How to Choose the Right Trolling Motor: Thrust, Voltage, Shaft Length and Features

A practical guide to thrust, voltage, shaft length, batteries and features

Reviewed for practical product-selection accuracy by Bill Vail, Sales Specialist at Lighthouse Marine Supply.

Choosing a trolling motor is not just about buying the highest-thrust model that fits your budget. The motor needs to match your boat, mounting location, operating environment, battery system and the way you plan to use it.

A motor that is undersized may struggle in wind or current. A shaft that is too short may allow the propeller to come out of the water. A motor that requires more batteries than your boat can reasonably carry may create an expensive installation problem.

This guide explains the main decisions in the order we recommend making them.

Start with six questions

Before comparing models, write down:

1. Will the motor mount on the bow or transom?
2. Will it be used in freshwater, saltwater or both?
3. What is the boat’s approximate fully loaded weight?
4. How far is the mounting surface above the waterline?
5. How much battery space and charging capacity are available?
6. Which control, GPS and electronics features matter to you?

Those answers will narrow your options more effectively than starting with brand names or feature lists.

1. Bow mount or transom mount?

Bow-mounted trolling motors

A bow-mounted motor pulls the boat through the water from the front. This generally provides better directional control, especially when fishing, working along structure or using GPS position-holding features.

Bow mounts are commonly used on bass boats, bay boats, center consoles, multispecies fishing boats and larger aluminum fishing boats.

A bow-mount installation requires enough flat deck space, a strong mounting surface and clearance for the motor to deploy and stow. You also need a suitable power connection near the bow.

Choose a bow mount when precise boat positioning, foot-pedal operation, wireless control or GPS features are priorities.

Transom-mounted trolling motors

A transom-mounted motor attaches at the stern and is usually controlled by a hand-operated tiller. It is often simpler and less expensive to install.

Transom mounts are commonly used on small aluminum boats, jon boats, tenders, utility boats and boats without suitable bow-mount space.

Choose a transom mount when simplicity, portability and basic low-speed propulsion matter more than advanced boat-positioning features.

2. Freshwater or saltwater?

Use a motor designed for the environment in which it will operate.

Saltwater-rated motors are built with corrosion resistance in mind. Depending on the model, that may include corrosion-resistant hardware, protected electronics, coated components and sacrificial anodes.

Use a freshwater motor for freshwater applications. Choose a saltwater-rated model when the motor will regularly operate in salt or brackish water.

Even saltwater-rated equipment should be rinsed with fresh water after use and inspected regularly for corrosion, damaged wiring and loose connections.

3. How much thrust do you need?

Trolling-motor output is usually measured in pounds of thrust. Thrust is not the same as horsepower, and more thrust does not necessarily mean a large increase in speed.

The purpose of thrust is to provide enough force to move the loaded boat, overcome wind, manage current, maintain steering control, hold position and avoid operating continuously at maximum output.

Use fully loaded boat weight

Do not size the motor using only the boat’s published dry weight.

Include engine, fuel, batteries, passengers, fishing gear, coolers, safety equipment and normal cargo.

A commonly used minimum starting point is approximately two pounds of thrust for every 100 pounds of fully loaded boat weight.

Loaded boat weight ÷ 100 × 2 = minimum pounds of thrust

Example: a boat weighing approximately 3,000 pounds fully loaded starts at about 60 pounds of minimum thrust.

That figure is only a starting point.

When to step up

Consider more thrust when the boat will regularly face strong wind, tidal current, heavy vegetation, open water, a high bow or large wind profile, substantial passenger or gear loads, or frequent GPS position-holding.

Additional thrust gives the motor more reserve. It does not mean you must operate it at full power.

Do not size by boat length alone

Two boats of the same length may have very different weights, hull shapes, freeboard and operating conditions.

A lightly loaded 18-foot aluminum boat and an 18-foot fiberglass center console may not need the same motor.

4. Choose the correct voltage

The thrust level and motor design determine the required voltage system.

