Radio contact is unstable

Loses the submersible motor, despite full batteries and a short distance (about 8m), suddenly the radio contact (mostly during cornering). We then drove the boat, without the possibility to influence it, so long, until it disappeared somewhere in the reeds. We had then, with an caused fetched kayaking, save the boat. The action lasted about half an hour. The engine was still running. Only through direct contact with the remote control, the wireless connection is restored and the engine could be turned off.
Conclusion:
Those looking for an adventure incl. Armed with anglers, who should buy the underwater motor necessarily. All others who do not have a particularly lifeboat, should either leave the swim part only in the bath or the engine just did not buy.