Master Thesis Online
Master thesis : The Hull Optimisation for an Open 60 IMOCA Single Handed Race yacht
Gournay, Lazare 
Promotor(s) : BARKLEY, Giles
Date of defense : 15-Sep-2022 • Permalink : http://hdl.handle.net/2268.2/16414
Master_Thesis_GOURNAY_Lazare.pdfDetails
| Title : | Master thesis : The Hull Optimisation for an Open 60 IMOCA Single Handed Race yacht |
| Translated title : | [fr] L'optimisation de la coque d'un voilier de course au large: IMOCA Open 60 |
| Author : | Gournay, Lazare
|
| Date of defense : | 15-Sep-2022 |
| Advisor(s) : | BARKLEY, Giles |
| Committee's member(s) : | Gentaz, Lionel
Bonnefoy, Fabien Boote, Dario |
| Language : | English |
| Number of pages : | 46 sans appendices |
| Keywords : | [en] Sailing yacht design, Open 60 IMOCA hull form design, hydrofoil design, Velocity Prediction Program (VPP), performance prediction, foil lifting-line theory, theoretical model development for hydrofoil performance prediction, hull optimisation, experimental hydrodynamics, tank testing. |
| Discipline(s) : | Engineering, computing & technology > Mechanical engineering |
| Commentary : | Over the last 5 Editions of the famous Vendee Globe SH Round the World Race, the boats have evolved from wide planing hulls, capable of speeds of around 18 knots, to still relatively wide planing hulls, now carrying various ‘lifting’ foil arrangements which physically lift the boat out of the water whilst also providing for no additional weight increase, extra righting moment. The consequence of this is that these newer 2016 & 2020 Vendee Globe veteran boats have higher top speeds, being easily able to sail in excess of 25 knots for considerably long. The reason is that these boats are lighter and also stiffer in terms of stability. Whilst this is good for racing speed, the traditionally shaped hull still has to slam through the sea, but now with considerably higher accelerations than before. This not only loads up the hull, but also the crew member(s), to such an extent that the results is the boat often needs to reduce speed even in moderate seas if both boat and crew are to survive in one piece, thus losing potential speed gains. In the last 2020 edition of the VG race, all but one Open 60 design opted for the typical flat-bottomed hull shape. The only new boat to consider reducing slamming accelerations by altering the hull shape was the scow bow Open 60, named L’Occitane, which was designed by Solent University Graduate Sam Manuard. This boat (as shown above) sporting her fuller scow bow softened the ride somewhat and her skipper Armel Tripon commented upon the smooth ‘softer’ ride relative to other more typical Open 60s he had sailed on. He stated that he did not have to reduce speed so much as he would have done on other yachts as the accelerations were relatively low. During the 2020 VG race, the boat was proven to be fast, but sadly did not win due to other issues and minor damage sustained en-route. However this new design was considered to have potential to sail at very high speeds for long periods without overstressing the crew member. That whilst good use is to be made of the modern foil systems currently deployed on this type of race yacht, it should be possible to develop and refine this promising shape of hull further, so as to: • Reduce the slamming loads and accelerations further on the boat when sailing at high speeds by updating the hull shape, so as to minimise slamming accelerations so that full advantage can be made of foiling speed potential. • To improve the upwind sailing performance particularly in light airs though reducing the hull wetted surface area. • To improve the upwind sailing performance by improving the overall hull/foil combination Lift:Drag ratio which is often referred to as the effective draft. The researcher would be required to: 1. Investigate current Open 60 and possibly Mini-Transat and other hull forms to look for suitable hull candidates from which to develop their boat. 2. Then to develop a hull form which they feel would satisfy both upwind and off-wind sailing requirement and potentially meet speed requirements. 3. There would then need to be a technical analysis of the hull, including a foil system and sailing rig to ensure that the vessel could reach required speed targets. This could include a VPP analysis. 4. To prove the concept, it would be useful to build a scaled model of the hull and test this in Solent University’s tow tank in both flat water and also waves, to validate the performance by measuring both lift and drag forces on the model, and in particular the slamming accelerations acting on the model. 5. You would be required to write a report giving an overview of your design proposal. 6. This would be based on the analysis of the performance and tank test results obtained during your studies, provide a reflective critique on the likely success of your design. 7. There would be the potential to expand the brief above to include CFD or FEA work within the scope of work to be completed if it was felt necessary to follow that path. |
| Research unit : | Solent University |
| Name of the research project : | The Hull Optimisation for an Open 60 IMOCA single handed race yacht |
| Target public : | Researchers Professionals of domain Student General public |
| Institution(s) : | Université de Liège, Liège, Belgique Université de Solent, Southampton, Angleterre |
| Degree: | Master : ingénieur civil mécanicien, à finalité spécialisée en "Advanced Ship Design" |
| Faculty: | Master thesis of the Faculté des Sciences appliquées |
Abstract
[en] This paper investigates the benefits of using modern foils on an IMOCA 60 sailing boat. This was achieved for a designed IMOCA hull form, and designed foils, using different approaches.
A parametric study and researches on existing IMOCA 60 was first realised. Different hull forms were then modelled in the nurbs-based hull form modelling software Maxsurf. They were investigated through VPP analyses to determine the fastest design. Two of them are the reversed engineered hull forms of Hugo Boss and L'Occitane. They were used as reference to validate the design, by comparing the boat speeds found using the designed hull and these reference ones, in various sailing configurations (headings and wind speeds) chosen in the VPP.
The selected hull form design was manufactured at model scale (1:10) using composite materials, to be tank tested with its keel and foil. Tank tests were realised with and without the foil, at different boat speeds, heel angles, and leeway angles. The data recorded during the tests comprises the total drag, the side force, the roll (or righting) moment, the heave, and the pitch of the boat.
The data measured without foil was subtracted from the one measured with foil, which allowed to determine the effect of the foil on the boat.
Meanwhile, a theoretical model was developed under the assumptions of the lifting-line theory, to try to predict the hydrodynamic forces generated by the designed foil, and their influence on the overall righting moment of the boat. The results were compared to the experimental foil results, which allowed to validate the model.
Finally, “direct experimental“ VPP analyses were performed based on the experimental data found with and without foil. It enabled to find the gains in boat speed due to the foil, in various sailing configurations. The influence of the righting lever ($GZ$) was also investigated.
%Add the main findings!!
After two iterations including a re-design process, the designed hull form proved to be relatively fast compared to the reversed engineered hull forms.
Moreover, it was found that the developed theoretical model provides realistic trends when compared to the experimental foil results. The theoretical foil results generally overestimated the experimental ones, which means that the foil was slightly less efficient than predicted in theory.
The direct experimental VPP analyses showed that the designed foils globally increased the boat speeds, when the increase in $GZ$ was accounted for.
However, a few boat speeds were smaller with foil than without it, regardless of the $GZ$ values used. It was found to correspond to configurations (boat speeds, heel, and leeway angles) in which the foil ventilated in the tank.
The downwind speeds were unchanged since the foil was not immersed at the corresponding small heel angles. Hence, a design modification was proposed to solve that issue, and also benefit from the lift of the foils when sailing downwind.
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