The Ultimate Guide to Underwater Thrusters

An underwater propulsion system is an electric propulsion device that generates forward or backward propulsion by pushing against water.

A complete underwater propulsion system typically includes:

a brushless motor
a propeller
a protective duct or housing
an electronic speed controller (ESC)
a power supply and control signal circuitry

Compared to traditional fuel-powered propulsion systems, underwater propulsion systems offer the following advantages:

——Lower noise
——More environmentally friendly
——Simpler structure
——Lower maintenance costs
——Therefore, they are widely used in recreational vehicles, ROVs, underwater inspection, scientific research equipment, and electric vessels.

II. Working Principle of Underwater Propulsion

The working principle of an underwater propulsion system can be summarized in one sentence:
Electricity → Motor rotation → Propelling water → Generating thrust

The specific process is as follows:

Battery Power Supply: 
The battery provides DC power to the system (common voltages are 12V/24V/48V).

ESC Motor Control: 
The electronic speed controller adjusts the motor speed and direction of rotation according to the control signal.

Motor Drives Propeller: 
The brushless motor drives the propeller to rotate, propelling the water flow.

Water Flow Generates Reverse Thrust: 
The water is pushed backward, giving the propeller body forward or backward propulsion.

When using multiple propellers (e.g., one on each side), the following can be achieved:

Steering Control
Rotation in Place
Precise Positioning

This is very common in ROV and unmanned surface vessel systems.

III. Wiring Connection Methods for Underwater Thrusters

The part that many users are most concerned about is actually not as complicated as they imagine.

1. Basic Connection Structure
The standard structure is:
Battery → ESC → Underwater Thruster
Where:
Battery: Provides power
ESC: Controls speed and direction
Thruster: Performs power output

2. Power cord connection

Red wire (+): Connect to the positive terminal of the battery
Black wire (−): Connect to the negative terminal of the battery
Note: The voltage must match the thruster specifications.
Overvoltage is not recommended to avoid damaging the ESC or motor.

3. Motor Wire Connection
Underwater thrusters typically have three motor phase wires:
Connect to the ESC output terminal.
If the rotation direction is incorrect, simply swap any two wires.

In many Apisqueen products:

For example, U92pro Two Set

✅ ESC is built-in
✅ No additional motor wiring required
✅ Easier installation, more reliable waterproofing

4. Control Signal Line (PWM)
Most thrusters use PWM control signals
Signal wire: White/Yellow
5V power supply: Red wire (optional in some systems)
Ground wire: Black wire
PWM signal logic is typically:
Low signal: Reverse rotation
Mid-position: Stop
High signal: Forward rotation
Directly connectable to:
Remote control receiver
Control handle
Arduino/ROV control system

IV. Core Components of an Underwater Thruster System

1. Motor

The "heart" of an underwater thruster, commonly a brushless DC motor (BLDC), such as the Apisqueen 5080.

Apisqueen 5080 brushless motor

Key parameters include: kV value, power, voltage range, and waterproof structure.

External rotor vs. internal rotor: External rotors generally have better heat dissipation; internal rotors are easier to seal and more pressure-resistant.

Brushless DC motors are highly efficient and have a long lifespan, making them the mainstream choice for underwater propulsion systems.

2. Propeller / Pipe Propeller

Apisqueen 60mm Metal Propeller - For ROV/Mini Thruster

The propeller directly affects propulsion efficiency: Key components affecting thrust and efficiency include: diameter, pitch, number of blades, and rotation direction (CW/CCW).

Tube propellers offer significant advantages in low-speed, high-thrust scenarios and can protect the blades.

3. Outer shell and fairing

AQ1121 Metal Casing

For structural protection, waterproof sealing, and improving hydrodynamic efficiency, ROV thrusters mostly adopt a pipe structure.

4. Electronic speed controller (ESC)

Feather 100A ESC

For controlling speed and direction, the current and voltage should be matched, and PWM signals should be supported.

Marine or waterproof ESC is recommended.

5. Battery System
Commonly lithium batteries or lithium iron phosphate batteries.

Voltage determines efficiency, capacity determines range, and discharge rate determines output capability.

