Rigging size/materials??

Discussion in 'Multihulls' started by ecoecoeco, Apr 1, 2013.

  1. ecoecoeco
    Joined: Apr 2013
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    ecoecoeco New Member

    Building a 20'x10' ply/epoxy cabin-ed CATAMARAN for near-shore cruising in SWFL:USA. Original design (ECO6) was gunter-rigged, but decided to go straight mast. Primarily as I've yet to see a gunter-rig for-real. Ever. Was I wrong? Anyway, and sorry for my mangled terminology, but I need appropriate SIZE/Configuration of:

    a. The front cross-beam's 2 "stays" (from each hull and which link onto the forestay.
    b. The forestay wire?
    c. The side rear stays?
    d. Stays from top-a-mast anchorage-to-cabin top's chainplates?
    e. And..what Configuration of actual wire should the rigging be made of, and if it should be Galv. or SS?

    Read some interesting and sage BD-post on using Galv. rigging exclusively, which made my "ears ring", and now wonder why I've always imagined SS as the default?? Glad for all advice, and further dialogue! And...THANKS.

    Yes, I know there are books I can buy for all this :) Rather talk to the Experts here!
     
  2. gonzo
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    gonzo Senior Member

    You are asking for a re-engineer of the whole design. Forces are going to be completely different and will stress the structure at different points and directions. It is a rather complex and probably expensive job. The original designer will be able to do it for the least price since he has the original calculations. There is nothing wrong with galvanized as rigging. However, the looks may not be what you are looking for.
     
  3. catsketcher
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    catsketcher Senior Member

    It's all trig

    You start off with reverse engineering the wires you have been given. Imagine the rig pulling the boat over on one hull. Pulling directly sideways will force the mast down and pull the hull up through the sidestay. After you have worked out the stability of the cat you can use this to calculate loads as the righting moment = rig overturning moment.

    You will find that breaking strain of the wire will be oversized to a certain degree compared to the load in the stay. This is your safety factor on this rig.

    When you push the hounds up on your new rig you will increase the loads on the sidestays. Do a new force vector and calculate the load in the stay with higher hounds. Use the same safety factor and then work out the new wire size.

    I would look at Dux rather than gal wire for a trailer cat. Corsairs and Frriers use it. I would stay away from gal as it will detract your resale. There is a lot written about SS sudden failure yet there are thousands of boats with stainless rigging.

    Cheers

    Phil
     
  4. ecoecoeco
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    ecoecoeco New Member

    hoped for more...

    Thanks from this 61-year old Florida Architect/Builder, and looong-time Prindle16 sailor. Your sage advice was thoughtful, but...you really don't think simply (and judicially) replicating an obvious configuration of wires and anchor points for a small cat sized as mine (or slightly bigger) would suffice? I'll post anew with my proposed rigging layout plan included, and ask again for guidance. Again, thanks for these thoughts you've shared, gentlemen!!
     
  5. jamez
    Joined: Feb 2007
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    jamez Senior Member

    Have you tried asking Bernd? The 6m Jarcat is similar in many respects to your eco. You could join the yahoo jarcat group and ask what spec they use.
     
  6. Milehog
    Joined: Aug 2006
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    Milehog Clever Quip

    Galvanized rigging works well if you are not obsessed with shiny wire. The new synthetic rigging options are worth taking a look at.
    What is wrong with the gunter rig? Ask yourself why the designer chose it. He had to have had a good reason.
     
  7. michael pierzga
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    michael pierzga Senior Member

    Come on, get real...Galvanized rigging rusts. You will replace it well before its theoretical service life. Cheap to begin with...expensive over time.
    Dont even consider it as standing rigging on a small craft
     
  8. ecoecoeco
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    ecoecoeco New Member

    I love Bernd's design :)

    No kidding, Bernd is a joy, but I just can't get my head around the gunter. Florida is full of sailboats, but I've never seen a such a rig. Have you? Great idea, but how does one maneuver the main's sliders/rope bolt up the gaff, easily? The plans showed no real details of that vital connection, no books seem to describe it but for mere commentary/fuzzy image, and all that has led to my rig-frustration.

    Old formerly-smart dog learning new tricks here, and I didn't want to appear a total-idiot on Bernd's Forum, more than I have already :) Yep, that gunter would be a great conversation piece, and utterly-smart for how it might work! I loved it till it got time to build it. Anyone else think I should go with it, instead of a straight mast? I will, if y'all think so, too. Bernd, and you Readers, are no Fools. Thanks for your kind replies.

    I must say, reading Catsketcher's opinion that "Designers ought to build before offering their services to others" rings utterly true! The hands TEACH a great deal when Doing, yes?! I'm on my 4th ECOhome, where the picture was taken. Oddly, I've been design/building such soil-bound structures with similar sensibilities as you wizards infuse your beautiful craft with...light, responsive, purposeful, sexy,....

    Ohhh...the ECO6 is a delight to build, with some added curves and useful nookies/amenities I thought vital. She's a gal, after all! Here's AMICA today:
     

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  9. jamez
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    jamez Senior Member

    Bernd is certainly an innovator when it comes to these things. But unless there are fairly detailed plans of how to build it [the gunter] you may end up having 2 or 3 goes to get it right. Alternatively a similarly proportioned marconi rig can be put together with off the shelf bits. You might even be able to build one out of a suitable second hand beach cat rig, get second hand sails etc.
     
