A Frame Masts

Discussion in 'Multihulls' started by Gus7119, Jan 20, 2016.

  1. Gus7119
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    Gus7119 Senior Member

    Am looking for anyone with any experience or knowledge of these mast thet look much easier on the boat with less strain and allow for a ferling main and double ferling jjbs. Really interested as would live to put one on the cat I am building if they are good as they shuold be but know nothing about them.
     

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  2. upchurchmr
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    upchurchmr Senior Member

    Gus,

    Do a search in this forum and Woodenboat.com
    There have been several extensive threads with actual examples of open ocean boats.
     
  3. PAR
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    PAR Yacht Designer/Builder

    The simple reality of the A frame rig is there's more drag associated with it, in spite of some advantages, so it's not as close winded, it is heavier, so stability is affected, more costly, etc., etc., etc.

    You can have roller furling on all the headsails regardless of the mast arrangement. The same is true of the main as well.

    In the end, the few advantages aren't enough to justify the costs, stability and weight penalties you have to absorb.
     
  4. RHP
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    RHP Senior Member

    Unless of course you build it in carbon.
     
  5. Gus7119
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    Gus7119 Senior Member

    Cheers upchurchmr I will do.

    And how do you do a furling main on a standard rig without a furler in the mast or a furling boom??

    Does the weight not get distributed better on a Cat? And with the ability to shift sails around to take advantage of the wind and conditions doesnt this also add a benefit?

    I have seen a design for an 11m A frame made from carbon flag poles that seems to cost a lot less than a standard rig but Im only just getting into the research. Those that have them on cats seem to find the benefits amazing so far. But Im new to the A frame so want to take all aspects on board.
     
  6. CT249
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    CT249 Senior Member

    How do you shift sails around easily?

    If it adds a benefit why don't the professional racing multis do it?

    Why is a mainsail furler on an A-Frame rig any better than an in-mast furler or furling boom?
     
  7. PAR
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    PAR Yacht Designer/Builder

    Even if the masts are carbon, there's still excessive weight aloft, compaired to a single carbon stick arrangement. Weight distribution is pretty irrelevant, it's stayed, so loads go to the hull shell and keel, where they need to be. Do the math and you'll come to the same conclusions everyone else has, which is why they haven't taken the worlds race courses by storm.
     
  8. Gus7119
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    Gus7119 Senior Member

    Ok Im not going to win anyone over who has a one track mind. I have nothing against the standard rig but most comments on this subject come from people with no experience in using one of these rigs nor ever seen one sail nor worked on one. I have done much reading and for a cruising boat they seem like a good alternative heres one user that actually had a boat with a a frame rig or wishbone what ever you want to call it this is one of the reads that got me thinking more about it as it just wasnt maths and so antidotal evidence so read this think about it and then discuss with logic. As the forums Ive read on this site most people just say because a sloop rig is the best. No its not used in racing as its not for racing so just because of that doesnt count it out.
    As said love traditional rigs real life users swear by these rigs in the right setup so I want to have a real life discussion not just no one does it no racers do it I dont do it so it sucks.
    Anyway have a read of this sounds interesting. O one last thing removing the load from the center of the beam cant be a bad thing is this a fair comment. Enjoy;


    Originally Posted by High Tacker View Post
    UTILIZING RIG GEOMETRY AND CATAMARAN BEAM TO GAIN STABILITY

    Since we're discussing capsizing, rig strength safety factors, etc., it seems appropriate to note that most rigging schemes seem to be still hung up on the conventional fore and aft vertical arrangement, i.e., the conventional monohull rig, whereas, on a catamaran, not only does it make no sense to put a huge mast and its compression load in the center of the boat (requiring a heavy wingdeck structure such that you might as well go ahead and build a trimaran), it also makes no sense to put a huge tension load on the center of a beam between the bows. After all, a catamaran is two boats in one, so why not treat it as such, and in the process take advantage of the width of the boat and utilize a geometry that allows angles for lift and/or anti-capsizing loads.

    See www.damsl.com and on the welcome page look to your left at table of contents and click on "A-frame Rig".

    I think of Catbird Suite as two boats connected by a wingdeck, each boat having a masthead cutter rig, and the two rigs are leaning together, their masts meeting at the top, over the center of the wingdeck. Or perhaps more aptly, she is two proas leaning together. The head of each sail, genoa, staysail, and main, is connected to the masthead. The tacks of the genoas are attached to the bows of the two hulls. The tacks of the staysail and the main can be attached on the centerline of the boat, i.e., the centerline of the wingdeck, or on either side deck.

    For sheeting, there are tracks and various other sheeting points scattered around the decks, and the clew of each sail has two blocks for sheets so that, for each sail, there are four ends of rope that can be moved around to sheeting points and winches so that, when the clew of a sail is inboard, ideal sail shape can be maintained on all points of sail without booms or poles. That is possible when the tacks of the sails are on the windward side deck. With the tacks on the leeward side, then poles are needed.

