Does a catamaran plane?

Discussion in 'Multihulls' started by Meanz Beanz, May 19, 2008.

  1. Meanz Beanz
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    Meanz Beanz Boom Doom Gloom Boom

    I got into a debate on this one once upon a time and I just thought I'd get the opinions of those here. My boat looks like its planing to me when sailed at speed, the water leaves the stern in the same fashion as any other planing vessel I have sailed. I looked up Chris Whites opinion and he refers to multihulls as planing vessels but it seemed that most I talked to didn't consider a multihull as a planing vessel.

    Anyone for any thoughts?
     
  2. Fanie
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    Fanie Fanie

    Short answer is yes.

    Longer answer is also yes, but of course :D
    Any object given enough speed (lift (shape) and power vs weight) will tend to skim over water's surface. Some objects just needs more help than others ;)

    I think in general it is accepted that a displacement hull has not been designed to plane specifically. When I got to the forum it was one of the first Q I asked... what's the difference between a planing hull and a displacement hull.

    A planing hull is usually associated with a flatter bottom and enough power to bring it to the speed where the hull shape would provide enough lift so the boat would plane on the water. The transom area shaped for planing only with little worry about the wake it leaves compared to displacement hulls that is ideally expected to slit through the water and no disturbance at all.

    Personally I think the displacement hull is suitable to be a displacement hull firstly, making it much more economic for slow and medium speeds (where the planing hull would fail to function properly) and secondly it could be a planing hull as good as a bona fide planing hull if you apply the same power and force of large motors. I'm not saying the hull shapes are ideal on all displacement hulls, but could be traded off.
     
  3. JCD
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    JCD Follow the Bubbles!

    Hello Meanz Beanz,

    I understand that:
    Hydrodynamic lift must exceed hydrostatic lift.
    Full displacement must ride or glide “on” the water.
    The vessel must also overtake its bow wave.

    The Froude Number will give a good idea whether the hull is at a planning state. I suspect the speed must be quite high and the power to weight ratio must also be high unless the hull is specifically designed to plane, and even then I bet it will need to exceed at least 2 to 3 times the square root of the Lwl.

    Here is information on Froude: Look for Cwave and FrCritical.
    http://en.wikipedia.org/wiki/Froude_number

    If the above are met...I would say yes. If not, I would say no.

    I’m inclined to answer no for a large percentage of hulls unless the hulls are assisted with foils. IMO.

    Thanks
    J:cool:
     
  4. terhohalme
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    terhohalme BEng Boat Technology

    If we first define "plane". Is it just going fast? Leaving stern wave far behind? Or is it having a hydrodynamic lift to support most of the displacement? How can it be measured? Why should "going fast" to be planing?

    Are the fast submarines planing? Are the monster catamarans like ex playstation planing or just going fast? How can planing be observed? Does it really matter?

    Hydraplaneur http://www.parlier.org/hydraplaneur/bateau/caracteristiques.php?lang=eng
    obviously plane sometimes. Does she win races?

    Planing in power boat requires 1) sufficient trim angle (3-4 degrees), 2) enough planing area (lot of width), 3) center of gravity well backwards from amidships and 4) a lot of speed (Fn > 1). Speed is possible, the other three aren't. Or, is planing in sailing multihulls something different from power boats?

    Terho
     
  5. Chris Ostlind

    Chris Ostlind Previous Member

    Aside from the fact that this is likely going to end-up as a non-decision, discussion, as have all the planing questions as they apply to multihulls that have been brought to this forum... I'll offer these bits and then excuse myself to the stealth mode to read.

    It would seem to me that if you want a really sound answer to that question as posed, then
    1. You have to first define just what constitutes a planing condition and then,
    2. Apply it religiously to the entire craft and not simplistically to one hull at a time in order to gain the so-called status of a planing vessel.

    As in:
    1. Define how the dynamic lift associated with the condition applies to a multihull (in this case, a cat, but can also be worked into a trimaran concept)

    2. Can the boat be said to be planing if one hull is in full displacement mode, supporting nearly all the weight, while the other appears to skim the surface, looking for all intents to be "planing"?

