Todd,   It took some thinking before I got it. Also a bit hard to tell since puffs are not that easy to see on the video. My analysis:   Dyna rig is more sensitive to correct angle to wind than traditional crab claw. Airflow must remain attached to the lee side of the sail to get the best lift. In the beginning dynarig moves slowly so I guess the sail is too hard on the wind and stalled. At the end when it turns upwind dynarig accelerates and starts moving very fast. Based on what you said about wind direction it probably had good wind angle to sail and looked like having a lot of power at the end of the video.   Traditional sail that looked like crab claw is a different animal. Based on the wind tunnel tests by Marchaj it is not sensitive to correct angle to the wind and has best lift coefficient when the flow is not attached any more and the sail is generating vortexes. Also according to the same tests crab claw is not at its best close hauled. In the beginning of the video traditional crab claw moves the boat very fast on a reach and tight sail but less so at the end when the boat turns to wind. It seems like you just proved the Marchaj wind tunnel tests :) At least your two rigs side by side acted in accordance with the results of Marchaj.   Arto --- On Wed, 6/9/10, tsstproa <bitme1234@yahoo.com> wrote: From: tsstproa <bitme1234@yahoo.com> Subject: [harryproa] Re: Predicting performance? To: harryproa@yahoogroups.com.au Date: Wednesday, June 9, 2010, 8:08 PM   Arto. Words get tricky to me. I know What I'm tring to accomplish and know the feel i'm searching for. Sounds hokey I know. Thanks for bearing with me though. As far a sheet angle and wind wangle look at this clip . wind is coming from about upper left had corner. Look at both trailing edges of each sail. Look at the leading edge of dyna rig. Watch as each boat gathers speed and there reaction to puffs. Look at the finishing angle as both as they approach the beach at end of clip. http://www.youtube.com/watch?v=s-AzmNEj0EE&feature=related Whats your explanation? Todd > --- In harryproa@yahoogroups.com.au, Arto Hakkarainen <ahakkara@> wrote: > > Arto: > > > > Do you have any idea what the AoA of the wind to the sail would be? Theoretically and based on old experience the sail should have CoE forward of mast when the flow is attached to the sail. Then the sail would need to be sheeted from forward. If stalled the CoE probably moves closer to the mast. Some videos you sent and your own description would back this theory. I might as well be wrong guessing here at my comfy chair :) > > ++++++Not a clue. On the rigid wing the leading edge at times seems straight into the wind on my JR I have seen it guesstimate 15-20 degrees to the wind. I think on my JR this is due to the camber not being as large and efficiently shaped being shape in the cloth vs becambered held by battens or a preshaped wing. The CoE of sail is foward yes and the CoE can be controlled precisely. Its the configuration of the sail that allows the sheeting arrangement along with its rigid camber at center chord and the whole sail rotating when sheeted that provides its uniqueness. > > Todd > > Arto > > >

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