Critique my sail design?

This is just what I have noticed in my encounters with this situation. The more I think about this the more it seems like having a vertically stable yard would be beneficial. Then I wouldn't have to worry about the orientation of the battens and binding.

I don't believe it would be any more windage than the more than 100' of line for lazy jacks. The method would be to let out the halyard while pulling in the sheet, the sheets keeping the battens from straying. But it would certainly be simpler and more fool proof to perform the operation with lazy jacks. I'm leaning more and more towards lazy jacks for that and other reasons, even though I don't like the idea of having another thing to fail, especially one way up the mast.

Yes, I understand. It seems as though if I choose not to have any kind of tie downs for reefed battens then I will perhaps not have enough tension to keep the sail from billowing in the vertical dimension.
What batten spacing would you recommend to take this out of the equation? It seems as though having more battens would be beneficial, and I'm sure Gonzo would be happy that my battens would then not snap like toothpicks.

I want it to be as unfancy as possible, especially since I will have 2 sails in a biplane configuration, on a catamaran. My goal is to only have a single halyard and sheet per sail and nothing else to ever mess with, to be able to reef with no fuss and no way for anything to get hung up, to never have to leave the cockpit for any reason while under sail. It is my understanding after reading several papers on the subject that the primary(almost exclusive) reason cruising catamarans capsize is due to wind action, with or without other factors at play. Having easy and quick control over reefing and being able to weathercock the sails in any position seems to be a key component in being able to prevent capsize. One of many reasons I am choosing free standing masts.

I'll see if I can find Bolger's writings. It seems as though having a yard which maintains it's orientation on it's own would allow for just one halyard, though if the mast bent very much it would take tension off the leech.

The boom, battens and yard would all have the desired sail shape on the inside, and the sail when filled would be in contact with them.

Yes, I am starting to realize that having more battens will serve a lot of important functions. Yesterday I quickly read the relevant portions of The Practical Junk Rig and it reinforced that conclusion. Perhaps I was too focused on keeping the weight and aerodynamic disturbance of the rig to a minimum.

A quick background on my sailing experience: As a kid my uncle used to take me to sail his RC sailboat, and I've had a few since then. As a teenager my grandfather took me out a few times on his monohull sailboat off the California coast. I've sailed on dinghies a few times throughout my life. I am 44 now. Other than that I've been fascinated by sailing and sailboats for a very long time and watch and read everything that seems worthwhile that I can get my hands on. The plan is to build a very small test boat for lakes, then build a 24' version for island hopping the Bahamas, then if I'm still into it build a larger ocean going version and sail around the world. We'll see how it goes, and if the finances allow. I'm not a wealthy person.

Thanks again for being interested and taking the time to help me iron this out. I'll try and draw an updated and more detailed plan this weekend.

 

Thank you, I read the relevant portions of Practical Junk Rig yesterday, which is available on Archive.org. They also have available other good books on sailing, like World Cruising Routes, and Aero-Hydrodynamics of Sailing. Principles of Yacht Design is available here: http://protei.org/download/20110417Principles of yacht design - Larsson, Eliasson.pdf. What resources are available as a member of JRA that are not available as a guest?

The concept of the junk rig is great, but I intend to create something simpler, and perhaps a bit more efficient, informed by it's design.

 

I think you believe the battens have infinite stiffness = rigid. That is not correct. You need to determine the stiffness to calculate the deflection.

That is not correct. The batten would have a force applied at the ends that is larger than the force applied on the sail.Lifting Sling Capacity Equations, Calculator and Considerations https://www.engineersedge.com/mechanics_machines/sling-load-calculator-equations.htm How to Calculate Tension in Physics: 8 Steps (with Pictures) https://www.wikihow.com/Calculate-Tension-in-Physics

Wishful thinking never kept a sailor from dying.

 

I think then you would need to worry about the yard binding.

That is what worries me. And the higher the panels, the more that is likely to be a problem.

M junk sail had panels about four to five times as long as they were high, and that worked. I have not varied that parameter to find out the trade-offs. I would look at pictures of junk sails taken with the camera about perpendicular to the sail, or drawings, look at the distribution of values, think about how many battens and their associated sheetlets I am willing to have, and adjust the aspect ratio of the whole sail if needed.

