Best rig for small catamaran circumnavigator?

Discussion in 'Multihulls' started by randy quimpo, Jan 23, 2006.

  1. randy quimpo
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    randy quimpo New Member

    Hi fellows,
    I'm an amateur designer working on a design for a small (27 foot) epoxy-plywood catamaran circumnavigator (please be patient - I dont know too much at this point). I need a recommendation as to what the best rig to use is. The cat will be sailed singlehanded, and mostly in trades (the leisurely route around the world - none of this cape stuff ). No carbon fiber masts please - plain wood prefered.

    Priorities will be ease of use (to be sailed singlehanded but lazily), reasonable performance and cost.

    I was thinking of a Prout-style large genoa / small main type. Or even ripping off some ideas from the Wharram tiki sail.

    I like unstayed masts due to the simplicity, but doesn't this mean that I need a thicker mast, therefore less efficient airfoil?

    One more thing - do any of the traditional rigs qualify? Cat ketch / Yawl anyone? I've heard so many good things about the Cat ketch rig but for the life of me I can't imagine how this will work on a catamaran.

    rgds / Randy Quimpo
     
  2. Deering
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    Deering Senior Member

    Go read Chris White's "The Cruising Multihull". It will answer your questions plus a bunch more you haven't thought of yet.
     
  3. randy quimpo
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    randy quimpo New Member

    Hi Deering,
    I've got that book, but it doesn't discuss the pros and cons of different types of rigs. You are right, though, in that it has lots of very useful information.

    I DO wish Chris White would update that book. The multihull world has changed a lot since he released it.

    Thanks / Randy Quimpo
     
  4. Eric Sponberg
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    Eric Sponberg Senior Member

    The alternative to a cat-ketch on a catamaran is a bi-plane rig, one mast in each hull. One may think that the windward sail will blanket the leeward sail, but that is not the case, because usually on a multihull, the apparent wind is well forward of the beam on most tacks and each mast is in clear air.

    As you probably know, I am a firm believer in the cat-ketch rig, particularly with rotating wingmasts. With properly shaped wings, the drag on the rig is particularly low, and the sailing tactics (read options against the weather) increase considerably and add immeasurably to the safety of the voyage because of the eliminate of wires holding the rig up. This is particularly true of a bi-lane rig on a catamaran, and even off-wind sailing, again with the masts in clear air, generate considerable lift at the expense of very little drag.

    Eric
     
  5. nero
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    nero Senior Member

  6. tamkvaitis
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    tamkvaitis sailor/amateur designer

    I have done some sketches, of cruising cat ketch catamaran. I decided to draw a huge cabin beetwen hulls (wel it is a must on a cruising cat), mast has two points to stand, and work. Two mast's makes the righting arm lower (the rig is lower than ordinary rig), so cat can sail full sail in stronger winds, but it increases the loads to the hull. I was thinking about airfoil problem, I think it is only diference in money, you can make carbon fiber mast witch, could work on cat, but is it worth the price?
     
  7. Eric Sponberg
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    Eric Sponberg Senior Member

    Masts should always be designed to the righting moment of the hulls, not the heeling moments of the sailplan in the wind. Therefore, the strengths of the masts should be the same at deck level, regardless of their height or the amount of sail they carry. I am talking about free-standing masts, but stayed masts are the same--you design to the righting moment of the boat, not the heeling moment of the sails.

    Wingmasts with an airfoil shape always perform better than round masts, which, of course, are simpler to build and cost less than wingmasts. You get what you pay for.

    Eric
     
  8. icetreader
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    icetreader Senior Member

    Crab claw?

    Randy,

    Since you're going to use a catamaran how about checking another Polynesian invention - the crab claw sail?
    I built an small, experimental crab claw style rig for my 10' W boat and it's very easy to operate.

    Yoav
     
  9. tamkvaitis
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    tamkvaitis sailor/amateur designer

    sorry, it is still dificult to me to talk in english. personaly I am using Russian literature. I know the have always been designed to the righting moments of the hull. Only I wanted to say that cat ceth rig would produce the same lift (It should) with smaler righting moment, than one mast configuration. As the lift force increases the loads to the mast increases to. Using cat ceth rig the load would be the same, only the heel should be smaler,
    sorry if I am wrong
     
  10. Eric Sponberg
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    Eric Sponberg Senior Member

    Yes, the rig then would have a smaller heeling moment, which is balanced by the hull's righting moment (equal and opposite.)

