A new rig for Leeway

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  • 24 Jun 2022 20:17
    Reply # 12828090 on 4138614

    You're aiming for high quality, long lasting sails, Darren - good!

    Just two comments:

    Be very careful not to build up too many layers, such that the needle won't punch through. Your tabling on the edges will add 2 layers to the panel -3 layers is easy going. Where the tabling crosses the seam between panel and shelf - 4 layers is still easy. But then if you start adding some more patching at the batten ends, and then try to sew webbing on top of all, things can very quickly start to get difficult. So, I suggest a test piece consisting of the area around a batten end, sequenced and sewn exactly as you plan to do it, to check this.

    I've not found that webbing tabling adds anything at all to a sail's edge, when the panel's thread line is parallel to the edge and a wide cloth tabling has been folded over it - that's super strong, not likely to hook, and good conventional sailmaking practice . Webbing's redundant - excepting possibly portions of the leech that just might get abraded by sheet spans, for instance. You won't know this until the sails are due for their 10,000 mile service; that's the time when you'll see where there's been chafe and protect against it. So please, no webbing along the edges, on the initial build. 


  • 24 Jun 2022 18:15
    Reply # 12827970 on 4138614

    I think I have a plan for assembling Leeway’s sail.


    I spent some time deliberating over construction technique and after borrowing many ideas from Erik and the rest of the JRA, I hope I’ve come up with something that is reasonably efficient to build and hopefully durable. All panels are made with vertically seamed cloths with the warp of the fabric parallel to the leach and luff. All seam joints are 20mm overlap joints, double stitched with 6mm zig zag. The sails are identical, except with an additional panel in the mainsail. The top panels have 2% camber, the second from top has 4%, and all the remaining panels have 6%. The top panel uses rounding-only for camber, the second from top panel uses rounding and broadseaming. I only used the broadseaming because I was already joining cloths and it helps make the lower edge of this panel exactly match the length of the lens that will come below. 

    The basic units of Leeway’s sails are the individual hour-glass panels and a 30o shelf foot that gives camber. The plan is to combine the shelf feet of the panel above and the panel below each batten into a single lens. Onto this “small” piece of cloth, sailmaker’s style batten pockets can be stitched.

    For a long distance sailing, it seems the consensus is that adding generous tabling is a good idea to keep the sail from fluttering itself to death, both when up, but also when reefed. If the tabling was added after the sail was assembled, I struggled with how to make the bend around the transition from the panel to the 30o shelf foot (as you turn this corner any patch will want to change course from the panel edge toward the middle of the panel). Instead, it seemed simpler to put the tabling on before assembly, which also lets you work with smaller pieces while sewing. So, the plan is to fold a single 350mm wide rectangular piece of cloth around the luff and leach with 250mm of cloth on one side and 100mm on the other. This is easy to do on the panels, but the lens would have tiny bits of cloth.

    Instead, it seemed like it would be better to have oval patches that span the lens and shelf foot, thus reinforcing the seam and providing tabling (stitching to match panel tabling not shown on patches). Each oval is folded over the luff or leach and covers both sides of the sail.

    On my paper models the oval patches seem willing to accommodate the deflection as you go down one shelf-foot, across the flat for the batten and then back up the other shelf foot. I plan to try sewing a couple of 1/2 scale panels to see if this will work in reality.

    To make room for the tabling, I ended the batten pockets a bit more than 250mm from the edge of the sail. I think at the aft end of the sail I’ll bolt the batten to the sail through a webbing reinforcement, similar to what Paul Fay did on Ti Gitu, but also include a batten insert like David Tyler and Erik Menzel have used, which will both keep the tube from collapsing if the bolt is over-tightened and provide a spot to anchor the sheetlets. At the luff of the sail each batten will get a webbing strap to help keep it in place and a lashing to tension it forward. 

