the egotistical quest for an expensive thrill

Discussion in 'Boat Design' started by deepkeeler, Dec 26, 2004.

  1. Vega
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    Vega Senior Member

    Sharpii2 and Milann, thaks for the input.
     
  2. MikeJohns
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    MikeJohns Senior Member

    Chris If you rock a sail boat you’ll get more or less equal loads on the symmetrical shroud attachments. The heeled sailing vessel has a wind load (from windward), a gravity component acting on the windward shrouds and some dynamic loads from her movement. When she is side swiped by a steep fronted wave a force is generated and the hull accelerates sideways along with the wave it heels and skids sideways often travelling down the wave front, the faster this initial translation ie the faster the acceleration the more likely she is to gain even more energy from the wave as it has a longer time to act on the hull. Higher forces (as you say) come into play when the hull encounters the bottom of the hole and it comes to a high acceleration stop with the high forces acting from the water on the lee side of the hull, the weather chainplates at this point suffer very high loads. Note that the hull is highly stressed on the landing (lee) side not on the wave impact side The wave now still has to be countered with your back to the wall (as it were, and this is a frequent knockdown or rollover precursor as she has nowhere to go). Yes the majority of hull damage is not from the wave but from the landing impact. The stove in port-lights , split topsides, bent railings and fractured hull deck joints are nearly always on the lee side. The heavy boat falling off a wave will land with greater force and experience higher loads at this point but she is less likely to get into this position (later) and her scantlings are considerably higher so she will have more reserve strength. The problem with the light boat for the designer is weight, as I have said before weight and strength are opposing criteria. A lightweight boat must sacrifice reserve strength to be lightweight. The same wave acting on a heavy hull has often passed before the vessel reacts significantly. Note that the energy is not dissipated on the hull but on moving the hull eg a boat than is 5 times heavier will experience one fifth the translation for the same wave energy. The wave doesn’t have to break or smash into the boat for this energy to be used it just has to move it. Often because of the heavier boats greater immersed lateral area and considerably higher roll inertia it heels only a little to the wave front (hull form important here too) and rises with the water-mass as the wave passes. It’s final sideways velocity is less than one fifth that of the light boat because of the other factors (WSA LSA) . The heavier rig reduces the roll amplitude for the same reasons; the energy required has a limited amount of time to act as the wave translates past the vessel. All we have been talking about here is sideways translations/ rotaions, we also have pitching yawing, vertical acceleration, impeding action of waves. It seems to me the only disadvantage of a heavier hull is the light air drag of the wetted surface, but if she were able to spread the full sail her hull could stand without rating penalty then that might not be such a disadvantage.
     
  3. CT 249
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    CT 249 Senior Member

    Thanks Mike, the way you put it is much closer to my understanding and experience than the way Sharpii did, as with respect to him it's the weather side chainplates and lee side of the hull that generally gets damaged AFAIK.

    I'm still unsure about the impact of breaking crests on the windward side, as you say the heavy boat moves much slower to lee and therefore must suffer more impact on the weather side in such a situation, mustn't it?

    The heavy hull is also definitely slower in a breeze due to greater wave formation; see the earlier example of the Finnisterre type which even in a breeze is significantly slower than an '80s IOR boat of similar length. The facts (as demonstrated by sophisticated VPPs and years of experience) are pretty clear. And I know my sailmakers charge for area of sail, not LOA, which makes a case for the lighter boat. If you put a bigger rig on the heavy boat without penalty then the lighter boats could put on a deeper keel and bigger rig without penalty too!

    But we'll both have to stick to our preferences, I think! :)
     
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  4. Vega
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    Vega Senior Member

    The contributions from Ct249, Mikejones and sharpii2 have been very interesting and informative. I am just an amateur who is very interested in the issues that are being discussed in this thread, namely seaworthiness in a boat.

    I have read a lot of information on this subject and it’s a controversial issue. For example, Eric Tabarly, one of the most outstanding sailors of the last century had an opinion that seems to collide with the one of Mikejones about seaworthiness in a boat. Mikejones talks about a heavy displacement with a full keel as the more adequate boat for heavyweather.

