Mingming lambda sheeting trials

  • 06 Jun 2019 16:04
    Reply # 7559662 on 4118174

    Bonjour

    During the "semaine du golf du Morbihan I sailed Mingming with the flat sail modified with the lambda sheeting.

    I've improved the system especially by stiffening the forward part of the battens (as recommended in PJR) to prevent the S bending I had on the first trial.

    We had limited wind but we experienced some squally conditions.

    I kept on purpose the two upper battens, as they were originally, to compare the cambers between the all and the new system.

    For the lower battens I used some flexible battens (round section, glass polyester). An other half batten on the forward half doubled the full-length batten. The second batten was taped with grey tape to the main one.

    It seems to be a "quick and dirty" to improve the power of a flat sail but the result is far from optimum. The forward part of the sale remains flat and the curve is limited to the rear of the sail. By comparison the two upper panels were very flat.

    On the positive point the curve remain rather constant when the wind increases and there is a very limited S bending that should not affect the performance.

    The two sheets are easy to handle and don't get catch.

    My headsails background made it sometime unnatural to use the windward sheet.

    On the view the difference in camber between the lower and upper panels is clearly visible. The rear position of the camber is also visible.

    With that more powerfull sail it was possible to sail in light wind, flat sea with the Mingming's old fashion bilge keels. Mingming was balanced and easy to sail. The sail was easy to trim.

    Eric

     

  • 09 Jul 2016 01:37
    Reply # 4120627 on 4118174
    Eric's photos can be seen here.

    It looks like a lot of camber to my eyes, Eric, but I could well be wrong.  Only time will tell, but it's an interesting sheeting system.  Great to see someone else experimenting.

    To put comments on your photos, go to your photo album and click on the photo.  When it comes up as a big photo, if you go down to the bottom left of the photo, you will see the option to put a caption.  Just click on it and fill in the  box.  But be warned - you can only write so much!

    Last modified: 09 Jul 2016 01:38 | Anonymous member
  • 07 Jul 2016 11:48
    Message # 4118174

    Bonjour
    After quite a while I finally succeed to sail in Mingming and by the way, to sail on a junk rigged boat.  Now ,I’m a junky !

    The trip was a short 15 Nm from Dives sur Mer to Le Havre and return on two days with my daughter as crew. The first day was a running with the wind and of course the return was headwind. The weather was so Normandy style with squalls and rain.

    During the winter, I modified Mingming to fitit with a double lambda sheeting. A sheeting system I would like to experiment with wingsails. There is a sheeting system on each tack with two sheeting point on each batten. I left the lower block anchorage well aft on the pushpit. The boom, all battens and the yard were linked to the sheeting systems.

    I keep the old Mingming Hasler M’cLead sail that I completry restiched. To stay conservative, I kept the two first battens made of 30 mm PVC tube with a wooden core and, for the parallelogram’s battens, I used some more flexible cylindrical fiberglass battens (as the one’s used for full battened pointy mainsail).

    The sheeting system was not set properly and the sail twisted too much, especially when reefed. Horizontal and vertical spans were too short. The lower anti-twist span was upside down. I must put more sheeting power in the upper part and less in the lower. The forward parts of the lower battens must be stiffened. In short, there are lots of possible improvements.

    The sail management is impressive: as simple as in the book !

    The lambda sheeting is efficient; it allows a cambered sail in light winds without having too much camber in squalls. The rear of the sail remains almost flat. The two, well aft anchored, sheeting systems never get fooled.

    As I’m used to headsail sheeting I, sometime, trimmed the lee sheeting system instead of the windward one, and surprisingly it worked !

    The forward part of the battens must be stiffened, as expected, to prevent the S-bending described in Fig 1.8 of PJR, specially the port tack, that may provide, on Mingming at low speed, some « interresting » lost of any control at the helm.

    Headwind, the camber, provided by the flexible battens, gives a usefull power on a flat sail in light weather.  I was not impressed by the tack angle but I can’t say if it was due to my lack of experience, to the non-optimised configuration or inherent to the sail. Without any tails on the sail the tuning was rather instinctive, aproximative and probably wrong!

    In these far from optimised conditions we succeed in sailing headwind for 15 miles on a 6.2 meters boat, maintaining progress against the tide, in a single day time. I consider it as a success.

    I don’t know if this technique is promising or not for junk sails. The interest could be to try and remain in the bamboo flexibility spirit of the junk sail as an alternative to the rigid carbon spars spirit.

    There are views in the file “Mingming lambda sheeting”

    I don’t know yet how to put comments under the photos so :

    • -       first photo shows the sheeting system with horizontal and vertical spans.
    • -       Second photo shows the camber of the two lower battens. The forward part of the lower batten is stiffened by a length of 30mm PVC tube.
    • -       Third photo shows the various cambers of the battens: top batten are almost trait; battens 3 and 4, those forward part are not stiffened, are cambered from the leech and batten 5 with a luff stiffener is only cambered in the central zone part.
    • -       Fourth photo shows the twist of the sail headwind. The top panel is almost flattering

    Eric

       " ...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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