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.

Thursday, January 8, 2015

The Rig

That's a lot of sail!
Sails are big business, and you can spend as much money on a set of fancy carbon fiber sails alone as on an entire good-sized sailboat in reasonable condition. But you can get around all that by going with a Chinese Junk rig. It has numerous other advantages beyond relatively low cost.

For starters, it gives you the ability to raise, trim, lower and reduce sail all without having to ever set foot on deck. It doesn't require a winch, just lots of blocks and plenty of line.

Junk sails are quite easy to make because they can be cut perfectly flat and still work. However, there are some complaints about them. They don't pull to windward when there is hardly any wind. Also, they don't point quite as high as a sloop, and the tacking can be quite slow. But they are much better than any sloop off the wind.

But it's not too hard to camber the panels, as Arne Kvernland recommends doing. Cambering the panels as shown gives them “belly” or “bagginess” so that it is the panel's shape rather than the flex of the battens that forms it into an airfoil that can take advantage of the Bernoulli effect to generate lift and move the boat to windward. A cambered Junk sail can be just as good to windward as a sloop rig.

(Here is a super-quick explanation of the physics: an airfoil generates higher pressure along its inner surface, and correspondingly lower pressure along its outer surface, thereby generating suction which can be used to pull the boat to windward.) 

I've gone through Arne's plans, and I am thinking of doing something just a little bit different. First, cambering the triangular top panels (the “storm sail” portion) seems unnecessary; they are shaped like Lateen sails anyway, which do work as airfoils even without any camber. Up there the wind is always a bit stronger, and I can rely on the flex of the battens to produce an airfoil.

Second, it seems like camber should be tunable, to be adjusted as the sails stretch and depending on the sort of sailing one tends to do. Third, I see no reason to add camber forward of the mast, since that will only be useful on the starboard tack, when the sail is pulling away from the mast, and will actually hurt windward performance on the port tack by rendering the sail forward of the sail useless. But I think Arne definitely has the right idea overall.

To make a sail, panels of fabric are stitched together along the selvage, then the whole ting is trimmed to size, reinforced and grommeted. The fabric doesn't have to be low-stretch, because the span of cloth between battens is rather small and no amount of it is under any great amount of tension. If made of ultraviolet-resistant Sunbrella fabric (which is used for dodgers, awnings and sail covers) Junk sails take a very long time to wear out.

I would like to make the lower panels cambered, and to make the camber tunable. My plan is as follows. Add to the sail some small grommets— large enough to admit two thicknesses of parachute chord—above the boom and to each side of the lower battens, as shown. Then, to induce camber, the grommets are laced up like a boot. The lacing is adjusted to produce the optimum amount of camber. The grommets at the luff and the leech are larger and will be strain-relieved using strapping. They will be tied together with several turns of thicker line, to deal with the higher strain at those points. When there is no wind, they will carry half the tension between the halyard and the boom downhaul (or the reefing line when the sail is reefed). The other grommets are more like reefing points and won't generate much strain, being responsible for the pull generated by just a small portion of one panel.

As the sail wears and the panels become baggier, the lacing is loosened gradually, until, when the sail is good and threadbare (Junk sails continue work fine even with fairly large holes in them) the lacing can be taken out completely, and the bagginess will remain because the fabric has stretched. The idea is not entirely original: there is a grommet on dinghy sails called a cunningham. It is used to take the belly out of the sail in strong winds. Well, these grommets are, I suppose, “reverse cunninghams.”

Because they have to slide almost all the way up the mast, Junk sails preclude the use of spreaders. It is still possible to use a forestay and straight shrouds, but why not go unstayed instead? Tapered aluminum flagpoles make very good unstayed masts. Not having to include shrouds, stays and spreaders saves quite a lot of money and an amazing amount of deck clutter when the masts are down on the boom gallows and the boat is being used as a canal boat.

For battens, I am thinking of using square-section aluminum tubing on the starboard side of the sail which faces the mast, and aluminum bar of matching width on the port side. It will be assembled by drilling holes every few inches through the bar, the sail and one side of the tubing, and pop-riveting through them with aluminum pop-rivets. Where the batten rubs against the sail, it will be sheathed with a half-round of PVC pipe (made by sawing PVC pipe in half lengthwise). These battens will be quite stiff, and the sail will rely on the camber of the rectangular panels and the Lateen sail-like characteristics of the triangular top panels to produce lift.

The sail plan I have in mind is quite large for a 36-foot boat: 1000 sq. ft. This should make the boat nice and fast off the wind in light winds, which is just the sort of sailing I like to do.

The sail plan shown above is based on Hassler & MacLeod's adaptation of the Chinese Junk rig. They introduced some significant simplifications and improvements into the ancient design, which is quite an achievement. I hope that my reverse cunninghams will be another leap forward for this wise and ancient design.

