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Freedom 40 Cat Ketch Junk Rig Conversion

  • 31 Jan 2017 19:43
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    Reply # 4578133 on 1424184
    Anonymous member

    I'm sorry, but a single 3:1 sheet is a fantasy on sails as big as these. I'm thinking of 3:1 on each sheet ( which is a lot easier to handle than a single 6:1 sheet, the alternative, and each option uses about the same amount of rope and blocks).  
  • 31 Jan 2017 19:22
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    Reply # 4578104 on 4577902
    Anonymous member
    Erik and Evi Menzel Ivey wrote:

    But I don't like going beyond a 3x1 sheet (if I get to keep it as a single sheet) due to the total length that ends up in the cockpit.  As it is, with our 5.8m wishbone booms, we have 30m long sheets.  I've not done the math on the sheet length for the junk sails, - with the shorter booms/sheetlets, and that go all the way up the leech - but I'm guessing the sheet may be shorter.  In any case, it is still my hope to get away with a single 3x1 sheet for each sail. 

    Erik

    Dealing with long sheets isn't an issue, as long as you get yourself organised properly.  The best way, I've found, is to have a deck box with a lid that lifts back over centre (so stays open even when the boat is heeling to put them in.  That way, even from a pram-hood steering position, you can just pile the surplus sheet back in the box.  If you are happy to sail from the cockpit, the lid angle is less important.  You just pick up the sheet that you hauled in and dump it in the box, (without, of course, capsizing the pile).  Sheets do not need the sophistication of flaking down, but prefer not to be coiled.  I am less fond of bags (a personal opinion - lots of other people seem to like them) because you can't usually just lift up the sheet and pile it in and, IMHO, they are an inelegant solution.  Your lidded box, on the other hand, if carefully thought out, can also provide a comfortable extra seat in the cockpit.  You can have one each side, for halliard and sheet, and in your case, have an athwartships separator to keep them from getting tangled together.

    I tried several ideas on Fantail, none of which was successful, and was at the stage of contemplating a box when I decided to build another boat
  • 31 Jan 2017 17:15
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    Reply # 4577902 on 1424184
    Deleted user

    David - I like the idea of either moving the upper sheeting point for longer tacks or possibly barberhauling it.  In any case, it would be preferred over a traveler.   But I don't like going beyond a 3x1 sheet (if I get to keep it as a single sheet) due to the total length that ends up in the cockpit.  As it is, with our 5.8m wishbone booms, we have 30m long sheets.  I've not done the math on the sheet length for the junk sails, - with the shorter booms/sheetlets, and that go all the way up the leech - but I'm guessing the sheet may be shorter.  In any case, it is still my hope to get away with a single 3x1 sheet for each sail.  

    So, in staying with the 3x1 (fantasy?), rather than adding another panel I've redrawn the planform with 1.6m tall panels on the mizzen.  This "forces" me to construct each panel with the cloth parallel with the leech and opens up the possibility for broadseaming.  The WeatherMax80 really has a soft hand and lays down/folds much easier and compact compared to Sunbrella, Odyssey, or Topgun.

    The mizzen now has an AR of 2.47 with boom/battens at 4.75m and sheeting is getting a bit easier.  I've left the main as is at 2.6.  Version 3 files are in the Box.  

    Erik
  • 31 Jan 2017 11:33
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    Reply # 4577316 on 1424184
    Anonymous member

    Sheeting: Remember to extend the top sheeted batten aft of the leech. This makes a big difference to the behaviour of the top sheet span, the one that is most likely to get caught when the sheet is slack. As Darren says, I meant upper and lower sheets. I tried port and starboard sheets, and found that they weren't necessary on the fore sail, which doesn't need to be sheeted in as much as the after sail. I did like port and starboard sheets on my mizzen, which needed to be sheeted in more, but I think that upper and lower sheets for your larger after sail will be better value for reducing twist. If you were going to be on a long closehauled tack where you needed the very best pointing ability, it would be helpful to have a way of shifting the upper sheet only up to weather - this would give the sole advantage of port and starboard sheets, without the continuous hassle.

    After sail: I was thinking of simply adding a panel, keeping P the same, only increasing B a little more than for the fore sail, and going up to seven point sheeting. Even consider adding two panels, with eight sheeted points. This is perfectly possible with upper and lower sheets.
  • 30 Jan 2017 22:47
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    Reply # 4576665 on 1424184
    Deleted user

    Erik, I think David likely meant upper and lower sheets rather than port and starboard.  I drew them like that on my sail after advice from David.

    You can get castable urethane in a huge variety of traits.  The trial hinges I made were from urethane with a tensile modulus of 370 000 psi compared to 410 000 for pvc.  However, that was just what I was able to get locally.  If I had gone ahead to produce a lot of them, I was considering ordering some resin with a tensile modulus of 420 000 psi.  This is still straight resin without reinforcement.  You can get fibre reinforced resin with even more impressive numbers.  I should probably have put a link to this thread instead, which talks a bit more about the hinges and materials.  I made the hinges for use with 2" OD .065"wall 6061 T6 tube.

