Logic in different length hulls

Discussion in 'Boat Design' started by Thule, Feb 19, 2024.

  1. CarlosK2
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    CarlosK2 Senior Member

    Seen and expressed from the history of the group mind, the herd mind (ape does what ape sees): circa 1975 the obsession of the tribe was Upwind; circa 2025 the obsession of the tribe is Downwind

    ---

    This (making the bow wider) started in the Mini Transat when they had exhausted the ways to further increase the capacity to raise more sails. That was the fuse.
     
    Last edited: Mar 13, 2024
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  2. jehardiman
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    jehardiman Senior Member

    Well before that. Just think back to the lakes scows of the 1970's and the west coast USA pram racing in El Toro's or SF Bay Pelicans in the 1980s+. Fast racers learned that they were never to be sailed flat, but always on the chine....like having your own hiking board so drive them hard. (remember when everybody was bending class stock Laser masts?). It is all about sailing shape, not static bow entry angles.

    Hypothetical beam vs draft question https://www.boatdesign.net/threads/hypothetical-beam-vs-draft-question.68756/#post-956113

    EDIT: Well that was well off the OP topic, but getting back to that...Once a lightweight multi-hull "sailing" form gets to >10 for L/B for the canoe hulls really it is a matter of righting moment and hull separation, since wavemaking (i.e. pressure) interference is 'small'. Heavyweight displacement cats...not so much.
     
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  3. Thule
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    Thule Junior Member

    So, the unequal length of the hulls of Ontong Java have no added advantage over the simple advantage coming from a smaller hull. Inequality of the hulls in itself does not provide added benefit?
     
  4. jehardiman
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    jehardiman Senior Member

    If any, it is minor and obscure. Contemporary with SLINGSHOT in the late 1970's early 1980's there was a staggered mono-tack catamaran. Additionally, there was some some work on ama stagger with tri's. Never seemed to gain much traction.

    (removed reference to EIRN and or AOTEA, not much real content data)
    Better article:
    https://www.researchgate.net/public...otion_characteristics_of_a_trimaran_hull_form

    and these:

    8. Wilson, MB, CC Hsu, and DS Jenkins. Experiments and predictions of the resistance characteristics of awave cancellation multihull ship concept. 23rd American Towing Tank Conf, pp. 103-112 (1993)..

    9. Suzuki, Kazuo, and Mitsuhisa Ikehata. Fundamental study on optimum position of outriggers of trimaran from view point of wave making resistance. FAST'93, pp. 1219-1230 (1993).

    13. Doctors, L.J. and Scrace, R.J. The Optimisation of Trimaran Sidehull Position for Minimum Resistance. FAST'03, Ischia, Italy (2003)
     
    Last edited: Mar 13, 2024
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  5. CT249
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    CT249 Senior Member

    Well, the iron law seems to bend a lot! For a start, the French shorthanded events aren't "the most famous regattas" in most places of the world so that's not the reason in itself. In Australia, for example, very few people know about Minis and Class 40s but most people in the street know that there's a Sydney-Hobart on the news just after Christmas each year.

    If we look at the world's most popular craft over the decades, there doesn't seem to be all that much evidence for the iron law, although it's often claimed to exist. The world's most popular sailing craft include the Sunfish, original Windsurfer, Snark, Hobie 16, Sabot, Optimist and Mirror, none of which imitate regatta boats. The Laser and 420 do follow the general style of the most popular regatta boats of their day, but the Laser's hull shape is very different from the Finn which was the most famous regatta singlehander of its time.

    In the small racing yachts the most popular types include the H Boat, J/24, Flying 15, and Star which didn't copy the most famous regatta boats of their day. The Dragon did, pretty much.

    In cruising or offshore boats the most popular seem to include the Catalina 22 (13,000 IIRC); the Folkboat and variants (12000+ built); Morgan Out Island 41 (1000 built); First 21.7 and variants (2,400 built); Bavaria 30 Cruiser (1900 built); Neptun 22 (9,900); Varianta 65 (4500) and Maxi 77 (4000). Not one of them really copied the regatta boats of their day closely, although there was a bit of racing influence in the Maxi and the First 210.

    I don't mean to be hassling you about this, it's just that I tend to think the "iron law" is overstated and may be untrue. It may be that most individual designs tend to copy racing boats, but that the designs that are more popular do not.

    I'm not sure that scows are better to handld downwind in pitch and yaw, although I haven't sailed any of the modern scow yachts. In Australian and British skiff and racing dinghy design it's pretty well accepted that nosediving is largely caused by having a stern that is too wide, which is one reason why there has been a long-term move away from the "wedge"planform with its very wide stern. The French Open style of boat still uses a wide stern for stability and therefore until the scows arrived they kept to the "wedge" planform. So the popularity of the fat bow may be caused by the popularity of the fat stern, which is itself arguably created by over-concentration on keeping a short overall length and on reaching performance.

