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.
Geir Audun, Løvdal, Technical Manager at "Juanita", confirms that they are still satisfied with the propeller system at the vessel. It 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.
Roald Håvik, Principal Engineer R&D and Henning Brautaset, R&D Manager 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.
The challenge with a CRP-system is to find good solutions for the shaft-in-shaft system and hydrodynamically solve the 2 propellers influencing each other. The goal is to deliver cost effective and reliable systems.
It was early decided 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. 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 with direct driven PM-motors.
Jahn Terje Johannessen, Principal Engineer Hydrodynamics, and main responsible of the hydrodynamic work in the CRP project, has long experience in propeller designs. 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. 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, operation profiles. Simulations have been performed as model tests, CFD calculations - some in model scale and others in full scale.
A contra rotating propeller technology obtains a 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 setup 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.
Jahn Terje expects great interest in the market;
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!
A case study made for a tanker of 12.800 dwt, 129 m length
Propeller types and diameter of single propellers and CRP:
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 optimize the overall efficiency of the system
The sales department in Brunvoll experience 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 of high interest as an extremely efficient electric propulsion system.
Geir-Arne Kaspersen, VP Sales in Brunvoll experiences that several design companies have their different concept where the CRP would be a perfect match, and Brunvoll is already in dialogue about potential cooperations. The response from the market has been very good, and several offers are submitted for cargo ships, containers and ro-pax vessels.
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 we keep control of all parameters influencing on the system, which is essential to design an optimum installation.