Bow and stern thrusters for leisure boats

Side-Power thruster system docking Princess yacht in windy weather

Choosing the best bow or stern thruster for your vessel is quite critical, as the thruster probably will accompany your boat for decades to come. In this article, we will share our collective knowledge from more than 40 years of designing and manufacturing thruster systems for leisure and workboats. Our goal is to guide you towards the best possible thruster system for your vessel and your needs. In this article, we will primarily address bow and stern thrusters with 12 and 24 VDC operating voltage.

For AC electric and hydraulic bow thrusters and stern thrusters, please visit our dedicated blog here.

Thrusters are well-established tools that come standard with almost every new boat designed over around 25 feet. But for those who wish to retrofit or upgrade an existing system, the product range of boat thrusters is now far more extensive than just a few years back, so it is important to research thoroughly and understand which solutions will work best for you.

We hope both boat owners, boat brokers, boat manufacturers and other interested parties will find our articles helpful and practically useful!

Side-Power thruster systems docking Princess 67

What is a boat thruster?

A boat thruster is a device that moves the boat in a sideways direction. Vessels outfitted with both a stern and bow thruster also have total 360 directional manoeuvrability. The most common type of boat thruster is a tunnel thruster installed in the bow or stern of a vessel with one or two propellers driven by an electric or hydraulic motor.

Brief thruster history

The relatively high costs of employing tugboats for every arrival and departure from port for commercial vessels was reasonably the main force behind the first thruster developments. Installing one or more thrusters on these large ships made sense also surpassing the point of running cost reductions, as they increased the vessels manoeuvrability and thereby increased safety in crowded waters.

In the mid-1980s, a few boat equipment manufacturers recognised the benefits that a bow thruster could provide for all boat types and sizes and the development and production of the first thrusters for leisure boats hit the market.

For many years tunnel-based bow thrusters were open to the market however, at that time the products were considered to be relatively expensive accessories. But as average boat size increased steadily from year to year and the ports did not many boat builders now saw that such a docking aid offered tremendous support for boaters in the increasingly crowded and tight harbours.

Here are some of the most common thruster types

Side-Power tunnel thruster
Tunnel thruster
Side-Power externally mounted thruster
Externally mounted thruster
Side-Power retractable thruster
Retractable thruster

What are the different types of bow thrusters and stern thrusters?

Today, there is a thruster for virtually any boat, regardless of hull type, material or size from about 20 feet and upwards.  The standard tunnel-based thruster is still the leading choice for most boat builders, but as the market has matured, the requirements for installation flexibility and increased thrust has led to many redesigns, allowing for a well-functioning thruster solution for almost any vessel out there.


The most common thruster categories in the market today:

  •  Tunnel-based bow thruster and stern thruster
  •  Ignition Protected bow and stern thruster
  •  Retractable bow and stern thruster
  •  Exterior mounted bow and stern thruster
  •  Proportionally controlled bow and stern thruster
Side-Power thruster systems narrow harbour

Why do you need a bow and / or stern thruster system?

Running your vessel in the open sea is a breeze, but come to a busy overcrowded or tricky harbour, and you may feel your blood pressure rise. As a mariner, you might have experienced that in these conditions manoeuvring your vessel can be far more demanding than it seems.


Calculating Wind, ocean current, tides and other crafts' presence create a chaotic three-dimensional dilemma in the brain, wishing you had the mind of an Apollo space astronaut.


Well, with one or more thrusters on board, you gain one of the most important factors to reduce stress while docking, which is time. Time to orient yourself, time to consider and plan, and time to wait for others!


Main benefits of a bow and stern thrusters on board:

  •  Better control under demanding conditions
  •  Less stress
  •  Lower risk of collision
  •  More attractive aftermarket value
  •  Being able to manoeuvre the boat on your own 


Many boaters tend to have a lifelong relationship with the sea. Unfortunately, as age slowly takes its toll, handling your vessel becomes more difficult. But this is where a proportionally controlled thruster system can keep your passion for the sea thriving and well. With proportionally controlled bow and stern thrusters onboard, you can pin the boat in the desired location and come alongside the dock and operate even a large vessel single handily the same way.

How to choose the best bow thruster and stern thruster

Few boat owners will voluntarily accept the cost or labour to replace a pre-installed thruster, even if it does not perform as desired. So, picking the right thruster the first time is crucial for many years of operation after installation. The right thruster is energy efficient, quiet and powerful enough to help you in the worst possible conditions when the thruster is needed the most.


