Propulsion by Controllable Pitch Propellers (CPP) has been around for a long time and is considered a well-established technology. Still, most major suppliers continue to develop and refine it, making incremental progress toward optimal hydrodynamic performance and reduced energy consumption.
Yet, the search for better alternatives is ongoing — and one of the most promising is Contra Rotating Propellers (CRP). CRP may not always outperform CPP, but in certain applications, it proves far superior. In fact, its energy-optimizing potential is so significant that it can seem almost too good to be true. While CPP optimization typically yields improvements of less than 1%, CRP can deliver gains exceeding 10%.
During the introduction of CRP, Brunvoll encountered vessels that require a protected propeller. To address this, our hydrodynamicist developed the U-duct — a solution that not only protects the propeller and its surroundings, but also further enhances propulsion efficiency.
Brunvoll’s pilot installation of the contra rotating shaftline propellers system was launched in 2014 and has since then gone through a maturing process. Although the pilot has been a success, there have still been some new developments with regards to energy efficiency with the development of a new propeller series, cost reduction by introducing standardized reduction gearboxes allowing for standardized electrical motors instead of expensive inline permanent magnet motors. These developments have made the product ready to be adopted widely across many vessel segments.
Read more about Brunvoll’s Contra Rotating Shaftline Propeller system in our lasts whitepaper, containing explanation of the physics behind contra-rotating propellers, the story behind, and the lastest technlogigaly enhancments:
To better grasp the potential of Brunvoll contra rotating propeller systems, the following graph have been established. This graph describes the open water efficiency of several types of propulsion solutions by the means of the thrust load coefficient, and is a great tool to evaluate the expected efficiency in different operational modes between different propulsion types.
The thrust loading coefficient describes the loading degree of the propeller, as the pressure of the propeller is related to the dynamic pressure of the incoming water flow to the propeller. The thrust load coefficient is expressed by the following formula where T is thrust in newtons, d is the propeller diameter, VA is the propeller’s speed of advance in m/s, and AD is the propeller disk area.
In the lower area of the thrust load coefficient axis, we typically find vessels with open twin-screw propellers. These are vessels with large propellers, with no need for bollard pull, and often twin-screw configuration due to redundancy requirements.
In the upper range to the far right on the thrust loading coefficient axis we often find vessels with highly loaded propellers that require a lot of bollard pull and it is in these operations where a conventional nozzle propeller comes in handy.
But most vessels are operating in the cyan-shaded area between the lightly loaded twin-screw vessels and the heavily loaded ducted propellers. It is this area where the contra rotating propellers comes into its right as well with significantly improved efficiency. And its now time to introduce the U-duct to make this propulsion system availible to an even wider range of vessel segments.
There are several vessel types that utilize propellers with nozzles as a compromise for safety and operability. These are vessels like live fish carriers, longline fishing vessels, research vessels, to name a few. These vessels do not need the brilliant effects that the nozzle provides when it comes to bollard pull operations, but have the nozzle to avoid getting fishing gear, nets, and other equipment tangled up or in contact with the propeller.
For these vessels has Brunvoll developed the U-duct, which together with the CRP provides outstanding efficiency and at the same time provides the protection needed for the propeller for safe operations.
The U-duct generates a positive thrust force in the same way as a nozzle, but not with the same magnitude. It also reduces the load on the propellers. At the same time, the U-duct enhances course stability, leading to less rudder input. Together, these benefits contribute to reduced power demand and lower energy consumption.
Not convinced yet? Feel free to get in touch with our team to get a better understanding if the U-duct and the contra rotating propellers could be a great match for your next vessel.
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