Split rig - luff, leach, sling point, downhaul...

  • 01 Nov 2016 17:41
    Reply # 4359224 on 4195606
    Anonymous member (Administrator)

    Scott,

    frankly, I would not be much concerned about the orientation of the cloth. The load in a correctly made (and set) junk sail is extremely light, compared to that on Western sails. As the photo of your model shows, the sailplan has been designed (or adjusted) to set even without any cloth fitted. My guess is that the correcting forces from any parrels are light.

    However, when a junk sail is rigged and sheeted in for close-hauled sailing, some device to keep the yard peaked up will be needed. On your fairly hi-AR sail like this, it should be easy.

    By contrast, my wide, low-balance sails really depend on the THP and YHP to set well. By moving the halyard’s slingpoint and the YHP aft of the middle on the yard, the needed forces are now moderate. Even on these sails, there is very little load on the sailcloth, thanks to the cambered panels and the stout boltrope around the whole sail.

    Arne


    Last modified: 02 Nov 2016 15:08 | Anonymous member (Administrator)
  • 01 Nov 2016 17:18
    Reply # 4359124 on 4195606
    Deleted user

    Please direct me to the 'child's table' for rig doodling.  Imagining a cambered-panel-split-junk conversion of a local, fin-keel day-sailer I did the following:

    1.  Placed the mast in the same location as the original.

    2.  Drew the jibs and main panels to approximate the size of the originals.

    3.  Drew a halyard sling-point in about the middle of the yard.

    4.  Came up with an aspect of about 1.0 in order to achieve about 10% bury:  21 foot mast (above the deck) with just over 2 feet of bury from the mast step to the deck.

    Two questions

    1.  Is it idiotic to proceed like this without maths?

    2.  Does a low-aspect rig really result in poorer upwind performance than a higher aspect rig?  I've never heard an acceptable rationale for that assertion.

    Warm regards,

    Steve

    Link to photos of the original and my doodle.

    Original marconi sail plan:

    My rig doodle:

    Besides maths, I'm also incapable of inserting a photo into this post!

  • 01 Nov 2016 11:13
    Reply # 4358630 on 4195606

    I've just one practical point to observe, about the angle at the peak of the sail. A previous rig drawing shows an angle greater than 90, whereas your model shows an angle less than 90. I try, unless other factors are more important, to get the peak angle as near to 90 as I can, so that the warp and weft are lying along the leech and head of the sail. I reckon this makes for less bias loading and distortion of the cloth at this, one of the more highly loaded areas of the sail.

  • 31 Oct 2016 16:47
    Reply # 4357473 on 4195606
    Deleted user

    I made model that I can manipulate at will - it's all about short sections of rubber tube, split lengthwise, with two holes drilled close together.  The tube can slide up and down the battens, and the string is threaded through the holes.  With a little tape to tighten up the splits if needed, there's plenty of friction on both the battens and the string. 

    The result is the model below.  It's got a halyard, lazy jacks, three downhaul/batten parrels, and one fixed yard parrel.

    My current question is regarding the yard angle as it blends into the luff of the upper panel.  Intuition says make it all smooth looking like in the model.  I'm thinking about Slieve's comments regarding wingtip vortexes.  Any thoughts out there on that?

     

     

    Last modified: 31 Oct 2016 16:57 | Deleted user
  • 23 Aug 2016 13:24
    Reply # 4205599 on 4195606
    Deleted user

    Slieve,

    It'll be impressive next year when two men with the over a hundred years of combined experience finish in the top 10% of the RTI, one napping, and the other sipping coffee and flipping through an old copy of JRA Magazine.  Then we'll know the split rig has truly arrived.  This geriatric ploy of yours is brilliant marketing.

    I've finally got my head wrapped around the batten parrel/downhaul and the overall way the rig can drape.  I think that's probably a good description - it drapes.  Thank you for all the clarification.  I'll rework the model this winter and post some images.  The way things are going right now, I don't think I'll be making the sail for another two years -  I figure I have about 1000 -1500 hours (no joking) of interior and structural work before she goes in the water.  It hurts to be off the water for that long.  But needs must.

     

    Last modified: 31 Oct 2016 15:59 | Deleted user
  • 22 Aug 2016 08:54
    Reply # 4203666 on 4195606

    Hi Robert,

    For the main panels we used 7% camber at 37% chord for panels 2 to 5, and 5% camber for the top panel. This was only a fraction more than we used for earlier rigs.

    It may be good to increase this figure, but it is never a good idea to change two variables at the same time as you will not know if either change has been beneficial. It is close hauled performance we are trying to improve and theory suggests that it is the jibs which effect this the most, and this seems to be the case in practice.

    The new 175 sq.ft rig seems to produce a similar performance on the Splinter hull as the original 220 sq.ft. rig. The original biggerr rig would be ideal on a slightly bigger boat. There may yet be more power to be obtained from this rig.

    Cheers, Slieve.

  • 21 Aug 2016 17:50
    Reply # 4202918 on 4201510
    Slieve McGalliard wrote:

    As the split junk was a completely new idea I was fairly conservative with the jib parameters to start with, but it would seem we can push things further. The 12°/ 10% sheeting angle/ camber seems to set well and give even better lift/drag, and as there is no point in not getting the best L/D ratio even on a cruising rig then it seems to be the way to go.

