Junk rig on modern hulls

I suspect that using a tear drop or even elliptical cross section mast may help some of that rather than a round mast. A round shape disrupts a lot of airflow, way more than even a very thick (30 or 40 percent) tear drop shaped mast, it should help the flow on the low pressure side considerable on the "off" tack. And using some means to hold the boomlets further off the side of the mast should improve the flow as well, as I noted above. Some of the things I want to try when and if I ever get to building something larger than a dingy.

 

Arne, I commend you for your attention to detail and willingness to experiment. You've done tests with different sail shapes on the same hull, so I don't doubt your claims to improved performance. It's interesting to see.

What material did you use to make your sails? What is the weight of the cloth?

PDW

 

PDW, sorry for my very late answer.
The cloth I use nowadays is called Odyssey III. It is 6.5US Oz (Measured to about 224g/sqm). It is a rip-stopwoven polyester cloth, meant for awnings and stuff like that. Coated on one side and quite elastic. The loads in a cambered-panel junksail is much, much lower than in a conventional sail of the same size.

Arne

 

Ming Ming II did a nice job building some shape into the lower 2 or 3 panels, which were also removeable. They were added for light air sailing above the Arctic Circle. The nice thing about carrying progressively more camber down low is you can add more twist in the leach so you still get an even break on the luff, and I suspect you get a more forgiving rig in gusts than you might otherwise get with a Junk Rig, so you may not have to reef as soon.
https://www.youtube.com/watch?v=0jsPOlg7Ovc

 

Roger Taylor's Min Ming II surely has a fine and efficient rig. My rigs are basically quite similar, except that I sew the panels together at the battens. My experience (junkrigs since 1990) is that reefing is so easy that I hardly think over it before adjusting the sail area.
Arne

 

Arne,
I just went back and reviewed your posts. Nice work. I agree with your idea of keeping the mast in the separations bubble where flow will re-attach. I think a round spar is probably as good as any where it sits on both tacks, and is the best shape for minimizing weight aloft. However, there might be an advantage to a different mast profile towards the top to minimize drag when reefed. Have you considered such an idea as a more elliptical shape up high? Also, is there any advantage to allowing some sideways mast bend with a Junk Rig, perhaps to create some twist in gusts?

Here is a picture of me sailing my Laser last year, and a little heavy for the boat at 220. As you know it is unstayed and is sailed with a lot of leech tension to induce mast bend. Normally this does not allow much twist, but when you hike hard enough that the mast bends more sideways, relative to the top and bottom the middle of the mast is to windward, which created some virtual twist in the middle of the sail, though not at the very top which is not shown. As you can see from this view the leech is actually very straight and tight, but there is what I call 'virtual twist' created by the sideways bend of the mast. I sail with a looser outhaul for more camber down low to match the increased twist off in the middle. I don't point as high as I would if I was 180 pounds but I make up some of that with footing speed, and can play the shifts a bit harder.



Anyway I digress. I wonder is some sideways bend might benefit a junk rig?

 

You already have great twist from the looks of this, but I was wondering if the top half for the mast was tapered more sideways and perhaps reinforced with carbon so it will have less drag when reefed, it might also work a little more bending and straightening sideways in gusts and in waves when not reefed, so the big roach in the upper part of the sail can open and close even more than it already is, and the mast can store and release some energy when sailing through waves and sudden gusts...



I suppose that upper most batten is effectively an extension of the mast as it is in a sprit, lug, or gunter rig, and can also bend sideways to release wind in gusts. The top panel gets some it's camber like a Pacific Proa crab claw sail. How high of an angle can that top batter be? Also, how much does it help to rake the mast of a Junk rig forward?

 

Jamie,
I admit that I am not quite in the fine-tuning category of laser sailors! I have made a couple of JR, wooden masts slightly oval, but then mainly because I assumed that the fore-and-aft load is the highest on the mast.

Still I have fiddled quite a bit with different sheets and sheetlet (shetspan) setups to get the twist about right. To see what I am doing I have fitted telltales at the leech of all the batten panels. When they collapse at the same moment (as I bear away), the the twist is good enough for my use. The attached video on Youtube shows the sail of my Oslo-Dinghy, Broremann, with the telltales flying.
Arne

https://goo.gl/CyRVGv If it doesn't work, just go to youtube and search for Broremann

 

Arne,
It would be fun to see a one design class with a junk rig to see what might come of it. It's impressive how much developed in the Finn class, much of it the work of Paul Elvstrom and Joerg Bruder. The laser is pretty simple and was originally very crude but Hans Fogh and Bruce Kirby pretty much nailed it from their experience in Finn and OK Dinghy, and it has changed relatively little. We just sail it a little different but not much. We sail in the wake of giants. ;-)

Nonetheless you and others have done a fantastic job of developing the Junk Rig despite there not being a one design class to fine tune it as you say. Do your masts rotate? I was assuming they do, but I suppose it it's round it doesn't matter, and it is simpler to make watertight if it does not. Your comment about fore-and aft made me realize it must not, as you must be referring to the fore and aft loading when going down wind, where the rig can be loaded more that when reaching or upwind. I can see some advantages either way.

It would be fun to try a junk rig in a Laser. I've been wanting to try a big Optimist Rig. Why should the kids have all the fun?

 

http://www.boatdesign.net/forums/attachment.php?attachmentid=101722&stc=1&d=1438334038

http://www.boatdesign.net/forums/attachment.php?attachmentid=101723&stc=1&d=1438334238

No, my masts certainly don't rotate. New to me lately is to build smaller masts as a hybrid of aluminium and wood. I use a 6m standard tube for the lower section and then the top section is made from spruce. This is a quick and easy way which saves some weight and windage over an all-wooden stick. The shown boat ("Frøken Sørensen"), above is a 6.5m un-ballasted centre-boarder. The lower mast section is 100mm with 4mm walls (6082 T6 alloy)
Arne

 

That sounds very interesting. Great way to go with aluminum in the bottom half, and then spruce in the upper half, which could be reinforced with glass/epoxy as needed.

Nice looking sail again, and smart looking boat and rig.
That would be a lovely little setup for a one design racing fleet.

 

Arne,
How does such a boat and rig like to sail down wind?
Does it like to sail by-the-lee and heeled slightly to windward?

 

The junkrig is generally easy to sail downwind, except that a good size rudder is helpful, as on any catrig. I have only sailed the rig by the lee a few times; I guess I am too relaxed to bother, generally. Still the few times I have done so (mainly to avoid gybing in a narrow passage), I have noticed that the speed goes up. Frøken Sørensen surely can be sailed in Laser style in this respect, if one wishes.

I know some have glassed the spruce mast top. The all-wooden mast for my Johanna(with that blue sail) was glassed, before painting it. On this hybrid mast I have just glassed the aluminium-wood joint and painted the rest of the top section with 2-pot polyurethane paint. I wanted to see how well it lasts.

 

Frøken Sørensen looks like a lovely little boat to sail. Rig looks perfect.

 

Thanks Jamie
Yes, she is very good for the protected waters around my town, Stavanger in Norway.
Now I will try to upload 2 files, one jpeg file showing the original Bermuda rig, and one PDF file showing the junk rig with details (like how each panel is being cut to create the camber, shown on Sheet 3 = "Ark 3" in Norw.).
Arne

http://www.boatdesign.net/forums/attachment.php?attachmentid=101725&stc=1&d=1438356902

http://www.boatdesign.net/forums/attachment.php?attachmentid=101726&stc=1&d=1438356993 (that PDF-file showing the JR)