why has high buoyancy become so important?

Discussion in 'Multihulls' started by peterchech, May 6, 2011.

  1. garydierking
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    garydierking Senior Member

  2. Doug Lord
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    Doug Lord Flight Ready

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  3. Samnz
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    Samnz Senior Member


    even tho you think theyre slower? sorry Gary you've confused me now...
     
  4. Doug Lord
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    Doug Lord Flight Ready

    flotation getting larger? yes, but it doesn't necessarily have to

    ------
    Seems like this comment originally had something about me ignoring large volume floats? I don't think so:
    Post #2 of this thread:
    ===============================
    More: many tris that use foils in the ama still need large volume because while the foils can lift up to 70% of the weight of the boat(depending on design) most tri's equipped with ama foils don't have rudder t-foils and ,therefore have to get pitch stability from the immersed part of the ama.
    --
    That is the way its done most of the time these days but I think there is a better way for performance tris. I think the best performance tri design may be to use a bi-foiler arrangement on the main hull and a single curved foil on the ama. The mainfoils control pitch and lift the main hull early*(much earlier than if heeling moment alone caused it to fly). Then they unload the faster the boat goes, reducing drag further.
    By lifting the main hull early speed is drastically increased. Because the foils lift the main hull in light air the beam can be greater than on a "normal" tri which comes in handy when a lot of RM is needed. Using this system does not require high volume amas and uses the mainfoils to control the pitch of the curved ama foil.
    *early=lighter wind
     
  5. Gary Baigent
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    Gary Baigent Senior Member

    Don't be confused, Sam, you've worked it out, yes, heavier boats are slower than light ones and full length, high buoyancy float, heavier tris (flavour of the month) are slower than foil versions - that is why I posted those performance figures. The Morrison 60 foot (18.28m) Umupro Jardin is one of the earliest, if not the first, full length, high buoyancy float trimaran, and set the standard, a very fast boat which won an OSTAR race ... but the smaller 50 foot foiler Ker Marine was faster in the speed/race trials.
    By the way, the world's fastest yacht, Hydroptere is a low buoyancy, float design foiler.
     
  6. Samnz
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    Samnz Senior Member

    ah yes now I see, your talking about going fast over 500m and top speeds, im talking about winning actual races ;)
     
  7. Samnz
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    Samnz Senior Member

    **** you must have read it quick, I edited it straight away after referring back to page 1 and reading your comments....
     
  8. Gary Baigent
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    Gary Baigent Senior Member

    Er, Sam, those posted figures were for around an Olympic type 30 mile course; a race with a fleet of 26 cats, tris and 3 foiler tris with times taken for each leg. First seven positions in race 1 when it blew 30 knots:
    Ker Marine (50ft VPLP foil tri), Umupro Jardin (Exmouth Challenge 60 ft. Morrison tri), VSD (52ft Kelsall foil tri), Royale 11 (85 ft GRAAL cat), Credit Agricole 11 (75 ft Ollier cat), Lessives St. Mark (50ft Langevin foil tri), Roger et Galet (46ft Greene tri.
    Nine boats retired along with Elf Aquitaine !! - ripped main.
    In race 2, same conditions, Credit Agricole won, Ker Marine 2nd, Royale 3rd, Umupro 4th, Lessives St. Mark 5th.
    Photograph: Ker Marine
     

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  9. Doug Lord
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    ===
    oh,well.....
     
  10. Gary Baigent
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    Gary Baigent Senior Member

    Realizing those Quiberon multihull race figures are old - but since the French have been consistently a quarter of a Century ahead of the rest of the world, (excepting C Class and other fringe developments in USA, UK and Australia) they have been used because, to my knowledge, there hasn't been any modern and well recorded race/speed trial examples with tris, cats and trifoilers competing together to quote from. Then we had a perfect chance to compare the types and record race times and speeds ... and the foil versions with small floats showed their superiority, especially to windward in strong winds - which must have surprised many.
    Ker Marine and Lessives St. Marc had, like most of the fleet, very conventional, non rotating, masthead rigs - with wing or rotating masts, like Elf and Credit, their performances would have been even better.
     
  11. Ilan Voyager
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    Ilan Voyager Senior Member

    http://www.youtube.com/watch?v=ZJtF0m208Vk&feature=player_embedded#at=280

    Paradox, a "cruiser" -with minimal but beautiful amenities- trimaran designed by Nigel Irens (who knows how to draw fast tris...). This tri shares a lot with the 60' racers, particularly the amas.
    A trained eye will see many interesting characteristics and features that I leave you discover. The boat looks deceptively simple, it's the result of 25 years of refined design. Very nicely made also.

