aerial - connectivity with the network

I want to put the M1306b appliance in the water in order to get from a microcontroler certain measurements send send them to the gsm network.
1)Which is the longest length of aerial (antena) can I use?
The M1306b will be under the water and outside the water will be the aerial (antena)…
2)Can i put bot of them ( M1306 with the aerial) inside the water and be connected in the network ? Is tha possible with the distance of the water and if it is up to which depth is it ?

My feeling is that you should discuss this point with an antenna specialist ! As your application is very specific and doesn’t look like to standard way of using GSM antenna.
Or do many tries if you have time …

Yes, this is certainly a question for an antenna specialist!

The main limiting factor on cable length is the signal attenuation - more cable = more attenuation.
Thus it is always best to have the Fastrack as close to the antenna as possible (ie, minimum cable length = minimum attenuation).

But, why not have the Fastrack at the surface, and just the data link going down to the remote microcontroller?
Surely that’d be far superior?