About 30 years ago, inventive anglers initiated a downward trend in fishing by deep trolling baits attached to window-sash weights rigged with homemade release clips. These crude devices were the embryonic versions of the downriggers that have become so popular among today's sport fishermen. I fish downriggers every day. In fact, the first two lines I put out are the downriggers, says Capt. Chuck Skinner of Sanibel Island, Florida, who's been using them for the past 17 years.When given the chance, downriggers prove their effectiveness and versatility in almost any situation when fish hold at depths below 30 feet. West Coast fishermen employ them to keep lures in salmon feeding zones; East Coast anglers use them to catch stripers hugging the bottom near the beach; and Hawaiian skippers slow-troll live baits clipped to downriggers to entice blue marlin and tuna up from the depths.Boom and BasesManufacturers offer booms, or arms, in lengths varying from 24 to 48 inches. Several factors should be considered when deciding which model to buy, including the type of boat you have and the placement of the downrigger. Short booms work fine if you plan to mount a downrigger on the transom of an inboard boat, but a long boom is required to keep the cable clear of an outboard's prop. Long booms prove advantageous in gunwale mounts because they can be used like outriggers to stay clear of flat lines. Ed Mesunas, director of advertising and public relations at Penn Reels, uses downriggers when fishing for bluefish and stripers off New Jersey. He believes that accessibility is the single most important factor in downrigger placement: You have to be able to clip your lines to the ball without leaning way over the gunwale, and you have to reach the controls in a hurry to raise the ball after a hookup. The more difficult your setup is to operate, the higher your frustration level will grow. And if it isn't easy to use, then your downrigger will stay belowdecks where it can't help you get strikes. Anglers have several options available when mounting a downrigger. Owners of large boats (30 feet or more) usually through-bolt a permanent base plate to the transom or attach a side mount to a gunwale. On smaller boats, most owners opt for a gimbal mount inserted in a rod holder or a mount that clamps to a rail. Boom length influences the choice between a fixed or swivel-base mount. Fixed bases work fine for short-boom models, while swivel bases provide ease of operation with long booms by rotating toward the cockpit.Manual or Electric?Skinner says that the no-sweat operation of an electric model is a definite advantage: I'll raise that 10-pound ball 20 to 30 times during a day's fishing. And I'm darn glad it's an electric. Skippers who troll deep with more than one line also appreciate the convenience and speed of retrieving cable with the touch of a button.Several electric downriggers include programmable features such as auto shutoff, jigging (raising and lowering the ball at regular intervals to cover more of the water column) and tracking (automatically adjusting the ball depth to follow bottom contour). Make sure any electric model you choose features a manual override - as most do - in the event of electrical problems.Capt. Jim Sharpe, however, prefers the simple, straightforward operation of a manual downrigger when fishing charters out of Florida's Big Pine Key for dolphin, wahoo, kingfish and other species. Sharpe carries a short-boom model below deck that he quickly sets up and deploys whenever needed. I rarely deep-troll with more than 50 feet of cable out, so cranking it in by hand is no problem. And manual downriggers have fewer parts to maintain or replace, he adds.Whether you opt for a manual or electric model, a drag system - as opposed to direct drive - is a must if you plan to troll near structure. Hang-ups are inevitable, and a properly set drag will keep you from having to replace expensive downrigger weights, advises Mesunas. Downrigger AccessoriesBefore you spend any money on a downrigger, do your homework and determine which setup will best fit your fishing situations. Some are sold as stand-alone units or in kits for specific applications, yet many models can't be used to full potential unless you purchase additional accessories. Don't be surprised if the downrigger you buy doesn't include a base plate, rod holders, or weight (cannonball). Such items are usually sold separately because where and how you mount a downrigger depends strongly on personal preferences.Cannonball weights range from 3 to 20 pounds, with 10 pounds being a good all-around size for most saltwater applications. If you expect to deep troll at speeds in excess of 7 knots, you'll need a weight heavier than 10 pounds. Although downrigger weights come in various shapes - some are even shaped like fish - all the skippers I spoke with use round weights since they stow easier and tend to track truer in the water.One unique accessory you might run across is the black box. The development of these shadowy units came from the belief that galvanic action causes electricity to flow from boat to downrigger cable. Its manufacturers claim that since fish are sensitive to electrical energy, this charge can be manipulated to attract fish. Does it work? Skinner says he's seen baitfish cluster around the cable after he's switched on his black box. Sharpe doesn't use a black box with his downrigger, but on many occasions he's seen hammerheads that seemed to be attracted by the cable's underwater vibrations, so he's not inclined to doubt their effectiveness.