    If all the hulls are not "planing" at the same time, can the craft really be referred to as a planing cat (or tri) Example: Could one simply drop a smallish, connected hull, from the larger leeward hull of a catamaran, suspend it so that it skims the surface with some measure of dynamic lift associated and then say that the entire boat is now planing?

    You see, it can get to be a really tricky thing and is full of pitfalls and convenient terminology for the possible benefit of a marketing position.

    Let the fun begin, gentlemen. I'm guessing that soon the air will be filled with unprovable solutions and convenient claims to the throne and lots of haggling and griping with ultimately.... no substantive solution.

    If you want to really mess with the claimants head, then suggest that they produce a well-shot video clip showing ALL of the hulls of whatever multihull they choose for the demo; to be up on dynamic lift support ONLY, while sailing under control for an extended period of time... oh, say, 1 kilometer for opening starters.

    Whooo Baby, this is gonna be fun.
     
  6. Nordic Cat
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    Nordic Cat Senior Member

    Given the first set of conditions defined above, I seriously doubt that anyone can deliver that video!

    In my mind, a cat or a tri never planes, some of the newer, wide and light monos seem to.

    Anyway, who cares as long as you can sail at 2 to 4 times hull speed under optimal conditions.

    Regards

    Alan
     
  7. Fanie
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    Fanie Fanie

    It is easy to determine whether a boat planes or not...

    While you pick up speed (as a displacement vessel), when it goes on the plane you should notice a fair increase in speed without adding aditional power. It is noticable since the hull's drag becomes much less than when displacing.

    A boat planing requires less power to stay on the plane than what it took to get it there.

    A cat or tri that burries a hull isn't planing, it's displacing. But when all hulls are out on top of the water and at speed then it would be planing.
     
  8. Nordic Cat
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    Nordic Cat Senior Member

    Fanie,

    Your statement is true for a given hull shape. Some of the newer motor cat designs are actually more efficient and use less power in displacement mode, than they would planing. Malcolm Tennant did a paper on this a while back, just can't find it.

    The thinking behind Parliers cat was to get it to plane, as at planing speeds, the power needed to increase speed rises roughly to the square, whereas in displacement mode it is roughly to the cube. As the power of the wind also rises to the square of the wind speed, a planing cat will need less power to continue accelerating, and would have a nearly linear function to wind speed.

    Regards

    Alan
     
  9. catsketcher
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    catsketcher Senior Member

    Chris Ostlind is laughing

    The reason that Chris has now ducked for cover is that this thread was almost covered before in different forums. Farrier used to say (maybe still does) that his main hulls plane.

    This may be okay except for the fact that the float doesn't plane so a long argument raged as to the merits of each case.

    My brother CT249 has done lots of study on this for a book he is writing. Our multihull shapes are very bad at planing. If you look at boats that plane they are usually short and fat - sailboards, small dinghies, ski boats. Short and fat is good for planing.

    Multis are long and thin and a pretty bad shape for planing. In terms of water flow they are like a very low aspect foil. The sorter and fatter the hull the more it looks like a higher aspect foil. The span gets greater than the chord. Formula boards take this to the max - they are outrageously fat and short - higher aspect planing surface.

    My take on it is that it doesn't matter. There is so much that I don't understand about boats that debating something that makes no difference to design is intellectual aerobics. Good for the exercise but in the end of little consequence.

    Considering that even dinghy designers (whose boats I think plane) can't agree on the definition of planing I like Chris will now watch.

    cheers

    Phil
     
  10. Fanie
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    Fanie Fanie

    Hi Alan,
    Of course hull shapes makes a big differnce.
    A marble planes on the water given enough speed (and power) although it's not ment to plane at all.

    I would be interested in seeing the article about the displacement hulls using less power than planing. I have read a similar article some time back, and if I'm not mistaken one of the SA boat manuf are switching to displacement hulls exclusively.

