm if I keep using it like this

Model # 0T186033

ktoelke54 · Aug 19, 2020

Paulio91184 said:
Hi all. I just got a new (to me) 16ft Starcraft Seafarer 16 with a 25 Mercury tiller outboard on it and took it out for a shakedown run and the motor pulls very hard right. Allow me to explain.

I was steering with my left arm and the tiller pulls hard to port making the boat steer starboard. It happens at all speeds and its bad enough that if I let the tiller go on plane I'm sure I'd be ejected from the boat!

Theres pretty much 0 tension on the pivot tube and the red lever to lock it doesn't work. Any ideas on how to tighten it up. My left arm is gonna be twice the size as my right arm if I keep using it like this [emoji1787][emoji1787]

Model # 0T186033

Had the same experience with a 25 Mercury 2 stroke. Here is what I found out. In order to neutralize the left-right pull the motor had to be trimmed where the cavitation plate was close to level with the bottom of the hull. If I trimmed it in to get up on plane faster it pulled really hard. I started trimming if out to where it was just a little past parallel with the bottom of the boat and it was totally neutral, no pull in either direction. I trimmed it back one pin towards the transom (to help it get up on plane) and I was able to compensate for the pull with the little fin on the bottom of the cavitation plate.

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Paulio91184 · Aug 19, 2020

ktoelke54 said:
Paulio91184 said:

Hi all. I just got a new (to me) 16ft Starcraft Seafarer 16 with a 25 Mercury tiller outboard on it and took it out for a shakedown run and the motor pulls very hard right. Allow me to explain.

I was steering with my left arm and the tiller pulls hard to port making the boat steer starboard. It happens at all speeds and its bad enough that if I let the tiller go on plane I'm sure I'd be ejected from the boat!

Theres pretty much 0 tension on the pivot tube and the red lever to lock it doesn't work. Any ideas on how to tighten it up. My left arm is gonna be twice the size as my right arm if I keep using it like this [emoji1787][emoji1787]

Model # 0T186033

Click to expand...

Had the same experience with a 25 Mercury 2 stroke. Here is what I found out. In order to neutralize the left-right pull the motor had to be trimmed where the cavitation plate was close to level with the bottom of the hull. If I trimmed it in to get up on plane faster it pulled really hard. I started trimming if out to where it was just a little past parallel with the bottom of the boat and it was totally neutral, no pull in either direction. I trimmed it back one pin towards the transom (to help it get up on plane) and I was able to compensate for the pull with the little fin on the bottom of the cavitation plate.

Sent from my iPad using Tapatalk

Thank you for the relpy...i am actually going to install an adjustable jack plate because i need the motor set back a bit off the transom for my side scan transducer to be unimpeded. I also did notice that my cav plate is about 4 inches below the hull so 2 birds with one stone.

Any idea how to add some friction to the steering? Also, the trim fin annode is already offset to about the 10 O'clock position from the previous owner (if looking down into the water)

ktoelke54 · Aug 20, 2020

I had the same problem with the friction adjustment lever. It just didn’t add much if any friction. It uses a thin metal plate to create the friction. In my case, the plate was greasy. I sprayed some carb cleaner on it and it cleaned up nicely and helped quite a bit. Even at that, tightened all the way, it adds just a moderate amount of friction to the steering.

My trim fin anode has a stop at about 20 degrees in either direction. When I trimmed the motor in one pin past what I found to be neutral, I had to move the anode all the way to the stop to compensate for the pull on the tiller handle. But it did compensate nicely. Under full throttle I can take my hand of the tiller and it tracks perfectly. Before I began the adjustment process, it was pulling so hard it made my arm tired.

Make sure your trim fin is cocked in the right direction to counteract the pull your experiencing.

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ktoelke54 · Aug 20, 2020

Oh, and what I said about having the cavitation plate level is probably confusing. What I meant is parallel. As far as how much and which direction the motor pulls it has nothing to do with level, but a lot to do with parallel. Moving the motor up and down on the transom didn’t change the pull. Adjusting the trim angle in and out changes it a lot. If I trim my motor in to the closest hole to the transom it pulls so hard it’s hard to hang on to. As I begin to trim out the pull lessons and at the point where the plate is just past parallel to the hull, stops all together.

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Pappy · Aug 20, 2020

You guys are pretty much on the right track.
Want to know WHY this happens?

DaleH · Aug 20, 2020

Pappy said:
You guys are pretty much on the right track.
Want to know WHY this happens?

Yes, please ... would appreciate your insight!

Pappy · Aug 20, 2020

It is called ASYMMETRIC propeller loading. This happens when the angle of attack of a propeller relative to the direction of travel is not symmetrical.
In other words, when trimmed down or under the downward turning blade (on right hand rotation props) takes a larger bite of water than the upward turning blade. Since torque is applied 90 degrees to thrust angle the engine will want to turn the boat.
As the engine is trimmed up the blades become symmetrical to the direction of travel and both the downward blade and the upward blade will begin to pull equally.
If you are standing to the side of the boat looking at the propeller from the side it is easier to see. If the engine is trimmed down the lower blade is more forward than the upper blade is.

On an engine that is trimmed under this happens......
The Thrust of the downward blade happens from about the 1 o'clock position to the 6 o'clock position and increases as the blade travels farther through this arc.
On the upward swinging blade the thrust happens from about the 7 o'clock position through the 12 o'clock position and diminishes throughout the swing.

Neutral trim (relative to direction of travel) produces equal torque.

Positive trim or trimmed out produces steering torque in the opposite direction of a propeller that is trimmed under.

DaleH · Aug 20, 2020

Pappy said:
It is called ASYMMETRIC propeller loading. This happens when the angle of attack of a propeller relative to the direction of travel is not symmetrical.

