Planing Trimarans

Discussion in 'Multihulls' started by Doug Lord, Sep 30, 2006.

  1. MMulti
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    MMulti Junior Member

    Couldn't the main hull of a Farrier tri get shoved into some kind of hydrostatic evaluation software and give a specific answer as to if/when the hull could/would plane? Just curious.

    Marvin
     
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  2. Doug Lord

    Doug Lord Guest

    Polars , People & On the Water Experience

    Sure, and there are polars available for at least the F27 .
    ------------------------------------------------
    But one damn good indication is F-boat owners talking about planing which is an important aspect of F-boat sailing/racing:
    "F27 planing speed from F- boat forum: "8.2 knot minimum....At 7.5 knots the boat is lifting."
    Martyn Adams,owner
    -------------------------------------------------
    " An F32 can do 12-14 knots planing to windward when the wind is between 15-20kts. under full main and jib"
    Glen Howell F32 #221
    -------------------------------------------------
    " Just look at Bob Harkrider. It's all in the name(Bad Boyz). He is a rebel. He is always the first one to get on a plane. The entire herd will be sailing the same angle,fairly slow, then you see Bob out of the corner of your eye. He is the one sailing 15 degrees higher and 10 knots faster." Todd Hutchins, owner
    -------------
    " Visualize a curve expressing power required(y axis) vs. boatspeed(x axis). This curve has a very gentle slope at first. As it approaches the displacement hull speed(maybe a knot below) this curve starts to steepen. There is a step (much steeper slope) from say 7 kts to 9 kts for an F27. Then the slope decreases at higher speeds because you're on a plane,and finally steepens up again in the teens,say above 15kts, because the hull-water interface has changed geometry(Think of the leeward beam plowing into the water).
    Many races seem to be won or lost based on who gets on a plane and stays there."
    ================================
    So we have the Science, the Designer, and the Sailors all saying that F boats plane. There is NO DOUBT WHATSOEVER !
     
  3. Chris Ostlind

    Chris Ostlind Previous Member

    Where are the video clips of all this planing? You know, the one's that show the boat up on a plane with the amas completely out of the water?

    Otherwise, this is self-delusional, after-race bar talk.

    Chris
     
  4. Dan S
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    Dan S Junior Member

    Doug, you can quote all the linear, or simple mathematical relationships you can find that say a boat will do this, or that. As I said before these relationships are simple and only designed to get you in the ballpark, not provide concrete answers. For every boat that you name that follows this guideline, you will find a boat that doesn’t. Contact the authors if you want; and ask them how many statistical out liars they eliminated.

    V=IR is a good example, in high school; they tell you that this is all you need to know. When you get to college, you will find that V=IR is pretty much useless in real world situations.

    You prove my point for me.
    It’s a planning design. Being designed to plane, and actually doing it are to vastly different things.
     
  5. Figgy
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    Figgy Senior Member

    Mabe the boats (F31 & F9R) are not being sailed to thier full potential. Nice boats don't equal a crew that knows what their doing. I'm a good El Torro sailor, but stick me on an ACC, and she is going to suffer.
     
  6. Dan S
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    Dan S Junior Member

    Again, Polars are approximations, which assume a lot. You can find people that can never get their boat to perform as well as the polars say. You can also find people that regularly exceed what the polars say the boat is capable of.

    Not to slight any of the people listed, but I think it’s safe to assume they are a little bias. Secondly, id be willing to bet, that maybe 1 person in 10, can distinguish between surfing and planning, when it comes to large displacement style designs.
     
  7. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    I looked a video of the Dragonfly. It sailed at 15 to 20 knots for long periods, it was not surfing.

    That brings us back to the discussion "what is planing".
    High speed doesn't mean your are planing.
    A lot of motorboats doing 30 knots are not planing, just overpowered :)
     
  8. Vega
    Joined: Apr 2005
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    Vega Senior Member

    You mean, this one that I have posted on post9 of this thread?:D

    http://www.sejlsport.tv/dragonfly/pages/df920extreme/df920movie.html

    A 29ft sailboat that sails consistently between 15 and 20 knots, is way over its hull speed. About motorboats I don't know, regarding sailboats, when that happens, I guess that the boat is planing;)
     
  9. Chris Ostlind

    Chris Ostlind Previous Member

    Simple Matters

    A trimaran is a three-hulled vessel. A catamaran is a two-hulled vessel.

