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Debunking Dodgy Sailing Theories

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Oatsandbeans View Drop Down
Far too distracted from work
Far too distracted from work

Joined: 19 Sep 05
Location: United Kingdom
Online Status: Offline
Posts: 329
Post Options Post Options   Quote Oatsandbeans Quote  Post ReplyReply Direct Link To This Post Posted: 20 Oct 11 at 10:47am
Following the great success of the Lee Bow Effect thread ( we can all now see what utter cr*p that one was) I got to thinking about other unsound theories that get peddled around sometimes by those that should know better. 

Well I will start this one off, by a comment from a post that I saw yesterday saying that the benefit of having twist in sails is so that in instable wind conditions at least one section of the sail is set correctly.  Well it is surprising how many sailors hold this view. 

Well here goes- Rubbish- If you think a the sail as a number of horizontal strips, say 4, that due to the twist are at different angles of attack and only one section is set correctly. This means that 75% of the sail area is set incorrectly either not enough angle or too much angle of attack this is obviously very inefficient (and slow). 

The reason that twist works is because the sails have to operate in different conditions at different heights. The effects of wind speed variation, wind shear, and the large effect of the jib on the lower sections of the sail all mean that a sail with no twist will lead to a stalled head and or a undersheeted base. The optimum twist will depend on the boat, the conditions (wind and water) and what the helm is trying to do at the time ( foot, squeeze,or depower). A good indicator of  when the twist is right is streaming of the leach tell tales with the top one one the point of stalling (30%).

Hopefully this will bring some comments and maybe even some more unscientific sailing "theories".

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