[hinkley]

Triangulation can tell you where a point is between three sources but you need four to determine elevation, because it’s not the radius of a circle but the radius of a sphere.

But at sea there’s not much to obscure satellite signals so I believe resolving buoy position was a solved problem back when gps car navigation still sucked balls because tall buildings make everything harder. You need a lot more satellites to see three or four at the same moment.