The most critical factors for choosing the right bow or stern thruster are:

  •  Sufficient thrust to cover your intended use with a good safety margin
  •  Location in the hull
  •  Adequate and sustained energy supply (battery voltage)

Common problems with boat thrusters and how to avoid them?

In our experience, there are two main common problems.

  •  Insufficient thrust force
  •  Noise

Sufficient power is paramount

A bow or stern thruster that cannot deliver adequate thrust when you get caught in windy conditions while docking when you genuinely need the assistance of a thruster to control the vessel is undoubtedly a poor investment.

Here are three common reasons why a DC electric thruster may perform less than desired, whereas point 1 is quite common:

  1.  Too low power supply to the electric motor under load. A drop of only 1-2V can correspond to a significant loss of thrust.
  2.  Obstruction to the flow of water through the tunnel from improper tunnel installation or hindrances.
  3.  The thruster is not dimensioned correctly for the vessels size from the beginning. Check if you can upgrade to a more powerful electric motor within the current tunnel diameter.


There is also a lot that can be done to reduce the noise produced by a thruster. The most important is to make sure the tunnel installation has been optimised. A thruster installation that screams throughout the harbour is usually due to incorrect installation.

To achieve a noise level acceptable to most people, one should:

  •  Select the maximum possible diameter for the hull
  •  Check the tunnel openings have the correct geometry
  •  Install the tunnel deep enough not to suck air from the surface and through the tunnel. If you want a larger heavy duty bow or stern thruster, we recommend a proportionally controlled thruster. Under most normal operating conditions, you will rarely need to run the thruster at full speed, which lowers the noise level significantly. Running the thruster at  50% load for instance, will usually be close to undetectable.

Furthermore, it is important to keep in mind that the bow of a boat may act as a speaker membrane when vibrations are applied. If you are very unlucky, the propeller will generate a frequency that resonates with the hull's natural frequency, which in turn creates a powerful gain in noise. Traditional sound attenuation used in cars and the like can make a big difference.

However, check that the material is suitable for maritime use.

A selection of thruster upgrades

Side-Power Q propeller upgrade
Q prop
Side-Power proportional control panel upgrade
Proportional control
Side-Power thruster wireless remote upgrade
Wireless remote

What kind of boat thruster upgrades are there?

For many vessels, there are several possibilities to upgrade or improve an existing installation.

  1. Fit a stern thruster. With a side thruster in both the bow and stern, you receive better control of the vessel than with bow thruster alone. You are also able to rotate the boat in any 360 direction while stationary.
  2. Upgrade to proportional variable speed control:
    • Lower noise under normal conditions
    • Longer run times
    • Hold function: With a single press of a button, the bow and stern thrusters will pin the boat alongside the pier. The amount of thrust applied can be adjusted, and in addition, the bow and stern thruster can be individually synchronized to get a balanced sideways motion - making single-handed docking very easy indeed.
  3. Apply higher voltage to the electric motor which generates higher thrust:
    • Evaluate the replacement of battery pack, thicker cables or a dedicated battery mounted closer to the electric motor if the voltage is low.
  4. Install a remote control
  5. Check if your model can be upgraded with new, more quiet and efficient propellers.
family confident boating with side-power thrusters

What does it cost to install a bow thruster or stern thruster?

Typically, a side thruster will represent a low proportion of the boat's total cost, especially when buying a new boat. For retrofitting it is a bit more complicated, as it will vary considerably from boat to boat depending on how accessible the area for installation is and the running of cables.


Our best recommendation to obtain a decent understanding of the overall cost is to contact an experienced installer and ask for an actual offer based upon his or hers experience from similar boats or by letting the installer do an actual inspection of your vessel.


A stern thruster installation would typically be an easier installation without the need for fibreglass work unless the thruster model is a retractable version.

What is the maintenance for a thruster?

A thruster will generally require little maintenance and have low operating costs after installation. If you follow the manufacturer's maintenance plan, which mostly involves regular cleaning, replacement of sacrificial anode and general inspection, the thruster can work excellently for many, many years.

Couple enjoying boating with low maintenance thruster

Who do you contact if you want a thruster system for your boat?

Sleipner Motor AS are dedicated to helping you understand your own needs and technical specifications to find the best thruster system for you, with more than 40 years of development and production experience of thruster systems.


Please see our distributor and dealer overview to find a local Side-Power representative who can guide you further in the process of securing a good solution for your boat.


If you cannot find an answer to a question in this article, you are welcome to send us an inquiry here


We wish you lots of great times at sea, also in port! 

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