    For a trimaran to be planing, it has to be interacting with the surface of the water in a very specific fashion.

    Most of us recognize the long held definition of planing for single hulled boats in that the hull basically climbs its bow wave and is then being propelled on the surface of the water at a speed that allows its underbody to support the full weight of the hull through dynamic lift.

    This accepted definition means that the three hulled vessel must have one or more of its hulls being held on the surface of the water, supporting the weight of the boat in the same fashion as is described above. If the tri is planing on its main hull, the other hulls must be either clear of the surface completely, with no load bearing immersion of the amas, or one or both of the amas must also be planing and sharing the load bearing operation through their own planing action.

    This means that the ama may not be running along the main hull in displacement mode, bearing the weight of the boat, while the main hull is being held at such an attitude that it is skimming on the surface, appearing to plane. It is not planing in that position as the full weight is supported by the ama and not the dynamic pressure being developed by the main hull's underbody.

    If this argument were to be held as a planing scenario, then virtually every catamaran out there could be said to be a planing design whenever the windward hull lifted enough to just kiss the surface. Clearly, we all know that scenario to be false in real terms.

    The same is true for a trimaran. Immerse one ama in displacement mode while the main hull is lifted to the surface and you have a great, performing boat that is moving at close to its optimal speed. You do not have a planing trimaran as long as the leeward ama is in displacement mode providing support for the boat's weight. The three hulls act as one integrated unit to form a complete boat and not independently in order to provide selective claims for high performance stardom.

    The Dragonfly video illustrates this argument perfectly. The boat is moving along at a high rate of speed with the windward ama well clear of the water, the main hull lightly loaded and the leeward ama clearly immersed; at times, significantly immersed. This is not a complete, integrated design that is planing. It's a trimaran in normal, ama displacement mode with a lightly loaded main hull on the edge of immersion.

    You simply can not regard the entities of the three hulled vessel as separate for the benefit of performance claims in order to make the boat sound better. The complete boat is weighed as a unit, it is structurally engineered as a unit and it should be measured for performance as a unit.

    Is it any wonder that monohull sailors regard the genre as more than a bit flaky when multihullers go around claiming that which is so obviously not accurate?

    A well-known N.A. has just written me a letter in which he observes that a typically canted Farrier design would be presenting a rather significant vee form to the water (due to the pronounced flatness of the bottom) when underway in the wind conditions one would hope to see to get a trimaran up on plane. By not presenting a nearly flat bottom to the water due to heel, one would expect the potential for planing to be seriously impaired, if it could be done at all. This further supports the observation that the main hulls are, in fact, not supporting themselves by planing form dynamics alone. They are being supported by the immersed leeward ama, which is clearly in displacement mode.

    I did a couple of drawings of the Farrier hulls in a front view. I heeled the boat 8 degrees in one and 12 degrees in another and it's pretty clear how much the bottom of the boat transforms to a vee shape underwater with even a generous take on the possiblity of a planing waterline. The amas also become seriously immersed at those heel angles. With the fairly pronounced keel ridge along the bottom of the ama forms, there's no way they can be considered as capable of planing. So, its clear that the F-Boats are likely not going to be experiencing anything like a planing condition unless the heel angles can be held to extremely low numbers. Even then, the amas would have to be well clear of the water to avoid them becoming displacement immersed in support of the rig's forces.

    Try it yourselves by opening the F22 page at:
    http://www.f-boat.com/pages/trimarans/F-22.html and holding up a straightedge to the computer screen at your best estimate of likely heeling angles for this boat. There's a yellow front view of the F22 with one ama folded that makes for a perfect analysis tool for this purpose. You can fiddle around all you want with how deep in the water the main hull would be immersed and that will tell you a lot.

    Make-up your own minds as to how far you are willing to stretch the definition of planing in order to allow the claims under these circumstances. I do not see the need to alter a well-understood hull behavior in order to spread the glory around in this fashion. Soon enough, the claims will be so rampant that they won't matter to anyone anymore and a new cycle of marketing hyperbole will have to be created to replace the worn-out phraseology of planing.

    You can end some of that hype by refusing to go along with the program as others are presenting it in the industry. Demand significant proofs beyond favorable data streams, expect those who make these claims to be accountable and then listen and look with an open mind if and when they do present appropriate documentation, such as properly vetted video tape.

    My last take on the subject. Moving on to other stuff that is more fun to think about.
     
  10. ActionPotential
    Joined: Oct 2006
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    ActionPotential Junior Member

    Planing?

