Hi Slieve,

thanks very much for your reply. How very nice to be sailing in warm weather , but not so great in November to return to good old Blighty! You've got a hole-in-one: an easier life aboard is what we seek!!

I'm sorry to say that, as I was writing my little update off-line, you were posting your reply and somehow they managed to cross in the ether. Anyway what you say is extremely helpful at this stage as I'm about to draw something nearer to the final version...

I remember you writing that if you were doing another sail for POPPY you might give her 35% balance. On our ANNIE's proposed rig 35% looks very good. Would you also hold with your comment about widening the slot a bit? I was mistaken in my last post (it was a bit past my bedtime) by mentioning a slot of 13 foot six! What I meant was 13 1/2 inches or about 340 mm. Does that sound about right? Should I at this stage be measuring the jibs separately from the mains'l to find a more accurate c/a? When I do the PJR "hang the sail by a pin" trick to find the c/a, I was thinking I might cut out the slot from the paper or card. 

You mention putting the 50% chord line right on the c/a of the Bermudan rig that you're replacing, if that rig was well balanced. In ANNIE's case she does carry a bit of weather helm as is common I'm sure with boats of her type. Does anybody have any views on shifting our c/a aft by 3% of w/l or is this just fiddling and more likely to end in tears?! 

In my simplistic way I reckon ANNIE has no balance on her rudder as it is suspended from its forward edge. Is this what you mean by hydrodynamic balance Slieve? I'm imagining that the only difference I can easily make to the balance on the helm is to get the mast and rig position correct.

ANNIE is just over 6 tons, 9'6" beam, and 26 foot on the waterline, drawing only something like 3'6" with the plate up. Her existing gaff rig is just over 600 ft.². I suspect that the SJR might provide more drive to windward than the existing gaff rig, so maybe that sail area is sufficient? I am tempted to add a bit though, on the grounds that it is so easy to reef!

I am so slow at reading and at sums, that the planimeter has really helped a lot, having not really known what it was when I was given it!

Thanks again for your comments.

Pol.

Hi Pol, I've just been off sailing Hobie Cats in a warm climate and on returning I'm reminded how cold the UK can be, and how much better the Split Junk is than the Hobie Cat rig. Fast reaching may be fun, but if you have to struggle to get to windward and have to think before you tack then it's not carefree sailing.

You've raised a number of points in this thread so I'll try to take them in turn.

1. Aspect Ratio. Here there are a number of considerations. Firstly, the higher the A/R the lower the tip losses and the higher the efficiency. You just have to look at gliders and the modern airliners to see that, however, you also have to think about the height of the centre of pressure and stability. The centre of pressure of a Bermudan rig is fairly low, and the centre of froward drive is even lower as the top (pointy) part of the rig tends to produce more drag which tends to heel the rig rather than drive the boat forward. This means that you can have the centre of effort of a more rectangular rig higher without having a greater heeling force.

There is also the aesthetic consideration. Sketch the rig you think looks right, and then do it again but with a reef down and see if it looks too squat. With Poppy I ended up with a mast which was about the same height as the original Bermudan rig, and have no problem standing up to the rig.

Another consideration is the depth of each reef. With hind sight I wouldn't have a jib with height to chord ratio any less than as on Poppy. A taller panel is to be preferred to let the jib make a better cambered shape. In recent rigs I have tended to reduce the number of panels. It is surprising how few steps of reef are needed in practice with this rig.

2. Regarding the sheet sweeping the cockpit, I'm a great believer in simplicity so have settled for a fixed sheeting point as far aft as possible, accepting that the sheet is only a consideration when tacking or gibing and the rest of the time is well out of the way. I've never used double sheeting and see it a an unnecessary complication of an essentially simple rig. Poppy sails like a Topper, with sheet, tiller and relaxation.

3. The $64,000 question is rig position and balance. Practical Junk Rig (PJR) is called the Bible of the Junk Rig, but perhaps it should be referred as the Old Testament as a lot has happened since it was written. The authors were working with basically flat rigs, which along with hinged and bendy batten rigs have a number of undesirable characteristics. As the first 30% of these rigs are flat the stall or separation of the airflow on the lee side tends to start from the knife edge separation from the luff, so the centre of pressure tends to move aft, and produce weather helm. I get the impression that many junk sailors with these rigs tend to sail in a semi stalled state most of the time, producing high drag, low drive and weather helm. In a rig with a good camber in the right position approaching the stall the airflow will start to separate from the leech and if anything the centre of pressure will move a little forward, as with the wing of an aeroplane. With the cambered sail tell tales help keep away from the stall. I think the information in PJR on balance is based on this flat rig experience, and I feel that it does not apply to the Split Rig. I will admit that I've never really followed the ideas in PJR on this topic.

Using drawings to establish rig position works on the rig centre of area, not centre of pressure, so the characteristics of the rig must be taken into account. My experience with the Split Rig is to put the centre of area in the same position as the centre of area for the Bermudan rig if the boat balances well. In practice I even simplify that and put the 50% chord line of the parallelogram section in the same fore and aft position as the centre of area of the Bermudan rig. It makes for easy sums and drawings.

Remember that the Split Rig has high balance so when the sheet is eased there is little heeling force, and in the extreme the heeling force can be to windward. Then you can increase area and fly!

You mention you dad at over 80 changing from a tiller to wheel. I have two thoughts on that. I agree with you about keeping it simple with a tiller and using a wind vane. There is no reason why everyone does not have a vane as a good one can be built for £20 - £30 if you keep it simple. The second one is that the helm should be light and the weight on it is not always down to boat balance but may be down to the hydrodynamic balance of the rudder. Sailing the Hobie Cats over the last couple of weeks the tiller was light, but when the rudder was swept aft when coming back to the beach it was almost impossible to move if not sitting in a well braced position.

Pol, you have a planimeter!. Wow! I've always wanted to play with one, though in practice I just do some simple sums (and guess).

I hope this answers some of your questions. If not, or if you have more, just ask.

Cheers, Slieve.

Hi Pol,

typing error, I meant 5%. The original c of a was 17% ahead and the new one I calculated was 12% ahead. With the keel addition we are back to 17% and have a balanced tiller again. With a split junk it may be different to Arcadian as she has flat sails and the center of effort with flat sails tends to be further aft than with cambered sails. Also you are considering a single masted rig whereas Arcadian is schooner rigged. All factors to be considered. Best of luck with the conversion.

Hi, on Arcadian I designed the new junk rig with a c of a three percent aft of the original Bermudan rig c of a and ended up with a huge amount of weather helm. I ended up adding a significant area to the keel aft of the existing keel and she now balances well. If I had used the same c of a as the original rig, all would probably have been well. Obviously PJR is not infallible so please take their advice with reservations.

Hi Pol, I've just seen your post, but am currently not at my homebased computer. If I haven't responded properly in about 10 days time send me an e-mail to tell me to get a move on. Cheers, Slieve.