Historical multihulls

Discussion in 'Multihulls' started by Gary Baigent, Feb 26, 2012.

  1. cavalier mk2
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    cavalier mk2 Senior Member


    Healthy thought process here. knots per payload pounds is a category that would produce more versatile multihulls.
     
  2. Ilan Voyager
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    Ilan Voyager Senior Member

    Even for that, the boat is antiquated. It was a race boat designed in a time when reliability and seaworthiness were not the greatest quality of multis. For a modern NA the boat has very serious seaworthiness flaws. The front decks of the main hull and amas can be a "shovel trap" in a serious storm, and the rear diagonal stability is frankly bad. Thinking that this boat is safer than a modern tri is a myth with no rational basis. Most 1965-1985 multis were unsafe, and you had to sail them very smoothly. For example the Newick tris, when pushed, become unsafe and sometimes unpredictable as the small ama sinks underwater giving the hinge for capsizing. Almost all the Newick tris when raced have capsized. That means that the margin of security is pretty small.
    In 30 years of design of tris from 1985 to 2015, a lot of things have changed.
    Prismatic coefs are higher, the boats have more volume at the sterns, the amas are more buoyant, bows are less hydrodynamic brakes and the sea motions are far better, with very little pitch in a formed sea.
    When performance is not the main goal all these features give very seaworthy boats. If you detune with a cruising rig, the modern shapes give excellent boats.
    So new does not mean unsafe, all the contrary, you have far better security coefficients. Race boats are by nature unsafe as they are overpowered to get the last knot, if you keep a AC 70 with its original rig you have a unsafe boat. As the last knots require a lot of power, depowering such boats of 15-20% with a lower center of sail does not mean that the mean performances will fall down drastically. You'll lose less than 10% but you increase the security by 60 to 85%. Add a more conservative way of sailing and you get a safe boat with a very big security margin. It won't capsize unless total mistake of handling or exceptional circumstances.
    A simple big tri like IDEC in its minimal configuration "solo around the world" would be faster, safer, with better possibilities of accommodations for an eventual RV boat. I even think that it would be cheaper with its quasi developable shapes with far simpler molds.
    Look at IDEC in detail and you'll understand that such a basis is almost ideal for a safe RV boat able of excellent mean speeds. Some mods to get more displacement and more spacious amenities, maybe (a big maybe) a schooner rig with 2 "big" main sails, small jibs tacking automatically, a moderate gennaker, while keeping the strong original righting moment and the diagonal stability, and you get a very safe boat.
    After all IDEC made a solo race around the world with no problem. That means that the boat is safe, reliable and relatively easy to handle for a 50 some years old man. And pretty fast, but the best is the excellent mean speed day after day in a very wide range of conditions of sea and wind.
     
  3. cavalier mk2
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    cavalier mk2 Senior Member

    Yawn.....commenting on the thought process not the Shuttleworth. These things have to be nurtured, a few days ago cruising boats were F40s.
     
  4. Ilan Voyager
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    Ilan Voyager Senior Member

    I commented the Shuttleworth and after the thought process, read it there are several paths...The "recipes" exist, were tried and approved by the results obtained.
    The transformation of rigs and calculus of security margins were made in 1989 and 1990 on 2 F40, one of 86, one of 87 of very different designs. One was a successful boat, the other was a failure, the NA office wanted to know the exact reasons of failure as well the ciphered reasons of success.
    We made the original VPP of the 2 F40 while they were racing, we knew the real weights of the boats and of the crews.
    After we made a systematic campaign of VPP's with 3 different cruising rigs, and for a wide range of loads with different placements. I can tell that we moved a lot of 20 kg sand bags. Besides we measured the stresses of some precise points and also local accelerations in different conditions of sea. The ciphers obtained were very interesting, but are not public as the campaign was paid by a private NA office.
    I know that around 2000 another campaign was made on 60 feet tris. This campaign permitted to get a basis of solid ciphers which served for the design of the maxi multis. The multis now are the result of the collaboration of several specialists from the "hydrodynamicist" to the structural engineer plus the composites engineer, and between them several consultants, all under the direction of NA.
     
