Lambda sheeting

  • 14 Dec 2014 16:50
    Reply # 3169993 on 3169698


    This forum is good place to discuss new forms of sheeting (such as you are using), as they may be of general interest, but if you want to move on to more specialised wingsail topics, I suggest that you start a new topic in

  • 13 Dec 2014 18:00
    Reply # 3169769 on 3169721


    I added 2 views of the junk wing demonstrator showing the sheets and span (thin black lines). I wanted to add a scheme but it was not in the proper format. I have a span between the end of the batten and the end of the wishbone part (70%, same batten). The spans of a pair of batten are linked by a span (as standard), but the top batten which is alone. I connected the spans and sheets with rings (adjustable but not running free).  

    As the inter batten span and the sheets are more forward they don't trap in the rear of the battens. Both spans ( intra and inter batten) are too short (when not reefed)  to get in the battens' rear. The difficulty should be divided at least by 2, I think. 


  • 13 Dec 2014 16:14
    Reply # 3169721 on 3169698

    Bonjour Eric,

    You can add jpg illustrations into the Technical Forum illustrations photogallery. Just click on the upload button.

    So as I understand it, as well as having a span between each pair of battens, in a common form of junk sheeting, you would also have a span at the ends of the first span, connecting it to two points on the batten. At first glance, this would appear to need much more drift between the sail and the deck blocks, when the sail is reefed or furled. Both spans would need to be running, with thimbles or blocks at their connection points with each other and the sheet, to allow for the changes of angle on different points of sail and different amounts of reefs - no problem there.

    The biggest problem I see is that most people, having tried port and starboard sheets, get rid of them as soon as possible because of all the fiendishly clever ways they find to get trapped behind the ends of the battens, and because the difficulties of getting them untangled. With your span-on-span arrangement, are these difficulties multiplied by a factor of two; or of two squared, I wonder? 

  • 13 Dec 2014 15:07
    Message # 3169698


    This topic was initiated around Mingming's change of owner to my benefit.

    I'll start from the beginning to try and explain my approach.

    I have no junk rig background. As Roger's friend and Roger's book's translator to French I was introduced to junkrig. My background is much on Bermudian rigs, old gaffers... 

    The evolution of junk rigging in western countries by introducing stiff (articulated or not) battens puzzled me. My engineering back ground tells me that soft and stiff hardly coexist and that stiffness leads to stiffness. 

    The issue is that with "classical" junk rig and flexible battens the more wind you have the more camber you have. Unfortunately cambered sail are efficient in light wind and flat sails are efficient in high winds. 

    I tried and find a flexible solution that would, at least, maintain the same camber independently of the wind force.

    My first idea was to forward the sail to have the mast at the level of the drift force (one third of the profile). It would use the forward part of the batten (the most important) to flatten the sail when the wind forces and by reducing the effort on the sheet reduce the cambering effect on the rear part of the sail. 

    The second idea was to forward the sheet on the batten, let say to one third of the leech, The rear part of the sail would counter the flexing effect of the sheet on the battens. In high wind it would introduce a non optimal S shape of the rear part of the sail. 

    The third idea was to use two sheeting points on the batten, one at the leach and the other one forward. The penny had dropped... 

    The two sheeting points would be linked by a sling and the sheet would be attached (free or not) on the sling.  

    The "price" to pay is to have a starboard sheet and a port sheet. 


    PS : Sorry I don't know yet how to add a file or image.  

       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

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