Based on the positive test results from the 1:12 scale model, the design of Quidnon nouveau-retro Chinese Junk sails is almost fully baked. But there are a couple more bothersome problems to solve. Junk sails are attached to the mast using parrels, which are short lines or straps running along the battens and around the mast. This generally works rather well, but produces a couple of unintended effects:
1. The sail tends to rotate forward on the mast because the part of it that is aft of the mast is larger and therefore heavier. To counteract this tendency, Junk sails employ an additional control line called a “luff hauling parrel” which is laced through the front of the battens and then around the mast. It is yet another line to adjust, and it would be nice to get rid of it. Depending on the design of the sail, other minor control lines may be necessary as well, further complicating the handling.
2. On one of the tacks (depending on which side of the sail the mast is) the sail drapes over the mast, distorting its shape and making it a less efficient airfoil. Without this distortion, each panel of Quidnon’s sails forms a very efficient airfoil, similar to a Lateen sail. This is an important effect when sailing hard on the wind, making one tack significantly more efficient than the other.
To get rid of these unintended effects, I would like to introduce a new piece of rigging: the batten standoff. These are basically sticks that fasten onto the battens at one end and onto the parrels near the mast on the other. The batten standoffs do two things: they keep the sail from sliding fore-and-aft on the mast, and they push the sail away from the mast. Under most circumstances they are self-tending and don’t require adjustment.
At their ends near the mast, the standoffs are daisy-chained on lines—batten standoff lanyards—that hang down from the end of the halyard. These lines make sure that the standoffs hang almost but not quite horizontally: they have to slope slightly toward the mast, so that they don’t ride up the mast when under compression. If the mast is to starboard of the sail, it may be necessary to walk forward and pull down the batten standoff lanyards after reefing while sailing on a port tack, when the standoffs are under compression. When they are under tension, they will be pulled into position by the battens and settle a bit further by themselves due to gravity. Thus, when reefing while on a port tack, it is best to release the sheet first, allowing the sail to luff, then release the halyard partway, then haul in and tighten the reefing line, and finally haul in the sheet to power the sail back up.
The batten standoffs have to be cheap, light, reliable and easy to jury-rig or to replace when they fail. To achieve this, I intend to make them out of aluminum pipe. The pipe is cut to length, the ends are tapped, and stainless steel threaded rod is screwed into the ends. The mast end consists of a triple clamp, with two horizontal slots for the parrels and one vertical slot for the lanyard, all tightened together using a single Nylock nut. The batten end, which goes through a hole in the batten, has a couple of washers and a Nylock. There will have to be 24 batten standoffs (6 battens × 2 sides × 2 sails) and they will cost a bit of money to fabricate (out of aluminum pipe and bar and stainless steel threaded rod, two rubber washers and two Nylocks). But I think that the improved performance and the elimination of extra control lines will make it worth it.
There is also an element of perfectionism to it. There is some amount of extra joy to be had in looking up and seeing a perfect, maximally simple, undistorted form of the sail lit up by the sun against the sky.
The purpose of this project is to design and mass-produce kits for a floating tiny house that can sail. It combines high-tech modeling and fabrication and low-tech assembly that can be carried out DIY-style on a riverbank or a beach. This boat is a four-bedroom with a kitchen, a bathroom/sauna, a dining room and a living room. The deck is big enough to throw dance parties. It can be used as a river boat, a canal boat or even a beach house. It's rugged and stable enough to take out on the ocean.
Saturday, December 16, 2017
The Sails Revisited
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Batten Standoff (patent pending)ReplyDelete
This solution brings to mind a soft-wing sail, but one-sided.
What's a bit different here is that the batten standoffs are optional—an enhancement for somebody who cares about upwind performance. Someone who doesn't want to bother with them can just install a luff hauling parrel and be done with it. But it opens up the possibility of hanging the sail further forward on the mast without sacrificing performance on one of the tacks. Doing so results in softer tacks and jybes and less tension on the sheets. Since the keelboards can be repositioned to fine-tune the center of lateral resistance and the sails can be repositioned on the mast to fine-tune the center of force, it should now be possible to make a perfectly balanced sail plan.Delete
Is there a particular reason that the mast has to be in the middle of the junk sail? Only purposes I can envision are clearing the other mast while jibbing, reducing torque on the mast (which shouldn't be an issue anyhow), and an engineering kludge to keep proper form on the top panels. What am I missing here?ReplyDelete
Also, will the batten spreader design have to be modified to accommodate the angle of the 3 topmost battens, to be able to stow the sail? It appears it is modified in the picture with the blue sail.
