Hi Guys

This thread is on points that pop up every so often and then fade away again for another period, unfortunately. This is the problem that confronts every amateur experimenter. Just how do you evaluate your efforts?

When Joddy Chapman took this to an academic level he ended up studying measurement systems rather than junk rigs and the net result was that we in the junk world were little wiser at the end of the process. In theory a wind tunnel would be useful, but in practice they only seem to give results for steady state conditions and my experience of sailing is anything but steady state. It’s fine for aircraft and cars, where wind direction can be measured in fractions of a degree, but with boats alpha can vary by many degrees in a second and then be back where it started a second later. A high performance section with a ‘bucket’ lift/ drag curve may be ideal for a glider, but would be a total disaster on a boat. Therefore, apart from cost, wind tunnels would be of little use for our purposes.

The idea of using models is attractive, and I am looking in that direction myself. Even with the most excellent model I have I can only see problems and have not rushed ahead as I realise I cannot scale a rig accurately enough to prove anything.

Arne is right is saying that it is not just lift that we have to maximise, but we have to maximise the lift/ drag ratio so that minimising of the drag is just as important. If he does improve his windward performance by improving his keel it will still make no difference to the L/D of the rig, but he will annoy the pointy headed brigade a little more.

Whichever way I look at this problem, I always arrive at the same conclusion. The only way to evaluate rig modifications is the America’s Cup way. Rig two identical boats and race them against each other, and making only one modification at a time. All we need is megabucks, infinite time and infinite patience. If we haven’t a ready supply of these then we have to find the next best thing, and again the answer requires identical hulls of a size that will not be effected by crew weight and position during testing. When I started playing with Poppy this was still impractical, so I had to settle with handicap racing, and the Round the Island Race was the cheapest way to get the best return. Unfortunately we all know that handicapping is a remarkably inexact science, and in the RTI the system used is quite crude. Some classes of boat regularly win, and some (Westerly, for example) never win. This is not sour grapes, as I have learned all I wanted from the exercise, but it has not obtained the publicity for the junk rig movement that I would have liked.

Edward and I have had numerous discussions on this, so it is no accident that he now has a boat that could get an interesting result in the RTI. It has one other BIG advantage in that there is a local fleet of identical hulls that race in his local area, so we should be able to get a more accurate indication of how his particular rig compares with race tuned Bermudan rigs. As Arne says, it is comparing a cruising junk rig with a racing Bermudan rig, but it is still the best we have at this time. I hope Edward’s expenditure and effort is recognised as the significant contribution to the movement that it is.

David is right in saying that the experimenters are spread through out the world, and it is great that we have the JRA to keep us in contact with each other. This thread is a fine example of the useful pulling of ideas that could move the junk rig movement forward.

Cheers, Slieve.

PS. If anyone is offering a prize for the first JR to beat a BM rig to windward, then I am claiming the prize as I know that Poppy regularly beats comparable BM boats to windward when her bottom is clean. The problem is, can I prove it with identical hulls, propellers etc, and identical sail areas? Alternatively, can anyone prove that Poppy is not faster to windward and deny me the prize? We’re back to the question of how do we measure our performance.

PPS. I’ve always had the thought that there is one way to perform some cheap rig tests, but have never followed it up. The idea is to build kites made of two identical rigs but with the masts butt to butt and joined at the ‘partners’, making the two wings of the kite. Flown from 3 lines alongside a ‘benchmark’ or ‘yardstick’ standard kite then the one that flies highest or more nearly overhead would have the lowest L/D ratio. I’m not sure how it would work in practice, but if anyone has nothing better to do then there is something they could play with.

                                                                    Stavanger, Friday

                            A tug-car contest

Pete Hill’s test with two cars on tracks with sails on, competing on forward thrust only, is interesting, but it only solves half the problem: The sideways force vector will in the tug-car test be neglected since the tracks will not allow the cars to make any leeway. In the real world it is the optimum combination of a high thrust force and a low leeway force that makes a boat sail well to windward (..the "high" thrust force will actually be much lower than the leeway force when close-hauled...). To achieve that one needs a sail with the highest possible lift/drag ratio, sheeted to an angle that suits the hull and the sea conditions.

My hunch is that the tug-car test will favour sails with more camber than will be optimal on sailboats.

A prize for the first practical JR to beat a BM rig to windward?

The problem is that the BM rig can be anything from a plain, strong cruising rig with very few trim facilities, to sophisticated racing rigs with perfectly shaped, superlight sails, and with dozens of facilities to alter the shape of the sails.

Boats with cruising BM sails are now within reach for the JR. We prove that this summer when sailing Edmond Dantes  upwind against similar boats. Boats with racing BM rigs (and a full and competent crew) simply play in another league. Ketil Greve in his Marie G has learned this the hard way by racing against other X-99s.

I like to say that my junkrigs turn boats into cruising machines, not racing machines. And yes, I do sail my boats to windward. Next step in trying to improve my Johanna’s upwind performance would rather be to make changes to her keel.

Arne

David Tyler wrote:Pete Hill sent me this, for inclusion in issue 61, but you might like to think about it and discuss it here:

Comparing Junk Rigs                                               

With the recent developments in junk rig design it would be very useful to be able to compare the performance of one with another. Since the only real drawback to junk rig has been its windward performance, relative to the Bermudan rig, this is what most would like to compare.

The JRA has made a start in this direction with plans to build and test sail different types of junk rig on a pair of Laser dinghies. The main problem with this approach is that the sails are quite expensive to make and the trials themselves very time consuming.

Ideally a wind tunnel and model rigs would provide an accurate comparison, but the cost of this is prohibitive. A more realistic solution using model sails might be for the JRA to fund building a low tech comparison platform. My idea is to have two ‘cars’ (with unstayed masts on them) running on low friction, parallel tracks (kitchen drawer runners?) on a table. The two cars would be attached to each other by a light line at the rear of each car running around low friction blocks. to the rear of each car. The table would be set up outside on a day with a suitable wind, The two model sails would be set up on the masts and the table angled to the wind for close hauled sailing. The two rigs would then battle it out, the more efficient rig will pull the less efficient rig backwards.

By using a standard size of sail, say ½ square metre, members could submit a model of their latest brilliant idea and over time the JRA could build up a very useful data base of the various junk rigs

Refinements to the comparison platform would be to have a wind speed and direction finder on it and also an accurate spring gauge to measure how much greater  the ‘pull’ of one sail is over the other.   

If there is any merit in this idea then maybe the JRA could fund an enthusiastic member to build the comparison platform and some initial trial rigs. Obviously a Bermudan rig would be one of the first sails to be used as a benchmark

W hat about a prize for the first practical junk sail to outperform the Bermudan to windward?