    In my opinion:
    planing can only occur if the planing hull is supporting all of the weight.
    If a trimaran has any of it's weight supported by the leeward hull then the centre hull is not planing, just as the windward hull on a cat can't be planing.

    I guess anyone can re-define planing and then insist that a boat is planing.

    So Chris and I will continue to believe that planing would require both amas to be clear of the water. Others may use other definitions and say what they like.
     
  11. ActionPotential
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    ActionPotential Junior Member

    Just had a look at the DF video. Yes it is going really fast. No it is not planing (according to my understanding of planing). Maybe it can even fly the main hull but I don't think it can plane. Guess the way to find out for sure would be to fold the leeward hull?
     
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  12. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    Yes, that's the one I saw.
    No, it's not planing :)
    Just because it's sailing many times faster than it's hull speed doesn't mean it's planing!
     
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  13. Doug Lord

    Doug Lord Guest

    Voodoo vs careful analysis

    A tri most certainly can plane if the ama is carrying part of the load. However, a high beam to length ratio hull is capable of at least 4 times the square root of it's waterline length before meeting too high a resistance. And it would never plane if it didn't have the right shape. On the other hand a hull like the seahugger Moth with a moderate beam to length ratio(10/1) has characteristics of both types: it begins to plane at around 10-15 knots because it's moderate beam to length ratio stalls the onset of serious wavemaking resistance and it's flat hull sections promote planing.
    It seems hard for some to understand but a tri with displacement amas can have a main hull that planes-for sure- as described by those that actually sail F boats. The key to understanding what, when and how is probably to look at the beam to length ratio of the mainhull as compared to the ama remembering that the high beam to length of an ama can allow a speed /length ratio of
    at least 4. The F22 REQUIRES some of the load to be carried by the ama before it can plane with only it's upwind sail area.Further, at an angle of heel of 13° a flat surface only loses 3% of it's projected area but in the case of the F boat the reduction in load carried by the main hull(33%) facillitates planing even at an angle. On the F22 in 1lb of pressure the main hull is still supporting 1200 pounds of load either thru just buoyancy or thru dynamic lift or a combination of the two. The descriptions of the owners match the science exactly since they describe planing begining at about 9 knots for the main hull.
    You can resort to voodoo or you can look at the facts and listen to those actually sailing the boats-and do a careful fact based analysis of the characteristics of of the boat you're looking at.
    I haven't seen the Dragonfly video but it is impossible just to look at it and know what is going on. It could have high beam to length hulls -above 15/1 and be able to achieve those speeds w/o planing.Or it could have high beam to length ratio amas and low beam to length main hull and have the main hull planing with part of the load supported by the ama which may not be planing.
    It's not simple and it takes some knowledge of the details of the design to be able to say exactly whats happening.
    When Parlier designed Mediatis Region Aquitaine with two stepped planing hulls AND high beam to length ratio hulls some people thought he was nuts but in speeds over 20 knots where conventional displacement amas have gradualy increasing resistance his hulls' resistance is going down- to as little as 20% of the displacement ama.
    I think what confuses some is that they have a notion of planing being extraordinarily fast like in some planing powerboats. The fact is that in a trimaran, depending on it's design, both ama and main hull can operate in a certain range of speed where the mainhull is planing and the ama isn't OR if the design is different both the main hull and ama might be planing or just the ama-OR NEITHER. It's absolutely critical to know the details of the design to analyze it properly.
    So, even seeing a video you would not, necessarily, know whats going on with any particular trimaran without knowing details of the design.
     
  14. Dan S
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    Dan S Junior Member

    Most likely, what you seem to think is planning is actually heel. As the weight transfers, from the main hull to the ama, and the main hull lifts out of the water, the un-trained or wishful thinking eye could see this as planning, but it’s not.
     

  15. terhohalme
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    terhohalme BEng Boat Technology

    Weird, Glacier Bay use an argument that their fast outboard catamarans use displacement hulls and therefore are superior.

    Well, I think it is quite impossible to have enough trim angle in sailing trimaran to actually plane. The one way to have lift at bow is a very long bowsprit and a huge gennaker (or kite?). Or can you move the weight backwards where it usually lies in a planing boat. Is there beam enough to plane at relative low speed? How about lambda (wetted length to beam ratio). Savitsky! Someone trying the number crunch?

    The main thing is a fast multihull either planing or not. Dragonfly video is awesome...
     
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