  10. catsketcher
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    catsketcher Senior Member

    Gday Eco

    I am building a 7 metre cat and am maybe a little further along than you. I also have thought very hard about the gunter rig for some very good reasons.

    The mast on my cat is around 9 metres. If I cut off the top 1/4 then only 55% of the torque of the full mast length is required to get it raised. I also have some other issues due to my cat's particular design and I will be able to show them when I am done.

    So the gunter will make it much easier to raise the mast. The only modern design I can find with a gunter is the Port Townsend 15 designed by Paul Bieker. There is not a lot of info I can find on it. There is a photo here

    http://www.flickr.com/photos/nwswb/sets/72157631658659096/detail/

    I have ideas on getting the gunter to work well but I am tired of innovation. I think that it is easier to innovate or use a well designed mast raising system than to go through the trials of a modern gunter. Still, if you build it soon can you show me?

    I would be using glass sleeves with unis to hold the pivots of the gunter. This would slide up the mast. I can't help but think that a carbon gunter would still be a good idea.

    So does Michael Schacht

    http://www.proafile.com/archive/article/beach_cruiser_reloaded

    You would be doing us a service if you want to make this thing work but there may be dragons!

    cheers

    Phil
     
  11. CutOnce

    CutOnce Previous Member

    Gunter rigs are a good compromise between performance, cost and convenience. Back when spars were made out of wood, gunters allowed shorter spans of timber to be used together to arrive at a sail profile very close to a typical marconi rig with much simpler and cheaper spars. Think of it as a gaff rig where the gaff is pulled up with the throat halyard and then the peak halyard is pulls the gaff peak up vertical in line with the mast.

    Gunters allow easy dropping of overall mast height to pass under bridges and things without dropping the mast. Since the gunter upper spar (gaff) is pulled vertical, the gunter rig doesn't twist off as bad as gaff rigs do and it points better. Paul Beiker did a modern take on the gaff rig that was almost a gunter in the Port Townsend 15 skiff. Gunters also can reef well without problems of dropping the sail head down to a less flexible part of the mast, as it does on a conventional Marconi rig.

    The single most popular gunter rigged boat was the Mirror Dinghy - sadly now converted to conventional spars due to the racing folks insisting.

    --
    CutOnce
     
  12. redreuben
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    redreuben redreuben

    One of the practical downsides of gunters is no masthead sails for off wind use.
     
  13. cavalier mk2
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    cavalier mk2 Senior Member

    How about kite sails for off wind? I used a gunter on my canoe with excellent results, composite yard fittings are the way to go. For a dink the spars can stow in the length of the boat but for any size lowering the CG as you reef helps with pitching. The thing to be careful of is chafe, dropping the yard could be dangerous but should come down slowly with the sail like a gaff. Some sort of safety line would add insurance to a bigger boat.
     

  14. ecoecoeco
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    ecoecoeco New Member

    GUNTER rig...like computers in the '70s?

    As many of you, I'm intrigued by the Gunter concept for the same reasons stated here. Yet, I feel like I'm doing the R&D work for the concept, surprisingly, after its existence a century. Whewwww...if its got YOU wizards pondering, what chance have I of success? Well...here's my drawing of what's possible with straight stick or gunter.

    A. Sail A is my redraw of Bernd's, overlaid with Sail C.
    B. Sail B shows my straight mast cut to the same height as the Gunter. Hmmm...cutting the extra from the base, yes?
    C. Sail C shows the straight mast the full height it is now.
    D. the green line is perpendicular to cabin-top, representing the straight mast as it would realistically-set.
    E. Sail B/C show my added side lower shrouds*, and straight spreaders from my mast (5"x4"), both un-necessary in the Gunter (it would be alum. pipe).

    My additional redraws are the Gunter's sail, and my presumed straight-mast version.

    *now thinking about it, probably requiring through-cabin-top chainstays, rather than shown. Haven't pondered this seriously, yet.

    The benchmarks are what you folks know better than me, and as provided me. The red ones are my "figured" locations, which if I understand it, Sail B us more-closely balanced as designed. Some of my cruiser buddies suggest, the more sail, the better. Might have been the beer talking :)

    Can I offer my website, and my offer to provide you my architectural expertise for free, for your kind advices? I feel I owe you my life. Its: www.HomePlansDrawn.com Great day! Ohhh...see the rudders-in-sleeves, as designed? I fret over their long-term survival in the near-shore conditions of the Gulf of Mexico/island-hopping hereabouts, but such it was designed. Made the gudgeon pins "expendable", like my old Prindle16's, as "insurance".

    Back on my picture, know the tiller's are from underground polypipe of 3" dia. Incredibly strong, light weight, good bend/recovery, alum. stiffener, and split/wrapped around the rudder sleeve. No connecting bar shown, yet. Same material as that black "toe-rail". Yes, SS316 is expensive, and I like innovating. Catsketcher, don't you stop doing so, or we're all lost! :)
     

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