Planing Trimarans

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

  1. Willallison
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    Willallison Senior Member

    So - here it is - the essential difference between the two 'camps'.

    Can a hull - regardless of type - be considered to be planing if it is in the planing condition as a result of the assistance of an outside force.

    Is a tender on the plane when it is tied to the back of its mothership, being pulled along at 20 knots?
    Is the same tender on the plane when its being pushed by its outboard motor at the same 20 knots?
    Is a 14ft sailboat on the plane when it is being pushed by its sails at 20 knots
    Is an inflatable tender on the plane when part of its weight is supported by the tubes?
    Is a powerboat on the plane if needs the help of its trim tabs to stay there

    I could go on (some say I do!;) ), but of course, the answer is yes to all the obove. Of its own accord, a planing hull cannot plane without the assistance of an outside force - be wind, engine, ama, trim tabs, or a combination thereof.

    Planing is a state - the condition in which a particular body is acting.
    And no, I don't care if there's a helicopter helping to hold it up.
    But then, I don't recall anyone claiming that the Farrier tri's need one of them either.....
  2. Chris Ostlind

    Chris Ostlind Previous Member

    Nice rant, Will. The camp reference was cool, but you left at least one item off the "Ripley's Believe It Or Not" list... Ahh, who am I kidding, here? There would have to be at least ten thousand other goofy planing scenarios that could make that honors list if we just sit down and dream them up. Let's see now... well, here's the first one:

    Is the tender still planing when it sits on its trailer and is being pulled through shallow water by the owner in his car?

    So, now you have everything out there as a planing vessel no matter the artifice to get it there? POOF! there goes the uniqueness of the F-Boat claims. My uncle's dog-***, waterlogged fishing dinghy is now, officially, a planing vessel. Film at eleven.

    Tell me something... would you say that a submarine that is inverted and clipping along with its hull just skimming the surface was planing?

    Really, PI... A bit mean? My day rate is more than Ian can handle or he'd have done it long ago.

    And I'm fine with the agree/disagree part. It wasn't an argument that was going to get solved anyway. When the professional world of boat designers can't agree on anything similar on the topic, it's essentially going nowhere... but it has been fun.
  3. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    Must not, must not, must not, can't resist.....

    The displacement of the center hull decrease when the ama is submerged.
    That makes the center hull able to plane, because it has a smaller displacement :)
    1 person likes this.
  4. Doug Lord

    Doug Lord Guest

    planing tri/planing cat

    Take a close look at this picture: 1) note the LEE hull and the wavemaking(crest at the bow, crest at the stern);2) now look at the windward hull: flat clean wake; obviously planing.
    Now, in my opinion, this conclusively proves the point regarding the concept of the ama on an F-boat operating as a displacement hull while AT THE SAME TIME the main hull is(can be) planing.
    In this pix of Parliers L'hydraplaneur(Mediatis Region Aquitaine) the windward hull is unloaded to some degree allowing it to plane while the lee hull going AT THE SAME SPEED is NOT planing. Case closed, again....
    Médiatis Région Aquitaine - Yves Parlier
    Address: Changed:12:17 PM on Wednesday, November 8, 2006
  5. Chris Ostlind

    Chris Ostlind Previous Member

    Sad Post

    Clearly, Doug, this whole thing has bothered you quite a bit.

    It's been nearly two weeks since the rest of the guys abandoned the discussion that has no solution and yet, here you are, once again trying with all your might to make it otherwise.

    Kinda pitiful, wouldn't you say?

    Nobody is going to win this argument, Doug. There are just some things in this world, which are not going to get resolved no matter how much you'd like to see it your way. A prudent person let's it go and walks on to better and more engaging past times.

    I urge you to do just that. Right now, it looks like you've lost your watch battery in the sewer and you just have to take the dive into the muck for that $1 item.

    Chris Ostlind
  6. fhrussell
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    fhrussell Boatbuilder

    It seems there isn't an agreed definition of 'planing'. Can someone provide this?

    IMHO, I alsways considered 'planing' a state in which high pressure under the hull needs to exist to create the state, therefore decreasing wetted surface. I would never consider a windward hull 'skipping' across the water to be in a planing state. It is raised by other forces, not high pressure from underneath.

    Also, If a monohull can plane, it is certainly not assisted by an ama lifting her is planing due to its speed and high pressure, lifting the hull, reducing wetted surface, and gaining more speed ultimately.

    A lifted windward hull...planing? ...I disagree.

