HMS President and stone-frigate geography

Which British stone frigate is furthest from navigable water?

Probably HMS President, though the result changes depending on whether distance is measured from the coast, the Thames Barrier, or the navigable river.

Most British stone frigates remain relatively close to the sea. HMS President is the technical candidate for the establishment furthest from it, depending on how navigable water is defined. Its position on the Thames lies beyond the Thames Barrier, where the river is distinguished from the tidal estuary. Measuring from the coastline, the barrier, or the navigable Thames can produce different answers. A shore establishment with a ship's name turns a simple distance question into a geographical definition problem.