I have been looking at the current OMNI frame classes and from what I can tell they are essentially just rover layouts and are more like theoretically ideal setups rather than what is possible. the reason I bring it up is that I have had some debates recently about how to apply omni frame control to real world boats.
these 3 frames can be easily modified to fit most existing ships and boats with bow or stern thrusters using some slightly different layouts
Omni 3A would represent most standard omni capable boats that are out there, something like a twin screw tug, 2 propellers and a bow thruster, the reason it would work as an omni is even through the bow thruster is really far forward and applies a lot of yawing force, it can still push the boat to the side as long as the main motors can counteract the yaw, it will move slowly and use a lot of power to do it but it will be possible. I added the rudder to show how it can also help divert some flow from the propellers to help with translating, twin rudders would work better but a single one will still help.
The omni 3 plus layout is basically a single screw boat with bow and stern thrusters. this is configured as a Omniplus with the 4th motor not used, since 4 and 2 just mirror each other it makes motor 4 redundant.
OmnPlus advanced is the omni plus configuration, but we have replaced motors 2 and 4 with left and right motor output. This gives the advantage of having much more yaw authority since you have both left and right motors doing yaw along with the thrusters. this makes sideways movement far more accurate, as your not relying just on small thrusters to control yaw and propel the boat sideways.
these 3 extra layouts can be done with current code as is the only issue I ran into was with prearm checks because it’s using 2 steering methods at the same time for omniplus A plus the lack of motor 4 for omni3plus.