Hi PH
This might be your problem.
If it is an RTR (ready to run) boat, were there any other boaters around when you sailed it?
Most RTR boats have a low power transmitter with a broad 27MHz frequency band. These might be described as toy grade, as most RC toys have this type of radio.
Other27Mhz radio sets that might be described as hobby grade have a very narrow frequency band (channel) and are much more powerful. They will swamp/jamb the signals from toy grade RC sets.
This is a common problems and easy to fix.
If this is the case, there are only two solutions. Firstly, sail on your own. Secondly, replace the radio transmitter and receiver in the boat, for hobby grade items.
Other than that, sorry I can't offer any help.