    Last modified: 31 Jan 2017 03:27 | Deleted user
  • 30 Jan 2017 22:29
    Quote
    Reply # 4576620 on 4574277
    Anonymous member
    Darren Bos wrote:

    I must admit I like the shorter yard of the Weaverbird style sail and am considering making that change. However, reading through the thread I feel like I've missed the point a bit. My understanding of yard angle was that you could decrease the yard angle as you increased the balance on the sail. However, if you have hinged battens you must keep the balance relatively low. Is it just that the higher AR rig used in the Weaverbird style sail is more tolerant to bending the rules around yard length and sail balance?

    No, I don't think so. The rules still need to be applied fairly rigorously. I'm not sure what you mean by more tolerant, Darren?  

    When I'm designing the upper portion of a rig, some of those rules are:

    1. Angle between halyard and mast less than 30 degrees.
    2. Halyard attached at centre of yard.
    3. Diagonals of upper panels not shortening too much, sending the yard so far aft that it loses contact with the mast when the sail is furled; but shortening enough for the after end of the yard to stay aft of the topping lifts when the sail is furled.
    4. Yard angle not so high that it risks getting underneath the topping lifts during the first part of the hoist; but not so low that the balance becomes unacceptably large.
    I have to go through a number of iterations and much trial and error before I'm satisfied with what I've got. Thank goodness for CAD, I couldn't do it using a pencil and eraser. But once I've got something that works (and the weaverbird shape is one such), with CAD it can be scaled up or down and I know the geometry will remain valid. (Arne does the same, with the templates for his kind of sail). Any deviation from that geometry means that the whole of the upper portion has to be re-evaluated. Happily, the lower portion is more straightforward, if it simply consists of parallelograms - adding or subtracting one panel doesn't invalidate the design. 
  • 30 Jan 2017 22:24
    Quote
    Reply # 4576603 on 1424184
    Deleted user

    Hokey, I have tried to correct my most grievous mistakes in my last post.  Darn small screens on smartphones,autocorrect, and bad English.

    David:  

    Foresail.  Its comforting to hear your opinion regarding an AR of 2.6.  Less so the possibility of having to employ double sheets - with which I assume you mean port and starboard sheets.  I've put some effort into following the PJR recommended 10% sheeting angle to the upper batten - is that too steep for a single sheet in combination with the AR?  I am thinking it may not be the worst retrofit if single sheeting is not satisfactory.  

    In any case - I feel like I keep doing a circular design process that hits the same wall with only incremental if any improvements.  In order to increase the overall sail area I've tried to make the foresail as large as possible within the constrained space between the two masts and work towards an:  

    • AR that accommodates a 10 degree sheeting angle, 
    • a P that equally divides the lower five panels of the sail, and 
    • a B at the recommended 11 degree angle with a length that gives me a reasonable Dmin and a height off the deck that still allows me to reach the clews.
    Moving to the aft sail.  The goal again is to have the size be as large as possible while moving the combined CE only slightly forward (2 or 3% of waterline).  If I use the same P (is this worthwhile aesthetically?) I arrive at a B of 5m.  I can increase P and still work within the 10% sheeting angle "rule" in order to get a higher AR, but then then the CE moves forward.  I could in combination with a taller P decrease B.  That may give me back the CE position and a higher AR yet.  .   OK, so maybe that's tonight's project.  

    Batten material:  I'll start a separate post on that since I am running out of time here.

    Darren - thanks so much for your nice note, the comparison of your current design and overlaid drawings and links to the previous discussion.  Your hinge design is very clever and I am definitely interested. It certainly lends itself more to casting than machining.  I am a little curious though - so far the urethanes I've found are less stiff than the PVC David has used - though the material may be beneficially flexible and help keep the battens from possibly breaking during some unfortunate event...  What amount of articulation what tube ID are your hinges setup for?



    Erik
  • 29 Jan 2017 20:15
    Quote
    Reply # 4574277 on 1424184
    Deleted user

    Erik, given the similarity of our boats I've been watching this thread closely. In fact, superimposing your Weaverbird style sails onto the ones I drew based on Arne's master sails and PJR shows pretty similar results (the sails in the drawing are pasted one atop another without any rescaling, although the balance on our masts differs somewhat). 


    I must admit I like the shorter yard of the Weaverbird style sail and am considering making that change. However, reading through the thread I feel like I've missed the point a bit. My understanding of yard angle was that you could decrease the yard angle as you increased the balance on the sail. However, if you have hinged battens you must keep the balance relatively low. Is it just that the higher AR rig used in the Weaverbird style sail is more tolerant to bending the rules around yard length and sail balance?