  5. cavalier mk2
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    cavalier mk2 Senior Member

    Come now, this is just a private little forum, do tell. We won't. Elixer recipes for bounding to the horizons shouldn't go to waste. After all you are in Mexico, Skippy's just stirring up trouble and Voyager can't be your real name..... I'm just cavalier.
     
  6. oldsailor7
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    oldsailor7 Senior Member

    On the matter of design for both speed and safety, can anyone tell me WHY some multis have such bad safety records, but others don't. :?:
    Take Crowthers Buccaneer 24 for instance. It was designed as a small cruising tri, but turned out to be a race winner. It is remarkable that the B24 has (to my knowledge) never had a capsize or pitchpole. Can anyone explain that.:?: It was Crowthers best selling design, probably because it was easy and fast to build and inexpensive. (I built mine in six weeks for about $1500.00, in 1971, but materials were a lot cheaper then.) Over 200 were known to have been built, but I think there were more which may have remained incognito.
    I ask:- Please explain. :?:
     
  7. Skip JayR
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    Skip JayR Tri Enthusiast

    This is a very one sided perspective of the thematic !

    Look at the sea accidents generally. By officially statistics this world looses every week one ship, in average. As it is documented in the annually Alliance statistic report "Safety and Shipping Review 2014"

    Analysing such accidents the main reason for accidents is the "human factor". It is not the boats. As mostly these are designed and built by very experienced designers, naval architects, engineers and warfts.

    Naturally some boats by their design bear higher risks, e.g. take the MOD70 Trimarans or ORMA60. Last became too dangerous even for the professional sailors.

    Another aspect is the target a sailor has to use a boat for, e.g. leasure sailing, day cruising, "coffee sailing" (mostly staying in the harbour), tough offshour racing, long distance sailing, non stop circumnavigations etc. ... The formula is simple: More competitiveness, more speed, more risks.

    Some sea areas have higher risks, e.g. the Roaring Forties or Pacific. Some coastal areas or even inner lake sailing have some risks, depending on the geographical environment.

    Last, its not just the human factor, e.g. on the psychological level or other factors (lack of sleep, dehydration, physical fitness etc. ...). Lower skills and lack of experience a sailor has, higher the risks. So it depends on the knowhow a skipper + crew has, too.

    I would not derivate from some statistics you get where more often one boat type is named, that as conclusion the (l)onley reason for "higher risks" lies in the design/boat type itself.

    Many factors come into the game, age of the boat, building method, boat materials are some other factors, too. Not to name that some multihulls are overpowered (take a 40 foot boat of the Formula 40 class, up to a 80 foot mast) with huge sails areas.

    Its complicated matrix one would have to analyse to come to an obviously result we can trust. Fact is: the world is full of dying ships and lost souls... http://www.shipwrecklog.com/log/
     
  8. oldsailor7
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    oldsailor7 Senior Member

    Skip, I won't press the Quote key. The essence of your long reply can be summed up in the first two words of your last line.
     
  9. Skip JayR
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    Skip JayR Tri Enthusiast

    Oh..... that was yet not long.. hehe... just a tiny warm up in the morning with a hot cup of coffee :) :D

    Yes, Sailing is a complex thematic. And it becomes more and more complicated. - Already became a science on its own as documented here: http://bit.ly/1LPJ304
     
  10. mcm
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    mcm Senior Member

    What is considered the most important factors that create a healthy diagonal stability in a multihull ?

    What about rear diagonal stability ?

    And where does Shuttleworth's 68' tri fail to provide optimum diagonal stability ?
     
  11. cavalier mk2
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    cavalier mk2 Senior Member

    I think he is referencing the flat decks on the main hull and amas, features that actually provide safety working on deck in a storm. Because the length of the ama bows is shorter and because of the flare there will be less tendency for them to be pushed under than longer wave piercing ones so it is arguable. What can't be argued is that piercing waves is faster than going over them.

