Thank you a lot. Unfortunately, I got used to ignoring this warning since until now there has never been a problem. Stupid me.
So then I will design the shapes in blender and import them so I can change the size without scaling.
The other issue was that in the demo project, the boat sometimes just disappears under water after changing propulsion value or rudder angle.
And great to hear that you will release it as an addon, that would be so cool. As far as I know hydro is the only way to do realistic boat or ship simulations in Godot without coding your own hydrodynamic model. We used Dynamic Water Physics before, which is great but unfortunately only available for Unity and Unreal, which is not so great. And we also would like to use open source if available, so we super appreciate your work. We will probably use it a lot in the future to develop interactive learning tools for seafarers and sea rescuers.
Many thanks for your help again,
Marie