Physics strange behaviour

im trying to simulate the movement of an underwater vehicle driven by externally attached thrusters.
However when i apply a force on the y-axis (global), z-axis(local) of the side thrusters, the whole thing flips up in the air, when i expect it to move along the axis

Also i’m not sure if its related but would the pivot positions affect this
and how exactly does it work?

the blend file

I’m looking at the file now. My theory is that there are 2 overlapping objects. When there are two objects that touch each other… well, obviously that can’t happen in real life so the GE gets rather upset when you try that.

EDIT: Nevermind, I didn’t know what you meant by “flips up in the air.” I’m still not 100% sure, but it’s probably something to do with the Python. Don’t quote me on that. I don’t know Python, but I do know Java, and from a couple Python tutorials I’ve glanced at, what you’re doing seems fine to me. But yeah. I don’t know.

Clarify: “flips up in the air”
If u run the file § and press keyboard up the whole thing moves forward and then up (shouldn’t do this, at least i dont expect it to)
run it and see