There are numerous efficiencies gained by positioning the sail across the mast. This is one feature of the Junk sail I don't see a reason to modify. It remains to be seen what fraction of the sail will be placed before the mast for optimum efficiency.Delete
At some point it seems the overall efficiency and simplicity of the chinese lugsail, honed over centuries of use, begins to suffer from too many add-ons. Colvin seemed to compensate for the drawbacks of the rig with a long lean waterline, deep forefoot, and long straight keel along with sheetlets to fine tune the sails upper shape. At some point a overly complicated chinese lugsail rig might better just be replaced by a different rig totally, perhaps more in tune with a scow hull. My junk rigged sharpie hull went to windward about as well as a bowling ball in a snow drift. And my Pearson keeler junk rigged boat not too much better. But, easy to see how nice it would be to modify the rig to something that works more efficiently too. In the end it's whatever boggles a skippers scrotum: it's HIS boat.ReplyDelete
Based on the tests I did with the model, Quidnon's unmodified Junk sail goes to windward very well and points very high, as high as a Lateen sail. I achieved this result by undoing the damage caused by Hassler and MacLeod, who went with inefficient square panels, which some people compensated for by adding camber, making a kludge within a kludge. Quidnon's sail is basically a stack of Lateen sails. The sheeting arrangement is likewise my own, and superbly efficient. The batten standoffs are the last, optional tweak to this design, to further improve windward performance, especially on the port tack (with the sail hung on the port side of the mast).Delete
By the time you get done modifying the rig, to the better it seems, sailing cognizanti may have to call it the Russian lug rig.... and enter the new era. Definitely fun to watch develop and kudos for the out of the box approach.Delete
I don't understand why you will need a standoff on each side of the batten. Aren't they only required on the side adjacent to the mast?ReplyDelete
The standoffs are between the battens and the mast. There is one standoff clamped onto the parrels on each side of the mast, to fix the fore-and-aft position of the sail relative to the mast. The couplings between the standoffs and the battens are flexible, so that nothing gets broken or bent if a parrel breaks or if a standoff slips along a parrel.ReplyDelete
Minor comment regarding the effects of Galvanic Corrosion. Stainless is further from aluminum than carbon steel in the galvanic table, with higher anodic potential voltage as well. You might be better off with painted carbon steel in both a cost and durability sense.
I don't expect a lot of electrical charge on your mast but perhaps the DC wind generator has some effect in regards to needing a grounding path? I'm not familiar with the level of potential galvanic corrosion but I am working on a facility near the ocean at the moment and we spend a lot of time worrying about dissimilar metals being joined and how to use di-electric junctions, sacrificial anodes and such to ensure our designed 35 year service life can be reached. This is along the lines of the Quidnon's expected lifetime (I think?).
I would definitely avoid any blending on aluminum/stainless on the mast proper, the stand-offs don't seem as critical (to me) though.
Maybe someone more knowledgeable can chime in. I may be over-engineering things here.
Aluminum and stainless gall together. Nevertheless, most boats use aluminum spars and stainless steel fasteners. Using anti-seize compound helps somewhat. But most people are resigned to the idea that galling will eventually occur and that the fasteners will never come out again. A typical example is stainless steel sail track screwed to an aluminum mast using stainless steel screws. Removing and replacing it involves shearing off the heads of all the screws, grinding the stubs flush, and then mounting a new sail track with a slight offset and drilling and tapping all new holes. Such is life. On Quidnon, deck rigging will be galvanized and running stays will be synthetic rope, but the mast and the battens, along with the batten standoffs, will be aluminum, with some stainless steel fasteners. This seems like a reasonable compromise to me.Delete
Stainless steel tubing is more expensive than copper water pipe, simply because of the production volume of copper pipe. Could these standoffs be made using copper water pipe?Delete
I believe the answer is no. Copper is too weak a material and too heavy. The only good choice (other than wood) for the standoffs is aluminum, with stainless steel fasteners at the ends.Delete
How will you keep the standoffs horizontal when the battens are on the windward side, and still be able to slide the sail up and down? Wouldn't a split junk be an easier way to deal with the mast interfering with sail shape?ReplyDelete
The standoffs are daisy-chained on two lanyards that hang down from the halyard and hang down at a slight angle toward the mast to keep them from riding up the mast when the battens are to windward. It will be recommended that reefing be done with the battens to leeward; if not, the two lanyards will require a strong pull to set the standoffs at the right angle.Delete
Has to be completed by June 2018, in time for the World Cup.ReplyDelete
Might be the most interesting project available for management because it solves Al Gore's fears of climate change flooding. Joking aside, the Quidnon is a proud idea.Delete
In practice, western junks sail better on the tack with the sail AGAINST the mast (usually the port tack). Counter intuitive, but true. Standing luff parrels can be used to hold the sail in place, if there's no camber in the sail. You should be able to rig a flat sail with just halyard, sheet and yard hauling parrel as running lines. One running luff parrel is usually required with a cambered sail.ReplyDelete
Hi Annie, great to hear from you!Delete
We considered using a Western Junk initially, played around with camber, and then decided that rectangular panels are a bad idea and went back to the Chinese fan sail design with no camber, functioning as a stack of Lateen sails. The design needs some more refinement and fine-tuning, and it isn't certain yet how big an improvement the batten standoffs will give versus hauling parrels. It may turn out that the standoffs are a bit of gold-plating, in which case they won't get used.
