Dynamic stability

Discussion in 'Sailboats' started by Bertil, Dec 8, 2008.

  1. Chris Ostlind

    Chris Ostlind Previous Member

    I give quotes directly from Sailing Anarchy by known Moth sailors, as well as quotes directly from Rohan Veal's personal website and what do you present.... Nothing but Hot Air. Why am I not surprised?

    Douglas, you must be running scared to find it necessary to refute the words of your very own foiling idol, Rohan Veal.

    The term, Amusing, doesn't cover half of the laughter I'm enjoying at present. Thanks for the chuckle, Doug.
  2. Henning P
    Joined: Dec 2008
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    Henning P New Member

    Mr Ostlind

    May suggest you and other interested people to read "Principles of Yacht Design" by Larsson and Eliasson

    Then we can have a serious discussion, this is like a kindergarten.

    Some people goes into future backwards
  3. bistros

    bistros Previous Member

    I have read this book and many others. I have also seen many published designs, along with many photographs of his designs on the water from Mr. Ostlind. As he has published multiple designs and actually built boats, perhaps you could concede he has reasonable understanding of design issues.

    Publishing a list of your own designs, qualifications and builder/owner's comments of your boats may be worthwhile to establish your own right to question his comments.


    Questioning other people's expertise while providing no evidence of his own expertise, education or successful full-size boat building results is a regular negative tactic employed by Mr. Lord. Mr. Lord claims to be an expert on scientific issues relating to foiling, but exhibits NO evidence of personally foiling on one of his own designs. He has shown ZERO foil supported full size boats designed by him that have been photographed foiling with ANYONE helming. Mr. Lord has been asked to leave on-line forums for his behavior issues.

    Here are some fair and reasonable questions for you:

    1) Do you believe that a Dynamic Stability Systems (DSS) style foil in a MOVING boat has NO lift-created load because the boat is tacking or gybing?

    2) Why would such a design require load bearings by Harken if there were no lift-created loads?

    3) Do you believe that manual actuated rope & block based DSS foil movement methods are adequate, timely and reliable - without additional crew? For a 30'+ performance keel boat?

    4) Do you believe that a DSS-equipped boat design, with reduced keel ballast (as per the designer's comments) provides the SAME level of fail-safe capability as a standard fully ballasted design?

    As I have state quite clearly in prior posts, I am NOT questioning the up-side potential of this concept, but I do believe that there are potential negative issues worth further investigation.

    Objective evaluation of sailing design innovations is the point of this web site, not unquestioned promotion of sales and marketing material. I'd rather see serious peer review of technology, along with the hard questions and solid answers than biased cheerleading and zombie-like promotion of every new idea.

    I would welcome Dynamic Stability Systems response and frank discussion about their concepts. I'm certain that they have encountered many of the issues raised here, and have most likely anticipated and dealt with these problems.
  4. Chris Ostlind

    Chris Ostlind Previous Member

    Read the book, Henny… several times, in fact.

    I’m reminded of another magical new techno solution to an otherwise slow monohull that never seemed to gain any traction in the sailing community. The guys who developed this concept, much like Welbourn, had a good deal of reputation in the community already, so the thinking process was not willy-nilly.

    I give you the Loop Keel. This could possibly be the most important contribution to weed collection, after the typical T-foil, that has ever been devised.


    Your buddy-in-thought, Doug Lord, had this to say within minutes of the initial thread posting...

    In response to Doug's post, the partner in the design process, Jon Howes, had this to say to Doug's effervescence about lifting surfaces and the loop keel concept in particular.

    Howes was actually being nice in his response in a very British way. So, you see, Doug, Henny and Bertil, you dudes have gotten all warm and fuzzy about another miracle answer to what ails the sailing business when it comes to monohulls. Bistros has enlightened you all about the engineering realities of not getting any free lunch when it comes to the design world... especially when it comes to boats, and you Henning, find it necessary to sling a Kindergarten reference to protect yourself all while offering absolutely nothing as a rebuttal to the points that were made. Very interesting tactic.