    Eric Tabarlay, who has raced long keel heavy boats and light boats with a finn and a bulb says:

    “The boats that have the worst behavior when heaving too without sails (capa seca) are the ones with heavy displacement and a long keel, specially when the keel is not heavily ballasted. The long keel and the deep of the underwater hull offer a big resistance to lateral displacement…then the waves that break against the boat push the superstructure and as the underwater offers a big resistance, capsizing can occur.”

    The ideal boat to heaving to without sails, is a light displacement with a finn keel with a good form stability. This kind of boat offers little resistance to lateral displacement and moves fast sideways…protecting the boat from breaking waves…”

    Sorry about the poor translation (from Castellano into English)

    From « Guide pratique de manoeuvre » by Eric Tabarly.
     
  5. MikeJohns
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    MikeJohns Senior Member

    Heaving-to is primarily a tactic for stopping the boat for more comfort for a break to cook, clean, repair, navigate or rendezvous while at sea, and also as a means of standing off a lee shore; eg waiting for dawn before entering an unknown harbour without having to tack to weather all night.

    It is not recommended as a survival heavy weather tactic these days, it is much safer to run off with the weather on the quarter carrying some sail if possible.
     
  6. Vega
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    Vega Senior Member

    No, thanks for the information (it’s an almost 20 year old book; I hope that it has been revised in recent editions, because boat designs have changed a lot and I have commanded that book).
    I have said that I have read a lot about the issue. Perhaps the better quality information about boats seaworthiness I’ve found comes from the new edition (5th) of “Heavy weather sailing” by Adlard Coles and Peter Bruce. From the original book only one chapter has remained. The book features chapters written by different authors, between them Olin j. Stephens jr, Andrew Claughton and Mike Golding. Have you read this one? This is the book that has deserved from Sir Peter Black this comment: “ This book should be read and reread by anyone who sails”.


    When he talks about light displacement boats, he is talking about one of his racing boats (Pen-duick III, designed by him) that carries the name of his first boat, the old and beautiful boat he has loved all his life and in which he found death, the original Pen-Duick a design by William Fife III . That one is the heavy boat he is referring to.

    This is Pen-DuickIII:
    http://www.club-penduick.com/bateaux/bateau_2.html

    This is Pen-DuickI:
    http://www.voilesclassiques.com/demo_yacht_penduick.htm
    http://www.historicships.com/TALLSHIPS/Latina/PenDuick.htm

    when Tabarlay says:

    ”The long keel and the deep of the underwater hull offer a big resistance to lateral displacement…then the waves that break against the boat push the superstructure and as the underwater offers a big resistance, capsizing can occur.”
    ”The ideal boat to lay ahull without sails, is a light displacement with a finn keel with a good form stability. This kind of boat offers little resistance to lateral displacement and moves fast sideways…protecting the boat from breaking waves…”

    he is referring to the hidrodynamics that are easily visualized in these drawings taken from his book:

    http://i19.photobucket.com/albums/b152/vega1954/penduick1.jpg
    http://i19.photobucket.com/albums/b152/vega1954/Penduick1a.jpg

    These dynamics are very well explained in another thread by Millan referring to the advantages of the center board boats over conventional keeled boats. The dynamics are the same, only that in a center-board with a keel up, they are even better (regarding stability) than in a deep keel with a bulb and a narrow finn. Worst dynamics, in what stability is concerned, will happen in big deep full keeled boats.

    Ok, sorry about my incorrect English:( . As you have pointed out I was referring to lying ahull when I was talking of heaving-to (capa seca). Lying ahull is in Spanish and Portuguese the correspondent of “Capa seca”.

    I found it amusing when you say:

    “….It is not recommended as a survival heavy weather tactic these days, it is much safer to run off with the weather on the quarter carrying some sail if possible.”

    I agree with you. That is the best survival tactic nowadays, the one that is recommended in all the books, more these days that in old days, because modern boats are better running with the weather than older boats. They are faster and therefore take less breaking waves and water from behind.

    But when you have a lee shore on your back you have to lie ahull, or stick to a floating anchor, don’t you?;)
     
  7. MikeJohns
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    MikeJohns Senior Member

    Vega
    I was just looking her and saw your last post that I missed.

    I thought we could re-visit some of these topics on the stability forum when it opens. This thread does contain many pertinent issues.

