So from the pictures it looks like you have the OTW module inside the boat with the water pump ballast system. I'm assuming you purchased this boat secondhand, and that is was put together by someone else. If so one of the snags with a secondhand purchase is that you don't always know the history of the model. Has it had a flood for instance- this tends to have implications for the long term health of the electronics inside.
There are so many things that could have caused your problems, it's impossible to accurately diagnose the source of the problem on a forum. All we can do is gives you a few things to look at and try.
Usually the receiver aerial is routed inside the tube of the module. This generally gives adequate reception, although some modellers like to route the aerial outside the module in the free flood area.
I'm assuming you sail in fresh water, if you sail in salty or brackish water, then that is likely to be your problem, as the radio waves can't penetrate through.
You should always fully extend the TX aerial before putting your boat in the pond. The radio signal is severely attenuated in model submarines, and running with the aerial down is bad for the signal and the TX's RF section if you do so for a long time.
Other things it could be- defective transmitter, defective receiver, defective ESC(s), bad batteries, duff cabling. As you see quite a few things it 'could' be. I would start with checking the cables and batteries, that is easy and inexpensive.
You may also want to try a range test in air, about 50 yards away with the aerial down, and you should still get reliable transmission. If it's bad transmission it could be a problem with the RX, TX, crystals etc. If you get a good reception, it's unlikely this is the cause of your problems, and you can tick that off the list.