without downriggers, the next best thing, in my opinion, is lead-core. you'll need a big baitcaster reel by shimano, okuma, penn, etc., and fill it with a hundred yards or so of low-diameter backing first, like spider-wire, and then with as much colored lead-core as you can fit on. then i tie a barrel swivel on the end, attach about 8 ft of 20lb fluorocarbon leader, and use that set-up to troll , minnows, flatfish, or flashers. i can sometimes make it down to about 80 ft. make sure you're only going about 1.5 mph or less with the flatfish. good luck, & bring back pictures.
