Если даже и есть какое-то магнитное поле (как в моем случае под высоковольтной линией), то отклонение можно устранить синхронизацией компаса. Вот выдержка из инструкции:

"Note: When the boat in the new environment, the compass will be interfered by the local magnetic field, the boat does not travel well or directly (compass direction is not correct, automatic driving and GPS navigation traffic will appear yaw), then need to open the menu to adjust the compass on the remote control and boat to keep the direction of the compass consistent with the new magnetic environment. (Note: do not have to always adjust the compass at the same environment, but only in the new environment to adjust them)
Please see the adjustment steps in details:
B. Adjust the electronic compass on boat
C. Adjust the compass direction on the remote control".