    Eric
     
  11. Seafarer24
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    Seafarer24 Sunset Chaser

  12. sharpii2
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    sharpii2 Senior Member

    I would go with a cat ketch or even a cat schooner with stayed masts. A catamaran has a very large righting moment and making unstayed masts out of conventional materials, such as wood, that can stand that kind of strain may require either too large a section (diameter) or too complicated a design or both. This could make the rig expensive and/or heavy. Niether of which is desireable in your case.

    I would go with the jibless working rig so I wouldn't have to extend the deck all the way to the bows of the boat. If you plan on doing that anyway, then I would go with a jib as well. The idea is to have as many sail combinations as possible so you can prtetty much 'ballance' the boat by the sails and not rely so much on electromechanical self steering rigs.

    Keeping the Center of Area (CA) as low as possible is another good idea.

    A 3/4 fractional sloop rig would be my next choice, because it is simple and sturdy and does not put a lot of rigging strain on the hulls and connectors. It also requires just one mast. And we are talking pretty small here, boat wise.

    My third choice would be a mast head cutter, where the mainsail area above the jib is cut off and replace with another jib foreward of the first with the forward jib stay attached to the same tang. That might be a good bet to get the (CA) lower and thereby make the boat safer. The mast could be much shorter too. You would, however pay for this in windward ability. The two jibs will not only interfere with each other, but interfere with the main as well. Not only that, but there would be considerable (visable) luff sag as well. Hence this rig would be my third choice. But, in its defence, I would say that it would be a handy one. You would reef the main and drop the outer jib as soon as it started to breeze up. The inner jib would now be within easy reach should it need to come down as well. More likely, you would leave it standing and strike the main, so you could keep your boat moving in a controlable downward drift once it got really nasty.

    The Prout rig, in my opinion, would be a poor choice. It worked on the Prout boat because the Prout boat was essencially one piece. It was really, structially, like a skinny scow with weight supporting sponsons tacked on. The bridge deck whent all the way from the extreme bow to the extreme stern. This dridge deck section had a very deep bottom that swept up to the deck at the ends. For a catamaran, it was an extremely rigid design. My advice would be: don't copy the rig design unless you plan on copying the hull design as well. Otherwise, you may see the jib stay sagging off to the point of windward usellesness.

    Good luck on your adventure.

    Bob
     
  13. randy quimpo
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    randy quimpo New Member

    Hi everyone,
    Thank you for your valuable suggestions. I am just wondering why no-one has brought up the Wharram soft-wingsail rig. Does it work as advertised, particularly since much of the sailing I am designing for will be in the trades?

    Thanks/ Randy Quimpo
     
  14. sharpii2
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    sharpii2 Senior Member

    I haven't commented on the wharram sail for two reasons.

    1.) I know next to nothing about its performance improvement over a standard gaff rig of the same size and proportions. (it would be an interesting experiment to have two nearly identical wharram cats race each other, one with the fairing on the sail and the other without.)

    2.) The fairing appears to be a sock that goes around the mast and is, otherwise, integrel to the sail. The problem with this is that it may bunch up as you try to lower the sail. Kind of the way a shirt sleve does when you try to push its cuff up your arm. This could slow the procces of reefing and/or lowering the sail. In my opinion, not a good idea on a boat that has only initial stability and one in which getting the sail down quickly may mean the difference between capsize and minor scare.

    For what you want to do, I would think that:

    1.) Safety,
    2.) Simplicity, and
    3.) Reliability

    should be the main criteria in chosing a rig.

    Bob
     

  15. Crag Cay
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    Crag Cay Senior Member

    Wharram Soft Wing

    For what you want to do, I would think that:
    1.) Safety,
    2.) Simplicity, and
    3.) Reliability​
    should be the main criteria in chosing a rig

    In that case, I think you would want to consider the Wharram Soft Wing very carefully, as it meets all these criteria perfectly.

    In fact, if you want to circumnavigate in a small epoxy/ply catamaran, I would buy some plans off Wharram and follow them to the letter. Unless of course, you believe your first efforts at design will be better than a man with 50 years experience.

    http://www.wharram.com/tiki_wingsail_article.shtml

    If you are determined to forge your own path, then Erik's suggestion of a bi-plane rig is a good one. Imagine a windsurfer rig in each hull.
     
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