What Size Trolling Motor Do I Need?

What size trolling motor do I need? Start with the weight you are pushing. Newport’s motor thrust guide suggests adding the boat’s weight to its maximum load capacity, then allowing about 5 lb of thrust for every 200 lb of that total. Move up from that number if you fish wind, current, tide, or chop. The thrust you land on then points to a voltage (12, 24, or 36 volts), and the mount position points to a shaft length. Those three numbers, thrust, voltage, and shaft, are what “size” means on a trolling motor, and together they answer how big of a trolling motor you need.

This guide is general product information, not repair or electrical safety advice. Follow the installation, wiring, and charging instructions in your product’s manual, stop using any battery, charger, or electronics that overheat, swell, or smell of burning, and contact the manufacturer.

The steps below work through each one, using sizing guidance that Newport and Garmin publish. Shaft measurement gets only a short summary here; the full method, with bow, transom, and kayak examples, has its own guide. If you are new to the gear, start with what a trolling motor is and how the mount types differ.

Step 1: Add Up the Weight the Motor Has to Move

Newport’s thrust guide uses total weight, not just the empty hull. Its worked example is a 1,000 lb boat with an 800 lb maximum load: 1,800 lb divided by 200 is 9, and 9 times 5 lb gives a recommendation of 45 lb of thrust. The guide adds, in capital letters, that this recommendation is only for slower fishing use, not for a primary motor.

To work out how much thrust a trolling motor needs for your own boat:

1. Find the boat’s weight and its maximum load. Both are usually in the boat’s owner’s manual or on the boat maker’s spec sheet, and many small boats also carry a capacity plate that lists the maximum load.
2. Add them together. Using the maximum load rather than your usual load builds in room for a second angler, a full cooler, or a livewell full of water.
3. Divide the total by 200, then multiply by 5. The result is the starting thrust in pounds.
4. Round up to the next thrust rating the maker sells.

Two quick examples with made-up figures show how this works. A boat whose weight plus maximum load comes to 1,400 lb works out to 35 lb, so a 36 lb motor is the starting point. A boat at 2,400 lb works out to 60 lb, which points to the next rating above that, such as 62 lb in Newport’s lineup.

Step 2: Cross-Check Against Boat Length

Length is a useful second check when you do not know the boat’s weight. Newport’s guide to choosing the right trolling motor for your boat lists an estimated maximum boat length for each thrust rating it sells:

Newport says these lengths are estimated for typical light craft, and warns that a motor matched to a length may not suit a deep-drafted boat of that length. Its article on thrust ratings puts a 16 ft boat at 55 lb of thrust at minimum. If the weight method and the length table disagree, go with the higher of the two, since a heavy, wide, or deep hull is exactly the case the length table does not cover.

Step 3: Add Thrust for Wind, Current, and Rough Water

The formula assumes calm conditions. Newport’s thrust guide says that choppy water, traveling upstream, fighting currents, tides, or wind, or wanting to get between spots quickly all call for more thrust, while anglers who mostly fish flat or calm water with little current can stay at the lower end of the estimate. The thrust ratings article adds that going up is a good idea for salt water or for working against a current.

In practice, that looks like this:

• Kayak on a small, sheltered lake: the calculated number often comes out below the smallest kayak motors sold, so on calm water a low rating can be enough. Motor weight and mount fit matter more than extra power.
• Jon boat on a river: current works against you on every upstream pass. Size above the calm-water number.
• 18 ft bass boat on a big, windy reservoir: the motor has to hold a heavy boat against wind for hours. This is where the higher ratings, and the higher voltages that come with them, make sense.
• Bay boat on tidal flats: tide and salt both argue for more thrust, and the motor must be rated for salt water by its maker.

Keep expectations straight: Newport’s buyer’s guide notes that more thrust doesn’t necessarily mean more speed. Extra thrust buys control under load, not a faster ride.

Step 4: Let Thrust Set the Voltage

Once you know the thrust, the maker’s lineup tells you the voltage. These are the figures the makers publish:

• Newport’s NV Series page lists the 36, 46, 55, and 62 lb models as 12-volt and the 86 lb model as 24-volt.
• Newport’s buyer’s guide says its 112 lb motors require three 12-volt marine batteries.
• Garmin’s Force installation instructions require a 24 or 36 volt battery bank that can supply 60 A continuously.
• Garmin’s guide to choosing a trolling motor says the Force Current kayak motor delivers 30 lb of thrust on 12 volts or 50 lb on 24 volts, so on some motors the voltage you choose changes the thrust you get.