The only other possibly new element I've introduced is the use of boom gallows for sheet blocks. It shortens the sheets by a large amount, and keeps the mass of line from invading the deck when tacking or jibing. On daysails, there may be people, children and small animals milling about the deck, and this arrangement will make it less likely that they will get entangled and pulled overboard.

The idea is that as the sail is raised, it rotates forward on the mast to the extent allowed by the parrels that hold the spars and battens onto the mast. When raised, the sail sits forward of the gallows, giving the sheets room to do their work. When the sail is dropped onto the gallows, it is sheeted in tight at the same time, pulling it back onto the gallows.

That's the theory. Will it work in practice? Well, we'll just have to see. The fallback is to have one extra line, going from the front end of the boom straight back, whose one job to pull the sail back before releasing the aft topping lift to plop the whole assembly onto the boom gallows.

What do you think, will it work?


  1. Both our liveaboard junk rigged boats were sheeted along a mizzenmast at one
    time. It seemed to lessen sail twist up high with the continuous Hasler type sheet. This would seem really advantageous on a high aspect lugsail like your design. Tom Colvin seemed to like fine tuning the upper sail with a euphroe. His long, straight keel and deep forefoot compensated for his flat cut sails and fine tuning via euphroe must have also helped to windward. Real advantages to that except a devastating chunk of wood wildly flying about in tacks. Nice to just tend that one sheet Hasler style. Probably worth the trouble to design and build in more shaping to the panels given a centerboarded vessel. Something to be said for ultimate simplicity though: a 430 foot square main we sewed up was gotten out of a single 20X40 polytarp. We staked out the perimeter boltrope, tied in the battens and yard, then unfolded the tarp, cut it out about 6” past the edges all around, then sewed it to the boltrope. Punched in batten hole grommets and tied the battens down. Super fast build and worked well. Shortly thereafter built a second sail (Top Gun fabric and Colvins choice) so no report on the polytarp sails longevity.

    1. Hi Bob,

      Good of you to weigh in. How do you like QUIDNON so far? Wanna build one?

      The reason I am going with "expensive" sails made of Sunbrella is that I want longevity. I want the sails to last 30 years or more. I am even thinking about black Sunbrella, to match the black topsides.

    2. The way this design process is structured for feedback and with the obvious passion I'd bet this vessel gets built. Really nice the way these component parts and systems posts are simplified so a layman (and aspiring disaffected youth too possibly) can get ahold of this with a a-ha moment and and hearty “hey... I can do this!!” realization. Nice concept for collapse since a long spell in a benign port might be required in some idyllic spot perhaps south of the
      equator. And what a nice baseboat for comfy living with something like a small sharpie tender for exploring and foraging a wild coast. Well capable of being built out of salvaged steel, strip planked salvaged wood, cement, etc.. with a rig one can build easily out of salvaged and natural materials if need be. If this project does indeed go all the way to a completed vessel what a grand, how-to e-book this might make with tons of pix. Or a bound classic to be passed on as a building reference long after the web goes down. Sharing a warm shelf with other classics like Dave Zeigers sail barge building manual near the wood heater in a snug anchorage and being hungrily devoured by some young, idealistic visitor aboard. My wife and I have not settled on a design yet but we have feelers out, with Florida friends, for a building site for our “final” liveaboard boatbuild. Hopefully somewhere the finished boat can just be slid into the water on rollers. Seems the only way to get a “appropriate” shoal draft, flat bottomed liveaboard is to build one for shoestringing types. Besides, we have carted two 225 foot square chinese lugsails all around Mexico this past year and they need a home. Watching your vessel as it defines itself is going to be fun.

    3. Yes, all of that! If this all works, it will be possible to make kits using an NC mill and then assemble the boats barn-raising style, with lots of people picking up plywood pieces, slathering them with epoxy and driving in square-drive screws into pre-drilled countersunk holes according to a master plan. The rest is just fiberglass, and paint, and then the boat can float and be fitted out while in the water.

  2. Dmitry, I'm a blow-in from ClubOrlov who has been following your sea-steading escapades with interest over the years. I'm not aware of any recent public writing you've done on this front. The last I heard about sea-steading from you was when you had decided to sell HOGFISH.
    Since you've now created the QUIDNON blog, I think it would be helpful if you linked all of your archived sea-steading blog posts here rather than ClubOrlov, and perhaps provided some "the story thus far..." narrative for newcomers to this blog. Why did you decide to live on a boat? Where do you sail it and why? Why did you sell HOGFISH and what is your timeframe for constructing QUIDNON? Will you post photos of progress? When you are finished, you could produce a comprehensive book of the entire process of sea-steading for collapse survival. If you've ever spent time reviewing David Holmgren's excellent eBook "Melliodora", that's what I'm thinking. You could produce the seminal sea-faring version of his land based permaculture life guide.

