RC Sail Boat speed measurement and transmission

Pascalou31: @Robin2 : You are right, I'm talking about racing boat and it should be better to find a solution which doesn't reduce boat speed in both racing and practicing mode.

I have no idea how you could measure speed, never mind mind measure it accurately, for such a small vessel.

Another significant issue is, if you do have a speed measuring device, how can you verify that it reads correctly.

It just occurred to me that a gyro/acclerometer might be able to let you know if the boat is speeding up or slowing down - in other words, if your control inputs are useful. However I suspect a sailboat would be subject to a huge amount of "noise" due to the effects of varying wind speed, angle of heel and water roughness (I don't know if there are currents in the water where you sail, but that would be an added complication). I suspect it would be very difficult (perhaps impossible) to filter out those effects to get usable data.


PS ... I'm assuming that timing the boat between two fixed buoys is not what you want.

@Robin2 : You assuming right...

I'm also afraid that the accuracy I'm looking for is quite impossible to reach with a lightweight system which doesn't reduce boat speed.

Maybe in a first step, we should reduce the use of such a system only for practicing/training in order to check different adjustments...

For practising, and assuming there are no other boats to get in the way, I would be tempted to try the old-fashioned type of log which was essentially just a bucket dropped over board tied to a rope with knots on it. The bucket would be stationery in the water so timing the passage of the knots over the stern gave the speed.

I reckon you could do that on a small scale using sewing thread for the rope and having it rotate a rotary encoder on the boat and use the Arduino to time the encoder pulses.

(Heath Robinson / Rube Goldberg lives)


Smajdalf: Yes, I assume the speed of such propagation is the speed of sound in the water. Of course "capacitance and resistance" of the tubes plays similar role as in electronics. It is mostly unrelated to the actual speed of water molecules movement.Similarly simple mental modes are insufficient to describe behaviour of your measurement system. IMHO you need take relativistic physics (and maybe quantum) into account, as well as lot of parasitics features of the actual circuit. Maybe a RF theory may help but I doubt it.

My feeling is that such measurement setup would be affected by so many unknowns and parasitics, it is hopeless. Theoretic description is out of "normal hobbyist" reach, time differences out of Arduino's resolution etc.

I think Doppler effect may be used for such measuring - which can be more easily accomplished with (ultra)sound IMHO.

Maybe you should watch the PhD's explain it without recourse to smoke about quantum or relativistic physics and hurt egos.

If you put a pressure sensor on the stern, pressure will drop with forward movement.

Or... https://globalmarinerenewable.com/how-does-a-boat-speedometer-work/