    Hi Slieve--I'm curious if the specs of the "mainsail" section of the lower panels were changed?

    rself

  • 20 Aug 2016 00:44
    Reply # 4201510 on 4195606

    Scott, you wrote, “is it strictly for the young steely-eyed edgy racers that you and Edward have become?”

    Is this the image we project? Ouch!

    Young? I've been receiving my pension for over 20 years. Steely-eyed? Both my eyes are scheduled for surgery in the next 2 months to clear my vision. Edgy? I drive in the middle of the road. Racers? My last serious boat race was over 35 years ago. Currently I am only competing in the human race, and not very successfully. Edward was probably born about the same time as I was, so I think you may have got the wrong impression. My wife laughed when I read out your words above.

    The batten parrels stop the battens moving forward and if you try that with the model you might be surprised at how it works. I sometimes just hoist the sail and ignore the downhauls as the batten parrels are short and go sailing. I do recall sailing on one day and only handling the halyard and sheet. In action nothing seems critical.

    I drew the batten rise at 5° for aesthetic reasons, but reckon none is needed. The bottom batten has to be at least half of the panel depth above the turning points at the foot of the mast for the spanned downhauls to work, so there is no problem seeing under the rig. On Poppy I simply have ring bolts at the base of the mast for the downhauls, so no great tension can be set from the cockpit.

    The split junk was conceived to overcome the inefficiencies of the accepted cruising junk rigs. It has been entered in the ISC class division of the Island Race which is for club cruisers to have a fun day out, simply to get a good comparison of performance with similar sized cruising boats. Unfortunately a few sailors do race to win and buy high tech sails and some even import professional sailors in their lust for line honours. The only concession to racing has been to make all panels split on Amiina for local club racing. There is no reason why the rig should not ocean cruise like a Bermudan rigged boat if the normal considerations for a jib are observed. I still recommend that the storm sail panels are not split for serious cruising, until we know more.

    As the split junk was a completely new idea I was fairly conservative with the jib parameters to start with, but it would seem we can push things further. The 12°/ 10% sheeting angle/ camber seems to set well and give even better lift/drag, and as there is no point in not getting the best L/D ratio even on a cruising rig then it seems to be the way to go. It might be worth considering more, but I haven't tried to draw that up yet. We're still learning.

    I guess that for serious cruising UV would be a greater consideration than strength of material. The 2.2oz nylon we used has a ripstop thread which is similar to the normal thread in a 6oz cloth, so should be strong enough for the sort of sailing that Edward is doing. There just doesn't seem to be any stress on the material as the luff and leech carry the stresses, and they have fairly conventional construction.

    I'm off to bed (to rest my steely eyes),

    Cheers, Slieve. 


  • 18 Aug 2016 14:17
    Reply # 4199053 on 4195606
    Deleted user

    Ah -thank you Slieve, that makes much more sense.  So if I have it right, by adjusting tension on only the downhaul, I can create a batten angle anywhere from -10° when it's hanging all slack and ugly, to probably up around +25° when it's tensioned to the breaking point, all of which is really controlled by the lever arm between the sling point at 50% and the downhaul at 33%.  So once I cut the sail and I'm on the water, I'm guessing the task is to adjust the downhaul/halyard tension to remove the wrinkles.

    I get that the 10° batten angle isn't needed as much with the split rig, though I imagine you now lose a little visibility under the rig.  Am I right in thinking that the motivation to decrease the angle is to remove even more of the tensions within the rig since 5° is achieved with significantly less effort?

    With regard to the increase in jib camber and the lighter sailcloth, would you recommend that kind of change to an offshore cruiser, or is it strictly for the young steely-eyed edgy racers that you and Edward have become?

    Last modified: 18 Aug 2016 14:27 | Deleted user
  • 18 Aug 2016 00:31
    Reply # 4198094 on 4195606

    Hi Scott, You're on the right track but haven't found the right conclusion, yet.

    1. In a model with jib luff strings and main leech strings only, when hung from the 50% point alone it looks awful, with the battens hanging forward and the clews hanging low.

    2. Tie a downhaul at the 'boom' 33% point and as you tension it downwards the rig perks itself up and comes into the shape you want. You then 'tweek' the lengths of the luff and leeches of the top tapered panels you will eventually arrive at the rig you want. It is the length of these edges and the angles they make with the battens and yard you want to measure to balance the shape and use for the sail plan.

    The tension of the downhaul seems to set the shape, but in practice I originally used long batten parrels which tied off just behind the 33% point on each batten to hold the shape with gravity to help, and then the later combined downhaul/ batten parrels did the job better. I have set the downhaul/ BPs quite short so that they are only just slack when hoisting with the result that simply hauling on the halyard raises a fairly well shaped rig which only requires a light tug on the downhauls to tidy up.

    Just a couple of points about how things are developing. On Amiina's new rig the batten rise has been reduced to 5° as the split rig does not suffer from stacking problems and the high balance means that there is little risk of the 'boom' hitting the water when heeled. The high balance also means there is no need to swing the rig across the mast when off the wind so the steering loads are low. The sheeting angle and camber in the jibs have been increased from the original planned 8°/ 7% to the latest 12°/ 10%, which seems to be a move in the right direction with additional drive. A much lighter material at 2.2 oz ripstop was used, and seems to be strong enough.

    I hope this helps, Cheers, Slieve.


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

                                                              Site contents © the Junk Rig Association and/or individual authors

Powered by Wild Apricot Membership Software