What percentage of the coast lines around the world are covered by cell towers, I wonder? It would be an improvement over having to find them manually, but if

What percentage of the coast lines around the world are covered by cell towers, I wonder? It would be an improvement over having to find them manually, but if you've gone to the effort to engineer an electronics package capable of connecting to a cell tower after years at sea you can probably get it to ping a satellite regularly "for free".