Experimentation will cost money as well as time, because there will be failures, and you will have to replace the things that don't work. If your primary goal is to get out there, start with something tried and tested. If you are willing to accept some delay to your ultimate goal while you experiment, I will be curious about the results. There are design choices that have not yet been explored, to my knowledge, and you identified some. For what it's worth, I think the attempts to keep battens and yard at a constant vertical angle are likely to be far more trouble than any benefit would be worth. The boom, because it doesn't need to move up and down, may be a different matter, though if you're willing to use lazy jacks (very low maintenance in my experience), you don't need that, either. You already noticed I don't like the rods. Wishbone battens only behind the mast are interesting. More complicated than straight battens going past the mast, but perhaps offering enough aerodynamic benefits to be worth the bother. I might even try out the alternative I proposed to you, if I can fit it into my own amateur research programme.

You can post to ask questions. I found a brief thread of someone asking for advice on a 51ft catamaran with biplane junk rig they were planning to build. David Tyler told them of members with such boats, and where to find the contact details of those willing to be contacted, so he could get advice directly from those who have experience. Another thread gave a link to an article on Dragon Wings Dragon Wings https://www.duckworksmagazine.com/04/s/vintage/multihulls/index.htm, and mentioned that China Moon has been described in Newsletters 36, 40, and 43. I don't know whether you can access those as a visitor. You could find out whether there are any JRA members within reasonable distance who might take you sailing.

 

I don't believe that, I believe that the maximum stress the battens will experience will cause insignificant deflection.

It would appear you are correct. According to a calculator the single leg minimum load capacity would be 408lbs, with a 36" chord and 3.6 draft(11.31 degree leg angle), with a load of 160lbs(80mph maximum wind force on 20 ft2 divided by 2). I still think it would be fine, and again, a condition it would never experience. You may not have noticed in this thread that the sailcloth is going to be laying against the battens, meaning that tension load will not occur(I think). Does this principle even apply with an evenly distributed load like that on a sail? Thank you though, you have just given me an epiphany about junk rigs.

It's not wishful thinking. Weather prediction is pretty darn good now and I'll never be more than 50 miles from land, unless both motors/solar/battery systems, both sails, and both rudders fail.

 

A great lot. Many of the more prominent members have archives of their own pages, documenting their personal work, and those people are no slouches; they design, build, and sail their own rigs. An outrageous bargain at about ten dollars a year.

 

I drew what I tried to describe in post #12, and it occurred to me that if you try to hybridise the junk rig not with a gaff rig, but a Gunter, you might need only one halyard. What is difficult to show in 2D is that the halyard is supposed to be a three-part purchase, and when it returns to the block on the yard for the second time, it should be redirected around the mast, then back to the yard. I copied that from a proposal for the head of a square top main. I hope it offers a suitable balance between pulling up and pulling the yard to the mast.

The lowest batten is supposed to flip like the others, I just wanted to draw a side view.

The curved battens have two advantages over the wishbone: you can use the same amount of material to increase diameter and wall thickness by sqrt(2), and I think that gives you more stiffness and strength; and you can have the aft end of the batten in a batten pocket, and tension the sail by pulling at the luff. That way, nothing sticks out beyond the sail, and sheetlets are less likely to foul. I don't know how to achieve that with a wishbone boom.

I suppose the yard could possibly stick up beyond the top of the mast, meaning a shorter mast would be possible, giving less windage when reefed.

I haven't drawn the lazy jacks. You would still need those.

Edit: I should have drawn the lazy jacks. If the top of the yard sticks out beyond the mast, it has a good chance of getting caught in the lazy jacks when the sail is raised. If it is as short as drawn, there is a good chance that it drops out sideways between the lazy jacks and the mast when the sail is lowered. This rig will have to be a gaff-junk hybrid after all, with the top of the yard always outside the lazy jacks, if the rig is to have a chance of working properly.

 

I see two major problems here.
1.) Binding. The holes cut to go around the mast will have to be over sized. Otherwise, when you raise or lower the sail, one end will go up or down faster than the other end. When raising sail, it will likely be the forward end. When lowering, it will likely be the aft end. when this happens, they will bind.
2.) Weight. To get adequate tension to hold the sail shape, the curved "battens" (I prefere to call them "boomlets") have to be quite stiff. Otherwise. they will bow in a fresh wind, and the sail will bag. In order to get sufficient stiffness to prevent this, you are going to need a combination of bulk and weight. Niether is a good idea on a sail as tall as this one. Single boomlets have some column strength to go along with the bending strength. Theses curved boomlets won't have that. So now, all their strength has to be in bending. This is harder to achieve per given bulk and weight. So, to get more of each, you're going to have to go with greater weight per material used.