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

Erik and Evi Menzel Ivey wrote:

A quick (un)related question regarding QCad - how do you guys calculate the CE for your sails?  I am using Barry's Excel spreadsheet and transfer the coordinates to QCad.  Is there an easy way of doing it in or out of QCad? 

Erik

 

Not that I know about. My method is to add a few well-placed cris-crossing helping lines on the Q-CAD drawing, and then print it out to a known scale, say 1:50. Then I find CE the old-fashioned way, by cutting out the sail and cross-balance it on a ruler. Then I can just measure the position of the CE relative to those helping lines, and transfer the numbers to the Q-CAD drawing.

BTW, the horizontal position of the CE on my range of master sails sits only about 50mm forward of the middle of the boom, so I sometimes use that for simplicity.

Arne

Erik,

you are right that I use to have 10% as the default value of the balance in my sails. However, Paul J Thompson has shown that the balance may well be increased to 20% without any problem. My sails with 70° yard can easily be made to set with a balance between 5 and 15% if the mast has been made long enough for it (no problem in your case). If 20% balance (or more) is to be used, then I guess it is better to lower the yard angle, as Paul has done.

My guess was that David’s sailplan could just as well be implemented with baggy panels as with hinges. Just remember that with baggy panels, the rules about boom rise and batten stagger when reefing do not work anymore. I use half-short batten parrels to keep the sail from moving further forward after the first panel has been lowered.

Arne

Arne -  thank you sir! I understand your comment re only relying on camber from the cloth and in general the concept of KISS (ignoring it has been a downfall of mine so please feel free to remind me.  Often). Of concern is that if I  don't do any hinge(s), the 15% overlap increases the mast interference in comparison to your more moderate 10%.

David -    I've created a folder in the JRA Box  and uploaded the latest drawing.  

Sounds like the single/front hinge is similarly situated bssed on both your.  If there is a second one, is it at 60% from the luff since the camber profile is straight aft of there? Or is the idea to position it where there is still a large  of changes in curvature?

Erik

Erik and Evi Menzel Ivey wrote:

David/Arne - do you have some rules of thumb as to hinge locations with respect to max camber?

 

Erik,

Now I had to look up newsletter 24 to check the position of the fore hinge on my Malena. It sat 27% aft of the luff. Most of the time that hinge worked well, but sometimes it flicked the wrong way. I solved the problem by adding a throat hauling parrel to shift the top of the sail aft. You should be all right if you fit your (one and only) hinge to 30-35% aft of the luff, and I guess that will put the max camber point in a good position as well.

However, the cambered panel sails have worked well for me, so I have never felt any need for bothering with hinged battens again.

Arne