First of all thanks for the new update, this is very cool!
I was wondering if you had plans to add a ground effect FlowPrimitive or something? Or if you could point me in the right direction for implementing it myself that would be great. I would probably need to create a custom one since my "ground" is water and I'd need to query the wave heights anyway.
Thanks,
Scott
Great looking boat and wake! For this use case it looks like you probably want to include ground effect to increase the effective aspect ratio of the boat platform (or more likely just the front wing) when its close to the ground so that it generates more lift at the same angle of attack. You dont need to mirror anything to do this but you would need some code that scaled the aero object shape (whilst keeping area about the same).
Getting the vortex wake to respect the water surface as a solid does require a reflection of the whole vortex system about the water surface plane. This is doable but probably not recommended as it is quite tricky for not much visual gain (and is not your problem anyway I think).
To understand the boat aerodynamics better you could try putting it on a gimbal (constrain the rigid body in translation), removing the water and set some external wind using a uniform flow. You would expect that with the CoM in the middle of the boat it would be very unstable in pitch. If this is the case, then it should flip when the aerodynamic forces are greater than the restoring forces from the hydrodynamics (hydrostatics?). Of course it is possible that the aerodynamic forces are fine and that its the hydrodynamic forces that are unrealistic. Good luck with this