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June 05, 2008

Troll Control

An inshore fisherman's guide to electric motors

In the vast, open marshscape of my low-country Georgia home, redfish and trout find thousands of creeks, holes, oyster bars and oxbows in which to hold, hunt and hang. Bay boats and trolling motors have revolutionized this region's fishing as much as high-tech depth finders changed fishing blue water.

Here in the salt marsh, trolling motors take us to all-new honey holes, add stealth to our mud-flat approach and help us position our boats in tidal currents that tumble in a torrential rush. But we're not the only ones exploiting this now 15-year-old saltwater technology.
Electric motors bolt to the bows of many inshore boats throughout this country's coastal regions. However, saltwater fishing still sees far fewer than freshwater. Many saltwater anglers still use trolling motors for only the most basic functions, and many remain unaware of the technology that has drastically improved these motors since the early 1990s.
To shed some light on new developments and update anglers on available options, we sent a list of questions to the two primary U.S. trolling-motor manufacturers - Minn Kota (Riptide) and MotorGuide (Great White) - to compose a know-it-all's playbook.

What kind of motor actually powers a trolling motor?
The simple answer: A brushed direct-current (BDC) motor - direct current because it runs off a battery. Brushed DC motors power many common devices such as fans and blowers, cordless tools and various electric automobile parts like window lifts and seat adjusters. They're made up of four basic components: stator, rotor, brushes and a commutator.
According to MotorGuide engineers, the stator, powered by magnets, generates a magnetic field around the rotor. Attraction from the magnetic poles causes the rotor to turn. After that, the process becomes more technical as the magnetic field must be controlled and manipulated to achieve various speeds.
Suffice it to say that all trolling motors use this basic form of power. Simpler, less expensive motors employ a step-speed BDC motor, which offers five set speeds. Unfortunately, step-speed motors burn up battery time.
To visualize how a step-speed motor works, Minn Kota brand manager Joe Brown offers this comparison: "It's like if you're driving your car, and you want to go 65, and you push the gas pedal all the way to the floor but then you slow yourself down using the brake."
Variable-speed BDC motors, on the other hand, prove three to five times as efficient. They employ a digital system that delivers energy from the battery to the lower unit in pulses rather than a steady stream, says Dallas Hodges, MotorGuide's director of marketing.
Both companies offer both types of motors, but Brown really believes in Minn Kota's digital maximizer technology: "To me, the biggest consumer value on a trolling motor is investing in that variable speed."

Why buy a bow- vs. transom-mount motor? Why buy an engine-mount or trim-tab-mount version?
A boat steers more easily from the front: A bow-mounted trolling motor can pivot a boat 360 degrees in its own length. "It's like pulling a wagon versus pushing a wagon. The reason you put the trolling motor on the bow is the same reason why the horse is not behind the wagon," Brown says.
However, while most bay and flats boats feature bow configurations conducive to mounting trolling motors, not all inshore vessels do. Many modified-V, flat-bottom skiffs, johnboats, bowriders and dual-consoles either feature slender gunwales or simply rise off the water too high. For those vessels, Minn Kota and MotorGuide make transom-mount models, which do carry their own advantages.
"The lower unit makes a certain amount of noise, and a stern-mount application moves that away from the fish," Hodges says. And because many anglers choose to mount two trolling motors astern, they gain increased speed for heading out over a flat or getting ahead of a bait school.
Both companies also offer trim-tab trolling motors: MotorGuide works in conjunction with Lenco and offers a unique joystick control system. Minn Kota designed its own composite trim tabs to work with its trolling-motor lower units, controlled by a remote keypad.
These systems place two motors astern and lower everything below the waterline, freeing up deck space.
Minn Kota also offers engine-mount motors, which fasten to the cavitation plate on an outboard or I/O. Larger center-consoles with deep-V hulls can best take advantage of these below-the-waterline options. Why would those boats need a trolling motor? To hold position quietly over structure, to slow-troll even more slowly, to maintain heading while kite fishing.

What is thrust and how does it equate to speed?
Thrust increases with the amount of electricity used, size of the lower unit and design of the prop, Hodges says. However, anglers are limited as to what they can get out of a motor: Too much voltage and the motor runs hot and loses longevity.
A 12-volt (one-battery) system usually generates about 55 pounds of thrust; a 24-volt (two-battery) system offers up to 80; and a 36-volt (three-battery) system provides as much as 105. What you need and what your boat can handle depend on the size and weight of your loaded vessel and where you operate (such as in areas of swift tidal current).
Thrust represents merely a static measurement of force, Brown says. It does not equate to horsepower, which is a measurement of work being performed. No magic formula exists to match vessels with motors, but he suggests anglers seek the most thrust their boat package can handle.
Many small boats simply can't accommodate three batteries - in addition to their starting battery - which can weigh up to 180 pounds total. But those vessels that can carry that load enjoy increased trolling time and maneuverability when needed, such as when snook fishing in a rough inlet around rocks.
Regardless of the system, maximum speed usually amounts to about 5 mph for any boat/trolling motor combination.

Under what circumstances should anglers choose digital remote control vs. manual hand control?
Most redfish pros choose hand-controlled bow-mounted motors because very little can go wrong with them. However, most pros also divvy the fishing chores: The angler with the most accurate cast takes the bow; the one with the better eyes takes the poling platform or back deck. They're more mission-oriented than weekend warriors, and they can't just call it a day if the battery on the remote runs down.
But hand-controlled motors require a mounting platform with a large footprint that takes up more space, and they usually require a longer shaft length, Hodges says. Wireless remote-controlled motors have a smaller footprint, allowing anglers to employ shortcuts like MotorGuide's removable mounting plate or Minn Kota's quick-release bracket.
Remote-controlled motors allow anglers to operate the unit from anywhere aboard; however, one person must still work the controls while fishing. Remote units can be fastened to the handle of a fishing rod, and those with autopilot  settings (unique to Minn Kota) can be engaged for totally hands-free operation.
Both Minn Kota and MotorGuide now offer wireless foot pedals for their saltwater remote-controlled units. Because cable-controlled pedals have suffered corrosion in the past, saltwater anglers never really used them like their freshwater counterparts.
Foot pedals also allow torque from choppy seas to transfer to the foot, which makes the mechanisms difficult to operate.

How do you choose the trolling-motor shaft length you'll need?
Fishing shallow water requires stealth. When a trolling motor's propeller nears or breaches the surface, it causes fish-spooking noise. It also stops moving the boat. The motor's shaft must be long enough so the propeller remains submerged in most conditions. This becomes especially important with bow-mounted motors, since rarely are bow heights standard.
Both MotorGuide and Minn Kota  offer motor-selection help on their websites ( and, but Hodges says you can get close to the right shaft length by measuring the distance from the gunwale of your boat to the water and adding 23 inches.

Another general rule of thumb, according to Minn Kota, suggests that the center of the lower unit should be 9 inches below the surface. To achieve that depth, measure from the mounting surface to the waterline in inches. If that distance is less than 16 inches, the recommended shaft length would be 36 inches; 16 to 22 inches would suggest a 42-inch shaft; 22 to 28 inches, a 48- to 52-inch shaft; and 28 to 34 inches, a 54- to 62-inch shaft.
Add 5 inches to the waterline measurement if you usually operate in rough water; add 12 inches for a hand-controlled motor if you plan to operate it while standing.