Light­weight engi­neering exper­tise at its best: arONE – devel­op­ment & produc­tion of an »Inter­na­tional 14« CFRP racing dinghy – Part 1

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.