David Tyler wrote:

...

But why build a problem into a sail, so that a fix has to be employed? Why not design the sail correctly in the first place? We aren't talking rocket science here, just recognising that a cambered panel should have a little bit shorter diagonal than a flat panel.

My main reason to do it my way is that I never build less than 8% camber into any of the parallellogram panels, and I don't want the prescribed 14 degrees rise at the boom. On none of my sails, so far, have i needed to  add downhauls to get the sails down, not even on Johanna (48sqm)  and Ingeborg (35sqm), with their 5-part halyard. I therefore reckon that I don't have a friction problem with my half-long batten parrels, described below.

And, as said; I don't bother with inventing problems. There are enough of them on other fronts in life.

Arne

Arne Kverneland wrote:

Another way of dealing with batten stagger

Folks,

frankly, I think you are about to invent a problem, or at least, turning a tiny problem into a big one. Having seen how easy it is to scare new or wannabe junkies, the matter of batten stagger can easily grow into a showstopper to them.

KISS :-D

Camber	Growth of diagonal, when measured along the cloth as opposed to the straight line distance, corner to corner
4%	0.45%
6%	1.0%
8%	1.8%
10%	2.7%

Camber;     P/B	Rise of batten above horizontal, to give 1% positive stagger
4%;     0.2	9.6 degrees
4%;      0.35	12.3 degrees
6%;     0.2	11.5 degrees
6%;     0.35	13.4 degrees
8%;     0.2	13.8 degrees
8%;     0.35	14.7 degrees
10%;    0.2	16.0 degrees
10%;    0.35	16.3 degrees

So as the camber increases, so does the need for a shorter diagonal, but so also does the differential between the diagonals needed for narrow and wide panels diminish.

For comparison, the rise of the sheeted battens in the fantail sail is  8.2, 11.5, 15.6, 19.6, 26.8 degrees. The geometry of the panels is very different, of course, from that of a HM sail.

Barry Stellrecht wrote:

Hi there! I decided to check back into the JRA as I'm starting to think about sailing again (Gonna launch and bounce around the Chesapeake this spring), and am glad to see you are going ahead with your conversion plans.

Anyhow, I did a bunch of calculations on aluminum batten scantlings a while back, and wanted to say that the 50mm X 1.5mm battens should be fine for your main sail; I used the same for my main, which are longer than yours at ~5.5m. I came up with a dimensionless number that is a stiffness/length ratio for battens, and yours would be ~50% better than mine, which have held up fine although a couple have a slight set.

If you really want it stronger, 62x1.5mm would be stiffer than 50x3.0mm, although I wouldn't expect either to be needed.

For your foresail, with shorter battens, you would get the same ratio with 38x1.5mm tube, and the same 50x1.5mm tube would be effectively twice as stiff as it is on your Main. I think going larger than 50x1.5mm on that sail would be way overkill.

Barry - thanks for checking in and your feedback regarding how your battens have performed.  There is a strong interest to minimize the final weight of the sail, so your experience with lighter battens is helpful.  BTW, your Excel spreadsheet has been great in quickly seeing what impact a change in sail shape does on the CE and sail area on a two masted boat.  Using it and then skipping over to a CAD program made drafting very straight forward. THANKS for creating it.

Shaping the Sail:  I am currently trying to decide how to put the chamber into the Weaverbird plan form.  

Hinges are still an option, but I need to figure out how the "batten sag" in light winds and the force necessary to lift the battens compares to the force necessary to fill a sail that is cambered only through the sail cloth cut.  Also, the amount of sag - proportional based on sail size - will be larger on a larger sail.  Are there any effects that may get "out of proportion" compared to David's experience.  There's smoke coming out of my ears.

I've plaid around with the shelf foot method and just started catching up on the JRA posting/info.  Using SketchUp (the software I happen to have but are there better programs?) I've drawn a 3D cambered shape (8%), and then two 30 deg upper and lower shelves.  The program then lets you unwrap it and lay the pieces flat.  What became very obvious is that using 8% camber creates very large shelves. The discussion by David here pointed me to the obvious that the method I used would create too much average camber if 8% were the drawn camber, since the sail billows out further in the section between the shelves.  So the starting point would have to be less camber.  This also matches with the pictures I've seen from the Tuchwerkstatt (Sebastian) .  Some thoughts and input from folks with experience would be very appreciated.  Also, if the drawn position of the camber is at 37%, will it shift aft when the sail inflates in real life and is a drafted 37% still correct then?

I am also considering the broad seaming method, possibly in combination with some of Arne's barrel cut.  Vertical seams may be necessary anyways since our larger sail has a P of 160 cm and our cloth width is 152 cm.  Once I'm sewing vertical seams to get a panel I may as well consider using them for shaping.  I've not researched this much other than the recent technical thread.  If I understand things somewhat correctly I visualize the barrel cut method "pushing" camber into sail in a very smooth manner compared to broad seaming or hinges - which may shape the sail in a more step-wise manner.  The accepted drawback of a pure barrel cut would be wrinkles due to excess cloth length along the battens.   So maybe a combination of BC and BS?  

Cloth orientation:  If I go down the road of "sailmaker's" batten pockets on its own "lense" I may be able to run the sailcloth parallel to battens (10-11 deg to the luff/leech) and get away from constructing panels with vertical seams.  Is that amount of bias in the orientation possibly a problem if there is good tabbing and or edge webbing on the luff and leach? 

 Finally a couple of sunny days here in California.  Off to the boat.

Erik

Erik and Evi Menzel Ivey wrote:

Arne  and David - Thanks...

Some of the points you raised:

Link - Not sure why the link didn't work- I thought I grabbed the URL by accessing the photo album through the search function, not through my profile as me.  

The way I've learned how to do it is to go to my public directory profile and open the photo. Then highlight the photo by dragging the cursor over it, so that it turns blue, and click 'copy' in my browser menu. Then come back to the open posting and click 'paste'

Then I have to find the little square 'handle' at the top right corner of the image, and drag it down and to the left, so that the image is going to fit within the frame. Hope that helps.