[marfish]

As the topic, according to the rules and settings, is that possible to have a local grid in deep sea? Giving every right condition expect it can't connect to the "main" matrix, so to speak.

If so, what is thost right conditions?
If not, what not?

[Sphinx]

Salt water effectively blocks wireless signals (SR5 p.231). Wireless devices in an underwater habitat could communicate with each other, but not with the Matrix — unless you had a fiberoptic hardline connecting the habitat to a relay station onshore, or an umbilical cable to a communications buoy on the surface.

[RiggerBob]

So...

A local grid in deep sea? No, because salt-water blocks signals.

A local grid in a enclosed habitat in deep sea waters? Possible with hardwiring to a transmitter above sea, that connects to the matrix.
But usually the isolation of an underwater-habitat is an integral part of it's security concept, so there's normally no reason to have such a setup...

[easl]

Salt water effectively blocks wireless signals (SR5 p.231).

But does it block resonance channels? New character concept: aquaman, the technomancer.

[BeCareful]

He can talk to the Emerged dolphins, and ask them to hold the other end of this cable and take it to the surface.
Also, house rule: the data connector port for boats are found next to the Captain/Pilot's chair.

[mcv]

Does that also mean you don't get any of your wireless bonuses there? Or in other areas that don't have any grid connection?

[Sphinx]

Does that also mean you don't get any of your wireless bonuses there? Or in other areas that don't have any grid connection?

A device must be able to access the Matrix, not just your PAN, to activate its wireless benefit. See "Wireless Bonuses," SR5, p.421.

[Michael Chandra]

Does that also mean you don't get any of your wireless bonuses there? Or in other areas that don't have any grid connection?

Heck, 3 Noise without Noise compensation is enough to shut down your smartgun's wireless bonuses.