Fantastic to have such specific help - thanks Dave! I'm slowly understanding more about servos and current.. I must admit the sail winch is running to one stop as the crane cable gets as close to the job as the stop allows, so I'll rejig this such that it doesn't work to a stop. The switcher is to gain an extra channel from the tx, one switch is for a spotlight on the crane when operating it, the other is for sound - it's rigged up to an MP3 player that plays a loop of sound - a bass tug horn!
Thanks again for your help, I'll post a video of the boat working once I've cracked it - nearly there now I think!!
Eric

HI Eric
I did suspect that you had something connected that was drawing too much current for the Mtronik BEC. To answer your question re separate battery you can either use the Mtronik built in BEC or use a separate battery. You cannot use both at the same time as the ESC will not function correctly.
As the sail servo is causing the problem I suggest you remove the red lead from the sail servo that connects to The ESC and make a separate connection for the red lead to the battery (6V). That way the servo will be controlled by the rx but won't draw any power from the BEC. Put a 1 amp (or less) fuse in this line as if the servo stalls it may self destruct and the symptoms suggest this may be happening hence the pulsing. The BEC is current limited so will be switching on and off. As a point of interest you should never run a sail winch servo to the stops at the extreems of travel to avoid this happening.
What is the two way switcher used for?
Hope you are nearer to finfing a solution
Dave 😀

PS I did a bit of disconnecting in order to move the rx away from the power, and started connecting things one at a time, the motor worked fine (with the full throttle lights working too!) until I connected the sail servo that runs the crane cable, at which point the ESC started pulsing and stuttering again! There's the problem... I start checking that now. Thanks again kind Sirs..

Thanks Dave, and pmdevlin for your excellent replies. I'm going to try moving the aerial and the ESC further away from the power lines as you say. Not sure what you mean by the voltage dropper, there isn't anything inline - it may be the two way switcher (ARCS2) you have spotted, attached to the starboard side of the boat? There's an inline fuse (black box) beside the reciever. in terms of range, it's having it's malfunction when it's on the bench (with the radio beside it!) as well as on the lake so possibly not a range prob?
You mentioned power to the reciever, is this worth a try? Do I need a separate battery for this, or can I use the 6v supply?
Look forward to hearing...
Thanks again, much appreciated!

HI Eric,

it all looks a bit "busy" with wires all together, I think Dave is on the money, separate the wires.

What are all the connections to the receiver? do you have a separate power supply to the receiver, I cant quite make it out. in the second video, the esc lights go out altogether, and the receiver light starts to flash, this means the receiver has lost contact with the transmitter, if so, this eliminates the esc, when the signal is back, the esc then re-arms. The frysky tx is used by plane and helI boys, so there must be a range test somewhere in the programming, I would try that out of the water, then if the problem happens you eliminate the water level for the receiver aerial. if you cant find the range test, just keep walking away operating something you can see, like the rudder, to a distance that would be acceptable.

Back to the connections in the receiver, something there could be causing a short. A few weeks ago, I lost signal with my Huntsman, momentarily no control, its fast, so it was very scary! Luckily I was able to stop it. its then detective work, the rx light was out, but the failsafe had not kicked in stopping the throttle. Imagine this was a rc plane, it would now be a flyaway. After disconnecting all leads to the rx, reconnecting one at a time, and bench testing, once the rudder servo was connected and operated several times, the rx went off, the rudder servo was causing a short circuit and was the culprit

I would sort this out of the lake, otherwise its waiting for it to drift in, or worse, as I experienced, loss of control.

Also, maybe not connected, but the lights on the esc signify throttle range, so full throttle and you should see the green light, full reverse, red light, you videos do not show this, perhaps you didn't use the throttle range in the test.

any questions, juts ask!

HI Eric
Seems a neat installation.
However the rx and aerial appear to be right next to the ESC and motor with the aerial actually running alongside the motor. Speed 600 motors are fairly good at generating electricaol noise, especially at speed, and it is possible that it is this interference that is causing your receiver to lose signal in the middle of the lake.
Ideally your high current power wires need to run as far away from any receiver wires and the aerial. With 2.4 Ghz the aerial must at all times be above the waterline as the signal cannot penetrate water, unlike say a 40Mhz system. I usually try and run he power wires on one side of a boat with the receiver wires on the other. Running power and rx low current wires in close proximity can result in noise being induced ( bit like a transformer).
I had a problem with a model Trent lifeboat where I had placed the rx with the aerial pointing down into the boat as it seemed sensible, but it was below the waterline and about 10yds out it started stopping and starting. Looking at your videos the signal is being lost causing the ESC to reset. As you apply power the signal is again lost and the process repeats.
Initially try just moving the Rx so the aerial is pointing away from the motor and ESC. ideally you need to move it away from the ESC as that is also a high source of interference. Hopefully your rx will then not lose signal. if this is a new TX/rx its possible you have a faulty set. Can you run the tx in reduced mode to check output? Sorry I do not have a FlySky set so am not familiar with its settings.
I also notice that you appear to have a separate voltage dropper. The Viper has a built in BEC so you can't use both at the same time. You can cut the red wire in the lead from the ESC to the receiver. I usually just remove the red connection from the plug and tape it to the lead so I can replace on another boat.
Please let me know how you progress. There are other steps that can help reduce the motor noise, but its not normally necessary with 2.4Ghz sets.

Cheers
Dave 😀

I've uploaded two videos to YouTube - hope they help..

More pics, hope they help, how do I upload a video?

Thanks Dave, here's some more info: the tug is running with a 6v 4,5ah battery powering a speed 600 motor, the tx/rx are by Flysky and the ESC is an mtroniks 20amp marine. Hopefully the pics and video help, there are lots of connections unfortunately.
Hope you can help..
Eric

HI Eric
To be able to give advice please will you provide a bit more info:
What kind of ESC do you have?
What type of radio gear are you using?
What is your battery type?
There are so many reasons why electrics can cause problems and the more we know the easier it may be to provide a solution. if you can post any pics of your model and its internal set up this would be useful.
Dave