Keel Design
Hello everybody,

Just joint this wonderful forum which I have followed from the side line for some month now.

I plan to be a proud owner of a S&S Swan within the next couple of month. In the mean time I am enjoying to study the S&S design.

I have a quite technical question which I believe only the Guru, Lars Strom, alias The Professor, can answer.

What keel profile design were used by the S&S for the Swan boats? Was it from the NACA series? or GOE? Jouk?

The reason for my question is that I am Naval Architect (yachts are not my trade, though) and like to play with yacht design by using computer software and I would like to be able to make accurate computer models.

I did sent an email to the S&S office in America asking for drawings but I did not received any reply.

Best regards
Bjorn

Dear Bjorn
I can agree that this is a highly technical question.
I feel that the information you ask for is proprietary, and should not be given out here. It can be mentioned, however, that maybe contrary to your expectations, highly sophisticated airfoil sections were not used, instead the emphasis was on practical considerations. The offsets were given in feet, inches, and eighths, and this does not produce accurate keel sections as known today. Much was left to the skill of the people doing the lofting.
For the older models, for example Swan 44, circular arcs were used, with a nose radius.
Olin's opinion was that as long as the keels are smooth and symmetrical this works very well.
For later models a NACA section was used, but modified so it was fuller aft than the standard section. Olin had found out that the filling did not affect the hydrodynamic performance, but allowed more ballast volume.
It can be added to this that yachts seldom sail in tank conditions, but often in rough water, and then a less sophisticated keel may well be preferable in the long run. Advanced keel sections are mostly very dependent on being kept at the optimum angle of attack in order to produce their advantage, while less advanced sections are more forgiving, and not requiring the utmost attention from the helmsman all the time.
Kind regards
Lars

Dear Lars,

Thank you so much for your answer!
Very interesting reading indeed! I love to read about Olin's approach to boat design and in particular in relation to the Swan production. S&S were famous for their design of the Metre Boats, 12 metre in particular, and with that background it make sense that the keel design was focused on high keel weight. S&S become successful in yacht design in the time where racing yachts still had long keel and knowledge of advanced foil theory came later. But I understand from your answer that they followed the development and implemented new keel design later on.

It is funny that you mention the Swan 44. It is exactly the design I am studying at the moment as I found a copy of the construction drawing on the website:

http://sparkmanstephens.blogspot.fr/2012/01/design-2112-swan-44.html

Thank you and kind Regards

Bjorn

This conversation is very interesting for me as I hadn't heard that Olin was using circular sections. Another gem from Lars.
I know that Olin had done quite a lot of tank testing at the Stevens Institute in Hoboken. I wonder whether their later approach of modifying the NACA sections was as a result of testing.
It would be very interesting to hear from someone who was working on keels in the S&S office at that time. Gavin

Tigris keel with centreboard down

Gavin
I am quite sure that tank testing was the reason for filling out the aft keel sections.
There may be a way to find out more about your keel.
Much design work in the S&S office was done by trainees, with the old salts overseeing.
There is a long list of trainee names on the S&S website, and some of them have become well known. http://www.sparkmanstephens.com/sparkmanstephens/alumni/
You can probably get the keel drawing from Mystic Seaport Museum
http://sparkmanstephens.blogspot.fi/2012/03/obtaining-plans-for-your-s-yacht.html
The designer who did this drawing put his initials on it, and if you are lucky he can be found. If not, the drawing shows the keel section used, and there is a table of keel offsets which may be part of the drawing, or separate, probably with a remark about the filled out aft sections.
Would appreciate to hear what you discover.
Kind regards
Lars

Lars, thanks for this. I will try the sources you mention. All that I have found out so far is this from Harry Morgan who is still at S&S
"Mario Tarabocchia drew the lines and most of the arrangements for the 76 in 1978. Some of the detail work was done by others. Mario was from Yugoslavia and a great guy. He was Olin's right hand man for drafting and did most of the drawings for the 12 Metre's for the America's cup."

Gavin

Tigris centreboard ready to go back in