ORIGINAL: srt10
It is possible your rudder servo is not holding under load..
I have a cat that did this, and when I went with a stronger MG servo, the issue went away!
FE baots are loads of fun
I have the JR z590m servo in there, its pretty strong i think. plus when i hold at a steady speed you can see the boat go side to side like one prop is pushing more than the other.