Yacht Yogi sinks

Cannot say.
But I assume during trials in level 8 sea (which was situation at time of accident) pools were empty.

Anyway, pools actually reduce GM but with strong list water comes out and situation is not so bad.
It is worse to have water trapped in superstructure.

 

When considering stabilty what is the definition of SUPERSTRUCTRE ?

 

Hum ? I will say any part of the ship which is above freeboard deck.
For all that, superstructure may be open, close weathertight, or close watertight.
Weathertight ones can withstand green water on deck but are flooded when openings are immersed.

 

I find motoryacht design confusing. This motoryacht pictured suntanning on the beach .... Is the superstructure everything above the stern passerelle ?

 

A superstructure is any ship structure which rises above the main deck. A main deck is the uppermost continuous deck which fully closes the hull, both in longitudinal and in transverse direction. Hull bottom and sides plus the main deck form the hull girder (upper decks may be included too, when of sufficient longitudinal length) - hence the main deck is also called strength deck.

 

Believe it or not : there is no weather criterion for this kind of motor yacht !!

 

http://www.boatinternational.com/20...uoise-comments-on-sinking-of-superyacht-yogi/
"Her stunning profile and interior was designed by Jean Guy Verges"

OK, this is what happens once stylist draws the windows close to WL.

 

Actually there is.
Which rules are You talking about?

 

No there is not.

MSN 1792 (M) - The Large Commercial Yacht Code (LY2) - 11.2.1.1 Monohull Vessels
French reg. Division 240 is copy/paste of that.

 

You may even say when a stylist pretends being a naval architect.

 

How is a yacht like Yogi designed ? A team of unknown naval architects design a " platform" then a stylist adapts this platform to the clients fantasy ?

 

OK agree on LY2;
But for example BV has it. See Part B #3.2.
In DNV Rules for Special Craft, Yachts are required to comply with main class requirements of stability, this means weather criterion is also applied.
LR SSC applies weather criterion to yachts, see P4 Ch.2 #8.6.

If the boat was under ABS, they do not have stability requirements in Motor Pleasure Yachts.

 

I found that ABS has got interesting requirements for portlights in Motor Yacht Rules. Say, min height of portlight above WL is greater of 500mm or 2.5% of beam. And internal deadlights are not required if portlights are recessed.

I would say 2.5% of beam is very low as it gets submersed in less than 1.5deg of heel. This is way too small compared with roll angle! Given large area of windows, one can imagine what has happened...

 

You are right on every points but problem is that flag requirements takes precedence on class ones. Specially as owner wants the minimum "trouble".
As you know for some owners safety means "trouble".

 

Fully concur; the owners choose the jurisdiction where they have less troubles. The Societies and Administrations are willing to compromise the safety to attract the owners... So the stylist draws windows and bulkheads where he wants as compliance to rules and common sense are 'not required'. Naval architect, builder and crew are left responsible for that.