Why the vehicle moving direction is opposite to the compass direction displayed in QGC?

Hi.
Recently, I am trying to make a arduboat based on the ardurover firmware. I have completed the assembly. And I can control the boat manually. There are four thrusters mounted on the boat. It is Omni plus type. But when I am trying to guide the boat using waypoints. The boat 's moving direction is just opposite to the arrow displayed on the QGC. Anyone knows how to figure it out. Besides, the thrusters are mounted on the surfboard, it is very sensitive to the force. How to tune the pid parameters to make the boat surge very well.
Thank you.