Sail Plan Advice

Discussion in 'Boat Design' started by MastMonkey, Jul 25, 2010.

  1. MastMonkey
    Joined: Oct 2009
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    MastMonkey Junior Member

    I am building a Wa'Apa, Gary Dierking's sailing canoe design, and I am doing it as a trimaran. I want to make some deviations from the original designs sail plan.

    The original may be viewed here:

    http://homepages.paradise.net.nz/garyd/Trimaran.pdf

    My intention with the design, due to my own requirements, has been to use a modernized junk rig. I bought "Practical Junk Rig" and have studied materials from the Junk Rig Association and Van Loan's book and have come up with the attached sail plan.

    The sail area is greater than the original design as advised by most sources; Hasler and McCLeod recommend a 10% increase and other sources have suggested a 20% increase.

    Can trained eyes give me any suggestions for the current design I have before I start building it? I have a few concerns that I have not been able to settle.

    My first is having the weight of the fore sail close to the bow. I know the junk rig is a heavy rig.

    The second is the bury on the mast. The length above the partners for each mast is 15'8". Each mast has a bury of 18". According to Hasler and McCleod this is feasible, but I would like a second opinion. For the mast I am planning on using round aluminum tubing. Following the guide lines in the book I can section a wooden mast. Is there an easy way to relate this to determine the proper size for an aluminum pole?

    The 3rd is the positioning of the CE. It is just slightly ahead of the CLR. not quite the 5%LWL Hasler and McCleod suggest.

    The drawing is at 3/8" scale. LOA is 24'. The double lines are the bulkheads. The distance between each batten in the sail is 2'. Boom length is 7'. Height of the clew above deck is 2'.

    Thank you for your advice.
     

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  2. garydierking
    Joined: Sep 2004
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    Location: New Zealand

    garydierking Senior Member

    I'd like you to contact me via my email address so that we can discuss this further. I am actually just now making a modern junk sail to try on my own Wa'apa. I feel that there have been some advancements since the Hasler book and am particularly impressed with non-flat panels and the possibilities of the Gurney flap.
    Check out: http://www.duckworksmagazine.com/06/howto/junkrig/index.htm
    My biggest problem with the sailplan that you've shown is the angle of the sheeting with the two sails so close together. They will do little to prevent excessive twist in the sail. I would vote for a single sail plan where the sheets could lead aft at a much better angle. The weight would also be better centralized.


    Gary
     
  3. Petros
    Joined: Oct 2007
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    Petros Senior Member

    I have been studying junk rigs for some time as well, and want to try one on the next boat I build. And I think Gary is correct.

    You either need more room between the rigs to get a better angle for the sheetlets or you have to go to a single rig with perhaps a conventional jib.

    You might consider putting a pedestal at the transom and just ahead of the aft mast to run all the sheet-lets through to reduce the downward angle. I am considering that for the boat I am planning, it allows me to carry more sail and still have a favorable angle for the sheet-lets. If you notice the traditional junk has an elevated aft deck so the sheet-lets do not angle downward as sharply, I can achieve the same angle with a short pedestal where they are fed through some fair leads down to the deck where the cleats are located. this will allow to adjust the tension on the sheet-lets at the deck level. Just make sure the pedestal can take the lateral loads from the trailing edge of the sail.
     
  4. MastMonkey
    Joined: Oct 2009
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    MastMonkey Junior Member

    Gary: that is awesome that you are also designing a junk rig for the same boat. I will certainly be in touch. Thank you for the offer. I too am planning cambered sails with a gurney flap. One of the reasons for the present sail plan design was the desire for higher aspect sails, which I thought would also facilitate windward ability of the rig and also improve light area performance. I was designing around an aspect ratio of 2.3. How important is a higher aspect ratio do you think? The other reason was that for battens I will be using bamboo. I can find solid pieces at the length required for the higher aspect sails. For an aspect ratio of 1.8 (the ratio recommended by Hasler and McCleod for a single sail) and 150 sq. ft. of sail the battens are 11 ft. long.