Typical thrust range	System voltage	Common battery arrangement
Up to approximately 55 lb	12V	One 12V battery
Approximately 68–80 lb	24V	Two 12V batteries
Approximately 101–115 lb	36V	Three 12V batteries

Some newer motors can operate across more than one voltage, so always verify the specifications for the exact model.

12-volt systems

A 12V motor may be appropriate when the boat is small or relatively light, moderate thrust is sufficient, battery space is limited, and simplicity and lower cost matter.

Advantages include one battery, simpler wiring and less weight. The limitation is less available thrust and reserve for larger boats or difficult conditions.

24-volt systems

A conventional 24V system usually uses two 12V batteries wired in series.

It is a common choice for midsize fishing boats, heavier aluminum boats, many bass boats and boats needing roughly 70–80 pounds of thrust.

A 24V system offers more thrust and reserve than a typical 12V setup, but requires two batteries, compatible charging equipment and more installation space.

36-volt systems

A conventional 36V system usually uses three 12V batteries wired in series.

It may be appropriate when the boat is heavy, wind and current are significant, maximum conventional thrust is needed, or long periods of position-holding are expected.

The tradeoffs are additional batteries, greater weight, more space and higher installation cost.

Decide whether the boat can support the required battery system before choosing the motor.

5. Select the right shaft length

Shaft length is one of the most important and most frequently underestimated decisions.

A shaft that is too short may allow the propeller to ventilate or come out of the water as the boat moves in waves. An unnecessarily long shaft may create problems with shallow-water operation, stowing and deck clearance.

Bow-mount measurement

Measure vertically from the intended bow mounting surface to the waterline under normal load.

Bow mounting surface to waterline	Typical shaft-length direction
0–10 in.	Around 36 in.
16–22 in.	Around 42–45 in.
22–28 in.	Around 48–52 in.
28–34 in.	Around 54–60 in.
34–52 in.	Around 72–87 in.

For measurements near a boundary, confirm the recommendation for the exact motor.

Transom-mount measurement

Measure vertically from the top of the transom mounting position to the waterline.

Transom mounting surface to waterline	Typical shaft-length direction
0–10 in.	Around 30 in.
10–16 in.	Around 36 in.
16–22 in.	Around 42 in.
22–28 in.	Longer model-specific options

A longer shaft may be appropriate when the boat has high freeboard, the bow rises and falls significantly in waves, the motor mounts above the normal deck level, the boat carries changing loads, or the motor will be used in open water.

Measure your own boat. Do not copy another owner’s shaft length unless the mounting height and operating conditions are genuinely comparable.

6. Batteries, charging and wiring

A trolling motor is only as useful as the battery system supporting it.

Trolling motors generally require deep-cycle batteries designed for repeated discharge and recharge. Common options include flooded lead-acid, AGM and lithium iron phosphate when approved for the motor and charging system.

For 24V and 36V systems, batteries should generally be matched in type, capacity, age, condition and state of charge. A weak or mismatched battery can reduce the performance of the complete system.

The charger must match battery chemistry, number of battery banks, battery voltage and manufacturer requirements. Do not assume an existing charger is suitable for a new battery type.

Wire size and circuit-breaker selection should follow the motor manufacturer’s instructions, taking into account current draw and cable length. Existing boat wiring should not be assumed adequate simply because the plug fits.

7. Controls, GPS and electronics

Hand-controlled motors are simple and common on transom-mounted applications. They are a practical choice for smaller boats and users who want direct tiller steering.

A foot pedal allows the operator to steer while keeping both hands available for fishing. Cable-steer systems are often chosen for quick response and mechanical feedback. Electric-steer systems may offer more flexibility, wireless control and GPS integration.

Depending on the model, modern motors may offer wireless remote control, GPS position holding, heading control, route following, saved tracks, incremental position adjustment, integration with compatible chartplotters or fish finders, automatic stow and deploy, and power trim.

