Having landed many tuna in excess of 150 pounds, sails to 50 pounds, white marlin to 100 pounds, blue marlin to 300 pounds, and dolphin to 65 pounds, I DO NOT recommend using a hand line - even if you're wearing leather gloves. Purchase an inexpensive 50 to 80-pound IGFA rod and reel, load the reel with 80-pound mono, then attach a rod holder to one of the aft quarter stanchions. Most skip baits, cedar plugs, etc..., are all effective for tuna when the boat is moving at speeds greater than 5 knots. Swimming plugs are a better bet when the boat is moving slower.
As for casting a fly rod from the deck of a sailboat - unless you are really skilled at double hauling and sidearm casting I wouldn't recommend it. And, anything larger than a false albacore on a fly rod is insane. I've never hooked a bluefin tuna on a fly rod, and I have a real beefy 13-weight outfit that is great for tarpon on the flats, but offshore and hooked to a 100-pound bluefin would be akin to lifting a school bus from the bottom with sewing thread attached to a noodle.
Next, get yourself either a long handled net with a 30-inch hook, or better yet, a long-handled gaff capable of hoisting a 100 pound tuna. These fish really don't like being hooked and they can really tax your endurance to the limit. I spent the better part of two hours landing a 150-pound bluefin off northern Virginia at a place called the Parking Lot. By the end of two hours my arms felt like rubber bands. Fortunately, someone else on the boat was able to gaff the fish.
Some of the best tasting fish are usually caught while bottom fishing with a simple top and bottom rig (High-Low Rig) using squid strips for bait. In southern waters its a great way to catch flannel mouth grunt, French grunt, grouper, mangrove snapper and a host of other tasty panfish species. When I didn't have squid on the boat one afternoon and was anchored near the Marquesses Channel west of Key West, I attached a small strip of bright red cloth the hook and loaded the cooler with grunts to 15 inches. They were the largest grunts I've seen - ever. That night they were dipped in beer batter and pan fried. Thought I had died and went to heaven they were so good.
I also caught a couple grouper that same day on the red rag, but the season was closed and I had to release them.