You're awesome Pappy - thank you !

LDUBS · Aug 20, 2020

X2 - thanks Pappy. I just learned a whole lot.

ktoelke54 · Aug 20, 2020

Thanks Pappy, good stuff!

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Paulio91184 · Aug 20, 2020

Pappy said:
It is called ASYMMETRIC propeller loading. This happens when the angle of attack of a propeller relative to the direction of travel is not symmetrical.
In other words, when trimmed down or under the downward turning blade (on right hand rotation props) takes a larger bite of water than the upward turning blade. Since torque is applied 90 degrees to thrust angle the engine will want to turn the boat.
As the engine is trimmed up the blades become symmetrical to the direction of travel and both the downward blade and the upward blade will begin to pull equally.
If you are standing to the side of the boat looking at the propeller from the side it is easier to see. If the engine is trimmed down the lower blade is more forward than the upper blade is.

On an engine that is trimmed under this happens......
The Thrust of the downward blade happens from about the 1 o'clock position to the 6 o'clock position and increases as the blade travels farther through this arc.
On the upward swinging blade the thrust happens from about the 7 o'clock position through the 12 o'clock position and diminishes throughout the swing.

Neutral trim (relative to direction of travel) produces equal torque.

Positive trim or trimmed out produces steering torque in the opposite direction of a propeller that is trimmed under.

WOW that's really interesting!

Coincidentally, my motor is currently on the lowest setting (all the way down) So of I bring it up a notch or 2 it might fix it? I attached a picture of its current setting.

It also came with a doel fin...not sure if that matters.

DaleH · Aug 20, 2020

Whoa ... one also gets 'bow steer' with it trimmed that far in and that can be dangerous!

Paulio91184 · Aug 20, 2020

DaleH said:
Whoa ... one also gets 'bow steer' with it trimmed that far in and that can be dangerous!

I'll adjust it for next run...i only had it out for 15 minutes to check for leaks and test the motor.

maintenanceguy · Aug 20, 2020

The zinc anode right above the prop is made to be adjusted to counteract this turning force. This anode has a "trim tab" that hangs down just over the prop. Loosen the bolt holding the tab in place and rotate the rear of the tab toward the direction your boat is steering. Tighten the bolt. These tabs make a big difference and it only takes a small adjustment to work. 5º - 10º is probably enough.

My boat always pulled to the right. As long as I had my hand on the wheel, everything was fine. If I let go, the bolt would swing right. I adjusted the rear of the trim tab just a few degrees to the right and the boat stays perfectly straight if I let go of the wheel now.

Paulio91184 · Aug 20, 2020

maintenanceguy said:
The zinc anode right above the prop is made to be adjusted to counteract this turning force. This anode has a "trim tab" that hangs down just over the prop. Loosen the bolt holding the tab in place and rotate the rear of the tab toward the direction your boat is steering. Tighten the bolt. These tabs make a big difference and it only takes a small adjustment to work. 5º - 10º is probably enough.

My boat always pulled to the right. As long as I had my hand on the wheel, everything was fine. If I let go, the bolt would swing right. I adjusted the rear of the trim tab just a few degrees to the right and the boat stays perfectly straight if I let go of the wheel now.

Mine is already adjusted as far as it will go...

Pappy · Aug 21, 2020

To the OP.....
What you may need to do is redistribute the weight in your boat or at least keep this in mind when you make your changes to the trim angle of your engine. A boat that is loaded towards the stern typically needs more negative trim to get on plane. Moving the weight forward allows you to trim the engine out more.
Also, with each trim angle change you should be able to change the trim tab angle a bit.

Paulio91184 · Aug 21, 2020

Pappy said:
To the OP.....
What you may need to do is redistribute the weight in your boat or at least keep this in mind when you make your changes to the trim angle of your engine. A boat that is loaded towards the stern typically needs more negative trim to get on plane. Moving the weight forward allows you to trim the engine out more.
Also, with each trim angle change you should be able to change the trim tab angle a bit.

When I went out it was just me and Im a big guy...i put mt big tool box up front for some weight up there. I also am going to move the gas tank up front and out my trolling motor battery up there as well

Ldmoss · Sep 16, 2024

Pappy said:
It is called ASYMMETRIC propeller loading. This happens when the angle of attack of a propeller relative to the direction of travel is not symmetrical.
In other words, when trimmed down or under the downward turning blade (on right hand rotation props) takes a larger bite of water than the upward turning blade. Since torque is applied 90 degrees to thrust angle the engine will want to turn the boat.
As the engine is trimmed up the blades become symmetrical to the direction of travel and both the downward blade and the upward blade will begin to pull equally.
If you are standing to the side of the boat looking at the propeller from the side it is easier to see. If the engine is trimmed down the lower blade is more forward than the upper blade is.

On an engine that is trimmed under this happens......
The Thrust of the downward blade happens from about the 1 o'clock position to the 6 o'clock position and increases as the blade travels farther through this arc.
On the upward swinging blade the thrust happens from about the 7 o'clock position through the 12 o'clock position and diminishes throughout the swing.

Neutral trim (relative to direction of travel) produces equal torque.

Positive trim or trimmed out produces steering torque in the opposite direction of a propeller that is trimmed under.

Thanks for the education Pappy. I had exactly the same situation that Paulio91184 described. After an accident I read your reply and changed my trim setting to a neutral position and I now have virtually no pull to port. Its just steady as she goes. The accident reinforced my thoughts on inflatable life jackets and kill switches!!!!!

Crazyboat · Sep 17, 2024

Looking at the pic, I'd say the engine has to be raised and trimmed out. Play around with it and dial it in.

2001 Mercury 25 pulling hard right

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