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Steering, I'm very confused

B

burkstar

Contributing Member
I have a D3 with SX out drive.
like many people I'm often confused as to where my out drive is pointing when reversing so I fitted a simple Davis devise that sits in the centre of my steering wheel that shows me where at any given time my outdrive is pointing.
But here is where the real confusion starts.
If I turn my steering from lock to lock the Davis devise moves from centre to starboard more and more each time I go from lock to lock.
So I went back to basics, got my out drive pointing forward, fitted I piece of white tape to the top of my steering wheel and went through the same process.
what I found is that ever time i go from ahead to starboard the taped mark moves a quarter turn to starboard?
also full lock to starboard is about 2-1/4 turns from centre and full lock to port is about 1-3/4 ?

very confused, any help would be greatfully received.
 
The steering (if mechanical) is via a push/pull cable. The Center rod of the cable is attached to the "tiller" bar on the transom on the top of the "transom shield". The outer sheath of this cable is clamped to the transom via a joint that stands off few inches from the transom and has some degree of ariiculation. If this clamp is loose and the outer casing of the push/pull cable is allowed to slip, you will see the symptoms that you see.

So much for the cheap fix... alternatively, the head mechanism ( that which the steering wheel is attached to) could be defective.
 
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What you describe may occur with "Hydraulic" steering and an "Un-Balanced" hydraulic cylinder!

Which exact system do you have???


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Although this came to mind for me, I'm not quite sure how this would affect the Davis rudder position device.
It may be more likely that the hydraulic cylinder piston seal is not holding and is allowing fluid to pass.


But here's the deal regarding balanced -vs- unbalanced cylinder:

The Seastar 92 VPS shows an unbalanced cylinder.

2503811.jpg

What that means to you is, that there is an un-equal cylinder volume between the base and stem ends of the cylinder.
IOW, it requires more hydraulic oil volume (greater helm wheel rotation) to extend the cylinder than it does to rectract the cylinder.

Example: If the cylinder is mounted on the Stbd side of the transom, then it would extend in order to move the tiller arm for a Stbd turn... thus requiring more turns at the helm wheel for a Stbd turn.

Whereas with a balanced cylinder, it would pose an equal volume between the base and stem ends of the cylinder.
IOW, whether a Stbd or Port turn, the helm wheel requires the same amount of rotation for an equal turn in either direction.
HC5331-3.jpg



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Does any one know how to assist the steering on a Tohatsu 70B. I have checked the steering cable and I greased all nipples that Tohatsu recommends.
The engine is loosening a bit but still stiff.
 
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Bobby S said:
Does any one know how to assist the steering on a Tohatsu 70B. I have checked the steering cable and I greased all nipples that Tohatsu recommends.
The engine is loosening a bit but still stiff.
Click to expand...

Rather than to Hy-Jack this thread with a Tohatsu question......, you'll have better luck if you'll start your own fresh thread in the outboard engine forum.


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RicardoMarine said:
Although this came to mind for me, I'm not quite sure how this would affect the Davis rudder position device.
It may be more likely that the hydraulic cylinder piston seal is not holding and is allowing fluid to pass.


But here's the deal regarding balanced -vs- unbalanced cylinder:

The Seastar 92 VPS shows an unbalanced cylinder.

2503811.jpg

What that means to you is, that there is an un-equal cylinder volume between the base and stem ends of the cylinder.
IOW, it requires more hydraulic oil volume (greater helm wheel rotation) to extend the cylinder than it does to rectract the cylinder.

Example: If the cylinder is mounted on the Stbd side of the transom, then it would extend in order to move the tiller arm for a Stbd turn... thus requiring more turns at the helm wheel for a Stbd turn.

Whereas with a balanced cylinder, it would pose an equal volume between the base and stem ends of the cylinder.
IOW, whether a Stbd or Port turn, the helm wheel requires the same amount of rotation for an equal turn in either direction.
HC5331-3.jpg



.
Click to expand...


Further Rick's post... According to the laws of hydraulics, the unegual cylinder volume would result inforce multiplication (for the larger piston side) for one side vs the other. This would allow the system to compensate for the greater steering force force often needed to turn to one side vs the other. The internal structure of the Davis device assumes that the helm makes same number of turns to port as to starboard for it to work. Likely nothing is wrong other than a misapplication of the Davis device.
 
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sandkicker said:
Further Rick's post... According to the laws of hydraulics, the unegual cylinder volume would result in force multiplication (for the larger piston side) for one side vs the other. This would allow the system to compensate for the greater steering force force often needed to turn to one side vs the other.
I understand that, but I'm thinking that the reason for an "un-ballanced" cylinder is that it's less expesive to manufacture.

The internal structure of the Davis device assumes that the helm makes same number of turns to port as to starboard for it to work. Likely nothing is wrong other than a misapplication of the Davis device.
Very likely!

However, does it not account for the un-equal turns?
Since it does return when the helm wheel returns to dead-a-head, I'd think that it would read correctly!
Which lead me to an internal cylinder leak, or an internal leak at the helm unit pistons! Yes/No???
Click to expand...
 
Re: cheaper to make... true

I had a Davis on my prior push/pull steering system boat. The Davis has an internal "pendulum" that is supposed to provide a virtual fixed point in space for the gear train in the device to move against in order to drive the "straight ahead" arrow, i.e. "count turns" ( assuming you do not turn right/left or visa versa too rapidly and swing the internal pendulum 180 degrees)

With unequal piston area for push and pull, it will require more turns of the helm to pump enough fluid to move the piston a given linear amount in one direction than in the other another. The direction with the larger piston area will require more fluid to fill the chamber and therefore less "force" at the helm than in the other direction ( more helm turns). Like a gear reduction, more turns, less force required.
 
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