    I understand the importance of beam in dynamic lift, but having owned a scow Moth as my first boat and still occasionally hopping onto my grandkid's Opti etc I've also had a lot of experience with the importance of low-drag bows and how a scow bow can "trip" very badly at speed. While yachts perform very differently to skiffs, small cats and dinghies, I'm still very unsure whether a scow bow is better all-round than merely extending the bow lines forward into a conventional bow. There's again an irony that the appeal of wave-piercing bows was largely said to be the reduction in nosediving, and in small cats they certainly work well.
     
  6. jehardiman
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    jehardiman Senior Member

    I'm not so sure on skiffs that it is the stern being too wide, but rather the bow down pitching moment caused by the rig. Even 40 years ago in Larks and 420/470s we would stack on the transom to keep the bow up, much like today.
    [​IMG]
     
  7. CT249
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    CT249 Senior Member

    The 420, 470 and Lark all have much narrower sterns than the wedge types I was talking about, so they benefit from getting the weight aft. The wedges were very rare in the USA and were more an Australian/UK creation of the late '70s and '80s.

    It's pretty well accepted among skiff and dinghy designers that the extreme wedge causes nose diving; I've spoken to the Bethwaites, Morrison, Bieker etc about the issue. Having a really wide stern, '70s and '80s Aus style, meant that you couldn't sink it to pivot the bow up. This was seen, for example, when the Aussie 14s were allowed to race the International 14s in the San Francisco worlds before the two classes were amalgamated. The wedge-style low-rocker Aussie boats won, but they were much harder to handle downwind than the narrower-sterned International designs and therefore actually slower downwind in big breeze and chop.

    In a class like the Moth, the "fat skiffs" of the '8os were often notorious for nosediving and John Claridge's later Magnums became narrower at the stern (as did the last scows like the McFrawd) to sink the stern and allow the bow to pivot up. The same thing continued when the Moths went to the skinny (c 12" wide) shapes - the first successful skinny Moth, the Axeman. had a comparatively wide transom and by the time the last winning non-foiler came out in the shape of the Hungry Tiger, Mark Thorpe had narrowed the stern drastically to allow it to be sunk to keep the bow up.

    Even the 49er gets a bit narrower at the transom than further forward, and because it's a comparatively long boat compared to older two-person skiffs it's inherently less likely to nosedive than say an Int. 14, R Class or 12 Foot Skiff.

    This info is pretty much all directly from those responsible to me. It seems that the Europeans, who don't have the same amount of development-class dinghy heritage, still favour the "wedge" even for dinghies because it works in Open yachts. It seems significant that according to European performance-based yardsticks the Euro "wedge" dinghies are often slower than they really should be based on their specs.
     
  8. wet feet
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    wet feet Senior Member

    I would take issue with the notion that we Europeans don't have the same heritage of development type classes.It may not be spread uniformly,but in the UK we have the Moths,Cherubs,National 12s,Merlin-Rockets,International 14s,10 sq.M Canoes,National 18s and several local classes that permit development.On the European mainland there are a number of classes in Germany,often designated by letters,that have seen lots of development with some going back to Manfred Curry's day.I know less about the classes on the Swiss and Italian lakes but they do exist and there are others in the Iberian peninsula.Admittedly some have rules that make it hard to achieve planing mode.
     
  9. CT249
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    CT249 Senior Member

    Sorry, by that I meant "mainland" Europeans aka "Continentals" - I completely and utterly agree that the UK's heritage of and contribution to development classes was and is enormous but (like many modern UK voters :). ) I see "Europe" as distinct from the UK. That's arguably completely reasonable given that the Continent and UK have quite different dinghy scenes.

    I love the European/Continental development classes (Swedish canoes, German Z, M, N class Renjolle, Italian 4.5, 5.5, Nazionale A dinghies, French Canetons etc) and have blogged about them (Pt 1.25 – The sailing scientists of the renjollen https://sailcraftblog.wordpress.com/2016/12/08/pt-1-25-the-sailing-scientists-of-the-renjollen/. ). The "Clippers Argentuil" were arguably the most advanced boats of their era (Pt 1.29: Continental Drifting: European dinghies to 1945 https://sailcraftblog.wordpress.com/2017/09/12/pt-1-29-continental-drifting-european-dinghies-to-1945/).