    We can pick on my old Nicol Vagabond mk2 which has fine floats and a cambered wing deck that goes far forward. "It will shovel !" the pundits scream. "Capsize diagonally!". None ever have in more than 50 years. The only one that capsized was Hedley's own boat in a 70 knot storm while he tried to carry full sail (went over sideways), he was into extreme testing and it cost him his life on that occasion. This is because the forward wing lower edge acts like an enormous flying scow bow and provides lots of buoyancy as well as dynamic lift at speed when contacting a large wave. The wave top gets sliced off and quickly rolls off the cambered deck to the side. Not done now because other things are faster, and we are used to seeing them. Other old 60s designs like the Searunner series ,1966 for the 37', and Norm Cross' older boats as well as Pivers have accumulated thousands of safe deep sea miles. Put on a tall rig and the game could change.

    Modern racing amas are going to give a bone jarring ride with the full shapes and flatter bottoms. Faster too. For cruising you'd be happier budgeting the change to more rounded v bottoms out there.

    I think the answer to Paddy's Bucc 24 safety is one of proportions. Rig, buoyancy distribution, beam, weight and shapes add up to the combination. A contrast would be Lock's Twiggy design where things got more extreme so they spent more time upside down.
     
  12. Richard Woods
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    Richard Woods Woods Designs

    Brittany Ferries was John's first independent design. Rob James wrote in his book that they had to be very careful not to allow the boat to sail backwards in big waves as it would capsize diagonally backwards

    I agree with Ilan.

    Years ago I had a long talk with Nigel Irens just before an OSTAR and he showed me the big differences in his outrigger designs over a period of about 12 years. By chance there were a number of his older boats anchored off the RWYC as well as his then current race boats.

    Even I could see the differences he was pointing out.

    One has to assume that designs improve as a designer gains experience with earlier boats. I have never seen a Bucanneer 24, I assume they are far faster than the 28 and 33, both of which I have sailed against. Neither of those designs could be considered "fast" even 25 years ago. I did go on the original Twiggy a couple of times but never actually sailed it

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  13. Skip JayR
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    Skip JayR Tri Enthusiast

    I think, John S. knows that very well.. and if a new client would come being interested in this 68 footer concept, he'd redesign it by sure.

    I like the size... it would give me lots of safetyness on high seas... e.g. similarly the stretched Orma60 up to 72-73 feet (originally built in 2000 and pimped up in 2006). I see it as a good length to handle by a small crew (e.g. skipper + 2nd hand + 2 scientists) as "RV vessel"... maybe with some supportive devices (electric winches).
    [​IMG]
     
  14. Skip JayR
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    Skip JayR Tri Enthusiast

    VPP for Formula 40...

    Interesting... I didnt know about that in the 80ths they used computer aided velocity prediction programs (VPP) *) for Formula 40 boats.

    I think the programmes in the market, e.g. French programme WinDesign or AeroHydro's AHVPP started 25 years ago or TechSail'sSailfish Yacht Analyzer came lately 2000 into the market.

    At least you can tell which two Formula 40 Cats/Trimarans had been tested... :) And: Was the test series part of an America's Cup campaign ?
    _________________________

    *) The first VPP was developed at the Massachusetts Institute of Technology during the early 1970s when Commodore H. Irving Pratt funded research to predict the performance "of a sailing yacht, given knowledge of its hull, rig and sailplan geometry".
     

  15. Gary Baigent
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    Gary Baigent Senior Member

    A B24 I doubt is faster than the 28 or 33 - but it is certainly a high end performance design for its time, and its size and even today. We altered B24 Miranda, angled float foils, no main hull dagger, longer stern floats - but very pointed, lengthened main hull in stern sections, reduced the rocker, (most important) new rudder, rotating small foil mast, changed rig to 7/8ths - so it was definitely a more performance version than stock - also was kept light (but haven't got figures), floated high.
    That boat has sailed many miles and the only time we ever looked to be getting into trouble was when close reaching two handed with shy spinnaker, the halyard jammer let go and the kite flew out to leeard but remained sheeted ... so the boat reared up, buried lee float, lifted main hull out until sheet was eased and halyard cranked back in. I thought we had reached the point of no return but really, although we pulled the right strings, the B24 saved its own self. Buoyant floats, light weight and lifting angled foil would also have contributed.
    Check out the clean wake.
     

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