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Dutch yacht builders and designers experiencing together hands-on innovation

A new concept is born: Comfort Draft for semi-submersible yachts

Over the last 20 years, the motion at anchor has been a focal point in yacht design as it is considered a major cause of discomfort. The issue has been resolved with the development of smart and efficient active and passive

stabilisation systems, which have flourished onboard all types of yachts. Guilhem Gaillarde,

Maybe because of the success of the active devices to reduce roll, less attention is given to the hydrodynamic properties of the hull itself, although there could be considerable advantages gained there as well. However, it is not easy to modify the hydrodynamic characteristics of a hull without performing major changes.

The key to further develop this potential innovation was found in September 2015, while discussing a yacht concept with designer Edwin van der Mark. At the MARIN stand at the Monaco Yacht Show, he presented his idea of a submersible yacht to enhance underwater views and sea access. While looking at the rendering, we thought it would be interesting to use such a drastic change of draft to modify the motion response of the yacht. This was the start of a fruitful and open cooperation to explore the idea.

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The study was started in 2016 by Yassir Chellaoui, a maritime student from Morocco.

The sole change in loading condition could however not be a success, as the stability requirements would not be met. We then came to the idea of changing the waterplane area while changing the draft. The results appeared to be amazingly good according to calculations, enabling a reduction of 60% to 80% of the roll in the most unfavourable resonant conditions. This was obviously obtained on a hull that had little inherent damping, selected to show the potential of the idea. These results were confirmed with model tests in spring 2017, when major yachtbuilders in the Netherlands were invited to participate in a workshop.

The concept, named ‘Comfort Draft’, was born. The effect of modifying the waterplane area

could also be obtained by creating side openings and allowing partly flooded compartments.

In order to further investigate the design space and explore the limits of the concept, MARIN proposes to do it in the form of a Joint Industry Project. This is interesting for both yards keen to explore new ideas and class societies willing to assist with the feasibility and safety of such a concept.

Such research has defined a new dimension in hull form optimisation for anchor operation, and can potentially be used to enhance access to the water, as well as to reduce the motions. This is valuable for yachts but also in segments where a stable platform is important during operations at zero speed.

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