Wings on Cruising Catamarans

Discussion in 'Hydrodynamics and Aerodynamics' started by Inquisitor, Sep 18, 2020.

  1. Inquisitor
    Joined: Nov 2005
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    Inquisitor BIG ENGINES: Silos today... Barn Door tomorrow!

    For many years I've been working on various designs for a live-aboard cruising boat... much of it already recorded on this site. I like the mental exercise even if hardships or the next shiny idea has shifted my focus and caused much of it to be sidelined or trashed.

    I have one recurring theme that I have not really explored publicly. I would like to get some feedback. I would like you to consider a rigid wing sail (think 34th America’s Cup) on a cruising catamaran. It would be free-standing and can freely weather vane (unlike the 34th America’s Cup). Over the years I've seen many designs heading in this direction, but they all seem to over-think the problems by adding complexity like telescoping masts or at least telescoping semi-soft wings. Then I see this and think... [​IMG]
    I am vindicated.


    · According to “Principles of Yacht Design” the drag of a single 3/8” cable shroud would be about the same as a 12% wing with an 8’ chord! Abbott & von Doenhoff’s, “Theory of Wing Sections” and just about any other reference concurs. Consider the drag on a standard mast, furled head-sail and at least four or five shrouds and you have probably less than a tenth of the drag up top with a rigid wing.
    · I am a little concerned about weight above, but I've read the mast on a Fountaine Pajot Belize 43 weighs 1000 lbs. I’m pretty sure I can beat that with a wing.
    · Consider that wing shape is nearly theoretically perfect (as least compared to a sail: cloth or 3DL)
    · Wind coming from aft, the sail would still function as a wing by pointing toward the wind (+AOA). That on certain points of sail the lift and drag both point forward so that both add toward thrust. On certain points of sail, the boat would actually heel towards weather. Wouldn’t that freak out an old salt?
    · Even in storm conditions, it would have far less drag than bare poles.
    · The simplicity, especially for the charter industry seems like it would be an asset. No lines, no winches. With some AI the wing could be made to work on all points of sail and conditions. It could even totally de-power by itself when in panic mode long before some fool gets off his bunk.


    · Nostalgia. Nothing is more beautiful to me than a J-Class America’s Cup. An old cloth sail is just a site to see.
    · Trying to assure all the other sailors in the marina that, “No, I don’t need to take down my sail.”

    Can you think of any other cons? Why hasn't someone like a Foutaine Pajot or Lagoon not made this as an option.
  2. bajansailor
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    bajansailor Marine Surveyor

  3. CT249
    Joined: May 2003
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    CT249 Senior Member

    I'm no expert, but as I understand it the theory does not match the reality. For example, the hard wing has to weathercock. One smart guy I knew found that even with a wingmast, rather than a full wing, the period between a gust hitting the wing and the wing rotating to weathercock was a major problem, causing the boat to sail around even in the marina. He got rid of the wingmast.

    Personally, I wonder about the loss of deck space. In real life, marinas and moorings are in areas subject to windshifts. If one cannot walk around within the swing area of the rig without risking it swinging into you, how does one move around on deck freely? Where, for example, is your anchor locker going to be? In most performance cats it's aft, to centralise weight - so how are you going to work on it if any time you straighten up, you may get smashed in the face by a swivelling wingsail? If you lift the bottom edge of the sail 7' above the deck to ease that issue, what is the increase in the height of the rig going to do to stability?

    I've never sailed with a wingsail but I own a bunch of wingmasts. None of them is as efficient as older theory claims. We've seen that time and time again for a century or so. We've seen it here, with wingsails promoted by people who promised to give us the results of trials - and never did. When that rig (the Omer wingsail) was trialled by a manufacturer, they tossed it because it did not live up to the claims.

    I still remember reading of sailors like Loic Caradoc and Peter Blake talking about the danger of their wingmasts in gales. Sure, a wingsail may theoretically weathercock - but so can many wingmasts. Blake got scared and Caradoc got dead........

    I've used fairly rigid windsurfer rigs for years. They have pocket luffs and stiff battens, so they seem like wingsails in many ways from a layman's point of view. They still go slower dead downwind when "still pointing towards the wind" (if I am understanding you) than when they are either stalled (in light winds) or sailed with normal attached flow at normal sheeting angles. Heeling to weather downwind is something that many people are very familiar with; boats like J/109s, Lasers, Optimists and Finns do it. So do the Int 12s/12 Voetsjoel, the very first International dinghy. So tens of thousands of sailors (as well as windsurfers) are not freaked out by windward heel.

