SHELF LENS METHOD

(Please correct me if this is a miss conception)

The main panel carries the load and the shelves carry little load.  Therefore the shelves could be a light/soft/stretchy cloth.  This should make the shelves very forgiving with few wrinkles.  

The shelf above and below the batten are one piece, lens shaped, with the batten pocket fixed before joining to the main panels above and then below.  Each panel + lens assembled before joining to the adjacent assembly, which could be with a simple Arne type seam.

(trust this all makes sense)

Update...  I've been working my way through multiple paper (1/8 scale) and cloth (1/2 scale) panels to both improve my sewing and to see how various ideas play out in practice.  Most of the work has been related to trying to develop a sail shape, i.e., camber, in a predictable and easy way. Some description of the process, results, and conclusions are not new, and I will also freely admit may only apply to my living room, not the real world.

Some general design outlines I am pursuing:

10% camber -  It may be a lot.  Sebastian from the Tuchwerkstatt recommended around 6%.  David and Arne seem to recommend 8% but Arne has also proposed that more may be better. My sailmaker thought that anything under 10% would be pretty flat - he's super smart but has not brackground in JR. But camber is camber regardless of the type of sail.  I am very aware though the the camber of a JR is fixed compared to a BM with outhaul, cunningham, and vang.  

I have tall panels 1450mm and 1600mm on the fore and mainsail respectively. I am hoping that this makes them fill easier.  I am thinking of using the light WeatherMax cloth, which is 6.5 oz/sq. yard (about the same as Odyssey).  At least for the lower five panels.  I am considering the WeatherMax 80 for the upper panels, which would have a flatter cut

30 degree shelf -   Because of the large camber, I am planing on using a 30 deg shelf.  This will decrease some of the cloth amount and hopefully help to fill the sail at low  wind speeds.  This does make the design more complicated.  Based on some math, I think the amount of cloth on Arne's barrel design for 8% is the same as on a 8% shelf foot or broad seam design with a 30 degree shelf.

Cloth alignment -  The sails are large enough that I can not fit a panel into the width of the cloth (nominally 150 cm wide, but the 11 degree batten angle doesn't allow for the leech to be parallel the warp).  So I am into segmented panels with three or four seams.   

The four methods I tried with were the barrel cut, broad seam, broad seam/barrel cut combination, and shelf methods.  

Barrel Cut - The ease of using this method became very apparent during the design.  It is straightforward to draft.  For the small paper models, the curvature of the barrel with 10% camber was too much to get it to conform to a batten.  Sewing a 1/2 scale cloth panel was simple, including adding Type B batten pockets (Evi calls them lollipop style pockets).  The segmented panels created some extra work. When done, there were the expected wrinkles along the battens that result from making the round barrel  shape conform to the straight batten.  Pulling the wrinkles out made the shape change and the sail had less camber.  

Broad seaming - Three  seams/four segments were too few to satisfactorily approximate the desired shape.  I had problems with:

• the location of the max camber, 
  
• achieving an entry angle better than 25 degrees, and 
  
• making the aft 60% of the sail flat.  

I used the free version of SketchUp Make to create the 3D shape and then the 2D panels.  The steps look something like this...

    I then exported the image to QCad and did the actual layout.

Because the intersection of the panel/shelf with the batten pocket is a straight line, both the paper model and the cloth model were happy to conform to the batten without any wrinkles. The design is more complicated, and I could not do it without a computer.  I used the printer to create the paper models and because the all lines were straight it was easy to cut out.   I lofted the 1/2 scale cloth panel by hand and again, it was pretty straightforward.  Sewing the segments together was easy.  I did use seam tape. The final shape was a little "digital" because the seams create a step change. This was less of an issue on the four seam panel than the three seam panel. 

Broad seam/barrel cut combination - In order to see if I could improve on the "three seam" panel I tried to combine the first two methods and used broad seaming to create half of the camber, and some barrel shaping to create the other half.  My thinking was that this is similar to a BM main sail with both broad seaming and luff round.  It turned out that this method had all the disadvantages of both methods without any satisfactory advantages.