    I've run the full breadth of Junk sail styles in my planning. Originally I was convinced a wingsail was right for me (I still dream of them fondly), but eventually settle on the simplicity of the cambered panel rig. However, I did go as far as to work up some hinges with David's advice and some experimentation of my own.  Here is a link to a thread that discusses the hinges and has another link to a video.  If you'd like, I'm happy to ship you one that you could use to make a mold and cast your own in urethane. There are many choices in castable urethane that let you tailor the hinge to whatever you desire in terms of strength and flexibility. I made a plaster mold in an afternoon and cast my first hinge the next day. My hinges should fit your sail without modification as my batten size choice was the same as yours.

    It's interesting to see how the process evolves differently for each boat. The sailcloth I chose forces me towards vertically seamed panels, which makes broadseaming and round an obvious choice to produce camber. My foremast position and rake means that hinges aren't practical on the foresail and out of simplicity I doubt I'll make one sail hinged and the other not.  I look forward to seeing your final design.  I'm planning to sail down the California coast in 2018, it would be great to sail the boats together.
  • 28 Jan 2017 16:03
    Quote
    Reply # 4573121 on 1424184
    Anonymous member

    Erik, I think you're heading down the right track.

    AR: If I could have got a higher mast at a suitable diameter, I would have gone for an AR up to 2.6 - no problems there, except that double sheeting becomes near-essential, I think. Otherwise, I still like the planform best. What I don't like is the different AR on each sail. Could it be a possibility to use the existing height of the after mast to increase the AR of that sail, reducing its width as well, by adding a panel (making seven sheeted points)? Reducing the width would make the sheeting easier, though the bumpkin would still be needed.

    Camber: It would be possible to use hinges alone, but the sailcloth will necessarily take a less smooth curve, fore and aft. It would be possible to use built-in camber alone, but this takes a surprising amount more cloth. It's actually not a bad thing that the mast gets "buried" in the lee side of the sail, as the wind skips over the hollow and reattaches. This probably cuts down the parasitic drag of the mast. The bulge of the mast on the windward side is not very important, as the air is moving very slowly. Either option on its own could be used, but still, my favourite option remains part-hinge, part-built-in camber. However, your batten pitch of 1.45m would mean that, using 1.524m wide cloth, you wouldn't get much depth of rounding if you made each panel from one piece of cloth. I don't see this as an insuperable problem, because it is better to lay the cloth parallel to the leech, and then a) the cut is more economical, and b) broad-seaming will give a better result, than the plain barrel-cut.

    Battens: I don't fully understand what you're saying. You say that aluminium is lighter, but quote the same diameter and wall thickness for aluminium and GRP. the density of GRP is 1.8 and the density of aluminium is 2.7, so like-for-like, GRP weighs 2/3 as much as aluminium. However, you should consider 16swg aluminium for all but the top sheeted battens, and then as you say, aluminium battens would weigh less. My personal preference would still be for the GRP. Using hinges, an 8ft length would actually be quite convenient for a batten 5m long, with two x 10 degree hinges. 

    Hinges: Yes, I'd use 2in PVC bar for the hinges.
  • 27 Jan 2017 07:55
    Quote
    Reply # 4571240 on 1424184
    Deleted user

    Thank you Ueli and Arne!  Good to know I'm not the only one that is using a work-around to find the CE.

    David -  I downloaded the DXF file of Weaverbird and used it to tune my drafts of the mizzen and main.  I worked within the constraints that the Freedom has regarding mast spacing and my desire to be able to reach the clew and am getting to an AR of 2.6 for the main and 2.23 for the mizzen.  Any concerns with the former or the planform of the sails in general? 

    et al...  based on what I've been told and learned on this forum, I think the current "Weaverbird" profile for the Freedome 40 CC couldn't  could work with camber created either by barrel-shape, shelf-foot or hinges.   Each design has it  advantages, but at present I would like to pursue a combination barrelshape/hinged design, for the following reasons...  The reduced amount of cloth for creating camber through the cut of the sail and the hinges, may help in the batten stagger during reefing, may also fill more easily in lighter winds, and with a 15% overlap, interfere less with the mast.  

    Given the size of the larger mizzen at 47 sq meters and batten length of 5 meters, I'm considering 50x3 mm 6061 T8 Aluminum tubing for the boom and battens.  I have a 150x100 by 5mm wall thickness catamaran mast section available for the yard.  Are these appropriately sized?  David - where the hinges engage I can double the wall thickness either on the od or id side of the aluminum battens . This is the current supplier I have in mind - the aluminum tubing comes in 12ft lengths..  They also have similar wall thickness pulltruded fiberglass tubing, but unfortunately those are only 8ft long and (obviously) not as stiff.  Whereas the lighter weight of the aluminum fiberglass is attractive, the lenght may not fit within your hinge spacing for my 5m battens on the mizzen?!  I realize the fiberglass battens would have to be reinforced at the ends with some sort of diagonal cloth.

    David - Can the hinges for this size sail(s) still be made of PVC?  Certainly it is one of the cheaper materials. 

    OK. I'm am out this weekend for a sailboat race, and some festivities...  Cheers everone,    


    Erik

    Last modified: 30 Jan 2017 21:12 | Deleted user
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