" it would be very interesting to know the bones of your discussion...."

Hi Pol, I had a chat with Chris this evening and must say he has done his homework very well. He says that, "The design violates several of Slieve's guidelines," yet when we discussed the hull and keel design, the boats displacement and waterline, as well as the CAD program he will use that it all makes sense. The only query is the yard angle which is lower than I would like, but I fully accept his thoughts and will be keen to hear the result of his planned tell-tale test. We all have something to learn from sailors who are prepared to experiment.

The one point where I was able to give some update was to explain that we had increased the jib parameters on Amiina's new sail to give a "sheeting angle" to 12° and the camber to 10%, and Edward feels that this has been a move in the right direction. With Chris's hull it would probably be a good idea to do something similar.

It will be very interesting to see how he gets on and how well his boat reacts to the rig. I feel confident that he will see a useful improvement in performance, and ease of use.

Cheers, Slieve.

Chris Gallienne wrote:

Camber in both the jiblets and main is by angled shelf foot - given that I have designed it using DelftShip, this gives me nice computer-generated panel patterns as part of the process.

Hi Chris,

You're breaking new ground....zero degree rise...double ellipse shape...short, flat yard...jiblets on all panels. Good stuff.

I'm curious, does the DelftShip app account for the catenary shape the sail takes? See my JPGs in Tech Forum illustrations. Taking off from Arne's hanging chain (which forms a catenary) method and Slieve's suggestion to put some hollow in the profile (pg 62). I web-searched for a way to model a catenary to get the profile I actually needed to start with to get the profile I wanted to end up with (or close).

I've been using this site:

http://www.had2know.com/academics/catenary-equation-shape-hanging-chain.html

which takes as input the distance between battens, the locations of the ends of the chain (both close to zero I used 0.0001) and the total length of hanging chain (or sail cloth in this case). The app returns a y=f(x) formula for the (x,y) coordinates and the max depth of the curve (the "camber").

You can check the output by plotting the points from the formula to check the shape. Also you can sum the distance along the path to check how close the math model came to the length you gave it.

I found that the max depth of the catenary curve, i.e. the "true" camber at that location on the profile were very different from what I expected (Slieve's profile on pg. 18 and 60). Entry and exit angles and max camber were different. Would they be different in the real world. Unknown. Assumes the math model replicates the real world. Assumes sail cloth between battens, inflated by wind pressure marks out a catenary.

At this point I'm modeling at 1/5 scale in a spreadsheet. It won't cost me too much to buy some Odyssey 3, have 3 jiblet sub-panels cut out from dxf files then sew the sub-panels together.

robert self

Hi Chris,I've just seen your posting and would like to have a chat with you before you cut cloth. My notes are rather out of date, and there is some useful information you might find worth including. Could you e-mail me you phone number, preferably land line, and I'll get in contact.

I hope to update my notes this winter.

Cheers, Slieve

Well, looking at this sailplan alongside Bryan's proposal for a new sail for Fantail, shows pretty well what a wide canvas is needed to illustrate all the different forms that junk rig can take!

Not having any direct personal experience of designing and making a split rig, I'm reluctant to comment in detail. I can only echo Arne's "looks absolutely fantastic", and wish you success in turning the 3D model into a reality that will look as good. 

After playing around with a great many designs for a new rig for China Girl (including a schooner) I have settled on a single split rig with an increase in sail area from 379 to 415 sq. ft. (original bermudan 315 sq. ft.). This requires increasing mast height by around 4 feet - I plan to use an oversize aluminium tube 2.5m long from mast step to 2' 3" above partners, giving me a height increase of 4 feet with bury of about 12.5%. Aspect Ratio is around 1.85.

I have designed the sail following (most of) Slieve's excellent guidlines, and have gone for a double elliptical shape, as can be seen in the rendering below. My thinking was that an elliptical planform is widely accepted to have the least drag for a given amount of lift (at least, an elliptical span loading, which isn't necessarily the same thing). Actually, my knowledge of aerodynamics is not nearly good enough to make an informed judgement about this - truth is, I just liked the shape, derived as it is from the classic Spitfire wing planform. Since the initial design, I have discovered the shape is almost identical to that of the proa Ping Pong.

The sail has uniform 31% balance in each panel, with camber ranging from 8% (main) and 10% (jiblets) at the bottom to around 3% and 4% respectively at the top. Sheeting angle of jiblets is 8 degrees. Camber in both the jiblets and main is by angled shelf foot - given that I have designed it using DelftShip, this gives me nice computer-generated panel patterns as part of the process.

The design violates several of Slieve's guidelines - the top panels are split (I'm not going far offshore); towards the top of the sail the jiblet height to length ratio grows well in excess of 0.81; the yard is very short - the sweep aft of Poppy's top panel to shed vortices is not present;

I am expecting delivery of 50yds of Top Notch 9 and other requisites on Monday, and will commence work soon after. So any observations and/or criticisms, while very welcome, will need to come fairly soon.