    Those windsurfer rigs, by the way, can be rigged to be extremely flat, with negative camber and twist high up. I've spent a lot of time hanging onto them sheeted in and when weathercocking, and I'd normally find even a theoretically draggy Laser mast much easier to hold up. The windsurfer rig has fairly low friction to prevent the rig rotating into the weathercock position, so my gut feeling is that the real-world flow may not match theory or that the slightest resistance to rotation is enough to prevent efficient weathercocking. In fact as a layman, the whole concept seems to ignore the fact that weathercocking won't occur until sideforce occurs, and that sideforce can be a major issue.
    bajansailor and Inquisitor like this.
  4. Inquisitor
    Joined: Nov 2005
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    Inquisitor BIG ENGINES: Silos today... Barn Door tomorrow!

    By what you write, you are an expert in experience and logically applying it and exactly what I was asking for. You've given me lots of reference points to go research. Thank you for helping.

    Time lag between wind shift and weather cocking due to the inertia of the wing. I can imagine this could be a deal breaker. Living land-locked, sailing lakes, often mountain lakes, I'm used to wind shifts all the time and should have given this higher weight. The little time I've been coastal was always the most enjoyable sailing I've ever done because of the relative wind consistency.

    I am now wondering... do you think all the cases you referenced had full 360 rotation. The few designs I've seen with wing masts, all had shrouds that prevented them from 360 rotation. The only way that I know to make a wing mast/sail fully 360 rotational is by free standing or shrouds going ONLY to the masthead. I could see a restricted wing mast being far worse than a standard mast because it makes lift.

    This one I'm not too concerned about. The design I have in mind would not be a problem. Any access to a typical cruise cat roof-top would just be for taking down a sail. No need here. Even flush to the rooftop, it'll be 7'+ above the decks. I am also assuming fore & aft cockpits (aka. Gunboat) and going from one end to the other would always/only be through the saloon; not over the top. Besides, I'm only looking at a 6' chord for a 40' cat.

    I think you understand fine... the wing points aft (+AOA). DDW could never be optimum. It would be more like AC boats being far faster VMG by jibing about DDW. Besides, my current thoughts still have large head sails... potential for jibs to code zeros.

    I meant to be tongue-in-cheek. No slight was intended. In my head, I was picturing a peg-leg Ahab on a clipper ship leaning to the expected roll on a course change. But, I curious... most of the cases you site, it is human ballast causing the heel to windward... isn't it? How does an J/109 do it?

    Last edited: Sep 19, 2020
  5. tspeer
    Joined: Feb 2002
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    tspeer Senior Member

    There have been several applications of wingsails to cruising craft, with varying degrees of success.

    Mark Ott did a lot of work on a wingsail that was mounted on a Condor 50 trimaran under the Harbor Wing project.
    And then there was the Walker Wingsail:
    Walker's Plansail was designed to be a cruiser and used electronics to control the wingsail. Ott's Harbor Wing was a prototype for development of a fully autonomous craft. It also had an electronic controls system, but was as dependent on the electronics as was Walker's design. The Harbor Wing was also divided into an upper and lower half that rotated independently. This made it possible to null out the heeling moment as well as the lift from the wingsail.

    One big issue with any wingsail at sea is being able to feather it in high winds. That's why the Harbor Wing was split. An earlier single segment wingsail mounted to a cruising catamaran nearly capsized at the dock in a high wind because wind shear caused a significant heeling moment even when the net lift on the wing was zero.

    Then there was Couseau's Alcyone with its twin turbosails. The turbosail was basically a wingsail with a very large thickness ratio that used suction to maintain attached flow. It had a fixed forward portion and a trailing edge flap that rotated around it. One of the problems it experienced was fatigue cracking from the inertial moments of the turbosails in a seaway.

  6. PeteK
    Joined: Oct 2020
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    Location: Busselton, Western Australia

    PeteK Junior Member

    Hello Inquisitor
    International C Class cats (sometimes known as the Little America's Cup) did a lot of pioneering of wings and wing sails
    One of the leaders in this area was Quest II and III designed by Lindsay Cunningham.
    Lindsay and his brother then went on to this: 50 knot out
    and achieved the holy grail of sail speed 50kts.
    I doubt that this will solve your challenges for a cruising yacht though, as the "Macquarie Innovation" could only sail on one tack!
    Fascinating stuff, as are all attempts to push the boundaries of sailboat design
    Cheers, PeteK
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