Brunvoll (at that time Scana Volda) delivered the first Contra Rotating Propulsion System in 2014 to the PSV ‘Juanita’ owned by Ugland Offshore AS, a project initiated by a request from Salt Ship Design to come up with a Contra Rotating Propulsion System for their PSV-design.
Long story short, ‘Juanita’ was designed by Salt Ship Design, built at Kleven Shipyard and equipped with the first generation of Brunvoll Contra Rotating Propulsion System – designed and optimised for a single skeg PSV.
They experienced that the system at Juanita is an efficient and reliable installation, well-functioning in operation and very efficient in transit condition. Juanita has been on charter to Equinor since delivery from building yard in 2014.
Designing a new series of cost-effective CRP-systems
In 2020, a new R&D program was started to further develop the CRP-concept
Roald Håvik, Principal Engineer - R&D and Henning Brautaset, R&D Manager at Brunvoll were both strongly involved in the first CRP-design and has since then collected experience and proof from 9 years successful operation of the efficient and robust propulsion system at ‘Juanita’.
In 2020, a new R&D program was started to further develop the CRP-concept, with the goal to come up with a new series of cost-effective CRP propulsion systems for different ship types.
Contra Rotating Propulsion (CRP) System
The challenge with a CRP-system is to find good solutions for the shaft-in-shaft system and hydro-dynamically solve the 2 propellers influencing each other. The goal is to deliver cost effective and reliable systems.
It was decided earlier itself that the new CRP-system would benefit from incorporating a gearbox to the design. The engineering team has designed a new gearbox for the CRP-configuration based on well-known and proven technology from deliveries of more than 2100 Brunvoll gearboxes.
CRP configuration with gearbox offers flexibility
A CRP configuration with gearbox gives the flexibility for use of standard el-motors and possibilities for different energy sources.
The new configuration is a less expensive system, with less weight compared to a CRP system and with direct driven PM-motors.
Optimum propeller designs by using efficient tools
Jahn Terje Johannessen, Principal Engineer - Hydrodynamics at Brunvoll, who is largely responsible for the hydrodynamic work in the CRP project, has vast experience in propeller designs.
It is crucial to have a good understanding of how the two propellers affect each other
He explains that the primary task when starting this new development program was to come up with optimised and dedicated propeller designs for different vessel types - and to have efficient tools to easily come up with good design proposals during discussions with customers.
It is indeed challenging to understand the interaction between the two propellers and to design an optimum propeller system. It is crucial to have a good understanding of how the two propellers affect each other.
Computational fluid dynamics (CFD) simulations
This can be done through computational fluid dynamics (CFD) simulations or physical testing in water tanks or with scale models. These methods will help determine the thrust and torque generated by each propeller and their effect on the overall performance of the propeller system.
During the development project, several propeller designs for typical design characteristics have been investigated - such as relative wake, merchant tonnage, and operation profiles. Simulations have been performed as model tests, CFD calculations - some in model scale and others in full scale.
Contra rotating propeller technology
A contra rotating propeller technology obtains higher propeller efficiency. On the other side, such a supreme technology will also be more expensive. It is thus an important task to identify the correct set up to offer the optimum cost benefit ratio.
Case studies and power speed simulations on CRP for the actual ship is essential when evaluating the right propulsion system. A CRP-system can be ideal for different ships but typically for single screw vessels with a certain portion of transit in their operating profile.
We are already involved in 10-12 projects - many different ship applications"
Jahn Terje Johannessen expects great interest in the market. He said “Not many companies can offer similar systems in the market today, and I guess we will be asked and challenged by shipping companies, ship consultants and brokers about what we can come up with. We are already involved in 10-12 projects - many different ship applications within traditional commercial vessels. Exciting times!”
- How the CRP propeller efficiency works?
In a propeller system with a front and aft propeller, the front propeller is designed to capture the load and pitch, while the aft propeller is designed for speed.
The aft propeller’s primary task is to cancel out the rotation generated by the forward propeller and optimise the overall efficiency of the system.
High demand for energy-efficient propulsion solutions
The sales department in Brunvoll has experienced an increasing interest in diesel-electric and hybrid propulsion systems, within all ship types. In a context with green shipping programs with focus on fuel efficiency and reduced emissions, the Contra Rotating Propulsion system is expected to be of high interest as an extremely efficient electric propulsion system.
Geir-Arne Kaspersen, the Vice President (VP) - Sales in Brunvoll experienced that several design companies have their different concept where the CRP would be a perfect match, and Brunvoll is already in dialogue about potential co-operations. The response from the market has been very good, and several offers are submitted for cargo ships, containers and ro-pax vessels.
CRP-system from Brunvoll
A CRP-system from Brunvoll includes a complete delivery of propellers, shaft-in-shaft propeller shaft arrangement, gearbox, electric motors, VFDs and control systems. In this way, they keep control of all parameters influencing on the system, which is essential to design an optimum installation.