    On a passage-making tack, especially if there is substantial wind, it's good to use the windward genoa and the staysail and main with tacks on the windward side deck. All the gear is then inboard and one can go from close hauled right through all the points of sail and maintain ideal sail shape without booms or poles. With the heads of the sails attached to the masthead over the center of the catamaran and the tacks attached to the windward side, the sails are effectively "heeled" and thus spill some wind.
    AND a substantial portion of the force on the sails is pushing the windward hull down, i.e., is an anti-capsizing force.

    In moderate to light winds, the sails can be deployed on the leeward side, and then a substantial portion of the force on the sails is upward, is lifting the leeward hull. Picture a windsurfer leaning into the wind so that his sail is tilted, not "heeled", rather the reverse, canted into the wind.
     
  9. PAR
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    PAR Yacht Designer/Builder

    You seem to be under the impression everyone is simply discounting the rig's potential, but you'd be simply misinformed. You also don't realize the level of expertise that is offering you advice. I currently own a canting rig (ketch) of my design and your assumptions and innuendo aren't based in study, observation or testing, though you'll find there are those that have. This subject has been extensively explored and not much has changed in the 20 years or so since I looked into it, initially. Some material and engineering choices have moved things around a bit, but the same set of issues still stand proud.
     
  10. upchurchmr
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    upchurchmr Senior Member

    Gus,

    You need engineering calculations, not general discussion.
    For example, a simple verbal comparison to a wind surfer does not automatically show that concept is actually beneficial for a full sized sailboat.

    Racers are as quick to seize on an advantage as a politician.
    They are willing to do anything that will let them win.
    They also can get the money almost no matter what it costs, if it helps.
    Have they incorporated this idea?

    I would also caution you not to make assumptions about who you are talking to.
    At least ask before you smear their comment.

    For instance - what is your sailing/ designing background?
     
  11. babu
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    babu Junior Member

    Two additions to the discussion

    Hi GUS and PAR

    Very much appreciate the discussion about A-framed rigs on catamaran here. I am currently myself planing a 37' catamaran featuring a A-rig. I think the pros and cons can easily be listed but it is the weighting of each of these facts that is subjective and may lead each individual to different conclusions.

    I however wanted to add two points for discussion:
    • It is out of question that rolling sails are a big innovation and offer great usability. For the mainsail two principal solutions exist: vertical rolling (e.g. into the mast) or horicontal rolling (into the boom). Rolling booms do not offer as many advantages as vertical rolling solutions: They require a battenless sail and the sail needs to be hoisted. Vertical rolling-sails come in two flavors: with in-mast furls and behind-the-mast furls. Behind-the-mast requires a gap which lowers the aerodynamical efficiency of the sail so much that the sail area has to be increased. This is why vertical in-mast furls currently are the canonical solutions for short handed cruising boats. In my(!) opinion there are however 2 problems related to in-mast furls:
      1. Safety: The sail may jam in the slit. This will most likely create a dangerous and hard to resolve situation
      2. Comfort: Having the sail passing the mast-slit prevents downwind reefing of the main.
      Both issues are mitigated by the A-frame mast. As far as I know only free-standing masts, beghind-the-mast furls, rotary masts and A-frame rigs enable true downwind reefing (to me relying on perfect batcars does not count). On a A-framed rig one can release the halyard in case of troubles with the furl.
    • I think that the masts of an A-frame can be built watertight and have a positive impact on the stability in the case of near-capsizes.

    My current matrix of pros/cons for a 37' low-end short-handed cruiser (simplified):
    Virtues of a Non-rotary-fractional-rigged-single-masted-sloop-with-in-mast-furl:
    • Aerodynamics up-wind: better
    • Triming possibilities: better
    • Top-weight/Pitching resitance: lower
    • Initial costs: lower
    • Resale value: higher
    • Maximize usage of commercial-of-the-shelf parts: yes
    • Structural properties of mast: better
    • Time-tested/Proven: yes
    Virtues of an A-framed-mast-headed-boomless-sloop-with-vertical-stay-sail-furling-main:
    • Ease-of-use on all point of sails: yes
    • Versatility: better
    • Load on hulls/bridgedeck/beam structures: smaller
    • Downwind main-sheeting angle: better
    • Upkeeping costs: lower
    • Ease of maintenance (e.g. taking down mast): better
    • Overall Safety (short-handed): better

    Best regards
     
    Last edited: Jan 21, 2016
  12. Gus7119
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    Gus7119 Senior Member