Voltage also decides how many batteries you carry, and that matters on a small boat. A 12-volt motor needs one battery, a 24-volt system usually two, and a 36-volt system three, each adding weight and taking up space. Before you choose a higher voltage motor, check that your boat has room for the batteries and that the added weight still fits under its maximum load. For safety, wire the system only as your motor’s manual describes, with the circuit breaker it specifies, or have a qualified marine installer do it, as Garmin recommends.

What Size Battery Do I Need for a Trolling Motor?

Battery choice deserves its own guide, but the basics are short. Newport’s trolling motor FAQ recommends a 12-volt, 50 amp-hour deep cycle or marine battery for its 12-volt motors and says it prefers lead-acid over lithium. Its thrust guide adds that a higher amp-hour battery extends run time, using the example of going from 50 Ah to 100 Ah to double it. Charge and store the battery as its maker directs, and if a battery swells, gets unusually hot, or smells burnt, stop using it and contact the battery maker. For how long a 12-volt motor actually runs on one charge, the run-time estimate depends on amp draw at each speed and the battery’s usable capacity, which a separate guide covers in the batteries and power section.

Step 5: Choose a Shaft That Keeps the Prop Underwater

The right thrust does nothing if the propeller breaks the surface. Newport’s Kayak Series owner’s manual sets a running depth with the propeller blades 6 to 12 in below the surface. In short: measure from your mount point down to the waterline, then add the allowance your motor maker specifies and read the result against its chart. Bow mounts measure from the deck, transom mounts from the top of the transom, and kayaks from the top of the kayak mount. The full steps, with both makers’ charts, are in the guide on how to measure trolling motor shaft length.

What Size Trolling Motor Do I Need? Mistakes to Avoid

• Sizing from the empty hull. Newport’s method uses the maximum load. Two anglers, batteries, and gear add up fast.
• Ignoring the hull shape. The length table assumes light craft. Deep, wide, or heavy hulls need more.
• Buying thrust you cannot power. A higher thrust motor usually means a higher voltage system and more batteries. If the boat cannot carry them, the motor is the wrong size.
• Treating a trolling motor as a main motor. Newport’s sizing rule is for slow fishing use. If you need to cover long distances, plan for a primary motor too.

Bigger isn’t for everyone. On a kayak or canoe, a heavier, higher voltage motor adds weight at one end of a light hull and needs more batteries. If you fish small, calm water, you can skip the upgrade and stay near the calculated number.

Frequently Asked Questions

What size of trolling motor do I need for a 14 ft boat?

Newport’s length table places a 14 ft boat in the range of its 40, 46, 55, and 62 lb motors. Work out the weight method too (boat weight plus maximum load, 5 lb per 200 lb) and pick the higher result, then add more if you fish wind or current.

What size trolling motor do I need for a 12 ft jon boat?

A 12 ft boat sits where three rows of Newport’s length table meet: the top of the 36 lb range (8 to 12 ft) and the bottom of the 40 lb and 55 lb ranges. Newport’s trolling motor collection page gives a similar general rule, saying boats up to 12 feet work well with 36 to 46 lb motors. Because Newport bases its lengths on typical light craft, run the weight method with your jon boat’s weight and maximum load too, and size up if you fish river current or wind. Choosing a trolling motor for a jon boat, from thrust to shaft and mount, has its own guide.

Is 55 lb of thrust enough?

For many small and mid-size boats, yes. Newport’s buyer’s guide calls 55 lb the most common or versatile thrust in its range, and its thrust ratings article treats 55 lb as the minimum for a 16 ft boat. For heavier boats, or for wind and current, run the weight method before settling on it.

What size trolling motor shaft do I need?

One that keeps the propeller underwater from your mount point. Measure from the mount down to the waterline and add your maker’s allowance. Newport’s buyer’s guide says a 30 or 36 in shaft fits most boats and a 24 in shaft suits kayaks and canoes, while Garmin lists its Force bow mount in 50 and 57 in models.

Can a trolling motor be too powerful for a boat?

The thrust itself is rarely the problem, since you can run a motor at lower speeds. The practical limits are weight, battery count, and mounting. A large motor needs a deck or transom strong enough to hold it; Garmin’s Force instructions, for example, say to verify that the deck can take the motor’s weight and force and to add a backing plate if needed. Also check the boat’s manual for any limits on motor weight or power.

Should I choose 12, 24, or 36 volts?

Choose the thrust first, then use the voltage that motor requires. In Newport’s lineup, motors up to 62 lb are 12-volt and the 86 lb is 24-volt; Garmin’s Force runs on 24 or 36 volts. The voltage then sets how many batteries you need on board.

For background on how AnglerTechLab evaluates gear, see How We Review, and browse the trolling motors section for related guides.

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