    The design of the multis have completely changed with the tris Apricot and Fujicolor (Irens), the "foiler" Ker Cadelac II (Lombard) - pic http://www.breath2000.org/gallery2/main.php?g2_itemId=685- and the cat Jet Services V (Ollier) - pic http://www.superstock.co.uk/stock-photos-images/4115-2650-. All around 84-86. The boats, representing the 3 main configurations (proas are anecdotal) made obsolete any multi made before.

    They are now completely antiquated when compared to the following multis' generations. One of the many changes has been in the hulls' shapes; higher prismatic coefficient, less rocker, flatter bottoms and fuller sterns.

    The French Flying Circus has benefited of a steady sponsor financing as the races are very popular in France. Thus many boats have been built and most configurations have been tried.
    25 years later, at least for oceanic races (that means a high sea all weather boat) trimarans are now the clear winners, with mean speeds now that are 30% higher than in the end of the eighties.
    Catamarans have been proved unsure and delicate to keep at max speed, "true" foilers are limited by the foils, fragile and difficult to design (cavitation), and tris are nowadays the all around solution.

    A good cruising multi (I mean not an overweight pontoon, these multis are condos that you can eventually move from one marina to another marina with all the due precautions) incorporates all this acquired knowledge; faster and surer.
    The Sea Cart 30 is a good example of modern fast cruising tri.

    So let's forget all the older designs (Wharram, Pivert and others).
     
  12. Gary Baigent
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    Gary Baigent Senior Member

    I wasn't referring to Piver (you make his name sound like pervert) or Wharram, Ilan Voyager, they were the real pioneers and yes, light years behind later developments ... but that is obvious and understandable ... but if you're believing that Irens' ORMA Fujicolor (I think you're mixing names with earlier Fujichrome) is/was old school, you're wrong because "higher CP, less rocker, flatter bottoms and fuller sterns" plus square platform, is exactly what Fujicolor had, as did all the following ORMA designs like VPLP's Geant, Groupama 2, Banque Populaire, and so on, admittedly differing designer variations but really all very similar.
    Although I'm definitely of old school age, I'd still like to see the new 50's, for example, take on old school Hydroptere in a fresh wind race.
     
  13. catsketcher
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    catsketcher Senior Member

    Data mining

    Gary - you left a few other examples of foilers out. Charles Heisdeck was much the same idea as Ker Marine in 1983 and did not spawn a new generation of similar designs. Paul Ricard in 1979 and then again in 1983 had the same idea. But Irens and others didn't follow their lead.

    Obviously smarter people than us saw the performance of these boats and surmised that powerful float tris were faster than these foilers. Exmouth Challenge (she was 53ft long) was one of the first of these boats. Apricot is one of my favourite pin up boats and definitely traces her ancestry back to the big float boats. She spawned a whole generation of sisters.

    As to a Seacart being a cruiser - wow. Having cruised a a 31ft racing tri I would say cruising such a boat would be a huge mistake. Where do you put all the gear and how do you get a nice ride all day when you are on edge? You end up really frazzled instead of getting there hours later but happy and relaxed. Definitely put me down as a crew for a few hours but to cruise for a month or so - go the Searunner or Wharram for family harmony.

    cheers

    Phil
     
  14. Gary Baigent
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    Gary Baigent Senior Member

    Hey Catsketcher Phil, I didn't say Seacart 30 was a cruiser, Ilan V is to blame - I agree that narrow, high buoyancy float boat is flat out racer.
    Charles Heidsieck was a failure because it ended up tonnes overweight - if kept down to designer Vaton figures, might have been a different story.
    Paul Ricard did okay, another pioneer with intestinal fortitude. Could be wrong but I think the French lengthened the Morrison tri's main hull to 60ft when they acquired it and renamed Umopro Jardin.
     

  15. catsketcher
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    catsketcher Senior Member

    Still book me in for a sail when you get your boat going Gary when I get to NZ. Or if you come to Lake Mac you can come out on the sedate cruiser. My bad for not putting in the different author about the Seacart. In my time cruising my Twiggy I went slower in it because the ride was so rough than in my much less top speed cat. At anchor we would bounce all around the place. It doesn't take long for that to wear thin. Hence the adamant response for liveaboards.

    cheers

    Phil
     
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