Kevin, please see the tutorial if you haven't already...
http://www.ifish.net/board/showthread.php?t=125197
One very important thing to realize is that....at some point in the season, there is a significant change in tuna behavior. It is usually around the 1st to the 3rd week in August. Before that, the fish want a fast-trolled jig. If you want to load the boat, trolling with feathers / clones at 7 - 10 knots is the way to catch them
When the change occurs, it is because they are changing what they feed on. When they switch over to baitfish, and start "jumping" or "boiling" or whatever you want to call it, they do not bite well on fast-trolled feathers. There might be a "crossover period" of a few weeks when they will bite fast & slow together. But at some point, usually by the 3rd week in August, they are chasing slower moving baitfish so you either cast to jumpers, or slow troll.
For slow-trolling with swimbaits, you want to be somewhere between about 2.5 - 4.5 knots. An example spread would be......(a) two swimbaits on 2 ounce jigheads, 150 feet out. These will be off the stern, or the stern corners. Then (b) you have two more swimbaits, on a 2 ounce jighead, with a 4 - 5 foot leader (50 - 60 fluorocarbon best) behind a 2 or 3 ounce torpedoe sinker. These two rigs will be in the forward rod holders (they will ride deeper) and will be around 125 feet out.
If you see jumpers, but can not get bit by casting, then often the slow trolling swimbaits between / around jumpers will be deadly. What is often happening here is that......the fish are cruising around at 40 - 60 feet deep, and coming up here & there to pick off small schools of baitfish. They come up, then go down quickly. The slow trolling gets the gear down a ways....tempting the fish to come up without having to come to the surface.
Experiment with a plug (like a Yo-Zuri or Rapala) in the middle of your swimbaits spread. The main thing is to keep the spread together! Do not put one lure 200 feet back, another 150 feet back, and 2 more 50 feet back. Make a "pack" out of them.
Hope this helps,
MM