Bow Thruster Guide

Today most yachts or motorboats over 45 feet have a bow thruster fitted as standard. The thruster will usually meet the expectations of most customers when using the boat under normal weather conditions. The sizes used by boat builders will vary depending on the boat's intended usage and price level. In today's production boat's of around 45-50, the typical thruster will push the boats bow against a direct side wind of 20-22 knots.
For boat owners who use their boats in more demanding conditions or have a strong current in their local marina, Lewmar can offer upgrades to a higher performance thruster. However, few pleasure craft need a thruster that can push the bow against a direct side wind of more than 25 knots.
The boat's wind area, the lateral wind draft area and the thruster's tunnel position in the hull determine the thruster's performance on a boat. By knowing these factors we can calculate the wind pressure on the boat and the centre point of this wind pressure. However the wind pressure is seldom from right angles and many boat superstructures are quite streamlined so we can reduce the factor slightly. From these calculations we can determine what thrust is needed to counter the wind pressure with the given thruster position.
Our selection chart - click here -gives you a general guide.
To gain total control of your boat in combination with a bow thruster the solution is to install a stern thruster, leaving the main engines to propel the boat forward and backward as they were intended

Choosing the right Side-Power thruster for your boat.

Every boat operator can benefit from having a thruster installed on their boat.

In principle, any thruster will do a job in any boat. However, the key to getting the full benefits of the thruster is to select the correct one to ensure that it will do the job you want it to. This is one of two main factors to consider when deciding on a thruster size for your boat.

Today most pleasure craft over 45ft. have a bow thruster as standard equipment. The thruster will usually meet the expectations of most customers when using the boat under normal weather conditions. The sizes used by boatbuilders will vary depending on the boat´s intended usage and price level. In today´s production boats of around 45ft.-50ft., the typical thruster will push the boat´s bow against a direct sidewind of 20-22 knots.

Some custom built or very high end boats may have a high power bow thruster that pushes the bow against a direct sidewind of 24-26 knots. For boatowners who use their boats in more demanding conditions or have a strong current in their local marina, or requiring high performance, boatbuilders can offer upgrades to a more powerful thruster system. However, few pleasure craft need a thruster that can push the bow against a direct sidewind of more than 25-27 knots.

The thruster performance on a boat is basically determined by the boat´s wind area, the wind area distribution and the thruster´s tunnel position in the hull. By knowing these factors we can calculate the wind pressure on the boat and the center point of this wind pressure. From these calculations we can determine what thrust is needed to counter the wind pressure with the given thruster position. The boat weight is normally not a major factor for most pleasure craft unless they are regularly used in areas where the thruster is required counter strong currents.

Conclusion
The two main factors that decide correct thruster sizing are:
- boatowner performance requirements
- boat size, type and shape

The example below shows the different wind speeds that two different thruster installations can encounter and the increased leverage gained when the thruster is positioned further forward.

Bow Thruster Guide

Why do I need a Thruster?

What size Thruster do I need for my boat?

I am buying a new boat but haven’t decided to have a Thruster installed can it be fitted later?

What Battery power do I need?

Can I install the Thruster myself?

Can a Lewmar Thruster replace my existing installation/ I have a tunnel and standard fit by another manufacturer?

Choosing the right Lewmar thruster for your boat.