    You are right about the sheeting angle. It is at the bare minimum suggested as feasible in Practical Junk Rig. To help with anti-twist I was planning on using a six-point sheeting system with anti-twist properties. Another alternative I have been considering is double sheets.

    I will draw a couple alternatives with only one sail and see what else I can come up with.

    Thank you.
     
  5. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    Why do you wish to use a junk rig? While there are some argueable advantages for use on a large boat, is there sufficient advantage for a canoe to offset the complication and complexity of lines, aloft weight, etc?.

    Dig around the net, find Hugh Horton and also the Geougeon brothers. They are very clever with rigs for narrow boats and multis also. All three of these gentlemen are stoked about skinny litle boats (canoe like) to which one attaches sails. Another good source of gospel, for out of the mainstream boats and rigs, is the main man at Dabbler sails.
     

  6. MastMonkey
    Joined: Oct 2009
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    MastMonkey Junior Member

    I have a few reasons for going with the Junk rig. Perhaps the primary reason is that I want to make this design an as nearly sit in trimaran as I can. I have a physical disability that makes it inconvinient to move around on the boat. My plan is to run all the lines to a single point and also build a whipstaff steering ssembly to accomplish this. Of the few different sail types that I considered the Junk rig seemed a good choice. On my other boat, a Bermudan sloop, I have been working to make the boat more accessible and have been able to accomplish much in this regard. I have all lines led to the cockpit, auto-tiller, lazy-jacks, and low friction sail plugs. Now I am able to hoist, reef, and furl my sails myself. But, I do not like the setup. I still have to move around more than I desire to, including lifting myself onto the cabin roof to either furl the sail properly or often even just to get it completely down. Sailing on San Francisco bay I do not regard this as safe and so despite being able to do so, I almost never do and always rely on crew. I can at least take comfort that in an emergency I am to handle the boat.

    I can think of more ways to make the sail even easier to hadle but those cost money, in many instances a lot of money, and I have already spent a lot on a system I am dissatified with. Thus, I regard the Junk rig as a nice alternative especially if the more modernized versions improve many aspects of its performance that has given it many critics. And I do not regard it as more complex. On my boat I have the following lines: haulyard, downhaul for the first reef, backstay, jiffy reefing lines, cunnigham, outhaul, mainsheet, jib sheets, jib haulyard, jib downhaul, and a line to loosen the lazy jacks. All of this is run aft. It takes more than a bit of effort to manage all of these. For example, the friction in the lines for the reefing system makes it a complete bear. In the chop of SF relying on auto tiller to keep you in the eye while I still have to strain to pull my sail down is not that good of solution. For the cost of the auto tiller for this setup I will have nearly built the entire sail plan for this boat and will be able to dispense with the heading into the wind, setting the boat on auto-tiller, lifting myself onto the cabin while the boat is pitching, and pulling hard on lines while hopefully doing it quickly enough so that the wind doesn't catch me and push me off while being in constant danger of falling overboard. I could do that or I could weather cock the sail and slack the haulyard for a secure seat.

    That is the primary reason, cost and convinience. I have other reasons too. I have long thought that when I am older and hopefully have the money my cruising boat will be a Junk rig, for the reasons already mentioned; this gives me an opportunity to test it out on a smaller scale. I also want to build as much as I can myself. The other two reasons: I like the way it looks and I am curious about it.

    Anyway, a few other reasons I arrived at the current sailplan was because I do not want to have to run any stays and I want to manage lines as little as possible, so it is a pirouge. Stays are one of the most incovinient things for me on a boat. The problem I had was getting a reasonably higher aspect ratio, which will actually reduce weight aloft a little bit, and keeping all sails of the size that none will require even a purchase to manage.

    But I need to rethink a little bit, especially if there is a problem with the sheeting angle. If I really don't want comlexity a single sail, lower aspect, with a purchase on the haulyard may be the better solution.

    Thanks messabout for the additional names to research. I'll check it out.
     
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