    I've had to do with planing hulls a bit, but I do like displacement hulls more.
    Makes more sense
     
  11. Fanie
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    Fanie Fanie

    He-he Phil,

    The more you learn the less you know. I know exactly what you mean.
    The moment you think you got it then something else comes along and trash the previous thinking :D
    Irritates the hibby jibbies out of me at times :D
     
  12. JCD
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    JCD Follow the Bubbles!

    Hello Chris,

    I also read that prior thread and it just went on and on and on like the battery bunny. I will also be asking Scotty to beam me up in a minute for a five year adventure before I return here, but I have a question.

    Doesn't the Froude formula fulfill this criteria and then answer it? Maybe a little calculated example would show if the result for the velocity is reasonable?

    To plane is like breaking the sound barrier (in our case climbing out of the hole) isn't it? It doesnt matter how fat or long the hole is, it is there. Given more and more speed, the bow will generate a greater wave as long as it is in the hole and wont stop until it climbs out of it.

    Don't get me wrong, I don't believe a multi can plane without the assistance of foils and indeed it may lift the hulls clear out of the water, but not without foils. I also don't think a multi will be very easy to bring to plane just on sail power alone. Even the hovercrafts have to power over the hump and they don't even touch the water!

    Okay... transporter is working now. Send me a deep space answer.:D

    Thanks
    J:cool:
     
  13. Doug Lord

    Doug Lord Guest

    This is a cat that does plane- Yves Parliers 60 footer with stepped planing hulls. Big advantage at high speed theoretically ,big disadvantage at low speed. The rough balsa models show a concept that allows a high L/B ratio displacement hull for light air and then is rotated to a stepped planing hull for higher winds. This will be tested on a full size boat before too long.
     

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  14. Chris Ostlind

    Chris Ostlind Previous Member

    De-Cloaking, momentarily...

    Parlier's craft is a boat with a very narrow bandwidth of performance operation. I also suspect that it is a boat with a very narrow bandwidth of sailors who could successfully keep it in said sailing bandwidth.

    The telling fact that it's not out and about much anymore says a heap about where Parlier wants to take his next vision.

    These types of exploratory vessels are really interesting as studies in theory. The concept is well known to designers. Curiously, with so many top-end design gurus aware of the stated potential, there just hasn't been very much in the way of actual craft being built to support the theoretical aspects of the design concept.

    Now, why is that do you suppose?

    It isn't because designers haven't known about slender stepped hulls for use on vessels. Look back at the seaplanes of WWI and going forward and you'll see stepped hulls on virtually all of them. Is it because the window of successful operation is quite narrow and the design purpose needs to fall within that window, or it's kind of a draggy hull?

    A successful boat design needs to operate in all sorts of conditions that regularly fall outside that window. I get that you want to solve that dilemma with some kind of coolish rotating gizmo hull form, Doug, but is it really pushing the design process forward?

    Perhaps little servo motors arrayed in a line down the center of the hull, well out of sight and potential damage, will do the trick? The manaual rotation thing for a boat that has to, potentially, go through several hull presentation iterations within the same reach will soon get pretty old.

    They tell me that modern folks are looking for less to fiddle with and not more. Automatic spinning hulls is the ticket for the future dude who wants to buy a boat like this. Just look at how cars solved the Traction Control issues? Turn it on and speed robbing wheel spin is eliminated. Set it and forget it, not "OK, everybody... to the other hull now, I have to rotate the form so we can go faster"

    Tell me that doesn't sound like the Star Wars thing when the Millenium Falcon is supposed to jump to light speed and it just goes: rung, rung, rung until it obviously shuts down with Han Solo and Chewey all pissed as can be?

    Just havin' fun here, Doug. Nothing personal intended.
     

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  15. Meanz Beanz
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    Meanz Beanz Boom Doom Gloom Boom

    Oh dear, bad question huh? LOL and here I was thinking the smart boat design guys will know this one...

    Just for the record one of my thoughts was that if at speed the boat was displacing less water than at rest it was then to some degree riding on the surface of the water and therefore planing. Difficult to measure I know, also is planing considered fully supported (doesnt happen by my observation) or above a certain % supported or what. It has to be a grey area really doesnt it :D

    I think I will side with you Nordic, I don't really care so long as I am going fast.

    Curiosity killed the cat.... :D
     
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