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Old 04-14-2013
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Keels

Quote:
Originally Posted by Anders B View Post
I found your very interesting overview on keels. I more or less copied the post to my personal blogg
You will find it by googling on "piano" and "Hansson31".
I hope this is OK, otherwise I will erase it immidiately. Please let me know.
One topic I am very interested in is - keels! Both design and structural characteristics of keels. I have been searching the web for investigations of keel design. There is some about IACC keels. But almost nothing else. Two master thesis have been made at Chalmers University Sweden (my native country). Many different designs are found on new boats and my feeling is that keel design is an ad hoc business. Are you aware of specific investigations related to racing/crusing performance keels for say 30 - 50 footers? Center of gravity is one business. Type and design of bulb and layout and section of the fin are other important issues.
I found a pic of the Safran keel in your overview. My professional area is material science and solid mechanics (structural science). The only information about the fracture of the safran keel I have found is the official report from the Safran Sailing Team presented on the Vendee Globe website. You live much closer to Les Sables'DOlonne. Do you know where I can find more in depth information, about the design and the cause of the fracture?
Hi Anders,

I read that report too and it seems very clear to me. As you know Safran (the sponsor) is an high tech company and the keel was made by them. They say:

Analysis
The specialists analyzed the break in the keel’s fin by microscopic observations to determine the failure mode. Samples were also taken from the metal to check if its characteristics matched the values used for strength calculations. At the same time, other experts calculated the loads experienced by the keel, based on observations of the break, and compared them to the standard loads used as a basis for its design.

Results
The investigation was able to exclude the possibility of a break due to a collision with an "unidentified floating object". It also noted that there were no metallurgical defects, and that the welds showed no anomalies that could explain the break. The investigation shows that the break was due to damage caused by metal fatigue, engendered by repeated shocks from contact with waves. There are no indications of a high-frequency vibration phenomenon.

A close look at the break spotlights the high loads due to the extreme sea conditions experienced by Safran over the last year, during the Transat Jacques Vabre 2011, the 2012 Round Britain race, and training runs for the Vendée Globe. The analysis confirms that the loads experienced by the keel were undoubtedly far higher than the standard values used by the design teams, as well as the values calculated from the shock recordings during the Transat Jacques Vabre 2009.

"The Safran Open 60 monohull ocean racer has undergone significant technical changes since 2010 to boost its performance," said Gérard Le Page, President of the Safran Sailing Team. "Facing increasingly fierce competition, the boat is subjected to ever-higher levels of stress, even under very sustained conditions. The shocks experienced by the boat and its appendages were also more violent, in particular exceeding the estimates used by the design team."

Safran will take advantage of the lessons learned through this investigation to design a new keel and work with Marc Guillemot to prepare for the next major race, the Transat Jacques Vabre 2013. Safran will of course make available all conclusions of this investigation to the IMOCA (International Monohull Open Class Association) Technical Committee, so that all shipowners and skippers can benefit from the lessons learned.


Results of the investigation into the causes of Safran's broken keel - Safran Sailing Team

Regarding keels they are as much studied as the hulls. In what regards performance cruisers that race at high level in handicap racing some brands even propose different keels for different rules. I mean they are not studied only in what regards pure performance but in what regards performance under a given rule. Any NA knows exactly were is the center of the gravity of a given keel and that is used to calculate the boat CG needed to the program computer to calculate the stability curves.

Regarding internet the information is not much but you can see here some studies made by ker regarding the Salona 35 and 38. The hull is not designed by him (they utilize the hulls of the 34 and 37 that are designed by J&J) he optimized the keel and rudder.

http://www.sailman.fi/documents/S38p...e19.5.2011.pdf

Salona 35





They sell the standard boat with a torpedo keel but if you want to compete on ORCI they can have the boat with one of these. They look odd but knowing the competence of Ker in design in what regards to winning races I am sure they will make a boat more competitive in ORCI but not in absolute performance.

This is a very complicated keel in the shape of a foil, with an interior light structure, lead on the bottom and a kind of foam on the top. The CG will not be as low as with a torpedo keel, so it will need to weight more but I am sure that will have less drag. Doing the maths in what regards the ORCI rule i am sure that will have advantages.

So you can see to what point those studies go

Look at the two possible keels on the JPK 38 (Valens).



A circle with a cross marks on both keels the CG. As you can see it is lower on the torpedo keel. That means that the swing keel will have to have more weight to compensate or have more draft. All this is completely dominated and studied by the NAs that study in computer programs also the drag of each solution even in what regards more complicated ones:



Take a look at these studies:

Naval Architecture : Owen Clarke Design - Yacht Design and Naval Architects

Regarding the effect a given keel and the ballast has on a boat in what regards the stability, all is studied in full detail and the NA knows how the boat is going to perform (if they manage to build it according with his specs and that is not always the case). Some differences are expected to occur, specially in what regards weight.
Now that the racing boats use canting keels those calculations are a lot more complicated but even so carried in great detail: Never saw a new Open 60 missing its inversion test:



That's because the NA had made previously their home work correctly

Regarding posting posts (or part of them) from this thread on your blog no problem but please make a reference regarding from where you have taken them.

best regards

Paulo
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Last edited by PCP; 04-14-2013 at 02:28 PM.
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