Bow thruster: which one to choose?

There are many pieces of equipment that are not mandatory but whose ability to improve your sailing experience make them valuable. This applies to the bow thruster. With the bow thruster, docking the boat or leaving the dock becomes child's play. You have mastered the three-point turn in a car thanks to your skill, but also (or even 'largely'...) because of power steering, right? It's the same on board your boat: the presence of a bow thruster facilitates tricky manoeuvres in the harbour. Remember that!

What is a bow thruster?

This is a propeller placed at the front of the boat, perpendicular to the direction of travel, and controlled from the helm station via a powerful electric motor. It lets you move the bow to port or starboard. Its position is crucial for optimum performance: the propeller must be below the waterline but as close as possible to the bow (see diagram below).
 
If your boat is more than 7 metres long, Band of Boats recommends investing in a bow thruster for easy and safe manoeuvring. Some thrusters, called poop thrusters, are installed at the stern. If you equip your boat with both, you will be able to pivot your boat 360° in a tight space, just like a pro!

What type of bow thruster for your boat?

To choose the right bow thruster, there are a few essential factors to take into account:

1.    What is the windage of your boat? : This refers to every part of the boat (except sails) that is above the waterline. The windage offers passive resistance to the wind and creates turbulence. If you have large windage, choose a thruster for larger boats than yours, and vice-versa.
2.    What type of port are you in? You should consider the average strength of the dominant wind, the currents, and access to your port to evaluate the necessary power.
3.    What type of boat do you have? For example, a 40-foot flat-bottomed model with little depth below the bow reduces the installation options. 
4.    What is your budget?

To narrow down your choice, Band of Boats gives you a detailed description of the different types of bow thruster and lists the pros and cons of each. It's up to you to select the most appropriate one!
 

type                what is it?                                Pros                                Cons
A tunnel            A tube passes through the hull from one side to the other 
                with the propeller inside and the motor above.                Easy installation                        Unsuitable for hulls that are too flat
                                                                                    Lower performance than a retractable system
                                                                                    Risks in case of objects near the propeller
Retractable            The propeller is on a ram. It comes out when needed 
                and withdraws back into the hull when not in use.            The propeller is protected 
                                                    Hull surface remains the same > does not disrupt sailing 
                                                    Better performance                        Complex installation; requires a special cut-out and structural                                                                                         reinforcement of the hull.
                                                                                    Risk of mechanical failure at inlet and outlet 
External            The motor and propeller are in a sealed unit
                submerged under the bow.                         Very easy installation
                                                    Possibility of attaching it the furthest towards          Disturbs the sailing performance
                                                    the front of the bow > better performance            Increases the motor's consumption

Water jet            A pump sucks in water on the opposite side, stores it 
                in an on-board container, and expels it on the other side.        A last-resort solution if the other types 
                                                    are impossible to install.
                                                    Safest solution > no risk of sucking in floating lines        High electrical power
                                                                                    High cost

Have you made your choice? Now please share your manoeuvring experiences with the whole Band of Boats community. We always value your opinions.