    While I can see sense in your arguments for a life on the sea, I have already begun establishing an agrarian permaculture community on 50 acres in the Adelaide Hills, South Australia. My wife and some of our children get horrible motion sickness, so life aboard a boat would not be nice for them. That, and the fact we have six children from 13 down to 1 means we'd need a very large houseboat. We'll do our best on land, trading produce with sailing merchants one day perhaps. Our farm is 440 metres above sea level, so the coast won't be lapping at our front gate any time soon.

    1. Hi Nathan,

      This is a single-purpose blog: to help me think through the design and logistics of building this boat. I'll probably write more about boats in the future. But this blog is for a specific, rare type of sailing nerd, not armchair sailor such as your.good self :) All the best with your Permaculture homestead.

  3. Dmitry,
    A excellent idea, one to stick in the to do/try box

  4. We built our Benford dory, with cambered junk rig and a 6hp OB in a well. For us it has worked exceptional well, the low power OB is fine to get around harbours/anchorages and motoring in flat calms, because we have sails for the rest of the time. Fuel bill is really low. One regret is I wish we did have a flat bottom for beaching. Too bad you guys weren't blogging 7 years ago with your square boat ideas, we may have ended up building something different. Not looking forward to the haul-out we'll need to do soon.. Other than that the dory seems to perform beyond expectations.

    I'm looking forward to reading more about this big live aboard platform, when are you planning to put skil saw to plywood?

    All the best.. Gary

    1. Hi Gary,

      As far as putting the Skil saw to the plywood, I am thinking of taking a major high-tech shortcut, drawing everything out in CAD and generating tool paths for an NC mill. All the plywood pieces will be cut out except for a few bridges here and there that will need to be cut away with a coping saw, and all the holes pre-drilled in the exact right places. That way I will be building from a kit of parts, optimally cut out of plywood sheets with minimal scrap, and assembly will go quickly with no mistakes or inaccuracies.

      Just curious, what do you do with your OB to keep it out of the water when it's not in use? Do you tip it up, pull it out, or leave it in?

    2. So, as an armchair sailor, it seems you are looking to produce an IKEA style flatpack boat, so that all us armchair sailors can benefit from the specific knowledge of you sailing nerds. That's worth sticking around for!

    3. Two-part answer:

      1. I am much more accurate with CAD and NC than with a Skil saw and a grinder, although I can get acceptable results either way.

      2. So I choose to use CAD and NC, and as a side-effect other people will be able to buy the kit, assemble it quickly and sail away.

  5. While sailing I leave the OB down. At anchor/marina's I sometimes haul it out with block and tackle hanging from the boom crutch - and lay it down on deck, 6hp OB doesn't weight much, but I get lazy about that. The double ender design of the dory doesn't permit a well long enough to allow tipping the OB up, which is another little negative compared to square transoms. You have the opportunity to completely sort that out. Some catamarans I've seen have nifty sliding frames (on jib sheet tracks) for OB's too.

    Just noticed this is the rig blog.
    I like the idea of the lace up sails, it would be good to have camber adjustability from 6 to 12%, the deeper camber is what your big barge would need to get moving me thinks. The bolt ropes are at their most strain at the top panel, and progressively less tension as you move down to almost zero in the bottom. After sailing our boat 3000nm its the top triangular panels that are getting stretched and roughed up.

    1. Ah, jib sheet tracks... I was wondering how I'd do that. Thanks, now I know!

      And as far as lace-up sails, 6-12% camber sounds just about right from Arne's calculations (which he performed using an actual physical chain instead of just plugging through the catenary function).

      Also, Arne recommends making the top triangular panels out of a stiffer material. They could perhaps be reinforced with a dacron strip. Also, they could benefit from a cunningham grommet that could be pulled toward the luff, to reduce camber once the sail stretches out, just like the sail on a Sunfish (which is a Lateen sail—same triangular shape).

      Thanks for good ideas!

  6. There was a production boat that was built out of ply a long time ago called A Newporter 40. It was a ketch rig but I did see one that was junk rigged.

    The manufacturer was a plywood company that made special 40' long sheets of ply so no joints fore and aft. You might approach a ply company with your project and see what they might be willing to do. Some here in Oregon are idle part time.

    They can do the CNC also.

  7. That's not a half-bad idea, although I expect I'll build up the topsides out of layered pieces "screw&glued" together rather than making scarph joints or using huge sheets that are a pain to ship.

  8. If I understand aright, the top panel (or two), are the stormsails in a major blow. Therefore seems to me that they should be as flat as possible and made of heavier material.