No idea sorry. He has good coverage at the marina the boat is moored at.Which SIM router and aerial(s) does your son use?
https://www.pedelecs.co.uk/forum/threads/4g-routers.47655/
I should make it clear - when he goes to Cyprus he flies and lives in Airb&B
He has talked about sailing there. I told him not to be so stupid and keep sending him links to stories about killer whales sinking yachts in the Bay of Biscay. He doesn't listen to me. Since he is 45, that is no surprise.