Low-peaked, balanced sails vs. High-peaked unbalanced sails

  • 08 Feb 2013 21:16
    Reply # 1202876 on 1202710

    David, it may be that we are not thinking along the same lines. I don't see a flat top as a low drag top. I believe we need the highest point of the sail to be as far aft as possible, perhaps like the top edge of a crab claw but with the sail centre line at about 25deg. I know that this gave me good performance with model aeroplanes, and I well remember re-calculating the fuel burn on De Havilland Tridents when they had to change from out swept tips to straight tips due to stress cracks.

    The shape I drew for Poppy and modified for Amiina to work with the simplified single top pamel are my early attempts at the tip shape I want. To achieve this with your fanned sail would require a very long, and possibly strong first batten. It might be worth looking at a few sketches.

    I've often wondered about curved yards, but have always rejected the idea as they would be awkward to stow. Anyway, the beauty of the rig is that there is so much to play with.

    By the way, I'm a bit out of circulation for the next couple of days as I've 2 experimental model boat rigs to build before a day's racing on Sunday, when it is supposed to be heavy rain and cold winds. Yes, I know I'm mad.

    Cheers, Slieve

    Last modified: 08 Feb 2013 21:18 | Anonymous member
  • 08 Feb 2013 18:27
    Message # 1202710
    Slieve McGalliard wrote:

    Even if you don’t want to risk the split rig, the van Loan rig also has high balance and downhauls and has the same convenient sailing characteristics and low stress advantages. For those who are happy with a flat sail then it would be well worth considering. Where some believe a high peaked yard is important there are also those of us who believe the longer tight leech [luff?] and the shallow yard angle give less vortex/ tip drag which can be a major inefficiency. I would not be surprised if a van Loan rig with about 7% camber would give good performance, even without a split, though it may need chafe reinforcement in way of the mast. The problem is that I am not prepared to try it myself as I’m very happy with the rig I’ve got.

    Cheers, Slieve.

    My problem with the low peaked yard is that I tried it, on Ivory Gull (lightly cambered panels + hinged battens), and while the performance was Good Enough, to borrow Kurt's phrase, it was by no means sparkling. I do think that it has to be combined with a lot of camber (as on Aphrodite), or a split rig, otherwise the performance is likely to be dull. On my present rig, when very deeply reefed, I can haul the sail aft, and peak up the yard with the YHP; or I can let the sail go forward, and ease the YHP to let the yard down to a shallow angle. The former is very much the more powerful. It seems to me that the camber introduced by fanning introduces so much more lift that the theoretical decrease in drag that can be obtained by decreasing the yard angle is of lesser importance. 
    What would be very nice to try to achieve is to get a very flat top to the planform, right aft, so as to decrease the vortex/tip drag, at the same time as keeping the yard well peaked up, so as to increase the camber through fanning. Would a curved yard do this, I wonder?  Of course, the Fantail planform goes a long way towards achieving the ideal, with the leech of the top panel near to horizontal, due to the yard being somewhat shorter than the top batten.
    Last modified: 08 Feb 2013 19:30 | Anonymous member
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