Mavlink control the blueboat

Hi, We have a blueboat and try to control it using the mavlink message generated by a simulator. We tested the boat that we can send the command in manual mode and control it using joystick. Once we changed to the guided mode and send the mavlink command, the boat behavior is not correct based on the command we sent. The GPS of the boat in qgroundcontrol is correct. Are there any suggestions on how to solve this problem. When we closed the udp and didn’t send the command, once the motors were armed, the boat will also move. is it normal? Thanks