I'm hoping that you are well and still using this email address.
It's a while since I looked at model submarines but my friend Robin and I have decided to resurrect our GATO RC conversion. We once showed it at your Edinburgh model show in Inverleith park.
We didn't give up on it but rather got diverted to another quite different project - an old car.
I've just been scanning through the AMS forums which are always very interesting.
I noticed some discussion about alternatives to radio as the remote control link. This seems to be because RC has moved to UHF plus which doesn't like going through water.
In the 70's I was involved in ECG telemetry from divers. We tried several systems other than radio. We could get heartrate using an ultrasound (40kHz) pulse on the "R-wave" but the reflections prevented us sending the ecg waveform. We tried a magnetic link (coil to coil - transformer) but that falls off with the cube of the distance although it can work OK within a limited range. Our most successful system used a varying "static" electric field which was created by electrodes on the swimmer who also had the usual ECG electrodes on his chest. I think we used about a 50kHz carrier FM modulated and there were some issues keeping the transmitter signal (several volts at 50kHz) out of the ECG signal (about 1mV). The receiver was a couple of electrodes at the pool side about a metre apart feeding an amplifier around 50kHz then an FM demodulator. That sort of link could be used for controlling a model sub. It could probably work in seawater.
However, my main reason for this email is to see how you are doing.
Great to hear from you.
I'd be very happy for you to quote me on the AMS forum as you suggest.
I think that there was an underwater electric field broadcasting system in the San Francisco bay area, probably in the late 60's, which simply pumped audio via beach electrodes into the sea and divers could receive it via earpieces.