Brunvoll Contra Rotating Propeller on single shaft line for main propulsion

Brunvoll counter-rotating propeller (CRP) in shaft line, for ship propulsion. The purpose of the project is to develop a series of counter-rotating propeller systems for shaft lines. This includes developing competence within the key subject areas, which are: hydrodynamics, mechanical / hydraulic design and electrical operation / automation / remote control. Counter-rotating propeller systems are very interesting, as they have a significantly higher efficiency, compared to single propellers, and thus lead to less energy consumption and lower emissions. A product portfolio has so far been defined for the propeller system from 1500kW up to 5000kW. The hydrodynamic research is a collaboration between Brunvoll and the two partners in the project, Sintef Ocean and SVA Potsdam. So far in this work, it has been investigated and assessed which vessel types are probably the most suitable for the propeller type. Typical operating profile and degree of load of the propeller are important parameters here. Several current propeller designs are specified with main parameters, and some of these designs are extensively analyzed, using both classical calculation methods and CFDs. In addition, one propeller design has been built on a model scale and experimentally tested in a pool by both partners. So far, experimental tests show good correlation with calculated results. A next set of model propeller designs is being planned, with associated calculation analysis and test plan. Within the mechanical design, in addition to the concept of the entire axle line, a lot of work has been done, especially with two subjects. One is the mechanical structure of the propeller. For, in cases where the propeller can not be delivered as a unit, because it is too large to be transported on a road assembled with the propeller shaft, several concepts of built up propeller have been developed, where one of these is selected to use. The concept includes that the propeller blades are separately mounted on the propeller hub. Hereby, propeller shafts with mounted propeller hubs, but without mounted propeller blades, can be transported by road. The built up propeller design is demanding in that strength conditions must be maintained - at the same time as dimensions should be limited. It must be safe against seawater intrusion in the individual parts, and that production friendliness and installation safety must be ensured. The second, very demanding subject, is to calculate the static and dynamic deflection of the shaft system during operation. It has, so far, been found that there are no calculation tools, in market, for analyzing such shaft deflection for a counter-rotating shaft system. We have therefore got developed a calculation tool for this, based on an existing tool for single propeller. This tool is, due to the complexity of physics, and that it is a special adaptation of a simpler system, demanding to learn to use and the results are also demanding to interpret. It is the supplier of the existing single propeller tool that has further developed this advanced tool for counter-rotating propeller. The advanced calculation tool is currently being tested with us, and we are looking at the effect of changing one parameter at a time on the static and dynamic deflection. Within the field of electrical engineering, a specification is being prepared for a propulsion motor, frequency converter and remote control. Relevant suppliers for motor and frequency converter have been contacted and requested for the possibility of delivery and price. Measures to avoid bearing damage as a result of frequency converter operation are also being worked on. We work with a supplier to find a system for condition monitoring of the shaft system during operation.

Brunvoll has together with SALT Ship Design and Inpower developed and delivered the propulsion line with CRP, driven by permanent magnet (PM) motors, for the platform supply vessel (PSV) Juanita operated by Ugland Offshore. This installation has functioned well for 6 years and the feedback from the shipowner on functionality and fuel consumption is positive. According to Ugland Offshore, the fuel consumption in service speed (14,0-14,5 kn) for Juanita is 19 % lower than for the sister ship PSV Evita which has azipull propulsion. The gross tonnage of Juanita is also 14 % higher than Evita. Brunvoll experience considerable interest from the market regarding CRP for main propulsion. Despite this Brunvoll is not in position to industrialise this propulsion concept. There are two main reason for this. First the mechanical and hydraulic concept for long contrarotating shaft in shaft is very demanding and involves significant risk. Second, CRP is hydrodynamically highly complex and we need considerably more knowledge about hydrodynamical design features to produce optimal propeller design. Brunvoll, by this project, aim to overcome the barrier created by too high investment and maintenance cost compared to fuel savings Through this project Brunvoll expect to establish control on CRP as an industrialised product for long shaftlines for ships. It is crucial to identify the basic propulsion factors as well as the hydrodynamical, mechanical and electrical design of CRP for ships. One or more CRP shaft lines could be installed in one ship.