Hi, sorry... you are true.
I try to explain better what i want to do:
i'm a spear-fisher and we use a small buoy floated with a red flag to advise other boats/people that we are somewhere nead the buoy (maybe under the water).
This buoy is connected to the diver with a string of some meters (from 5 to 30... in depends on many thins) and this string is very annoying because it gets around your legs, makes noise, alerts fish, etc etc....
So, what i want to do is to put a small elecrtic egine on it and then control the direction of the buoy with and arduino system, the buoy should follow the diver in the water (not under the water, just follow the diver on the surface of the water), consider that usually the diver stays 1 o 2 minutes under the water (from 5 to 15 meters, in my case) and then takes breath for 2/3 minutes before to dive again.
So, my idea is to have some kind of object / quarz / reflector of signal on myself (must be small and water proof) and then put a sensor on the arduino system to know how far i am, where i'm going and so on.
Is not important to follow the diver even when he is under the water, it is enough to understand how far he is and try to reach him staying in a range of 5-10 meters of the diver.
I have an excellent knowledge of coding and programming with many different languages, i'm not worried about how to code that, but i don't know if exists this kind of sensors.
I've seen that is possibile to use ultrasonic sensor with arduino but i'm worried with this kind of sensors as i will get too many false positive, i need a sensor that can give me the distance (or a noise/analogic level) between the sensor (put on the buoy) and the diver (maybe another sensor / something like RFID but with long-range capabilities?)
Do you have enough information?
Thanks to all in advance