Boat, two engines and steer

Dear team,
Trying to setup my boat with two engines. Both engines are mounted on a rotated column.
Left Engine – Servo 1 – Throttle (SERVO1_FUNCTION - 70)
Right Engine - Servo 2 – Throttle (SERVO2_FUNCTION -70)
Ruder – Servo 3 – Ground Steering (SERVO3_FUNCTION 26)
In that setup everything seems to work fine.
I want to set up in manual mode that I can do manually engine momentum, so I want to drive each engine on different radio channel, ie. left full ahead and right full back. I wonder whether I pass through separate channels to different engine it will work in manual mode, BUT IN AUTO MODE WILL probably not. Means that I will not set up throttle function on no servo so algorithm will not have information which servo is throttle.
I’ve setup also 73 ThrottleLeft and 74 ThrottleRight on servo 1 and 2 hoover its generate momentum according to steer stick. It is not what I want.
Just enable momentum in manual mode for harbor maneuvers, and normal mode, both engines working in auto mode in the same order.
Any ideals.
I will show this boat in short time.


At the moment, there’s no way to allow controlling the left and right engines separately in a manual mode but together in Auto.
I guess the reason you’d like to do this is that it’s possible to control the heading of the vehicle a bit using just left or right engine? Any reason you’d do it this way instead of just moving the whole column?
To be clear, I know someone with a real full sized boat (not using ardupilot) and I see them making use of the separate left and right engine controls especially while docking… I just don’t undestand why this is useful (although it obviously must be).

@rmackay9 Thank you for a quick response.

The project is a 4 meters long catamaran with two engines based on Ardurover (soon photos or on priv message)
The reason for the separate engines control is, as you mentioned, is only for docking maneuvers.
In that case we can turn the boat (pivot turn) in one position, using engine momentum.
This is typical way t use engines for large boat.
Maybe it can be done in some additional flight mode, like “docking” flight mode.
I will sent photos for your info on priv msg.

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Ok some improvements.
I’ve setup servo function to 73 ThrottleLeft for left engine
and 74 ThrottleRight for right engine.
Seems that it will work even better I thought.
There is some mix in engines and steer.
Steering left is slows left engine, and steering right slows right engine.
When steering with engines zero, steer left creates momentum left.

Hope will work with in auto.

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Ok, interesting. Issues may come up with the steering response if you want/expect the steering servo to turn the engines as well. in -rc4 you may find the steering servo does move (although I was planning to disable it in future releases if skid-steering is enabled)… but the scaling for speed will be incorrect. In a regular steering vehicle (like a car) the steering response needs to be scaled for speed because as the vehicle is moving more quickly, the response to a small steering input increases. With a skid-steer vehicle the response doesn’t change as the vehicle speeds up.

Now, if the vehicle always tends to move at the same speed it may be possible to tune it to work OK… but it’s uncharted territory!