Princess Taiping: quilting & camber

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  • 28 Nov 2011 08:39
    Reply # 761013 on 759836
    Anonymous member (Administrator)

    I see. I can copy and paste photos from the web, like from my personal album on this site, but not directly from my pc. Still, that can be useful. It just appears that I must preset the size of the photo first. The ugly mug you showed us Karlis was having a great, but cold time, sailing at 30th December...

    Cheers, Arne

    PS: Now I opened a photo in my album befor copying it. That seems to get the size right

    PPS: Well that appeared to be oversize. Whe downloading the photo to my pc, nothing is cut away however

    Last modified: 28 Nov 2011 08:45 | Anonymous member (Administrator)
  • 28 Nov 2011 02:06
    Reply # 760796 on 760534
    Arne Kverneland wrote:

    Stavanger, Sunday

    Could anyone give us a crash course in how to insert a photo in a posting, like that above? That could be very useful.

    Arne


    Arne Kverneland, Norway's photo Hi Arne.  I can't speak to if this will work on any computer, but I'm using a Chrome web browser on Ubuntu.  To insert an image I highlight the image on whatever web page, copy it (control-C or select from right click options), then paste it (control-v or again from right click options) into the forum edit window.  It seems to work OK for me, if you can  see the accompanying photo of a sailor, whom I believe is sailing a junk rig if the satisfied look in his face is any indication. . .
  • 27 Nov 2011 09:58
    Reply # 760534 on 759836
    Anonymous member (Administrator)

    Stavanger, Sunday

    Could anyone give us a crash course in how to insert a photo in a posting, like that above? That could be very useful.

    Arne

    Last modified: 27 Nov 2011 10:00 | Anonymous member (Administrator)
  • 27 Nov 2011 07:40
    Reply # 760492 on 759836
    Er, perhaps what we're seeing here are multiple Hong Kong parrels!
  • 26 Nov 2011 19:01
    Reply # 760193 on 759836
    My guess is that the mizzen is made in the same way, but is empty of wind, being sheeted to the lee side instead of to weather as it should be; it is just hanging loosely. 
    It looks as though extremely stretchy cloth was used, and the diagonal lines are the seams, which have been sewn too tightly, or reinforced. 
    I, too, can see no aerodynamic benefit in making sails this way. I think most western sailors of junk rigs  are agreed that we are looking for a smoothly cambered lee side to the sail, though we might disagree on the shape and amount of the camber, and how to achieve it. 
  • 26 Nov 2011 18:29
    Reply # 760177 on 759836

    Hi Karlis

    From an aerodynamic point of view the type of sail construction on Princess Taiping would appear to have little to recommend it as seen through western eyes. The overall shape of the sail is basically flat and it is just that the area is covered with lots of small bumps. The bumps may increase the pressure differential across the cloth, but it may also simply increase the form drag and lower the lift/ drag ratio of the sail.

    Off the wind this sail should have plenty of drive, just like any other with well spread canvas, but close hauled there seems little to produce a decent lift/ drag ratio to give good wind-ward performance. Looking at the flags in the picture there seems to be a reasonable breeze blowing but looking at the wake the boat is not making much speed.

    Having only seen a few photos of the boat my guess is that they are using a very weak material and to make up for its lack of strength have reinforced it with heavy stitching at the seams or have sewn strengthening tapes over the surface. That, along with close batten spacing would mean that there would only be light stress in any area of the cloth.

    It looks attractive, but I can’t think of anything aerodynamic to recommend it.

    By the way I did not intend to say that only the front side of the camber produces lift. Any cambered airfoil can produce a lifting force, perpendicular to the surface, so the forward facing slope is producing a force tilted forward and helping the vessel to move forward, but a force produced on an aft facing slope will tend to slow the vessel down. Low pressure generated near the luff will tend to increase the upwash and therefore enable the boat to point higher, and conversely rigs with a flat, or even worse S-bent, entries will not point well.

    Sorry I can’t give a clear cut answer, but I hope this has been of some help.

    Cheers,  Slieve.

  • 26 Nov 2011 13:51
    Reply # 760076 on 759836
    Deleted user

    I think the vortex theory as discussed in early JRA newsletters got itself discredited when Arne started cambering his sails. What I can tell from my reading of Chinese maritime history, ocean going or coastal junks north of Hong Kong used quilted sails. I think the purpose of quilting was to take the strain out of the weak sail cloth and not for aerodynamics. They would have relied on twist to get lift, much like Hasler McLeod did with their flat panel rigs.


    Hong Kong junks were ahead of the game as they at some stage noticed better performance by making bigger panels without quilting. Without the quilting lines the sail can not hold its shape, so they invented Hong Kong parrels. The bigger panels enabled the cloth to billow out into a curve and thus superior aerodynamic lift.


    Thats my take on it and am interested to read what others say on the subject.

    BTW,  I forgot how to post pictures here, glad someone has done it!

    Last modified: 26 Nov 2011 13:52 | Deleted user
  • 26 Nov 2011 04:25
    Message # 759836
    Hi, this is sort of a question for Slieve or one of the areodynamic specialists.
    I've read a few posting members talking about "quilting", by which i think they mean camber on each panel, but the mental image of quilting made me think about multiple quilted sections per panel.

    If you look at the photos of the Princess Taiping,  for example:



    http://www.latitude38.com/lectronic/img_lectronic_480/2008-10-15_4341_Princess%20Tai%20Ping%20Junk.jpg

    http://imgs.sfgate.com/c/pictures/2008/10/15/ba-junk16_ph1_0499302054.jpg



    The panels on the main do not show smooth camber.  Are these the sew lines on the quite blown-out sailcloth?  Or are they some sort of full-sail diagonal parrels designed to induce a true quilting effect (multiple quilt sections per batten panel)?  They do look somewhat intentional, as they are missing on the mizzen.  

    When I saw this, it made me think of some articles I didn't fully understand, including articles about high-lift vortices, and Slieve McGilliard's "some thoughts" article on the split rig that discusses how only the front side of the camber generates lift.  

    What effect would inducing a multi-quilted effect like the Princess Taiping have on lift?  Would it create lots of little lift vectors over the whole sail, instead of just at the fore of the sail?  Or would it create some magically advantageous vorticies?

    I submit it to you for comment.
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