    I’m not sure I have the gap in the batten pocket in the right place. A short batten parrel seems like a good idea to keep the sail from misbehaving. However, I also like Paul Fay’s idea where each batten has two parrels, one long and one that is like a throat parrel (around the mast with both ends of the parrel attached to the end of the batten). In which case, perhaps it is better with long parrels that could be set up tightly to keep the battens against the mast while the second parrel keeps if from moving forward???

    I think I’d like to rope the sail with seatbelt webbing. It’s really attractive as a way to reinforce and add mass to stop fluttering. If I ever end up with a hooked leach from stretching cloth and unstretchy webbing, I suppose I could just take off the webbing and I’d still have a sail with tabling.

    It looks like the consensus JRA batten recommendation for a 50m2 sail has settled on 2” by .065 wall (50 x 1.5mm) for most of the battens with the top sheeted batten and the boom being increased to 3mm (.125”) wall. Material is 6061 T6. This is my plan.

    I’m less sure of the Yard. Like everyone, I’d like to save as much weight aloft as possible, but a bent or broken yard also seems best avoided. Reading the recommendations in Erik’s Raven build thread (also a 40’ schooner with shorter yards) it looks like the recommendation was that a 4” x .125” (100 x 3mm) tube would be enough with a span to spread the load. Unfortunately, I don’t have room for a span and was planning to use the method recommended by Paul Thompson of a 3:1 halyard with a block at the midpoint of the yard and a second fixed point located 10% aft on the yard (thus the load is spread slightly with 2/3 at the midpoint and 1/3 slightly aft). Would it be prudent to go up to a 5” x .125” (130 x 3mm) yard? The plan would be to lash the block and the fixed point to the yard without holes in the yard (maybe holes on the side for an eye to keep the lashing from slipping).

    Any comments or thoughts are appreciated.  Things are still evolving, but I really must get disciplined and start sewing soon.


    Last modified: 24 Jun 2022 19:41 | Anonymous member
  • 18 Jun 2022 18:08
    Reply # 12821025 on 12820746
    Anonymous wrote:
    Darren wrote:

    David,

    Also, won't I miss out on earning my aerodynamics badge if I don't put less camber in the mainsail than the fore-sail (don't say put 4% in the mainsail, I just can't do that).

    Where does this come from? I don't recall having heard it.



    This is a bit of shade-tree aerodynamic guesswork considering there isn't much to look at where a Junk Rig Schooner has been studied directly. 

    Here's a fluid dynamics example from a bermudan rig.  Because, the mainsail acts in the downwash of the fore, it's more effective for it to have lower camber and to have that camber further aft.  Effectively the two sails are working as one sail. 

    https://cdn2.hubspot.net/hub/209338/news/Ad_aerodynamics/images_ad_aero/ThinkOne2s.jpg

    Of course, this is only for close-hauled sailing and a Junk Schooner is going to have more space between the main and foresail.  However, Paul Thompson described exactly this effect with his schooner la Chica, with most of the drive coming from the foresail and the luff of the main having trouble staying filled probably due to a bit too much camber in it.

    Part of the reason I don't want to take too much camber out of the sails is that I'd like enough fabric to partially engulf the mast on the "bad tack", such that the mast becomes part of the "airfoil".  Here's another example from fluid dynamics that demonstrates that the mast might not always be just a drag creating entity but can be part of the airfoil and create lift.  I think Arne has also empirically come to the same conclusions (see the myth of the bad tack).


    Last modified: 18 Jun 2022 18:09 | Anonymous member
  • 18 Jun 2022 07:53
    Reply # 12820746 on 12820667
    Darren wrote:

    David,

    Your like that little angel that sits on ones shoulder and encourages us to do the right and good thing :-)   I want to be good, but then I see the curvaceous sails in New Zealand and Arne starts talking about Samson surging forward and my resolve weakens.  Do 8% sails slat that much harder than 6%?