    Perhaps you guys can all take a breath of fresh air and approach the process rationally and leave the emotional stuff out of the formula? The loop keel was introduced just about two years ago and still, there are no commercial boat manufacturers using the technology... that I know of. If I were to make a wager on the DSS foil, I'd have to say, at this point, that there are some very significant marketing arguments that need to made and solved publicly, for something like this to catch-on as a mass market product. It will add complexity and expense to a boat in a marketplace where buyers are already running off to smaller and less complex craft as an answer to the present realities of global economics. As long as we're making suggestions to books, let me suggest that you all do some significant reading about marketing strategies, economics and just plain old common sense.

    The comment by Bistros, that the mark of a product's success will be measured by the buying public, has proven itself on the Loop Keel and will likely do the same for the DSS fin. When you add complexity, you also add expense. When the expense factor hits the buying public, and they weigh that against a perceived value for the type of sailing they will do... you will have your answer.

    I assume that you three guys have gone out to buy something and you weighed the cost benefit of any purchase you were going to make. I further assume that if that expenditure were being measured in the many thousands of dollars, it would be scrutinized even more. Since you are not going to be knocking-off any multihulls of the same length, that means that the decision to incorporate the DSS fin is all about the ego. Is that where you guys live in your decision making process?

    Henny, if you knew anything about me and my design work, or my approach to modern thinking, you'd discover that I do invite new concepts in design, especially when it comes to boats. What I do not embrace, is a dramatic rush to a new source of technology when it has not been proved functionally AND it adds unnecessary complexity to the genre.

    Isn't our world already complex enough for you? At some point is not a significant aspect of the designer's craft a need to resist the rush to ever more complexity and, instead, seek out creative solutions that are, at once, simpler and ultimately more effective for the end user?

    Isn't it thoroughly amusing that you guys wish to add more and more stuff to a monohull in order to extract some hope of being able to sail as fast as does a multihull without any of the tricked-out devices that invite problems of a wide variety of types?

    You refused to answer my position: That even if you included one of these DSS devices on your 30' monohull, you'd still be defeated convincingly by a whole host of 30' multihulls that are already on the market, starting with the comparison to the Seacart 30. If you really want to look into it seriously, I'd also be willing to bet that a large collection of smaller multihulls could also do the same thing. By refusing to address the issue placed before you, I can only conclude that you have no substantive answer that could come close to winning the point and that you are submitting.

    I'd suggest that you guys cease adding more and more crap to your boats so that you can, hopefully, compete with what is already out there in the marketplace, as if it were some mystical pathway to the future, open to only you. All you will end-up doing is overly complicating the design process, exposing yourself to a significantly larger catastrophic failure regimen and increased maintenance and operating expenses for what should be a fun, albeit slower, boat.

    Attached Files:

  5. Doug Lord

    Doug Lord Guest

    You are an outright liar and more than that you do what you accuse me of all in an attempt to besmirch the name of a well known ,proven Naval Architect(Hugh Welborn) and his tested and proven DSS system. You associate his name with Madoff in the 50 billion dollar ponzi scam and raise questions about
    his system that have been fully dealt with on two different sites that you have been referred to. You ,apparently, cannot carry out a discussion without attempting to PERSONALLY DISCREDIT anyone who holds a view other than yours. Pitiful!
  6. bistros

    bistros Previous Member


    Go back and re-read the post. I indicated that reputation CAN BE fleeting. Nowhere did I indicate Mr. Welborn's reputation was in question. The association of Mr. Welborn and Mr. Madoff was made by you, not me.

    Nowhere on the websites listed was data presented, analyzed or conclusions reached. You confuse Internet promotion with scientific evaluation.

    Merry Christmas! I hope Santa Claus is good to you and your friends and family.
  7. Boston

    Boston Previous Member

    hate to interrupt the party
    but I have a question about dynamic stability

    I recently found a set of prints for a friendship sloop "Black Star"
    and was wondering
    why is the center of lateral resistance so far behind the center of sail area
  8. Timothy
    Joined: Oct 2004
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    Location: canada

    Timothy Senior Member

    added complexity

    Did not a multihull begin as a momo hull with the added complexity of an out rigger.
  9. Chris Ostlind

    Chris Ostlind Previous Member

    Great question.. so, let's turn the idea around 180 and ask if monohulls did not come from the inherent stability of a multihull way back in the dawn of time? As long as we're talking on a thread about stability, that is.

