Major u turns in sailboat design?

Discussion in 'Sailboats' started by Omeron, Oct 1, 2007.

  1. Omeron
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    Omeron Senior Member

    To me, one of the major u turns in sail boat design is the bulbs attached to
    fin keels.
    Whereas this was a commonish application in the sixties and before, they
    dissapeared in the seventies, only to make a strong comeback in the
    past decade or so.
    What do you think influenced this major u turn?
    Was it IOR or any other rule which penalised stability? Or was it due to some
    other developments taken place in between.
    (I doubt IOR measured actual righting moment,independent of form stability)
    I dont think it is the new materials or building techniques, because a lead is still a lead, and if anything, we must have learned to attach them better.
    If it was all due to rating rules,how come, boats not built to race gave them up too?
    Do you think designs are simply influenced by trends and fashions?
    Are there any other major u turns you can think of in this respect?
  2. PAR
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    PAR Yacht Designer/Builder

    The majority of trends in yacht design are trickled down from the racers, which of course are attempting to circumvent the rules in some fashion. If a fad is employed in the buoy boys, rest assured the production manufactures will follow suit the next year. Yachting isn't the only industry that is subject to these trends. Do you really think a 4 door sedan Suzuki needs paddle shifters, which has less HP then many of the motorcycles they sell? Of course not, but it's a selling point they're willing to utilize to full advantage.
  3. Jimbo1490
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    Jimbo1490 Senior Member

    And how about every engine 'needing' DOHC pent-roof heads, 4 valves/cylinder? 4, 5, 6 and even 8 valve cylinder heads have been used in racing engines with the number of valves being in inverse proportion to the allowed engine displacement. Honda built 8 valve/cylinder 250cc race engines in the '60's that made over 100HP! But if allowed to build 500cc or 1000cc, do you think you really need that kind of specific output? On the street where we can build engines any size we like, it's demonstrably cheaper to just add swept displacement and simple 2 valve heads. It's often lighter and less cams have less friction/per unit valve area, not to mention MUCH cheaper to build. Is has even proven out on the race track as well. When the rules give a displacement allowance to engines with two-valve heads, those vehicles compete nicely. Sometimes they even dominate as Mercedes did in the 90's.

    Let's call all this nonsense 'stupid trickle down':D

    And we still see street cars with completely inneffective 'ground effect' skirts (they are not low enough to actually work) almost 20 YEARS after racing has abandoned even effective ground effect skirts.

    We'll call this 'persistent stupid trickle down"

  4. alan white
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    alan white Senior Member

    Then there is the open transom "Hey... where'd the baby go?" on production boats that are hardly competitive.
    Here in Maine, enjoyable coastal cruising (and even racing) is impossible unless you've got a full keel, due to the snagging effect of lobster pot warps. Older designs do well, sliding over easily. Fin-keelers (and those dagger-like rudders) get stopped all the time (not that fins are new!).
    I think companies know their market, but think of it---- most boats built are inappropriate to the intended use in some very significant ways.
    I hear of lead bulbs on long pendulous foils, and wonder where anyone would dare sail, except well offshore----- but see how inshore production boats move in that direction.

  5. CT 249
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    CT 249 Senior Member

    It's not always as simple as cruising boats following trends. For example, while the Beneteau 40.7 has a bulb, it's only a minimal one.

    Why didn't the Farr office give the 40.7 a bigger bulb? Because of the design spiral. More stability would have meant more rig load. More rig load means a bigger, heavier, more expensive spar; bigger more expensive sails; more load on the crew; bigger winches; bigger deck gear......

    Similar considerations apply to fitting any bulb, I think. And then again, many boats sail in light winds when a bulb is more drag, and a higher aspect keel is a bit demanding for many buuilders and crews.
  6. jehardiman
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    jehardiman Senior Member

    This is very true. Bulbed keels are less efficient (i.e. have more drag for a given lift) than a plain keel. In order to pay for this drag you need a bigger rig.... which needs more righting moment....which needs a lower CG (weight being fixed)...which means a longer keel...or a bigger bulb.....

    It is also important to remember that it is only the recent (say last 10-15 years) ability to easily construct very light, strong hulls that allows a bulb to be added in the first place. For a given design displacement, there is a given weight, which includes hull, rig/outfit, and ballast. If the hull is a very large a precentage of the overall weight, then there is no weight available after subtracting the rig/outfit to put into a bulb after you fill the volume of the required sized keel. By having a very light hull, there is weight available at the end of construction that you can move around to start to optimize cg and inertia.

    Which brings up the need for ballast in the first place. One of the necessary trends in modern 'faster is better' sailing is to lighter overall weight. It is known that efficient hydrodynamics requires a long narrow hull. The trade off here is the ability to get a light enough hull construction in a narrow hull because narrow hulls are less weight efficient than wider ones (i.e. it requires more material to get a given displacement for a long narrow hull than a shorter, wider one). This effects the tradeoff between the two types of stability; form and weight. For some, the way to combine good hydrodynamics with light weight is to go to a catamaran hull form...all form stability...but for monohulls you must tradeoff between both. In small boats with a high precentage of moveable weight (any dinghy), the trend is to form stability...wide shallow hulls... with righting moment mostly provided by moving ballast (i.e. crew) outboard. In large vessels, the crew is only a small portion of the overall weight so you need to move them well outboard, either by making the hull wider or by adding wings/hiking platforms. As making the hull wider is less efficient and wings are not being allowed by most rules, this leaves adding weight stability to the hull as the way to make a narrow monohull go faster. This drives the designer to try to put as much weight as low as possible. As real world hydrodynamics limits the effective span and aspect ratio of the keel, the designer made the keel fatter at the bottom than at the top to get weight low while minimizing displacement low. It is important to remember that this is not new...look at the very common 'hourglass' full keels of the turn of the last century or the 'hatchet' keels of the 12's (a much better option than a bulb IMHO). I think that blubs, like plumb bows, sugar scoop sterns, and shark fin keels is just the lastest fad in the constantly elvolving material-to-performance tradeoffs in sailing.