    Looking at Taberly's drawings above I would say two things, firstly that beam on to a large sea is never the seamanly approach in any vessel. Secondly the lighter dish type vessel with long strut/bulb combination does indeed give to the sea, but this causes its own problems. The boat accelerates sideways and this gives a dangerous sideways dynamic component...what happens then depends on the sea state and the vessel roll inertia. See my post 167 above.

    There are other factors too but we'll save the discussion.

    cheers
     
  8. Greenseas2
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    Greenseas2 Senior Member

    Considerations

    Consider the guy who has only a few extra bucks, but wants to ocean race with other boats of a class. How about MORC racers (Midget Ocean Racing Class) Class boats like the Nordica and Hilman are small, well designed and can take some relatively heavy seas. Here, both skippers and Race Committee do their homework and will get word to the boats in advance of heavy storm conditions. You will see Nordicas, Hilmans, Pacific seacraft Flickas and other of the same breed all over the Caribben and Bahamas just cruising. There can be, and are, larger designs that are both good racers as welll as good cruising boats.
     
  9. Guillermo
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    Guillermo Ingeniero Naval

    Running may not always be the better technique. Technique to be adopted depends very much on the boat design and sea state. I've personally run a gale with 5-6 m waves under storm-sail alone, in a 30 double-ended-long-keeled ketch with an stern hinged rudder, and I can tell it wasn't a nice experience. The hydrodynamical center of effort moves back and forth with passing waves, and a long keeler has a lot of room for it to to move, thus creating strong broaching pairs. This, added to the loss of efficiency of the rudder when coming down a crest (because oscillating water particles run in the direction of the boat's movement) can make a long keeler incontrolable (And other types too). Towing a series drogue, is probably the best solution to this most unsafe situation.
    I recommend a careful reading of:
    http://seriesdrogue.com/coastguardreport/
    From its pages:
    "Sailors who survive such storms may conclude that the tactics they employ, such as heaving to, lying ahull or running off, are adequate to prevent capsize. This is a serious mistake. There is very compelling evidence to show that while a well found boat will survive a storm in non-breaking waves, none of the above tactics will prevent capsize in a breaking wave strike"
     

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  10. MikeJohns
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    MikeJohns Senior Member

    Guillermo

    Without being patronising and as my own opinion of course ...

    The first law of science is "Beware of anecdotal tales", the vessel you describe has far more design characteristics than you mention of course. (as I am sure you know ) All these factors relate to her response to the sea. If you applied some minor alterations you may have found her quite different.

    None of the designers a few decades back had the benefit of computers or tank testing at the design stage, designers knocked them out and hoped the sailors would have enough skill to overcome the flaws . There were some great successes and lots of abysmal failures that should never go offshore as there have been in any design era. We can never generalise for a whole era of design on individual performance. (Current or past)

    You can of course design any shaped hull for a specific sea-state and relative course with predictable confidence. The real trick is compromising some aspects of hull-shape to provide the best overall combination of comfort safety and performance.

    There is also a size factor, as the vessel gets larger the design factors tend to change significantly.

    As for my own sailing experiences:
    I have sailed on a 100 yr old full keel sailing boat with a massive amount of wetted surface area in large following seas and been delighted with her comfort, performance and her incredible lack of any broaching characteristic at all ... .
    This is a narrow deep fore-footed, heavy displacement , very deep vessel . Few sailors these days have experienced such as vessel and they have a strong prejudiced view about how they perform.
    I have also sailed on exhilarating fin keeled speed machines that broach if you take your eye of the course for 2 seconds. My own cruising boat is a well balanced moderate fin keel and skeg (because I like the light air performance without huge sail areas).

    The old saying is "Horses for courses"
     
  11. Guillermo
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    Guillermo Ingeniero Naval

    Of course. What I was trying to exemplify is that running is not always the best technique. Depends on many factors, as sea state, boat size and design, experience of crew, etc, etc. That's all.
    An interesting thread on parachute anchor and the like, is at:
    http://www.boatdesign.net/forums/showthread.php?p=87444
     
  12. Vega
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    Vega Senior Member

     
  13. brian eiland
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    brian eiland Senior Member

    Canting Keel Monohull vs Multihull

    ...... last paragraph of an interesting interview
    with Juan Kouyoumdjian (aka Juan K.) in September Sail magazine.