    GOOGLE will set you free, Tim. Enter Tamil and Catamaran for one search and in another, enter seafaring and Polynesian. That should get you rolling.

    What I suspect you are going to find is a Western-centric viewpoint as to the evolution of boats as used by mankind. There is quite a bit of evidence that ancient civilzations, such as the Harappan culture of the Indus valley were actively trading along the coasts of the Middle East, Africa and all the way to China, as far back as 4000 B.C.

    When you couple this reality with the fact that the term catamaran is a word evolved from the Tamil (an ancient part of the Indian sub-continent cultures) Kattu and Marram, you begin to see the truly ancient establishment of the multihull type, be it two hulls or three. Here is a description of the development of the genre, as it might have taken place many thousands of years ago.

    "The concept of the catamaran is indeed ancient.
    The word catamaran comes from the Tamil word “kattumaram”,
    meaning tied wood. Indeed, in ancient times the word was used to describe a raft made of logs or boats lashed together.So it is quite likely the concept of twin hulls came from the Indian continent.

    Parava or Paravas, also known as Bharathar, Paravar, Meenparavar and Fernandos, is one of the oldest Tamil castes.Paravars had traditional sea based professions, such as pearl-diving,
    fisheries, navigation, salt making, etc., The catamaran was the invention of the paravas,a fishing community in the southern coast of Tamil Nadu, India.
    They could stay at bottom of deep for many hours (hmm..are these people employed in Navy as Divers? I don't think so)
    Their engineering skills in ship-building in the olden days were profound.
    Thousands of years ago, Tamil fishermen discovered that when they tied logs,hollowed them and made the logs pointed, they had at their disposal a vessel far more stable and nimble than an ordinary canoe:
    Thus was the catamaran born."

    You can make of it what you wish, recognizing the obvious ancient connections, or simply ignore the potential and maintain a comfortably western take on how it all took place; this business of boats meant for the business of, as well as pure sport of, sailing.
  10. Timothy
    Joined: Oct 2004
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    Location: canada

    Timothy Senior Member

    I have read that the only reason that the west did not embrace the multi hull is because we are trammeled by what is termed a cultural imperative. private property, and hence the need to transport it and protect it. Large whale bodied hulls although they cannot sail well .can carry copious amounts of goods and cannon.
  11. Bertil
    Joined: Feb 2006
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    Location: Sweden

    Bertil Junior Member

    It seems this tread turned out to be a disc comparing monos with multis. I don't mind, cause that is interesting too.I still have a believe that the weight of monos with leewaywing is narrowing(perhaps beeing alike) a multi with the same accomendation,(not a racermulti with only amas and a net between the hulls).
    Take for example my 40-footer (width 4,5m) bulit in 2001, with a deep keel weighing 800kg and a total weight of 5200kg. I think a 40-foot multi with accomendations weighs about the same. If we produce my hull today with modern material I think you can reduce the weight on that monohull with 1000-1500 kg. Remember all weight the multi need for connecting the 2 or 3 hulls.
    Then the potential for speed will be at least the same as for the multi as long as it sailing on at least 2 hulls.
    And you get rid of the disadvantages with the multi as can suddenly turnover, space in harbor, wet area with 2 or 3 hulls compared to 1 hull, expensive to build and the jumping movements.
    I have had multis my self, a catamaran 40feet, and 3 tris up to 30feet. And what I did not liked when sailing alone especially with the cat was the feeling of loosing control/risk for turning when it was windy here in Sweden between the islands, where suddenly the wind comes from shifting directions.
  12. Chris Ostlind

    Chris Ostlind Previous Member


    Please name the designer, manufacturer and model of your boat.
  13. bistros

    bistros Previous Member

    Actually it has turned out to be another thread almost destroyed by Mr. Lord, where his unbridled, irrational obsession for all things foiling has turn attention away from your interest in modifying your boat and increasing performance.

