Pol,

I guess you were aiming for 10% camber in the first place. Then you came in fact very close to what I found (R=36cm). However, if you look again in TCPJR, Chapter 4, Fig 4.5, I have put a little warning on the sails with the AR from 1.80 to 1.90 and with a camber/chord of 10%. I suggest one tries a test panel before making these deep panels in a real sail.

Looking carefully on those cells in fig 4.5, you will find that the Chain Camber exceeds 50% of the vertical batten distance, P, with a good margin (it exceeds 50% even with AR is up to 2.05).

However, on page 9 you can see the chain camber set up with the round we actually used when making the sail of Edmond Dantes. As you can see, the chain camber in centimetres came out at 60cm when P= 120. Since that ratio worked well on ED, I see no reason why it should not work on your boat. The AR of ED’s sail is 1.87.

In other words, with Annie’s P=126.7cm the Chain Camber could safely be 126.7:2=63.4cm, and the resulting
Sail Camber 63.4cm :1.2= 52.8cm, which happens to be 9.1% of the chord (5.9m x cos 10°).

Now I brought out my chain calculator which suggests a round, R=32cm to achieve this camber.

Lots of words, but somehow we ended on the same round!

The resulting camber in the sail will depend a bit on how you rig the sail on the battens. Keep it slack and you will get close to the predicted 9%. Stretch it a bit and it is more likely to drop to about 8%. Edmond Dantes’ sail looks good, even without the use of broadseams, so I have a good hope that yours will look good as well.

As said before, this is not rocket science, and the quick (55%) method you used hit well enough.

Arne

Reading your great write-up on your "chain calculator" made the whole thing about camber much clearer for me. As you wrote somewhere, your writing is not for arm-chair theorisers but for doers. In hanging my little bit of chain the other day I knew what you meant. On a B of 5.9m and A/R of 1.9 with s/a about 51 square metres, as you suggested, the rounding looks huge at about 370mm, but I do now understand that despite that, full-grown adults will not be able to lie in rows in the bunt above each of the lower battens! 

Thanks!

Pol.

Thanks, Arne, for your VERY quick response. You were on the late watch! I was a bit worried that with the fibreglass batten being quite floppy compared with your 20mm squ. timber it might be giving me a funny curve but looking at it again it looks nice and fair so I think I'll leave it that way. After all, if I start manipulating the air flow too much I'll probably upset what would have worked quite naturally on its own. Sounds like what you have with Ingeborg is spot-on. The video shows her to be a real peach!

After a little bit of my day job to do, we should get to cutting out and joining a couple of panels today. Very exciting!

Cheers

Pol

I have had quite a good look about on this forum and elsewhere but have not found much on the actual curve in the rounding to build camber into the panels. I've got some fibreglass batten, (40mmx4mm roughly and in diamond profile) the kind used in pointy rigs, to use as a spline for shaping the round using Arne's method. Now that I've got to marking it onto the lining paper template, I'm really not sure of the shape of the curve I'm getting. With max round at 37% of B aft of luff and the aft 40% straight, I thought it was going to be pretty straightforward. I was expecting to have a sharper curve forward of the point of max round than aft of it, but in fact there's precious little in it. Should I be "making" a bit more curve forward of that point, or am I thinking about it too much? Given the 40% straight to the leech, there's really not much that can be done without putting a kink in it - not desirable. Any suggestions gratefully received, even if it is "just get on with it...."

Thanks,

Pol.