The new Carbon Azipull 65C is a mechanical steerable propulsion thruster with a pulling propeller, for propulsion of leisure craft and commercial vessels with speeds of up to 30 knots. Similar components are currently comprised mostly of steel. The idea was to optimize the component for a high power to weight ratio and hydrodynamic shape.
In order to achieve these objectives, Rolls-Royce looked for a partner who could develop and manufacture new components using composites. Rolls-Royce sought to achieve technical advantages such as weight reduction, optimized design (based on flow optimization), corrosion resistance and better attenuation properties by using a composite solution manufactured by SAERTEX.
This new component is an excellent example of our customized composite solutions – from development and prototyping to the serial production of demanding high-end products.
CHALLENGE: THE LAYUP PLAN
The layup plan and the fabric requirements were developed by our SAERTEX offices worldwide. This way, the strength of the part was considered along with its practical application, based on our extensive experience in composite parts. Due to the geometrically challenging shape, especially of the inner shells, particular attention had to be paid to the manual draping of the fabrics.
CONSTRUCTION WITH IDEAL MATERIALS: THE MOLDS
The prototype molds were made using a special polyurethane formula, CNC-milled from the block. This provided a cost-effective solution with the possibility of easy adaptions. The layout and all vacuum-infusion requirements were worked out in close contact with the mold builder, with whom we have a long-standing business relationship.
ENDLESS OPPORTUNITIES: SAERTEX FABRICS
For the outboard unit, a combination custom-made SAERTEX unidirectional carbon PES and bi-diagonal glass fabric were produced at our headquarters in Saerbeck.
BEST POSSIBLE METHOD: VACUUM INFUSION
The infusion concept for each part was developed based on experience and prior trials with the respective fabrics. Using epoxy resin and vacuum infusion also means no emission of any curing gases, particularly when compared to an open mold application. The primary reason for using a vacuum infusion is its inherently controllable process, with a specific resin-fiber ratio. Due to the optimized material consumption, the component exhibits high strength. Detailed documentation of every process and challenge has left us well prepared for any future serial processes.
EXCELLENT BASIS FOR A SERIAL PART: THE PROTOTYPES AND PRE-PRODUCTION
All in all, two prototype sets and several preliminary articles were produced, consisting of 42 individual parts. Trimming and fairing was completed at SAERTEX Stade. A close exchange with our customer in Norway will allow us to learn from the assembly of the parts, so we can implement all amendments necessary for a perfect serial part.
“It is still amazing to see components of such size in this quality. I really like what you did with the outer shells – using just two pieces of fabric joined right at the edge where the shape totally changes, so that it is not visible.“
Dariusz Dorochowicz, Mechanical Engineer bei Rolls-Royce
SAERTEX fabrics, also known as NCFs (non-crimp fabrics), are characterised by stretched fibres within the individual layers. In comparison with crimped fibres, as found in woven textiles for instance, straight lay-up (non-crimp) fibres have the greatest possible load-bearing capacity.