Feature availability varies by exact model and configuration. Do not assume every motor within the same product family includes the same controls, sonar or networking features.

Some models include integrated sonar transducers. Before ordering, verify sonar type, connector type, chartplotter compatibility, required adapter cables and networking requirements.

“Built-in sonar” does not mean universal compatibility.

8. Check the installation before ordering

Before choosing a motor, confirm:

• deck space;
• deck strength;
• access to mounting bolts;
• motor-head clearance when stowed;
• shaft clearance when deployed;
• interference with rails, cleats, lights or anchors;
• power-cable routing;
• plug and receptacle location;
• battery location;
• charger space;
• quick-release bracket compatibility;
• trailer clearance.

Review the manufacturer’s mounting template and dimensional drawings for the exact model.

A motor can be correct for the boat and still be difficult to install because of deck hardware or limited access beneath the mounting surface.

Common trolling-motor buying mistakes

• Choosing by boat length alone
• Buying the minimum possible thrust
• Selecting the wrong shaft length
• Ignoring the battery requirement
• Assuming every model includes GPS or sonar
• Using freshwater equipment in saltwater
• Reusing inadequate wiring
• Forgetting mounting clearance

Quick selection table

Your situation	Starting direction
Small freshwater boat, simple propulsion	12V transom mount
Small-to-midsize fishing boat, bow control	12V or 24V bow mount
Midsize boat exposed to wind or current	24V bow mount
Heavy boat or demanding positioning use	36V or compatible high-thrust system
Regular saltwater use	Saltwater-rated model
Need GPS position holding	GPS-equipped bow mount
Prefer hands-free steering	Foot-controlled bow mount
Want control from several areas of the boat	Electric steer with wireless remote
High bow or rough-water use	Measure carefully and consider a longer shaft

This table is only a starting point. Final selection should be based on the exact boat, load, mounting height and manufacturer specifications.

Frequently asked questions

Is more thrust always better?

Not automatically. More thrust can provide useful reserve, but it may also require a higher-voltage battery system, more space, more weight and a more expensive installation. The goal is adequate performance with reasonable reserve.

Will more thrust make the boat much faster?

Usually not in proportion to the increase in thrust. Trolling motors are designed primarily for low-speed control and positioning. Hull shape and displacement limit speed.

Can I run a 24V motor on one 12V battery?

No. A conventional 24V motor requires a proper 24V power supply, usually created with two suitable 12V batteries wired in series.

Can I use lithium batteries?

Possibly, but verify compatibility with the exact motor, battery-management system and charger. Follow both manufacturers’ requirements.

How far below the water should the motor be?

The motor section should remain sufficiently submerged to avoid ventilation and loss of thrust. Rough water and high mounting positions may require additional shaft length.

Is GPS position holding a replacement for an anchor?

No. GPS position holding uses the motor to maintain position and depends on battery power, motor thrust, conditions and GPS reception.

It is not a replacement for legally required anchoring equipment or safe anchoring practices.

Before you order

Have the following information ready:

• boat make and model;
• boat length;
• approximate fully loaded weight;
• bow-to-waterline or transom-to-waterline measurement;
• freshwater or saltwater use;
• preferred mounting position;
• existing battery system;
• fish finder or chartplotter model;
• preferred steering method;
• typical wind and current conditions.

Need help choosing?

Contact RV & Marine Supply before ordering if you need help comparing motor specifications or identifying compatible installation accessories.

Phone: (631) 405-5565
Email: sales@rvandmarinesupply.com
Hours: Monday–Friday, 9:00 AM–5:00 PM Eastern Time

Our Riverhead location is a business office and customer support center. It is not open for walk-in shopping or product pickup.

Technical and safety note

This guide provides general product-selection information. Confirm voltage, thrust, shaft length, battery, wiring, circuit protection, mounting and electronics compatibility using the documentation for the exact motor and boat.

Installation and operation should follow the motor, battery, charger, electronics and boat manufacturers’ instructions.