6. Mounting Brackets and Accessories
Includes ROV frame bracket, stern bracket, waterproof connectors, cables, control board, etc.

V. Key Factors Affecting Performance

1. Low-KV Brushless Motor

Apisqueen's thrusters primarily utilize low-KV motors:

Easier to propel loads in water
More stable thrust output
Lower heat generation during extended operation
Especially suitable for:
ROVs
Underwater inspection
Boat auxiliary propulsion

2. Propeller and Duct Design

The efficient propulsion structure can:
Improve propulsion efficiency
Reduce energy waste
Enhance safety
Protect the propeller

3. Built-in ESC Structure

Advantages of the built-in ESC design:
Fewer wiring
Better waterproofing
Faster installation
Higher system stability

VI. How to Choose the Right Underwater Thruster

1. Application Scenarios

Recreational/Entertainment (Kayaks/SUPs/Inflatable Boats)
Primarily auxiliary power, emphasizing portability, ease of installation, and long endurance. Suitable for personal recreation, fishing, or short trips.

Small Boats/Fishing Vessels
Require stable and continuous thrust output. Can be used as primary or auxiliary power, balancing speed and load capacity.

ROVs/Unmanned Underwater Equipment
Requires precise control and rapid response. Supports forward and reverse speed adjustment, with multiple thrusters combined for forward, backward, lateral, and attitude control.

Engineering Operations/Commercial Applications/Rescue Equipment
Requires high power, high thrust, and long-term stable operation. Higher requirements are placed on waterproof rating, corrosion resistance, and structural strength.

2. Thrust Reference Range

≤ 8 kg Thrust
Suitable for miniature ROVs, experimental equipment, or lightweight auxiliary propulsion.

8–20 kg thrust: Suitable for kayaks, SUPs, small inflatable boats, or lightly loaded small vessels.

20–40 kg thrust: Suitable for small boats with two or more people, fishing boats, or medium-load equipment.

≥ 40 kg thrust: Suitable for heavy-duty vessels, engineering platforms, commercial operations, or rescue scenarios.

3. Voltage and ESC Matching
All components must operate within the same voltage range.

Example 1: 12V System (Most Common, Safest)
Underwater Thruster: 12V Rated
ESC (Electronic Control): Supports 12V (3S LiPo)
Battery: 12V / 3S Lithium Battery (11.1–12.6V)
Result: Perfect voltage matching, stable system, suitable for small ROVs, model boats, and underwater equipment.

Example 2: 24V System (High Thrust Applications)
Underwater Thruster: 24V Rated
ESC: Supports 6S LiPo (up to 25.2V)
Battery: 24V / 6S Lithium Battery
Result: Higher thrust, lower current, suitable for medium to large ROVs or long-term operation.

Example 3: Voltage Mismatch (❌ Incorrect Example)
Underwater Thruster: 12V Rated
ESC: Supports 12V
Battery: 24V

❌ Result: Both the thruster and ESC will experience overvoltage, easily burning out the motor or ESC.

Example 4: ESC Support Range ≥ Battery Voltage

Thruster: 24V

ESC: Maximum Support 6S (25.2V)

Battery: 22.2V (6S)

✅ Result: The ESC voltage margin is sufficient, ensuring safer long-term operation.

Summary in One Sentence
Thruster Rated Voltage = Battery Voltage, ESC Support Voltage ≥ Battery Voltage

4. Durability and Efficiency
Prioritize aluminum alloy casing, corrosion-resistant materials, and mature sealing solutions.

VII. Cleaning and Corrosion Prevention Steps for Underwater Propulsion Units After Use

1. Rinse thoroughly with clean water immediately after use to remove salt, silt, and impurities.
2. Focus on cleaning the propeller, shaft, and crevices.
3. Wipe the surface dry with a clean cloth and allow to air dry naturally.
4. Avoid direct sunlight or high-temperature drying.
5. Apply a thin layer of rust-preventive oil or anti-corrosion lubricant to the metal shaft and screws.
6. Keep the environment dry for long-term storage and avoid moisture.

VIII. Summary

Underwater propulsion units are not complicated. Once you understand:

How it works

How the wiring is connected

How much thrust is needed

you can quickly build a reliable underwater propulsion system.