Redesigning steering system for twin AQAD31A-DP290 setup

So for our dual setup here I am looking to replace the power steering system we are currently using for an electric power steering system from Seastar Solutions. The current system gets power assist from the steering pump attached to one of the AQAD31a diesel engines and steers both DP290 stern drives linked by a tie bar. The current steering actuator is the Volvo Penta SX PA Cylinder(photo attached), which as said before steers both stern drives.

With the electrical steering system both stern drives will be individuably steerable, only now the following problem has come up: The steering cylinders (EC5360 sterndrive cylinders) aren't a direct fit on the steering arm from the stern drive, as well as on the mounting bracket. Is there a retrofit kit available for this, or do we have to redesign a steering arm for the whole steering mechanism, or even a whole steering fork? Hopefully someone can help (last resort option is new sterndrives but we all know that is really expensive :/)

Re: "With the electrical steering system both stern drives will be individuably steerable"

And you doing this so you can go to a joystick style steering??? Before doing this, does the existing drive spacing allow both drives to be "toed in" , i.e. Port Drive at full STBD turn and Starboard Drive at full PORT turn???? And why new drives???

We are going for an autonomous sailing system, so joystick style steering will be implemented yes.
In the manual for the DP290 stern drives it says this:

[FONT=&quot]In a twin installation the 'Toe-out' angle between the stern drives must be adjusted until an operation free from cavitation has been obtained. Increase the angle between the sterndrives on a boat with a deeper V-hull. Adjust the sterndrives in accordance with the picture. If the measurement at the transom shield is 'A', the measurement at the screw-head of the trim tab must be 'A' minus 15-25mm (9/16-1").

So I don't know or I am interpreting it correctly, but it seems they aren't allowed to be both toed in. But correct me if I'm wrong


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You are adjusting the steering "Ackerman" by inducing toe out. The idea is to be sure the steering is neutral. I looked at the Optimus pages on the Seastar site and by the look of it, you'll have to go with the smart cylinder attached to a tie bar. I think independent steering is overkill and not needed.
Because they're dual prop, you treat them like a jet drive. That is, you adjust the engine speed and even FWD/REV gear to enable turning the boat inside its own length or even walking it sideways. Sometimes you don't need to "steer" to turn the boat.

o2batsea said:

That is, you adjust the engine speed and even FWD/REV gear to enable turning the boat inside its own length or even walking it sideways. Sometimes you don't need to "steer" to turn the boat.

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Good advice. When I was taught helming larger displacement hulls, (42footer), we learned “walk it on the prop”.
There is a slight bonus of having an Ackerman angle. I have it on a performance catamaran. The idea is that because in a turn the inside rudder prescribes a smaller arc, that rudder requires a slightly different steering angle. Having each rudder matched to its respective arc results in decreased drag.

We will need 2 steering actuators for precision sailing like f.e docking, but for other sailing purposes we just steer them in sync. But it's now just the question of how we are going to make it fit on the steering arms of both sterndrives

I guess you put a smart cylinder on each drive and Bob's your uncle. However, I can't imagine a situation in which you need to turn the drives independently from the other. It just doesn't make any sense. But you do whatever you want it's your dime.

We are going for an autonomous sailing system, so joystick style steering will be implemented yes.

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Our boat will have to be fully autonomous, as part of the R&D project. But it's now just a matter of whether I can get a custom made steering arm for this new steering cylinder, do I need to design myself one or is there a retrofit kit in some sort available on the market?

There are stainless steel clevises available at McMaster Carr which should do the trick.
You want this configuration:


Replace the outboard motor cylinders with smart cylinders and replace the clevis on the ends with ones from McMaster. When I put hydraulic on my (now defunct) OMC Cobra drive, I used a ball joint rod end and just ran a bolt up through it into the steering arm. Worked great.

How are you driving the helm signal? That must be one of the major challenges of the project.