    The speed potential for two boats, one a catamaran and the other a monohull is not the same at the same displacement. The effective increase in waterline length of the catamaran leads it to a much higher hull speed in displacement mode. Reducing the weight of the monohull - even significantly does not mitigate the difference in effective waterline length.

    Facing reality, when comparing similar monohulls to catamarans, the cats generally win hands down on performance issues.

    They don't always win on many other accounts as you have pointed out.

    From a distance, you appear to want to increase performance of your boat.

    Adding the DSS-style foils may help, but there are many questions that should be asked & answered first. This is not like a bolt-on Nitrous Oxide kit for a Honda 4 cylinder sedan.

    1) Is this particular boat the right choice to modify, and can you afford the risk to the boat and it's resale value in it's current condition? A 40' boat built in 2001 as a heavy displacement hull has got to be worth a fair amount. Cutting the hull to add a hull-wide daggerboard trunk is serious surgery with a lot of risk.

    2) Does the outcome of the "Leeway Wing" modifications have enough potential for success to meet you goals in terms of performance and value? I know you've done some preliminary calculations, but if the modified boat does not keep up to the multihulls will you be disappointed?

    Personally, I'd rather do a small scale experiment on a much cheaper hull than roll the dice on a 40' boat that may be valuable. Time is your friend, and waiting to see if the DSS system succeeds for other people reduces your risk dramatically. Out in front of leading edge technology is the bleeding edge, and sometimes it pays to let others do the bleeding.

    I'd consider paying a professional Naval Architect / Professional Naval Engineer to review the design changes proposed - if your ideas are sound, you've got a written third party opinion that will be required for insurance & survey purposes. If you ideas have problems, it is far better to have them pointed out before money starts flowing.

    My preliminary thoughts are that an appropriately sized DSS foil solution for your boat is going to require hydraulic (or similar reliable) actuation and control system development. This indicates to me that some type of reliable power source is going to be necessary to run the pumps. Much as Mr. Lord fails to understand, the DSS foils are highly loaded when the boat is moving, and you have to deal with that load to tack or gybe.

    I also believe that IF your boat can have weight reduction done, the worst place to remove weight is the keel bulb - you have indicated it is a heavy boat, but the best place to have weight is in the keel bulb. I would look at every other option before reducing keel weight. You want your boat to fail safely if the DSS system was broken on a fishing buoy you failed to notice.

    Best of luck with you decision making process!
  14. Paul B

    Paul B Previous Member

    Agreed. There are some here who glom onto every piece of marketing and act as if it is gospel.

    I noted the DSS folks had their site go live and did the rounds "selling" their idea for a couple of months earlier this year, then nothing.

    It seems they claim a Boatspeed 23 was fitted with their system. How has that boat faired agaist similar "standard" BS23s on the racecourse? It seems a good practice would be to fit the system to a known entity (BS23 or other) and then sail it in all conditions and on all points against a control to determine the validity of the new system. Scientific Method or somesuch?

    Wasn't the Druggie all fired up about a canting keel Melges 24 a few years ago? Didn't the folks running that project also shy away from direct comparisons with a standard M24? Wasn't it later shown that the stock M24 was faster?

    How about putting the DSS system on a M24 and racing in a major regatta against the fleet? That might prove something.

  15. Hansen Aerosprt
    Joined: Mar 2007
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    Hansen Aerosprt Junior Member

    From personal experience, there are problems. Foils only work when they are moving appropriately in their design envelope. In the mid-'70s, I built a foil-stabilized speed record craft using an FD hull, a crossbar with adjustable AOA T-Foils (one pulled down and one lifted) and a semi-rigid wing similar to Ilan Gonen's. It was very fast and stable underway right up to the point of tacking in strong winds at which point it capsized irrecoverably. 6 hours in the water and a night in the hospital with serious hypothermia sorta 'cooled' us on the idea.
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