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The fishing industry currently would appear to be a critical field of activity. Because of global competition and the lack of natural resources, companies in the fishing sector are obliged to develop technological R&D programmes to improve their competitiveness. Naval construction would be well-advised to incorporate technological advances from the production sector, especially in terms of materials and processes.
(Published on October-November 2005 – JEC Magazine #20)
BY NEREA MARKAIDE, SAFETY AND WEIGHT REDUCTION DEPT., TRANSPORT UNIT, INASMET-TECNALIA, SAN SEBASTIÁN, SPAIN
Given this context, Inasmet and its technological partners aim primarily to increase the fishing sector’s competitiveness by introducing advanced technologies that improve the characteristics of fishing vessels. Here, the innovation focuses on the propulsion system and, more specifically, the propeller. Development focuses on important aspects such as weight reduction through the use of composite materials; crew security and comfort; energy savings; vessel steering; and reduction of noise and vibration in the propulsion system.
Inasmet carried out two projects in collaboration with different industrial partners. The first project, which has already been completed, focused on the propeller concept design. The second one is in progress, and is focusing on industrialising the propeller.
The first project, which took place during 1998-1999, was part of a programme that was funded by the Basque Government and promoted by Estudio de Ingeniería Naval Enrique Lekuona, S.L, a Spanish company that designs all kinds of vessels and propellers. The first phase involved concept design, validation through the finite elements method, and materials selection; the second phase involved the manufacture of a prototype propeller and validation by bench and service tests.
The design of the propeller in multimaterials was based on: - a propeller shape consistent with the geometry and propulsion system of the selected vessel, a 22–metre-long fishing boat with a 5-blade bronze propeller 1400mm in diameter, - the design configuration of the composite propellers currently manufactured for the aeronautical and naval sectors, - the use of a manufacturing method providing process repeatability and high propeller performance in a marine environment, and - blades screwed onto the central bushing.
During the second phase, the propeller blades were manufactured entirely in composite materials (carbon/glass fibre and epoxy resin) using prepreg technology. Once the propeller prototype was assembled, several pushing and resistance tests were carried out in the laboratory, and then in service conditions on a fishing vessel, where the composite propeller’s power saving, noise and vibration characteristics were measured and compared with a traditional bronze propeller.
The following items were considered for improvement during the validation step: - concept design: the design is considered to be adequate for the application, and the selected materials (carbon-epoxy for the core and glass-epoxy for the skin), to be valid, - blade manufacturing process: economic and technical factors made it necessary to find an alternative to prepreg technology.
An RTM process is being considered due to the following advantages: - reduced raw-material and labour costs, - similar mechanical properties, - optimum surface finish for the coating, - assembly-system manufacturing process: a more industrial process is needed to produce the system for mounting the blades on the central bushing. - propeller pitch modification: due to higher deformation of the composite blades compared to the bronze ones, this is necessary to optimise performance.
The second project is being developed now, also with regional and national funding. In addition to Estudio de Ingeniería Naval Enrique Lekuona, S.L, another Spanish industrial partner is involved in the project – Idec Ingeniería y Desarrollos en Composites S.L, which is in charge of manufacturing the prototype. The company has a wide experience in developing and manufacturing composite structural components for several sectors, such as aeronautics and boatbuilding.
Based on the results obtained in the previous project, the main objectives during the second one are: - redesigning the initial concept with the required modifications, - combining product design with industrial development, - improving product competitiveness.
The second project was also approached through a series of tasks: incorporation of design criteria and calculation, prototype manufacturing by an industrial technology and final tests, both in bench and in service.
As a manufacturing process for later prototype industrialisation is required, prepreg technology has been refused due to its high labour, material and investment costs, and RTM is proposed as a manufacturing method, since it is a very flexible process in terms of raw materials selection and complex shapes manufacturing. It also allows the manufacture of high-performance, large-sized components.
During the redesign, a solution based on a tricellular box protected by outer skins was selected for the blades. The tricellular box is a beam shape structure that uses a composite laminate (mainly carbon fibre and epoxy resin) to hold up and transfer the tensile, torsional and flexural loads produced in the blade. The stru c t u re is wrapped in an external skin also made of carbon-fibre and epoxy-resin laminate, in order to give the blade its geometrical shape, transfer the pressure load generated in the beam, and protect the whole from external impacts. The tricellullar box and outer skin are joined by a non-structural foam. The blades and the central bushing will be assembled by a dovetail joint.
The surface finish of the blades includes a Hempasyl coat system that is being developed and tested by Pinturas Hempels S.A, in order to ensure a low friction rate and to protect the blade from the aggressive marine environment, thus avoiding the proliferation of micro-organisms.
The concept design validation includes optimising the RTM manufacturing process, and thus defining the process parameters (injection pre s s u re, vacuum pressure, temperature, injection time, injection methodology, etc.). It also allows the manufacture of a representative set of elements that, once characterised, make it possible to obtain the set of mechanical properties. These properties are necessary to carry out the detailed calculation and design of the propeller.
After validation of the design by the finite element method, the blades are currently being manufactured and tested. Afterwards, they will be integrated into the central bushing and the whole propeller will be tested in a fishing vessel. The final trials (with vessel tied up, in navigation and during fishing) should be carried out by the end of the year.