Hi I set up on the principle that everybody else on the pond with me is too occupied with their own boat and very often not knowing where it is going.

So maximum speed forward is simply do not push the stick any further than you need to, but have full speed instantly available in reverse to stop.
Roy

Nick,
Pre-setting the max speed of the vessel can be done on most transmitters. It is done the same as setting the servo throw. This is what the Admiral was talking about(he just used fancy words).
If your transmitter allows you to set the end points of your servos, just do the same for your throttle. Consider your ESC to be a servo.
You should be able to do it while you run your boat, but make sure that someone is with you to watch the boat while you fiddle with the transmitter. 😀

It was to preset the maximum scale speed for the vessel with the manual control fitted after the ESC Then use the TX to control vessel up to pre set speed. Just curious.

You can program that feature into most modern Transmitters now,

Just wonder if we go back in thé past where we used a servo with 2 switches for forwards and backwards and a second servo/device for speedcontrol ?!?!?

Hi Nick,
Are you planning on wading / swimming out to your model to make manual adjustments? Or is it big enough to sit in?😁
In which case just pull the throttle back😂
Seriously (🙄)
The ESC works with a string of pulses from the RX.
These are sent from the TX as PWM (Pulse Width Modulation) impressed on the radio frequency; e.g. 2.4GHz, 40MHz etc.
This means the the wider the pulse the faster the motor turns.
So the simplest (and cheapest😉) way to limit the pulse width is not to mess with the boat electrics but to adjust the modulation at the TX.
This is done by using the 'End Point' function of the proportional channel you are using for the throttle.
Using this you can limit the max speed to 75%, 60% or whatever you want and suits the type of boat / ship you have built.
Check your TX manual for how to do this.
Cheers, Doug😎
PS @ChrisF; Hope you're feeling better now🤕

Well, I've pondered, and my head hurts!

First question, why would you want to do that? Second question, what exactly are you trying to accomplish?
I agree with the previous response, ie, puting a "manual" speed control in line between the RX and the ESC accomplishes nothing. The manual control does not hook up to the RX and it would block any signal to the ESC, if it did.
Go back to my second question and let's see if we can help you out.😀

Hi are you suggesting that you want to effectively connect the battery direct to the motor? By-passing the esc?
Not sure how the esc can take a signal from a manual control.
Please elucidate.
Roy