I took a charter out of Koh Samui and ended up with some great King Mackerel (I think that's what they were - there are photos on the Holiday snappers forum somewhere) . Brought them to a restaurant and they cooked up 4 steaks for us if we gave them the rest of the fish !
Started out catching small bait fish and floating them with no success - I took off the float and free lined - had an instant take - freelining was best. I did the same on a charter from Phi Phi - freelining again out fished floated baits.
When I say "Charter" these were pretty much thai long boats with "skippers" who couldn't speak a word of English. Made things tricky to begin with but after a fish or two, when you get the feel for what you're at , it doesn't matter - he's only there for the money and as long as you pay him and he gets a fish, he's happy ! You won't find these charters online for pre-booking, but there are enough of them to arrange on the night before fishing.
Tight lines - you jammy get !!