Using nRF52840 to send data over open sea surface

[Harry94]

I am currently working on a project where I try to send data from a swimmer in the open sea to a point on the land (beach). I know that Bluetooth communications are blocked by the water, but would it be possible to achieve this communication whenever the wrist of the swimmer (wearable) is out of the sea? Will the sea environment allow this communication?

[Edvin]

Hello,

This doesn't sound like a case where BLE would be very suitable.

As you say, water is a medium that blocks the BLE radio communication, so it will not be possible to maintain a BLE link under water. In the case that you mention, to transfer data when the wrist is above water, this also sounds difficult, because you need to establish the connection and then send whatever payload data you want to send before the wrist goes back into the water. 

To establish a link very quickly, you would need a very short advertising interval and a short connection interval once the link is connected, if you want to transfer data fast. So depending on how long your device is above water, this may or may not work. In normal swimming conditions, I would say that it wouldn't work very well.

The short advertising and connection intervals will also use a lot of power, so your battery life will not be great. 

Best regards,

Edvin