Shelf method - I've took the same approach via software as in the broad seaming method and did some panels using a "true" shelf. Sebastian uses curved shelves and no broad seaming. The scale models in paper and cloth were without any wrinkles. And the final shape was very smooth with none of the step changes I saw in the broad seam method.  But the lofting was complex because of the two different curves of the shelf and the panel which is a result of doing a 30 degree shelf.  If the shelf were at 90 degrees to the panel, the panel would have straight sides.  

Sooooo...  Input, comment, questions...

I am biased toward the broadseam method at present.  At lease for panels 1-5 (from the bottom up).  I will explore using either broad seaming or the barrel method for six and seven.  

I myself have some questions, and could use some input from folks!

Seam allowance - The sails are nominally 38 and 48 sq meters.  My sewing machine will do up to a 8mm wide zig zag (Bernina 217).  For a single seam I've been using 13 mm overlap and 6 mm zig zag.. Any thoughts on whether I should use two rows of stitching and what amount of seam allowance? 

Leech/Luff Reinforcement-  I am considering treating these separate from the designed sail shape.  In other words adding material along the luff and leach that goes beyond the sail shape. I would like to use webbing reinforcement of about 20mm wide/ 700 kg breaking strength.  I keep thinking that webbing, esp. if especially wide, may distort the designed sail shape.  My preference would actually be to use rope, but I can not get my machine to stitch it on without causing the material to pucker.  Webbing may also cause pucker but i think I can adjust the foot pressure on the machine to prevent this.

I am planing on using webbing loops like Arne does to support the battens and take any vertical loads, and either pressed eyes or sewn-on webbing loops to stretch the sail along the battens and take on any horizontal loads.

It is way past dinner time here, so I will give it a rest 

Erik  

Greetings.

I set out to purchase a Freedom 40', aft cockpit cat/ketch specifically for cambered junkrig conversion. Should my transaction close as expected, I'll have the boat transported across the US to the mouth of the Columbia river in the Pacific Northwest in a couple of weeks. 

I'm very interested in this thread, and your progress aboard Raven, Erik. You've already addressed many of my concerns, and exposed more pitfalls which I'd not envisioned. I'm certain that I'll face some of my own within the evolution of my process, but I'm grateful for your considerable contribution, as well as those who've assisted your efforts. Thank you, one and all.

I anticipate sailing for a spell with the original rig as designed, but I expect that the existing sails are well and truly ready for retirement. My plan is to commence my junkrig conversion in the fall, and perhaps benefit from your progress in the meantime.

Again, thanks for sharing.

~Dave 

Annie Hill wrote:

David Tyler wrote:

I use them, as they also damp down excessive fore and aft movement of the sail in a seaway, and they permit me to get away without a LHP.

I found a good fix to this problem was simply to fit two boom parrels - one that went aft around the mast and one that went forward around it.  With the boom more or less fixed, the rest to the sail didn't appear to be able to lurch around much, either.  And, of course, it doesn't add any friction when raising the sail.

We are getting through some serious rain here.  Good time to keep working on all this stuff.

Erik

Erik and Evi Menzel Ivey wrote:I do think a batten angle greater than 10-11 degrees looks odd.  I would love to do less of an angle, but I need the rise to get the Dmin to work.

I'm thinking that one way to "fix" that problem of two steep a batten angle looking odd would be to design the bottom panel different and having the remainder of the parallelogram panels normal with the batten angle a bit steeper.

Arne does something like this by shortening the boom. You could also make the bottom panel wedge shaped so the next batten up has a steeper angle, or perhaps do both. The geometry is very solvable one way or the other.

Now I'm starting to think...I just remembered that when I reef my sails, the sail bundle doesn't end up parallel with the battens above it anyways. These junk sails just seem to find their own set, despite my efforts to keep everything orderly!