    It's not only slatting. It's also about having sails that can be set without much conscious thought when sailing 24/7, reefing and un-reefing multiple times during a squally week, in the pitch dark of a new moon... Less Is More, as someone once said.

    Also, won't I miss out on earning my aerodynamics badge if I don't put less camber in the mainsail than the fore-sail (don't say put 4% in the mainsail, I just can't do that).

    Where does this come from? I don't recall having heard it.

    As always, your guidance is appreciated.  Time to have a drink and contemplate my sins.

    You're welcome!

    Remember that if you go for a calculated, "tinplate" camber of 6%, you'll actually get ~7 - 8% in the centre of the panel, as James confirms. In the end, it's a personal choice - a little more performance requires a little more input from the crew, but in any case, a long hard windward leg with JR is a lot less work with JR than with a pointy-top, whatever the camber. 
  • 18 Jun 2022 05:08
    Reply # 12820667 on 4138614

    David,

    Your like that little angel that sits on ones shoulder and encourages us to do the right and good thing :-)   I want to be good, but then I see the curvaceous sails in New Zealand and Arne starts talking about Samson surging forward and my resolve weakens.  Do 8% sails slat that much harder than 6%?

    Also, won't I miss out on earning my aerodynamics badge if I don't put less camber in the mainsail than the fore-sail (don't say put 4% in the mainsail, I just can't do that).

    As always, your guidance is appreciated.  Time to have a drink and contemplate my sins.

    Last modified: 18 Jun 2022 05:27 | Anonymous member
  • 17 Jun 2022 08:12
    Reply # 12819619 on 12818296
    Darren wrote:

    OK, time to make some decisions on camber and do a test panel.  Do you think I'm being too conservative about camber?  Plan is for a tradewind circumnavigation starting from Vancouver, BC.  Although, who knows which way we might end up turning along the way.

    Not quite conservative enough, IMO. I've said in the past that the further offshore you venture, the less camber you actually need, and a lot of camber brings with it some downsides, in the real world of long distance voyaging. OK, there are times when you are struggling to make progress to windward in light airs, such as breaking out of the far side of the ITCZ (it's easy to get into the doldrums, less easy to get out); but seen as a whole, a tradewind circumnavigation doesn't involve a high proportion of such sailing.

    I'd settle for 6% in all the parallelograms.

  • 16 Jun 2022 19:40
    Reply # 12819118 on 4138614

    Thanks Arne,

    I've started another thread Exploring a Simple Way to Draw Shelf Foot Panels.  If it is found to be useful, it should have its own place where it is easy to find.  If not, then it won't permanently mar the thread for building Leeway :-)

    I'll definitely check your notes regarding the masthead and rigging.  Actually, I check your notes regarding virtually everything.  I often think about how much harder this would be without your contributions and that of others.  Thanks.

  • 16 Jun 2022 16:28
    Reply # 12818878 on 4138614
    Anonymous member (Administrator)

    Darren,
    I hope you know what you are doing when you calculate camber with shelf-foot method. Better let Paul Th. look over the plan to get the curves of those lenses right.

    Before dressing the still horizontal masts, I suggest you look up Chapter 7, p.2-3 on how I fit the halyard. That method has saved me from lots of worries and trouble.

    Good luck!

    Arne


  • 16 Jun 2022 06:08
    Reply # 12818296 on 4138614

    OK, time to make some decisions on camber and do a test panel.  Do you think I'm being too conservative about camber?  Plan is for a tradewind circumnavigation starting from Vancouver, BC.  Although, who knows which way we might end up turning along the way.

    I did quite a few paper and fabric models using the various camber methods and I'm pretty sure I want to use a 30o shelf foot.



  • 15 Jun 2022 08:25
    Reply # 12817047 on 4138614

    I like the sailplan, and can see nothing major that I’d want to change. Maybe set the foresail lower, with single sheet spans, for better access for maintenance? I never got the running lines right first time; be prepared to experiment with the sheeting and hauling parrels a bit.


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