SEMI-SUBMERSIBLE YACHT CONCEPTRETHINKING BEHAVIOUR AT ANCHOR AND

GENESIS OF THE COMFORT DRAFT

24th International HISWA Symposium on Yacht Design and Yacht Construction14 and 15 November 2016, Amsterdam, The Netherlands, Amsterdam RAI Convention Centre

PRESENTATION OUTLINE

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• Introduction of the project

• Back to basics

• Stability requirements

• Finding a concept solution (finding Nemo…)

• Seakeeping calculations

• Conclusion & Further work

INTRODUCTION OF THE PROJECT

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The NEMO concept was discovered by MARIN at the MYS 2015 when meeting Edwin van der Mark. The concept derives from study on submersible and semi-submersible yachts developed jointly by Edwin van der Mark and Harley O’Neill.

This new design allows the Yacht to submerge partially at anchor and give to the guests splendid views above and below the water‘s surface.

The main goal was pure aesthetical and design.

INTRODUCTION OF THE PROJECT

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MARIN thought that this feature could bring also hydrodynamic advantages at zero speed given some adaptation of the design.

If this could be achieved, the name of the submerged draft could be so-called a comfort draft.

DESIGN + HYDRODYNAMICS= INNOVATION + ENGINEERING

= PRODUCT

INTRODUCTION OF THE PROJECT

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MARIN thought that this feature could bring also hydrodynamic advantages at zero speed given some adaptation of the design.

If this could be achieved, the name of the submerged draft could be so-called a comfort draft.

DESIGN + HYDRODYNAMICS= INNOVATION + ENGINEERING

= PRODUCT

BACK TO BASICS

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BACK TO BASICS

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Effect of varying the metacentric height on roll response

BACK TO BASICS

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Existing ships of floaters changing drafts in operations

BACK TO BASICS

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Goal is then to change the loading condition (while changing draft) in order to reduce the metacentric height and improve the seakeeping (mainly roll)

STABILITY REQUIREMENTS

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The intact stability requirement according to the IMO code of intact stability applicable

to the monohull Yacht (13-36 passengers)

❖ The area under the righting lever curve (GZ curve) is to be not less than 0.055m.rad up to θ =30 angle of heel.

❖ The area under the righting lever curve is to be not less than 0.09m.rad up to θ =40° angle of heel or the angle of down flooding θf if this angle is less than 40°.

❖ The area under the righting lever curve between the angles of heel of 30° and 40° or between 30°and θf, if this angle is less than 40°, is to be not less than 0.03 m.rad.

❖ The righting lever GZ is to be at least 0.20 m at an angle of heel equal to or greater than 30°.

❖ The maximum righting arm is to occur at an angle of heel preferably exceeding 30° but not less than 25°.

❖ The initial metacentric height GM0 should be not less than 0.15 m.

STABILITY REQUIREMENTS

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The interior spaces that could be used to ballast the ship and attain the required submerged draft were used to calculate the new stability.

Symbol Magnitude UnitLppBTV

GMt

KMKGLCG

CbCmCp

10517,44,2

3526,8

1,4

8,016,654,7

0,520,790,66

10517,46,87202

0,9

7,7956,952,53

0,710,840,71

mmmm3

m

mmmm---

Figure 2: GZ Curves

By calculating the GZ curves corresponding to the second loading conditions, we realize that the first model hull doesn’t respect the intact stability requirement.

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In order to :

• Satisfy the stability requirement;

• Reduce the ship motions;

• Reduce the capacity of the ballast water necessary to submerge the Yacht.

We have conceived different hull forms, where, instead of ballasting to change draft and reduce the GM, we would reduce the stability also by changing the hull form when sinking.

This is achieved by changing the waterline area while changing draft.

