I previously lived in Ranong on my own liveaboard boat. The only time I ever saw 50 Thai fishing boats at one time was at the waterfront, The actual borderline at sea is non existent. Local lore said that Thai waters were depleted of fish and the Ranong fleet had bribed heavily to fish Burmese waters, It's hard to imagine Thai boats respecting a boundary. I remember a day years ago when a Thai fleet "fled Indonesian waters" and docked at the "Multipurpose Port" in Ranong. They were painting over the boat names on the stern and a convoy of refrigerated trucks arrived to unload the catch.