Which rudder?

[booster]

Ad hoc et al!
Yes, good engineering knowledge is a must. Regrading Castro's Justine:

www.freebase.com/view/en/tony_castro

"Tony Castro, is based on the South Coast of England in Southampton and has been designing sailing and motor yachts for 25 years, with about 6,000 boats launched to date that include custom boats and One-design production models. After leaving Ron Holland’s design team in 1980, Castro's first significant racing yacht design was Justine, the first and only yacht to win the One Ton Cup with five straight firsts."

Regards,
Booster

[booster]

Hi!
How can a Naca and Wortmann-profile be combined? I found an article on the site below. It is in Swedish so I will try to translate (but first in Swedish!). The rudder- and keeldesign of the Omega42 is discussed by Peter Norlin on the site:

http://www.omega42.org/Historien%20om%20Omega%20422.asp

"Rodrets profil kände vi sedan tidigare. Det är en konventionell NACA 0012. Kölprofilen har däremot varit ett frågetecken som Peter nu rätade ut då han inför sitt framträdande sökt i sina arkivgömmor och till slut hittat hemligheten om Omega 42:ans kölprofil - en unik N-profil:

"Det är en kombination av en NACA 64010 (Anm.: NACA=National Advisory Committee for Aeronautics, en federal amerikansk myndighet som främst under 30- och 40-talet utförde forskning om effektiva vingprofiler) och en Wortmann (Anm.: Professor F.X. Wortmann var under många år chef för tyska Institue of Aerodynamics and Gasdynamics i Stuttgart och är världsberömd för sina fina vingprofiler för främst segelflyg). Det är NACA 64010 i början och från halva profilen bakåt är den gradvis övergående i en Wortmann. Jag lade dom här två på varann och så gjorde jag en egen profil, en N-profil. Den är lite fylligare akter om där den är som bredast - den går inte in lika snabbt, och är alltså mer lik de här laminärprofilerna som man faktiskt använder idag. Vi valde en sådan profil för att vi skulle ha så mycket volym som möjligt. Men det rör sig inte mer än om några millimeter på vardera sidan, så jag tror att ytfelet kompenserar alltihopa...

Procentuellt är den (Anm.: i bredd av kordan) 9,33 procent upptill och 12,2 procent nertill, 10 cm från botten, vid raka generatriser. Om man säger att det är en kombination mellan en NACA 64010 och en Wortmann 10 procent så hamnar vi rätt. Jag har tabellen på den, men det är svårt att hitta det exakta ursprunget. Det rör sig hur som helst bara om millimeterskillnader mellan de två. Lite tokigt var det kanske att vilja göra något eget, men resultatet är helt OK."

Translation:

"The rudder design is well known. It is a conventional NACA 0012. The keel-profile, on the other hand, has for long been a questionmark that Norlin now straightens out. Deep in his archives Norlin found the drawing of the keel-profile of the Omega42. It is a unike N-profile.

It is a combination of a NACA 64010 ( NACA=National Advisory Committee for Aeronautics, a federal American authority that mostly during the 30- and 40-performed research on efficient wingprofiles) and a Wortmann ( Professor F.X. Wortmann was under several years manager of the German Institue of Aerodynamics and Gasdynamics in Stuttgart and World-famous for his fine wingprofiles for mainly airoplanes). The keel of Omega42 is a NACA 64010 in the front and from half the profile and backwards it is a gradually transformed into a Wortmann. I put these to profiles on top of each other and made a profile of my own: an N-profile. It is little more volymnous after its maximum beam. It does not go that fast and is more similar to the laminar-profiles that one in fact uses today. We choose this kind of profile to get as much volume as possible. But it doesn't differ more than some millimeters on each side. Procentually is it (beam divided by corda) 9,33 percent in the upper part and 12,2 percent in the lower part, 10 cm from the bottom of the keel, using straight generatrices. If one says that is combination of a NACA 64010 and a Wortmann 10 percent, on gets it OK. I have got the table of it but it is hard to find its exact origin. However, it does only differ millimeters between the two profiles. Perhaps it was a little bit strange to do a profile of your own, but it works OK."

Regards,
Booster

[Petros]

Interesting thread, but no one has answered the question.

Does any one have a foil section they would recommend for a rudder?

My inexperienced preference would be the 12 percent NACA profile, and I would not go too high an aspect ratio.

The AR issue was brought up early, and I have often wondered why they would use such high aspect ratio rudders. They stall too easy and are vulnerable to damage. I have had bad experiences with stalled rudders. It seems basic and stupid simple to me, especially on a cruiser, that they would put such a high aspect ratio rudder on a sail boat. The difference in rudder drag can not be that large compared to the keel and hull. And in rough seas, the stall resistance of the lower AR seems to be would be an advantage.

[fng]

I used naca 64-012 for both the keel and rudder on my last yacht with fantastic helm from 8 - 19 knots, My mates sportboat has an eppler 836 rudder which is also great - the data shows the eppler to be a more forgiving section and more lift. I've sailed on boats with 0012 rudders and they truely are a barn door in comparison