Part 1 /5 from the series: Lightweight engineering expertise at its best: arONE - development & production of an »International 14« CFRP racing dinghy
Dear Reader,
An optimised structure leads to better performance. This is true for this CFRP racing dinghy, but it is also true for many other areas of part optimisation of composite structures – be it in the maritime sector but also in industries such as automotive, wind energy, transportation, to name just a few. Possible objectives here are: Weight savings, higher stiffness, resource savings and improved durability, which then also have to be optimised simultaneously – depending on the respective objective. In this respect, the arONE project is a proof of concept of the lightweight engineering competence and working methodology of ar engineers: Based on the externally specified boundary conditions of this boat class, an optimal structure has to be developed that has a competitive performance and »survives« many training and competition runs under the toughest conditions.
In this and the following blog entries, we’re providing you with exciting insights into the development of the arONE - the latest »International 14« sailing racing dinghy made in Germany. Even for non-sailors, it offers a very interesting journey into the possibilities and limits of lightweight composite engineering with a clearly defined task.
Background & Motivation
The International 14 is a sailing racing dinghy that first competed in a championship in Australia in 1898. It is a development class, so it has been evolving for over 125 years. Development classes have very broad rules that everyone can interpret in their own way. The opposite of this are one-design classes that are produced by selected shipyards with no room for design alterings. Boats with GRP hulls were already being built in the 1960s. In the 1990s, the first CFRP masts were developed. From the 2000s onwards, hydrofoils were developed, which have since been installed as standard equipment on the rudder blade.
Our motivation: to create International 14 boats that are ready for series production, with reproducible quality, but which nevertheless meet the highest demands on ultra-lightweight design and the use of the latest sailing technology.
Lightweight design has a special importance for racing.
Therefore, racing offers us the opportunity to put our lightweight design expertise to the test under the toughest conditions and to further develop our expertise through the diverse experiences.
Basically, the following applies to racing: every kilogram must be carried through the race. Since propulsion power is limited (in this case by the sail), extreme lightweight design is the solution. However, if one or more components oft the boat fails, the race cannot continue or the performance is severely limited. These aren’t pleasant prospects. Therefore, a successful design for racing (and thus later also for our customers) is characterised by the fact that – keeping the global objective in mind – an optimal trade-off between weight, manufacturability and stiffness/strength is found. In other words: more weight means higher stiffness, more stiffness leads to better performance, as forces are optimally transferred. However, more weight also reduces performance, as more mass has to be moved. Therefore, we simultaneously optimised the parameters weight and stiffness of the design in an iterative process until the best compromise between stiffness and weight was found.
Globally, it is important to optimise the boat as much as possible in terms of stiffness and thus ensure the best possible power transmission between the hull, rigging and centerboard and rudder. If the hull and the appendages are optimally stiff, they are usually also sufficiently dimensioned against failure. Of course, this also has to be checked separately. However, special focus should be placed on local joints, such as the shroud attachment, the forestay attachment or the mast base. The loads transmitted here are so high that they must be subjected to a specific strength check.
The racing idea is that every gram counts. So if you save weight in many small areas, e.g. 20 times 100 grams, 2kg are saved. With a structural mass of 45kg, as in our boat, that is a significant percentage.
This idea can and needs to also be applied to large systems/assemblies in industries outside of racing.
Concept & Strategy
An essential part of the design is experience with the boats and the class, the class rules and the loads as well as the custom of using the boats in training and racing.
For our work on this boat, but also for all projects that we realise for our customers, the following applies: The best possible optimisation of individual components or complex assemblies can only be achieved if there is not only comprehensive expertise in the design and calculation of these. There must also be the know-how to compare the results of this simulation with the real-world possibilities of fibre composites. A simulation is always an abstract simplification of the real world. Therefore, a plausibility check with regard to the real-world applicability and the already accumulated practical experience is always necessary. Especially manufacturing experience must be included here. We have implemented this approach for the design of the arONE as follows:
On the water, loads and especially maximum loads are difficult or impossible to precisely define. We have estimated loads from the sailing scenarios and crew masses that arise in practice. The basic rig loads (tension forces in the shrouds, etc.) can be estimated or measured in advance, but it is not possible to precisely record the peak sailing loads. This is where you have to rely on sailing experience and compare it with the engineering assumptions.
Workflow of the arONE development
The hull design was given by British yacht designer Dave Hollom. With the estimated and determined loads, a good engineering gut feeling and the experience from the boat class, a first structural design was established. Now it is important to plan ahead for production at an early stage so that any influences of the manufacturing process on the structural design can be applied. This is particularly important for fibre composite manufacturing, as the manufacturing method and the associated influences on the component quality – such as fibre volume content or curing temperature – have a direct influence on the laminate design. If no proper planning is done in advance, unnecessary, costly design loops and additional costs in production for faulty prototypes will result.
With Design Freeze, production planning and the associated mould design can begin, including laminate drawings. Here, often design alterations come up that lead to a better result in coordination with the production. As a result, further verification may also be necessary in the calculation. Simulation enables the comparison of different designs with regard to stiffness and strength in the shortest possible time and to confirm or even exceed engineering estimates. This saves a large amount of prototyping costs.
So much for our onboarding for you, our readers, on the subject of developing the arONE racing dinghy. This way of working is exemplary of our methodoloy in customer assignments. We hope we have made you curious about what is to come: In the next blog post, we will give you detailed insights into our development work. Stay curious. If you like this blog post, please feel free to share it.