    Just my opinion on this.......
  7. Doug Lord

    Doug Lord Guest

    planing tri

    Fhr-when the cat begins to heel it reduces the displacement of the windward hull gradually leaving the windward hull still supporting weight from half the boat weight to zero when the hull fly's. As the speed increases it seems clear to me that the PARTIALLY unloaded windward hull( a stepped planing hull) will plane BEFORE the lee hull does which seems to be clearly shown in the picture.
  8. fhrussell
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    fhrussell Boatbuilder

    Doug, OK..I think I follow your thinking here... but, if planing is then not defined by a high pressure beneath the hull (and I'm not saying it is), do you consider a hull flying just above the water, planing? Also, consider a deep v or deep asymmetric hull in this attitude, lifted without a semi-flat area, would you consider these hull shapes planing?
    Just trying to make sense of this and define what is 'planing'.
  9. Doug Lord

    Doug Lord Guest

    planing tri/planing cat

    Fhr,there are at least two definitions of planing in the previous posts including one by Eric Sponberg and one by Daniel Savitsky. Here is one by Douglas Philips-Birt:
    "Planing may be defined as the condition existing when a proportion of the weight of the boat is carried by an upward pressure created by her motion on the flat or nearly flat areas of the bottom".
    Now visualize Parliers hulls(remember they are stepped planing hulls) as not connected together. For the purpose of this discussion assume the one on the right weighs 50% more than it did when it was part of the cat and the boat was level and not sailing. Assume that the one on the left weighs 50% less than it did when level as part of the cat.
    Then start moving both at exactly the same speed; it does not take a rocket scientist to see that the lighter one will plane first.Which is exactly what you see in the picture.
    In reality, the windward hull is lighter and the leeward hull is heavier due to heel ; the fact that their displacement changes due to heel makes no difference: one is lighter and one is heavier.
    That's what is evident in the picture.
    The windward hull, thruout the process of heeling from zero up to just before flying a hull, will support some weight; it can do so thru buoyancy or planing or a combination of both. What makes the picture so good is that at that angle of heel the windward hull is still supporting a bunch of weight but there is clearly an observable difference in the way the two identical(one heavy ,one light) hulls are going thru the water.
    Heel reduces weight on the windward hull of this cat or on the main hull of an F-boat and that reduction of weight is what permits the F-boat main hull to plane and is why the Parlier cat's windward hull is planing while the lee hull is not. Hope that makes it clearer...
  10. Jimbo1490
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    Jimbo1490 Senior Member

    I made a feeble attempt to make this same point earlier in the thread. In my example I propsed an overwieght hull that could not plane because of its weight that went on a diet and could plane thereafter.

    Point is, if the weight is reduced, by whatever means, to a point where planing becomes possible at a given speed, does that make the planing invalid? Eventually, yes, since if we declare such planing to always be valid, then we are forced to accept as 'valid planing' situations which clearly are not, such as a cat with the winward hull flying ie unloaded completely.

    Suffice it to say that there exists a continuum of conditions between full planing and full displacment for this special case of a hull that gets 'lightened' under way by heeling forces acting on a multihull sailboat.

  11. ActionPotential
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    ActionPotential Junior Member

    It's quite simple really.
    Ian Farrier has defined planing as skimming across the top of the water.
    Monohulls have some difficulty planing because they don't have any other forces helping them to plane.
    Trimaran windward amas plane pretty easily.
    Trimaran centre hulls plane with a little more difficulty.
    Trimaran leeward amas hardly ever plane.
    Catamaran windward hulls plane about as easily as trimaran centre hulls.
    Catamaran leeward hulls hardly ever plane.
    Hull shape is important for monohulls to plane.
    Hull shape is irellevant to multihull planing.
    The F22 doesn't plane yet.
    When one is launched I expect it will plane as long as the amas have sufficient buoyancy.
    Trimaran centre hulls do occasionally plane like monohulls, when they don't have any other forces helping them plane.
    My catamaran goes fastest when it has the windward hull planing on the tip of the daggerboard.
  12. ActionPotential
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    ActionPotential Junior Member

    One more thing. If a trimaran has one of its hulls not planing then the boat as a whole is not planing, although one of its hulls is. Only when all hulls are planing is the boat planing.
  13. RHough
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    RHough Retro Dude

    Horse = Dead
  14. Vega
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    Vega Senior Member

    Yes, you are right.

    Tris are very fast boats (when they manage to stay upright:p ).

    By the way this one is flying or planing?:confused:

    (That's the second one to arrive to Guadalupe, on the "Route du RHum" race. The first one was really flying:p )

    Attached Files:

  15. Chris Ostlind

    Chris Ostlind Previous Member

    Glue Factory

    Since the horse is so obviously dead... I'll offer-up this little bit of detritus for you all as a way of saying goodbye to the thread.

    Click on the above link and go to the video. You'll find a nice clip of a Gunboat 62 cat blowing off a Reichel-Pugh 80 at terminal velocity.

    Of course, as any knowledgeable devotee would already know... the Gunboat is "planing" and the Reichel-Pugh's only shortcoming is that it needs a big set of foils and some sort of sliding ballast system to make it worthwhile. Not that our buddy Doug wouldn't have clamped-down on those potential claims like a Pitbull. Or, is it more like a Disney animation process, I can’t really decide.

    Laters Brah,

    Chris Ostlind
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