FINDING A CONCEPT SOLUTION (FINDING NEMO…)

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Changing the waterline area while changing draft

FINDING A CONCEPT SOLUTION (FINDING NEMO…)

Cross opening full width

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Changing the waterline area while changing draft

FINDING A CONCEPT SOLUTION (FINDING NEMO…)

Dock

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Changing the waterline area while changing draft

FINDING A CONCEPT SOLUTION (FINDING NEMO…)

Side gangway over the full length

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Changing the waterline area while changing draft

FINDING A CONCEPT SOLUTION (FINDING NEMO…)

Mixed solution that could correspond to gangway and side openings.

FINDING A CONCEPT SOLUTION (FINDING NEMO…)

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Symbol Magnitude UnitLppBTV

GMt

KMKGLCG

CbCmCp

10517,44,2

3526,8

1,4

8,016,654,7

0,520,790,66

10517,46,8

6831,6

0,9

6,55.654,7

0,570,770,74

mmmm3

m

mmmm---

Figure 3: GZ Curves

An expected side effect of the reduced waterline area was that the vertical plane motions could also be affected, on top of the roll…

zy

T=4.2 mGM

GMt=1.4 m

M'

G'

GMt=0.9 m

T=6.8 m

Design draft (departure)

comfort draft (anchor)

• The capacity of the ballast needed to submerge the vessel is around 3387 m3.

• The space dedicated to habitability is 40% less compared to a yacht of the same size.

FINDING A CONCEPT SOLUTION (FINDING NEMO…)

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• Based on the concept, the designer made a new superstructure and rendering. Such solution brought by hydrodynamic consideration proved to be even more creative than the original concept!

FINDING A CONCEPT SOLUTION (FINDING NEMO…)

SEAKEEPING CALCULATIONS

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The calculations are represented in term of RAO, at anchor (zero speed) in beam seas, for 2 loading conditions in order to compare the behaviour of the vessel at the initial draught (Config_1) and when it submerges (Config_2)

Description Value Unit

Lpp 105 105 [m]

Bwl 15.4 16,7 [m]

Ta 4.2 6,8 [m]

Tf 4.2 6,8 [m]

Displacement 3526.8 7026,3 [m3]

Awp 1238,7 1189,8 [m2]

GMt 1.4 0.9 [m]

LCB 54.8 52,53 [m]

KB 2.5 3,97 [m]

LCG 54.7 52,53 [m]

KG 6.6 5.6 [m]

10.816 15,87 [s]

kxx 6.9 6,9 [m]

kyy 26.25 26.25 [m]

kzz 26.25 26.25 [m]

SEAKEEPING CALCULATIONS

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Figure 5: Roll Excitation Force

Figure 4: Roll RAOs in 1 m amplitude (u=90°)

SEAKEEPING CALCULATIONS

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SEAKEEPING CALCULATIONS

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SEAKEEPING CALCULATIONS

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Figure 6: Heave RAOs in 1 m amplitude (u=90°)

SEAKEEPING CALCULATIONS

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SEAKEEPING CALCULATIONS

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SEAKEEPING CALCULATIONS

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Figure 7: Scatter diagram of the Mediterranean Sea

CONCLUSION & FURTHER WORK

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Creating a comfort draft concept can inherently improve the performance at anchor of yachts. This is obtained by working on immersion of the hull and modification of the hull characteristics.

The principle of the comfort draft is:

• Change of waterline area to reduce stability and thus modify excitations;

• New waterline area is achieved in the present concept by the recesses created in the hull which are immersed when changing draft;

• Such new waterline area could also be achieved by creating side opening (like with garage doors) and by “flooding” part of the waterline area at intact draft.

Further work should obviously be addressed for the engineering of such solution (interior arrangements, damaged stability study, noise & vibration ballasting systems and strength calculation), the possible side effect during ballasting operations (safety, free surface effects), and the acceptation of such concept for the yards and owners, as well as requirements from classification societies.

THANK YOU !

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T=4.2 mGM

GMt=1.4 m

M'

G'

GMt=0.9 m

T=6.8 m

Design draft (departure)

comfort draft (anchor)