Comments invited on schooner sailplan

  • 10 Apr 2012 03:13
    Reply # 885800 on 872150
    Deleted user
    I assumed the yard sleeve is to overlap the top panel. Since the luff edge is only 10cm long on that panel it is pretty well swallowed by the sleeve as is.

    I'm surprised the draft in one panel would make enough difference to boat speed.
    FWIW Arne's sails in pictures always look very full (powerful), even though he cuts his sails with only 4% camber (but calls it 8%), while your shelf footed sails always look less full, despite being cut at 6%. Is a dilemma. I had my sail plan with barrel cut a few days ago, but changed to tucks because, it uses more camber (on paper).

    Maybe Footprints needs more sail area.
    Last modified: 10 Apr 2012 03:14 | Deleted user
  • 09 Apr 2012 19:51
    Reply # 885540 on 872150
    You might consider moving the draft a bit further forward on panel 3, Gary. Footprints is not sailing as fast as she should, and we suspect that it's because the draft is too far aft in the equivalent panel.
    Also, are you sure the yard sleeve is wide enough? It would be better to have a shallower angle between the sides of the pocket, to decrease the peeling stress on the stitching.
  • 09 Apr 2012 15:58
    Reply # 885377 on 872150
    Deleted user
    After several redraws, panel drawings are here.
    Decided to make camber by sewing tucks. Top 2 panels are tuckless and near flat, because, Odyssey III feels quite elastic, could almost make leotards with it..
    Last modified: 10 Apr 2012 06:07 | Deleted user
  • 03 Apr 2012 04:37
    Reply # 880545 on 872150
    Deleted user
    Well, at least I got to operate a real live (model) junk rig.
    I think I know how they work now...
  • 02 Apr 2012 20:13
    Reply # 874711 on 872150
    Anonymous member (Administrator)

    Don't worry Gary,

    you have built a great boat, and that rig looks fine too. Its AR of just below 2.0 is not extreme in any direction and I see no reason why it should not work, Go for it!

    Arne

  • 02 Apr 2012 15:27
    Reply # 874497 on 872150
    Deleted user
    Made my model rig 1:20 scale. Without the sail cloth, since cambered sails don't control the batten position much, I wanted to see if the yard/battens/boom with bolt rope can set the right shape without HK parrels. The idea being to do away with HK parrels, which press into the sail, spoiling the shape at the luff.
    Pictures of my model are here.

    First I tried with just 3 lines holding the whole rig up: Halyard, Yard HP and Throat HP. Luff wouldn't set completely straight.
    Added a tack parrel, improvement but no dice.
    Shortened the yard, made no difference.
    (Tried adding a HK parrel (sticky tape) to one panel, fixed one batten but all battens need them.)
    I also tried threading the throat parrel through a few more battens, becoming a running luff parrel, but it pulled battens into different positions, or maybe that is a problem with my rough model.

    Then I added a boom downhaul, pulled tight and everything lined up! Amazing.

    Conclusion so far
    I don't know how much downhaul tension is required on a full size rig, probably too much!
    But the sail cloth in the top 2 panels could play a part in lining up the top 2 battens if they are flat in the thin forward end of the panels. If this is the case, 3 running lines on the yard, combined with tack parrel and downhaul makes for a well set rig without HK parrels.

    The standing luff parrels omitted from my model are still needed,  they keep the rig together while raising sail, because before the throat hauling parrel can be tensioned, the rig goes out of control without them.

    Last modified: 02 Apr 2012 18:31 | Deleted user
  • 02 Apr 2012 08:26
    Reply # 874315 on 872150
    Well, let's say that besides the heeling effect, the considerable spanwise flow up there might be parallel with the second panel down, and it can be cambered too. It will all work. 

    That there are actually benefits to flat panels, I continue to believe, (but not with a missionary zeal, quite...)

    Kurt
    Last modified: 02 Apr 2012 08:27 | Anonymous member
  • 02 Apr 2012 07:57
    Reply # 874296 on 872150
    Deleted user
    Kurt,
    Top 2 panels being flat, fair enough (with only enough rounding to allow for yard bend).
    But the view from my armchair (which may not count for much either) sees when the boat is heeled 10 to 15˚, panel #3 becomes horizontal and parallel to airflow. So full camber might work on it.
  • 02 Apr 2012 06:44
    Reply # 874237 on 873996
    Kurt Jon Ulmer wrote:Hi Gary & Susie,

    Top panels and camber - My intuition and my experience with mehitabel convince me that your top 3 panels would develop a lovely smooth and powerful fanned camber if cut flat. If each of those three panels has camber built in, I humbly suggest that the smooth shape of fanned camber and its effectiveness will be hurt by dips and bumps, especially when reefed down to 3 or 4 panels. Other opinions exist, though.

    Structurally, tight flat sailcloth distributes strain; easing panels out with built-in camber concentrates strain in spars and edges. In the top part of the sail, I'm happiest with flat panels.

    Yard weight - I question altogether the need for lightness in yards. I want ours to lay down when the halyard is let go, and to be bomb-proof against the varying forces when raised up. With 5:1 halyards, I think you may be frustrated getting yours to fall obediently. In tough weather, reefed, the weight of a yard is low, yes? A place to overbuild for confidence, rather than tweak a few kilos for any reason, I think.

    1 1/2% rounding on the head of the top panel of the sail will allow it to lie flat. All yards bend. The worst possible scenario is a straight head to the sail, combined with a flexible yard. The middle of the sail is "starved", the leech goes slack and flogs.

    I see a need for lightness in yards. Heavy spars aloft, thrashing around in a light wind and a confused sea, can be very destructive items. "Bomb-proof" is non-negotiable. After that, add as much lightness as possible. With 3:1 halyards, even my wingsails, without any yards, will drop fully when the halyard is let go, under the weight of the battens. It's scarcely possible to make a yard so light that it won't drop. Even if you helium fill it :-) 
  • 02 Apr 2012 05:59
    Reply # 874226 on 874039
    ... haven't decided how much rounding on the upper panels yet, probably not a lot. I realise for off shore sailing upwind performance doesnt count for much, but we will be doing a fair share of coastal trips, which means beating to weather to get home! So I am a fan of a foil shape or two.


    Me too! With fanned battens like your top ones and flat cloth up there, you create smooth camber, effortlessly. I've been beating with reefed sails quite a bit lately. The air over fanned camber, as I suggested, has no dips and bumps added by tucking or shelving or whatever method. So smooth.  How she schoons...
    Kurt 
       " ...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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