I just tested snorkeling today and it works absolutely perfect.
You can raise the snorkel with a toolbar command. Yes the toolbar is confusing, but I found it eventually, and so will you
I believe Snorkel depth isn't important. You can raise the snorkel on the surface and dive to periscope depth.
I believe the button for snorkel depth is the one right to the P. No idea what this is on English keyboard. I use the SH3 Keyboard layout from OMEGU and a german keyboard.