I hope you like other aspects of Quidnon's design. Voyaging on a small income was a major part of the inspiration.
frankly I think the stand-off battens will not improve the performance to windward. I and many other sailors with practical junk rig experience have come to the conclusion that the JR is just as good, or better with the mast on the leeside.
I have written a little note on that:
Arne Kverneland, Stavanger
Thanks for your thoughts. I initially designed the sail based on Hassler & McLeod, with rectangular panels except for the top two and no camber. Then I played around with adding camber. All of this was rather dissatisfying. Then I hit on the idea of a flat sail with roughly trapezoidal panels (shorter along the luff than the leach) so that each panel acts like a Lateen sail. I then discovered that the mast did interfere with the lift. It makes sense that interferes more when it is on the windward side than the leeward side, because when it is on the windward side it reduces the Bernoulli effect. But overall the sail I designed pointed quite high and was fast to windward (based on the scale model). And then, finally, I realized that it would work best with the sail NOWHERE NEAR the mast, but mounted on batten standoffs. That is where my concept stands now, yet to be tested at scale. The mast will add some amount of windage, but it will not interfere with the operation of the sail on either tack.
This comment has been removed by the author.ReplyDelete
You certainly do have lots of clever ideas in your design and it's a great idea to get people living on the water. Although local authorities don't tend to like it so much. But back to your sails. What you are describing sounds more like a Reddish rig and I have to say that there is no illustration that shows your sail looking dramatically different from any other junk sail that I've seen. The Chinese themselves had a myriad of shapes, but they were all variations on the theme. I think your standoff battens are an unnecessary complication, especially bearing in mind that you are putting this rig on a boat that isn't going to be a 'witch to windward' anyway. If you don't like camber, articulated battens with one or two joints would be a better way to go. I shouldn't bother with re-inventing the wheel at this stage: better to use your ingenuity on the boat itself than to try improving a rig that you have yet to sail. I'm not saying that it can't be improved, but junk rig's strengths come from simplicity and ruggedness and there needs to be a really good trade-off to compromise either of those.ReplyDelete
Yes, the batten standoffs are definitely optional; something to try. If they don't help, they won't get used.Delete
I was very pleasantly surprised by how well the model of the boat went to windward. Heeled over slightly, it presents an asymmetric 100º V to the waves in a way that mostly follows Bolger's "sea of peas" recipe, so that it slices through the water cleanly with no wake. I don't know about "witch to windward" (too much to ask in a houseboat) but it should be able to hold its own just fine.
I think you will get much clearer answers from any rig if you rig a dinghy in the 12 - 18ft range and actually do some sailing in it. A Model, in particular a static model, cannot give clear answers, although it is better than just making sketches. Garry Hoyt (Freedom boats) made a balanced lug rig which was offset from the mast for the same reasons that you give. He claimed that it was very good (see his video), but on that video he was just beam-reaching back and forth. Anyone can do that.
Yes, that's close to my plan, although I intend to test out the sail on dry land and use strain gauges. The model I made was radio-controlled and I played around with short-tacking it in a stiff breeze. I was quite happy with the result.Delete
This is all so technical; I'm just wondering how easy/difficult it would be to raise/lower the sail with these batten standoffs in place. Also; how easy/difficult to replace a batten standoff if one was to fail, say, if it was one of the harder to reach ones.ReplyDelete
Raising the sail is easy regardless; lowering it is easy with the sail to leeward, harder with the sail to windward. When the sail is to windward, it is necessary to ease the sheet and give the standoff lanyards a pull after reefing.Delete
This is completely unrelated but maybe can be used for the interior. The joints are very well designed in my opinion.
Yes, these are the types of joints we wanted to use originally, but backed off that plan for a number of reasons. Mortise and tenon works relatively well for orthogonal joints and works very badly for curved joints.Delete
Hiya! I know this is kinda off topic but I'd figured I'd ask. Would you be interested in exchanging links or maybe guest writing a blog post or vice-versa? My website discusses a lot of the same topics as yours and I feel we could greatly benefit from each other. If you might be interested feel free to shoot me an e-mail. I look forward to hearing from you! Superb blog by the way! boat designers nzReplyDelete
Yes, this is pretty wildly off-topic. This blog is about designing and building one particular affordable, economical houseboat. Yours is about high-performance toys for rich people. I don't see the overlap.Delete