    As a personal opinion, I would never have a bulb or hatchet keel on a crusing boat. The hassles of keeping it clear of debris or flotsom are too great. But they do have thier place on racing sailboats where you spend 90% of the money to get the last 10% of performance.
  7. Doug Lord

    Doug Lord Guest

    U Turn of U turns

    This boat represents one of the most significant "U-turns" in the history of sailboat design. From 2D sailing to 3D sailing-an 11 footer capable of beating the fastest catamarans under 20'.
    But it's not just that: it is the 'proof of concept' performance against other boats in its own class around a course in race after race.
    The technology represented and proven by the Foiler Moth has direct applications to other monohulls from two and three person dinghies to sportboats to large monofoilers that could have speeds comparable to todays ORMA trimarans yet be self-righting.
    In multihulls, the applications range from Kotaro Horiuchi's experimental bi-foil trimaran to my experimental bi-foil tri with planing ama's to Rob Denneys supercool C-Class "cat" with just two foils to larger versions of all of these.
    The technology pioneered in the Moth class has set off an irreversible revolution in sailboat design that is in its infancy and is one of the most exciting new frontiers in sailing in the last 100 years.

    Design Revolution
  8. MalSmith
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    MalSmith Boat designing looney

    Thanks Doug, another good thread ruined!

  9. Mychael
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    Mychael Mychael

    Doug, I don't have the knowledge to comment on designs but from my reading of the initial post that started this thread I think you may have taken it out of context.
    I read it as being about things that were once in fashion, then dropped and now coming back. Not new concepts entirely.

  10. Doug Lord

    Doug Lord Guest

    Thanks, Mychael-you may be right....
  11. Omeron
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    Omeron Senior Member

    Going back to the original thread....
    Let me propose another one...
    What do you think about flat head, square head (i do not know what is the proper name) mainsails as seen on AC boats today as a U turn to gaff rigged boats of the past?
    How different do you think the top batten of these modern mainsails are compared to the spars of the gaff riggers? OK the aspect ratios are very different, but what if the old timers had the materials available to us now?
  12. jehardiman
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    jehardiman Senior Member

    The extreme roach seen on modern racers has nothing to do with a gaff rig. Indeed, it is rather that the last, short yarded, low peaked, gaffs that occured right before the bermudian were attempting to get to were we are today, but couldn't because of material issues.

    Today we see extreme roach because 1) it is free sail area under almost all rules, 2) modern low stretch cloths and strong lightweight battens allow the roach to grow to emense sizes, and 3) modern materials can be engineered to provide the required twist-off to depower during a gust allowing the free area to provide more power than heeling moment.

    Twist in a gaff rig was always a big problem, the cloth was too stretchy. If you control the twist (by vangs) you can't depower quickly. By going to bermudian rigs, twist off was controled with the fabrics availabe at the time. As fabrics and batten tech grew better, the roach grew larger.

    Omeron; modern designs are never "going back" to the past. The reasons for modern designs are modern materials and working theory applied to the requirements, just like the reasons for past designs were available materials and working theories appiled to the requirements. The fact that they look alike has more to due with the constant physics of the sea and winds and the unchanging requirements rather than retrenchment.
  13. Doug Lord

    Doug Lord Guest

    Square topped main/ Gaff

    A number of people, includng me, have and are now experimenting with versions of square topped sails(incuding jibs) that use a modern version of a gaff instead of a diagonal upper batten.This allows a more or less rectangular planform sail without full battens. On rc models the gaff is superior to the batten because it allows the sail to move easily during a tack especially inlight air. But a major advantage of the modern gaff is that it can be configured in a "peaked up version" which may be aerodynamically superior to a AC type square-top. The "gaff" is molded and fits into the top of the mast in a bushing and is free to rotate. The "peak" of the sail is also controlled by an upper outhaul which gives control of the camber of the upper half of the sail. The twist is controlled by a more powerfull than usual vang which gives nearly instant control. The nature of the square top is that it automatically depowers without a complicated rig.The vang adjusts the range of twist.
    I'd think that this "peaked up square top" directly represents a u-turn as I understand the meaning of Omerons question.
    This is a picture of a model using the "gaff"-the horizontal part of the gaff at the"peak" end allows fore and aft movement of the peak of the sail:
    This is a picture of what could be described as a"gaff" holding up the top of a square topped jib. It could also be called an "upper jib boom" and has an upper outhaul as well. I think it has more in common with a gaff; both of these originated due to my experience with sailing and racing the 20' gaff-headed Fish class:
  14. k76
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    k76 Junior Member

    Cutting edge stuff:

    I don't think a well designed square top main needs a gaff. Have you looked at an a-class sail or an AC main? What exactly are you hoping to achieve with a gaff?

  15. Vega
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    Vega Senior Member

    Hey,...Great post!!!

    Two observations:

    Regarding: “As making the hull wider is less efficient ..., this leaves adding weight stability to the hull as the way to make a narrow monohull go faster”... I would say that with a well-designed wider hull you have more form stability and therefore you need for the same RM less weight stability (and have more drag). That’s another trade off (less weight/more drag). If you put water ballast on the boat, the wider hull can even generate more RM, especially important on fast cruising boats that have not 13 guys to put by the side.

    Regarding: “I would never have a bulb or hatchet keel on a crusing boat. The hassles of keeping it clear of debris or flotsom are too great”. I believe that you will see more and more this kind of bulb on cruising boats. Not really a bulb but has the same effect without the disadvantages you mention.

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