Forgot password

Luff parrels - and throat hauling parrels - for cambered sails

  • 13 Sep 2012 09:13
    Quote
    Reply # 1071282 on 1067661
    Anonymous member (Administrator)

                                                                            Stavanger, Thursday

    Graham, it seems to me that you have things very well under control with the use of throat hauling parrel. In an earlier posting you described how you controlled the lowering of the sail by "following" the sail down with that parrel through a clutch. This is exactly how Håvard, the new owner of Edmond Dantes is lowering and reefing his new sail. I think I must install a clutch for it on my Johanna as well.

    As for rise of the boom, this certainly is not rocket science. I have settled on around 10° rise of the boom for practical reasons:

    1. The rise gives about enough view under the boom even when heeling a quite bit on a reach..

    2. The clew is mainly kept clear of the sea

    3. I can still reach up to the clew

    4. It lets me set up the fixed lazyjacks to let the reefed bundle have about 5° rise and still run clear of the sprayhood. With this setup I can tilt the whole sail a bit more aft (or less forward) with the sail reefed and still have the lowest batten a bit clear of the bundle at the leech. This gives a nice and taut leech.

    So there are no ingenious secrets behind this boom rise, at least not in my sails.

    Cheers, Arne
  • 13 Sep 2012 04:41
    Quote
    Reply # 1071178 on 1067661
    Anonymous member
    David's comments about the geometry of a cambered HM sail are interesting.  Arion's sailplan, based on the one used by my sistership Minke with a flat sail, has a tack angle of 80 degrees, giving a boom lift of 10 degrees when the luff is vertical.  It is designed to the standard PJR form (forward diagonal from clew to luff of .99).  Looking at the sail, I think that is what I have but perhaps it is not enough.  I seem to remember Arne using a tack angle of 75 degrees (A boom lift of 15 degrees) on at least one of his sails?  It would certainly be interesting to determine an ideal value for the forward diagonal of the parallel panels on cambered HM sails.

    There may be other reasons for my negative stagger but I am unqualified to say.  It would need an expert like David or Arne to look at the sail and they are too far away!  It is not a disaster though, it has a beautiful shape when the hauling parrels are set up - and practice hauling on the throat parrel when reefing and furling should improve the process.  The throat hauling parrel certainly changes the behaviour of the sail dramatically, it is like taming a headstrong horse with the right halter.  
  • 11 Sep 2012 18:52
    Quote
    Reply # 1069829 on 1069606
    Anonymous member
    Arne Kverneland wrote:
    Annie Hill wrote:Fantail's mast is raked forward by 6 degrees and the battens stack nicely without problem.  I just left go the yard parrel and halliard and down it all comes.  I have put a photo in my profile, in the Fantail album, showing the stowed sail from above.

                                                                          Stavanger, Tuesday

    Annie,

    from the safety of my armchair I can only guess what makes your sail reef so well: From David’s drawing I notice that the boom and lowest batten are shorter than the four next battens (of the same length). This no doubt helps to get positive stagger in the aft end. Further up the fanning effect takes over and will lead to positive stagger (too much in flat sails, I’ve read). Last, but not least, you have rigged your sail with a vertical luff or even with it leaning a bit aft. That is probably a good idea.

    Cheers, Arne

    Arne,
    In fact, the boom need not be so short, from the point of view of sheeting, but the shorter length does help in other ways - keeping it out of the wavetops, for example.
    The Fenix style of extremely fanned sail did have an enormous amount of positive stagger. It made a very poor cruising rig for this reason, whatever it's performance may have been. I've learned from that, and designed a sail planform that builds in as much as possible of the advantage of a fanned shape, without going so far as to build in any of the disadvantages.
  • 11 Sep 2012 18:41
    Quote
    Reply # 1069812 on 1067661
    Anonymous member
    Graham,
    I do wish that your sailmaker had called me over to help in laying out your sail, or at least to have seen the finished product, since I was very close to him at the time.  I've  a hunch that he may have misinterpreted the drawing, resulting in the positive stagger that you're now finding. A pity, but it's water under the keel now. 

    I think that a parallelogram panel needs to be designed with camber in mind, adapting the PJR rules a little. PJR recommends that the diagonal from clew to throat of each panel shall be 1% less than the length along the lower edge. It seems to me that the panel, as it is laid flat on the loft floor before any camber is built in with tucks, broad seam or shelves, should have a diagonal that is 1.5% to 2% less than the length of the lower edge - measured corner to corner, not along the edge. It's difficult to be dogmatic about this amount - it will depend on the amount of camber and the depth of the panel - but I don't see why a HM sail can't have cambered panels if the diagonals are shortened up by rather more than 1%. If I were making such a sail with a generous amount of camber, I'd be inclined to make just one test panel first.

    As for the fantail sail - I took great pains over the design of this planform. I can report that on Tystie, as on Fantail,  the aft ends of the sheeted battens stack nicely one above the other, without having to take any particular care over how the sail is lowered. I don't need any positive stagger, since the deck blocks are a long way aft of the leech, but I would expect there to be some, if the sail were to be cut flat, rather than with 6% camber in the lower panels.
  • 11 Sep 2012 14:45
    Quote
    Reply # 1069606 on 1069097
    Anonymous member (Administrator)
    Annie Hill wrote:Fantail's mast is raked forward by 6 degrees and the battens stack nicely without problem.  I just left go the yard parrel and halliard and down it all comes.  I have put a photo in my profile, in the Fantail album, showing the stowed sail from above.

