A light-to-medium-weight setup like the Shimano TLD trolling rod and reel combo will do the trick without breaking the bank.
Whether you're casually dragging a single lure behind your boat or actively fishing a spread of six or eight lines, it's important to have a trolling rod and reel capable of handling large fish, which can critically damage under-equipped gear and leave you with an even deeper hole in your pocket once you've made the necessary repair(s) or replacement(s).
While passing through a particularly remote part of Fiji, our trolling gear gave out on us and we were reduced to hand lines — which work perfectly well, but aren't for everyone — and otherwise inferior tackle until we reached New Zealand, where the captain ended up having to invest in all new gear. We lost more fish than either of us care to recount along the way.
Choosing the right trolling gear can be difficult: too lightweight, and you might destroy your tackle, or leave a fish with a lure and spool of line attached to it; too heavy-duty, and there won't be much sport involved in retrieving (most) smaller fish. Consider where you'll be trolling most of the time, and whether or not the chances of hooking a trophy are worth the extra weight.
If you're trolling inshore and your catch is most likely to stay within the 50-pound range (think inshore species like salmon, and maybe small mahi mahi and tuna offshore), the Shimano TLD rod and reel combo will work perfectly.
If you do find yourself trolling offshore more, something a little sturdier will save you time, money in the long run, and quite possibly even a little heartache, which is why I would go straight for one of Penn's International series reels and pair it with Penn's Ally Standup Rod.
Tip: If you'll be using this setup on a sailboat, consider a short — either 5-foot-6-inch or 6-foot — model for better maneuverability around the boat's rigging.
Penn's International reels have been a favored reel since my grandfather was catching tuna, and I still have and use a few of his old ones. The modern version of the International V comes with a one-piece machined aluminum frame, which helps prevent salt and grit from entering the inner workings of the reel. The more seams there are in a reel, the more points of entry there are for water and grit to find their way in, and in the case of saltwater, that can mean game over without prompt attention.
Penn's Ally standup series suits most purposes, but choose the style that's best accommodated by you and your boat, and make sure you at least purchase a model with a gimbal, which not only locks the rod into its holder but allows it to pivot in a fighting belt or chair — as opposed to, say, your hip or thigh, which can be painful. You can step your rod up or down as needed, but it's best to purchase a rod with roller guides if you're using line over 50-pound test, which will wear groves in regular O-ring guides over time.
Pros: Most models of both setups will work for bait and bottom fishing, too
Cons: Heavy, cumbersome to stow
Buy the Shimano TLD trolling rod and reel combo on Bass Pro Shops for $269.98-$309.98
Buy a Penn International series reel on Amazon, starting at $502.71
Buy the Penn Ally trolling rod on Bass Pro Shops for $66.97 to $249.95