Actually you only have to worry about starting your car when charging, this will cut power to the battery and stop the charge. I have an inverter in my trunk and do this all the time.
You can outmaneuver any bird by flying strait up, I often get hawks and eagles flying up to mine as soon as I am above them they get scared and fly away. I don't worry about seagulls or pigeons, they fly up to it, but never make contact.
My guess is: if the water is calm the radar should reflect but "may" not on turbulent water.
40kHz hmm what would vibrate that fast? A humidifier? I would hate to see my bird crash when flying next to a vibrating toothbrush ;-D
Shouldn't radar bounce off water? I flew over a calm creek and it seemed to work. I was curious if anyone else tested this. I dont think it will hold a horizontal position because the camera can't see stable texture over water.
Was it windy? Mine switches to atti mode over half the time and drifts with the wind. If not probably an IMU issue. If the firmware isn't the latest than the IMU can mess things up if you dont check.
I fly a mile out fairly often, I have been out 7500 feet. Thats how far the cargo boat was. It was down wind I flew at 75mph there and 29mph back in atti. A little nervracking but I kept 65% battery for the return home and landed with 35%.