                                                                          Stavanger, Tuesday

    Annie,

    from the safety of my armchair I can only guess what makes your sail reef so well: From David’s drawing I notice that the boom and lowest batten are shorter than the four next battens (of the same length). This no doubt helps to get positive stagger in the aft end. Further up the fanning effect takes over and will lead to positive stagger (too much in flat sails, I’ve read). Last, but not least, you have rigged your sail with a vertical luff or even with it leaning a bit aft. That is probably a good idea.

    I guess you have finished the setting-up work and debugging of Fantail’s rig now. Could you describe what parrels you are using now, standing as well as running?

    Cheers, Arne
  • 11 Sep 2012 12:10
    Quote
    Reply # 1069520 on 1067661
    Anonymous member
    My comments about mast rake only apply to boats with Hasler-Mcleod type sails.  As I understand it, flat fanned sails have a lot more positive stagger than the standard HM sail and the cambered Fantail sail seems to benefit from this (as well as from the short, convex luff).  Perhaps it is the best shape for cambered sails, perhaps the standard HM sail is less than ideal for cambered sails.  However, the Batwing (my black sail) is probably going to outlast me so I will just have to keep working on it.  I'd like to get to the stage where I can reef or furl it in a squall at night without getting into a tangle.  To that end, I am encouraged by Paul Fay's comment that his plastic-hose-covered standing luff parrels significantly reduce friction, so that will be my next experiment.
  • 11 Sep 2012 07:11
    Quote
    Reply # 1069410 on 1067661
    Anonymous member

    Hi All, Since writing the Article about Ti Gitu and how we are making the cambered panel sails work we have been out experimenting several times.

    First I agree that the way we have the batten parrels does cause friction when hoisting but the use of the plastic tube almost completely overcomes this. I must point out that our masts are painted metal which may have less friction than other materials and that this plastic is fairly hard. It is domestic water pipe, not the soft type of plastic pipe normally used aboard yachts.

    With the batten parrels holding the battens back we now have negative or slight positive batten stagger. With also having cut the boom and first batten shorter there are no more problems with the sheets fouling.

    Since starting to experiment with a throat hauling parrel and also moving the fall of the yard hauling parrel to the forward of the yard, the sail can now be set perfectly. We have totally removed all the Hong Kong parrels.

    Paul

     
  • 11 Sep 2012 01:42
    Quote
    Reply # 1069097 on 1067661
    Anonymous member
    Fantail's mast is raked forward by 6 degrees and the battens stack nicely without problem.  I just left go the yard parrel and halliard and down it all comes.  I have put a photo in my profile, in the Fantail album, showing the stowed sail from above.
    Last modified: 11 Sep 2012 02:16 | Anonymous member
  • 11 Sep 2012 00:27
    Quote
    Reply # 1069044 on 1067661
    Anonymous member
    Arne, I think you are right about the forward mast rake contributing to the negative batten stagger, especially if the tack is hauled back until the luff of the sail is parallel to the rake of the mast or more.  The battens then need to move further aft than they otherwise would to develop positive stagger.  Fellow JRA member, Don Halliwell, had a cambered sail built by Chris Scanes that is a scaled down version of my sailplan.  He has a vertical mast and he has positive batten stagger.  (It is also built in Dacron with the shelf foot method, though I have no idea if that might affect furling.)  

    I have moved my tack as far forward as possible to keep the luff and leech vertical and this, along with the use of the running throat parrel, allows me to control the sail but if I could do the project again I would make the mast vertical and move it a bit further forward to keep the centre of effort in the same place.  (This would also make it less intrusive in my bunk!)  I understand the objections to aft rake though this would only apply in ghosting conditions.  My bermudian rig had a lot of aft rake and the sail stayed out most of the time, except in sloppy seas and light wind.  Many gaff rigs also have considerable aft rake (and a heavy gaff!)  I don't think I will change my rig now, at least not until I have some solid evidence, but will watch with interest if any members experiment more with aft rake.
  • 10 Sep 2012 23:29
    Quote
    Reply # 1069009 on 1067661
    Anonymous member (Administrator)

                                                                            Stavanger, Monday.

                                    What about the mast rake?

    Until recently I’ve thought that semi-short batten parrels and, more recently, the cunning use of luff (throat) hauling parrels would hinder negative batten stagger when reefing or furling the cambered panel junk sail. Those methods work for sure, but now I wonder if a third factor should be considered: I have sailed my dinghy Broremann quite a lot this summer, reefing and un-reefing frequently under the shifting wind conditions. Yesterday I had a wet and wild upwind sail when delivering the boat to the Sandnes sea-scouts, Broremann’s new owners. For once I had a most competent dinghy-sailor with me so I could spend more time gazing at the sail than just sailing. I have wondered why Broremann’s sail is so well-behaved in all sort of reefing conditions. For long I thought the rather high AR (2.15) played a role (could be right), but now I actually think it could also have to do with the aft-raking mast. I haven’t measured the rake in degrees, but it is clearly visible. Thinking of it, it is logical that the sail is less prone to falling forward (negative stagger) when it is suspended from an aft-set mast top. Opposite; on a forward raking mast, the sail should always want to move forward as one lowers the sail. Correct use of throat hauling parrel (as described by Graham, above) should still control this as long as the sail is set up to have the luff and leech vertical.

    Aft rake on a JR has always been warned against as the weight of battens and yard is supposed to hinder the sail from swinging out in light winds. On Broremann this surely is not a big problem as the light sail is filled and swung out even in very light winds. Now I also think Johanna’s rig may have a little aft rake, but not much. I will check the rake with a plumb-line, both on Johanna and ED.

    Preliminary conclusion: I will avoid rigging a sloop with a forward-raking mast; rather have 1 - 2° aft rake to ease handling of the sail.

    Cheers, Arne

    PS: I am only talking about the Hasler-McLeod type of sail here.
       " ...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