    He's a naval architect who designed the runaway winner (ABN One) in
    Volvo Ocean Race.

    At end of article they asked: "What is future of canting-ballast
    technology?"

    He replied:
    "It depends on acceptance. I could argue that a canting-keel monohull
    is a very inefficient multihull. Imagine canting a keel to leeward
    and instead of ballast you have air. You would achieve the same
    increase in righting moment in a lighter solution, and in fact you get a
    multihull. Our sailing community is divided, and choices are made on
    style or fashion; otherwise we'd all be sailing multihulls
    "
     
  14. CT 249
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    CT 249 Senior Member

    So why should someone who sails where I sail, sail a multi?

    The local puddle 300 metres from my house is too small for a fast beach cat to fit comfortably. We know, because we own a fast beach cat, and we run out of room very quickly. Launching the cat is also a hassle there. Still, we sail there (on monos) because it's fun, and we don't always want to drive 45minutes to the more open waters where we sail the cat, and have the hassle of messing with the bigger, more complicated boat.

    The monos are clearly more practical on the puddle, which is why the old cat fleet died out and we get 100+ starters from the dinghy and windsurfer fleet most weeks. This is just one example......thousands of small-boat sailors choose to sail monos for very good reasons such as this. Hell, even the owner of the fastest small cat (Steve Clark of C Class fame) sails small monos as well as cats. So do the world A Class champs, at times.....they appreciate the Laser for what it is. Is Juan saying that all these guys are wrong when they see value in monos?

    And what about if we want to go out on the yacht for a cruise around the harbour for the day or weekend? Why is a multi better? The water around here is deep - shoal draft is no advantage really. For my yacht, I want headroom......not readily available in a small multi. I also want nice tight racing....not readily available in a small multi.

    Ok, so big multis sail flat - but (cruising apart) we don't HAVE to prefer a cat to a heeled mono. I happen to love heeling in a mono, or the sensitive act of balancing a mono upright, and so do many sailors. The foiler Moth sailors banned wingtip foils because they don't like super-stable boats - you can't call foiler Moth sailors boring. They just know what they like, and they like a boat that responds with heel as well as acceleration and deceleration. This is not style or fashion, it is the personal taste of intelligent experienced people.

    The ideal sailing angle for many small cats is higher than it is for many dinghies, but that doesn't worry beach cat sailors. Our F16 type cat "going wild" is sailed at much greater heel than a Laser or Tasar or something like that.....no problem, the boat's great fun at that angle! Cat sailors often fly a hull for speed and fun. so why should sailing flat be such an advantage for big-boat multis when daysailing?

    Many windsurfers are sailed on heel, with the lee rail digging in. Many windsurfer sailors love the feeling of having the board tilted as their body leans to windward. In the same way that bike riders love scraping the pegs as they lean through turns, millions of sailors LOVE heel and leaning and we see no reason not to sail leaners. So merely being able to sail flat is not a great bonus for day sailing. For extended cruising, yes it's great. If you happen to like sailing flat, great! But we shouldn't be told that we are slaves to fashion or style because we happen to enjoy a mono's reaction and the subtle art of balancing a mono.

    OK, multis can be faster - who cares? If sailing was all about speed, all the Tornado sailors would junk their cats and sail speed boards. But sailing isn't all about speed and anyone who looks at the vast number of highly intelligent people who sail boats like Beneteaus, Westsails, Catalinas, Hobie 16s, Prouts, Dragons, Lasers, Shields, Sea Views, Snipes, J/24s etc can tell that most people don't really care about speed.

    On the waters I sail, a big cruising cat runs out of water too quickly. They are a nightmare to slip here (it appears now you have to go up to 45 miles to find a slip you can fit on). They go faster in some conditions, some go faster in all conditions, big deal......many give you little feeling of speed (to my taste) so you may as well be motoring (as far as I'm concerned).

    I'm in a family that's now in its third generation of multi sailing....we've formed cat clubs, built multis, lived on multis, raced Tornado worlds, still own and race and build and sail cats. They are great - in many situations they are the most logical boat - but NOT in all situations.

    The fact that Juan believes that most sailors are ruled by style or fashion tells us more about Juan than it does about the sailing community.
     

  15. Doug Lord

    Doug Lord Guest

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