    However apart from small Int 14 and Moth fleets, normally using Anglo designs, the only Continental development class that is still running OK seems to be the H-Jolle and a few Swedish canoes. The H Jolle is a lovely looking boat that deserves more prominence IMHO, but the simple fact is that the development dinghy classes have formed a very small proportion of Continental (and North American) dinghy sailing for the past 50 or more years. In contrast, the development classes have been proportionately and in absolute numbers much bigger in the Antipodes and the UK although over the last couple of decades they have been losing numbers even there. Not surprisingly that has arguably led to Continental designs lacking the sort of modern development seen in the UK and Australia.
     
  10. CarlosK2
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    CarlosK2 Senior Member

    "Well, the iron law seems to bend a lot! For a start, the French shorthanded events aren't "the most famous regattas" in most places of the world so that's not the reason in itself. In Australia, for example, very few people know about Minis and Class 40s but most people in the street know that there's a Sydney-Hobart on the news just after Christmas each year."

    And, perhaps, this explains why the trend towards the Scow form is stronger in France than in Australia ... or no, i don't know.

    Dialoguing with you is somewhere between exhausting and impossible.

    Well, the Iron Law says: on site H the sailboats imitate the sailboats of the most admired and/or famous regattas in H

    Now we can discuss admired and famous, and then later when these words are sufficiently well defined we'll move on to a fierce discussion about one comma, LOL.

    Clearly ... communication is not about intelligence, it's about goodwill.
     
  11. CarlosK2
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    CarlosK2 Senior Member

    Perhaps it would be better to say: the cruising sailboat imitates the racing sailboat.

    A statement that already appears on the second page of Skenne's Elements.
     
  12. CarlosK2
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    CarlosK2 Senior Member

    Screenshot_2024-03-14-11-30-14-81.jpg

    The trend towards a very wide bow is a very strong trend, so strong that restrictions have been placed on some class.

    This trend is strong because

    1) it increases the capacity to hoist even more Sail

    2) it increases the vertical Lift force at the bow.

    3) it adapts better to the Waves

    4) ultimately on a Ocean sailboat it is a silly idea to go through the bow wave when you should be leaning on it and going over it.

    5) it is a good way to improve Yaw control and Pitch control.

    The context of this trend is an Oceanic context: crossing Oceans ... Downwind.

    (This is great: you demand from me the precision of an expensive corporate lawyer, and you can take the conversation from an Ocean to a bay, and from Downwind to upwind.)
     
  13. CT249
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    CT249 Senior Member

    But does the cruising sailboat imitate the racing sailboat? When the Folkboat came out, for example, the Swedish racing sailboats were Skerry Cruisers and Metre boats in general - completely different to the Folkboat. When the Neptun 22 came out, very few "racers" had external lift keels and transom hung rudders. No racer was much like the Out Island 41. The Bavaria Cruiser 30 is very different from the racers of the time, which were perhaps typified by the Farr IOR one tonners or Opens.

    We know that the rating rules often ensure that racing boats largely imitate fast cruiser or cruiser/racers. That's why the CCA, for example, was centred around a "base boat" that was a fast cruiser or racer/cruiser rather than a high-speed racing machine. That's why the IOR gave allowances for heavier displacement, and why the IMS didn't encourage lightweight deep-keeled boats that were totally stripped out with very low C of Gs.

    So - and this is just a conversation intended to develop ideas - perhaps there's an interesting twist in that most cruising designs follow racers, but the most popular designs do not and are more innovative?

    Isn't communication also about developing ideas by throwing them back and forth and analysing them, rather than just agreeing with them? You made one statement, can't say I make another to discuss it?

    Yes, the difference in the most famous race probably does explain a lot about why there's scows building in France, but it doesn't explain why the scow movement is getting so much publicity in the UK sailing press, for example, where the Open events aren't the most famous ones.

    Personally I tend to think there's a lot of marketing involved, and as a former sailing journalist I also feel that writers and editors are inherently attracted to over-play developments that create what they seem as good copy. That's just an inbuilt factor that I was guilty of, just like others, but that we should perhaps be aware of and wary of.
     
  14. CarlosK2
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    CarlosK2 Senior Member

    Viewed the other way around:

    To justify a sharp bow you need either

    1) low Speed (Froude < 0.40-0.50) or

    2) low Heeel as in a dinghy or

    3) not wanting to cross an Ocean Downwind.

    (sorry: the company's lawyer tells me that I should add the word "monoHull").
     

  15. CarlosK2
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    CarlosK2 Senior Member

    IMG_20240314_123637.jpg

    The long-suffering cruiser. For 400 K Euros you get a wagon, a slow wagon with the Center of Gravity (CG) forward of the Center of Flotation (CF) for fun and enjoyment of the Waves, only a playful Orca that eats your rudder in one bite is missing.
     
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