    Sorry to those who took offence but again it just turns into a theoretical discussion with no real world experience of the design. This is what I want to avoid otherwise I just would of stuck with one of the many other Posts. below is a most helpful post. and the Post that I made previously with a outline by a user of the rig in real world applications was helpful also. Im not looking for everyone to agree just think the silly bun fighting that went on in the other post about the setup was not helpful. Comparisons like below and not sweeping statements are more helpful. Although I could be wrong.
    As I said Im not trying to cause offense neither am I trying to say this is the best idea. I was commenting on how the other post just became bashing for bashing sake with only minimal technical information given. I mean saying that it puts stress on the stay points, really doesnt every rig? Plus Ive never liked the comparison between racing boats and a cruising boat because the setup is coming from two completely different ends of the spectrum.
    Now no doubt there are many very experienced designers builder and novices here hence why Im asking. We all know traditional rigs are great but are the downsides of the A frame or wishbone mast so great and stressful on the hull that its just junk? If so the question is why do people who have sailed for 40 years and gone with an A frame loved them so much? I dont know. Plus and Ive been a mono man for 40yrs and have sailed cats and now am building on as mrs gets sea sick and cats work for her monos she wont go on. So if you hate Catamarans or have never sailed one and dont like them then maybe it may be different. I know the loading is.(again traditional rigs work great although would love a furler on a main instead of mast or boom furler due to price and easier to repair or jerry rig at sea)
    And where did the windsurfer comparison come in? One of the original posts was called the wishbone mast which is what it was known as at one stage. And we are talking about putting this on Catamarans not monos by the way.
    As Ive said I know traditional rigging rocks and have sailed and built boats for 30yrs but always open to exploring and trialing new designs.

    Also if youve got your own design (canting rig) like what was put on the Fan Class 32 good on you that looks so cool and keeps a mono nice and flat. is yours a mono or cat?

    Again sorry to any experts out there no offense was intended.

     
  13. babu
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    babu Junior Member

    Beware

    @PAR
    I have the highest respect for your abilities and do not want to challenge the oppinion of experts. However I am always on a lookout for scientific papers on these subjects. Do you have any references worth reading concerning the design and/or performance-penalty of A frame riggs. So far the only paper I know is the investigation "WIND TUNNEL AND CFD INVESTIGATION OF UNCONVENTIONAL RIGS" authored by F. Fossati et. al. from 2008 which is investigating a 51ft IMS cruiser-racer monohull.

    @GUS
    I hope you keep posting your experiences and findings.
    BEWARE that I am a very inexperienced sailer and do not have a engineering but a scientific background.

    Best Regards
     

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    Last edited: Jan 21, 2016
  14. Gus7119
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    Gus7119 Senior Member

    Unfortunately I can not find any other documents. Have read over theyears of people whove used these rigs because they were sick of being told they sucked and were hopeless only ti find the real life experiences wete diffrent.
    No ones argument is that a sloop rig is the best. But for cruising a simple A frame from my reading offers great advantages on a Cat. I think most of the arguments arw based on mono hulls. But anyway it seems that this thread seems to be going the same way as all the others where discussion is out and dictation in. Theres many experts here who only point out 12 or 3 flaws that in reality can be worked out or comprises made. But so much offense is taken when questioned like your personally attacking them.
    A great thing I was hoping to do was build some sort of pros and cons list with real life users or designers that have hands on with this rig and experts in rigging in general like a couple of the other threads did but it seems even though Ive only sailed monos my 40yr sail career and now am switching to a cat which so so many people seem to dislike even after years of out preforming monos I know see the true feelings of so many mono sailors. I dont have that problem.
    Now that said there must be a better way to rig a cat. After all you have two hulls and much more spacw. A traditional sloop rig works great and can easily be used single hand in any weather like it can on a mono. But itd be grwat to get real and figurw out a bettwr setup. And as stated this kind rig seems to work for those that use it. I just wish id kept all the stuff ive read over the years from users.
    Anyway still keen on pros con list. And still have mocho respect for those experts just hoping do have a different discussion to the other threads get all the silly you dont agree so you dont respect my expertise. I dont agree or disagree just wanta ask questions and question answers.
    Aftwr all theres no silly questions except those that arent asked.
    Cheers
    Gus

     

  15. brian eiland
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    brian eiland Senior Member

    SMG50 A-frame Rigged Catamaran

    Hi Gus,
    Here is a real life 50 catamaran that made use of an A-frame mast very successfully
    http://www.sail-the-difference.com/index.php?id=16
    http://www.sail-the-difference.com/index.php?id=44

    Shame they couldn't sustain the effort thru both the 'gaining acceptance phase' and the downturn in the boating market worldwide since early 2008

    Of course they were inspired by the Olaf Harken experiment Procyon that I wrote about here:
    http://www.boatdesign.net/forums/sailboats/procyon-project-bold-experiment-10771.html
     
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