Planing Trimarans

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

  1. cavalier mk2
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    cavalier mk2 Senior Member

    Hi CT, it seems the sensible thing for you to do is to pick a definition of planing that suits your beliefs and not care what 99% of other people think. The idea about planing was to define a special kind of dynamic lift where greater speed (part of the Baader definition) is involved. The wave separation is referring to the stern transverse wave system that some long thin hulls don't even make. Your under water board probably won't count in anyone else's definition because it is underwater, not going faster than 1.35 -2 times the square root of waterline length and has yet to make waves let alone ride them. But what the hull call it whatever you want. It certainly has dynamic lift. The best thing about this thread is that everybody is thinking about the different ways a boat can go fast ,the worst is fighting over definitions. Baader's definition agrees with many others so it works for me freeing me to think about other concepts. Like the stern on the Antrim ama. To me it seems like a planing stern to provide lift at the stern as the board provides lift to the front . The bows would definitely ride higher without it but the Catri is doing the same thing with its ama stern fins so there may be speed benefits. I do wonder if the force it is depressed with also causes more drag than a conventional shape. Thanks for the links I'll watch them when I have a little more time.
     
  2. C 249
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    C 249 Junior Member

    Re "Hi CT, it seems the sensible thing for you to do is to pick a definition of planing that suits your beliefs and not care what 99% of other people think."

    Ignorning what most people think is exactly what I was not doing. The point was that there is NOT one accepted definition of planing. For you to say that I'm ignoring what most people think is utterly wrong.

    Baader's definition seems to have some issues, as do many others. If Baader's definition works for you, that's fine, but I'm not ignoring what 99% of people think.

    The first part of Baader's definition seems to tie in with the definition that seems best to me (from the reading of naval architectural journals, speaking to America's Cup and skiff designers and books like Larsson and Elliason). This definition simply says that planing occurs when the dynamic lift is sufficient to lift the craft's centre of gravity above its static C of G.

    However, the sinker windsurfer example shows that the 'statis CoG' definition isn't perfect. I'm agree that my underwater board shouldn't really fit anyone's definition of planing, because it is underwater. However the underwater board DOES plane under some definitions; therefore those definitions must be wrong.

    Secondly, when planing it's often hard to see a transverse wave at right angles to the course (see attached pic which shows no such thing as far as I can see) and the wave train that is visible is definitely hanging with the boat.....I suppose it can depend on one's definition of when the waves are 'left behind'. I can see a big stern wave coming straight off the back of the boat, similar in distance astern to the wave some lightweight craft get in displacement mode although this wave is much larger. I used to waterski and I can't recall a big transverse wake but I can recall a distinct wake that it very much attached to the boat. I also think our cat had a stern wake rather like the one seen below, which is the wake of a planing hull.

    [​IMG]

    Yes, I agree that getting stuck on definitions is not all that interesting, but unless we define exactly what we are talking about we won't get anywhere. The main point is that we haven't agreed on a definition and that seems to cause most of the dispute here.
     
  3. CT 249
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    CT 249 Senior Member

    Here's a pic of a Lechner-style round-bottomed windsurfer*, known as a "displacement" type but definitely capable of planing. Note the detached stern wake, similar to the wake above - but in this case, the craft is still at displacement speed. This is a classic case of a stern wave that appears to be as "detached" as a planing boat, but in this very slim and light craft the stern wake is like that of a heavier boat in planing mode.

    To me, it shows the difficulty of coming up with a definition to argue about.

    [​IMG]

    * not a Lechner, but a lengthened Div 2 type board for unlimited class racing.
     
  4. cavalier mk2
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    cavalier mk2 Senior Member

    The windsurfer in that photo would probably be classified as operating at forced displacement speed as it is pushing past its stern wave but not rising on its bow wave. It looks like it is traveling less than 2 times the square root of the waterline length. I'd guess about 1.5 -1.7.
    What definition of planing do you suggest? Do you have a source you would like to nominate for a forum standard?
    While contemplating your underwater windsurfer it did remind me that the up and down control surfaces on underwater craft have been referred to as diving planes to compound the confusion:)
     
  5. CT 249
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    CT 249 Senior Member

    Having spent years racing windsurfers of that general type, with a fair degree of success, I certainly would not classify it as operating in the "forced mode". At that stage it would be feeling very much like a displacement boat, but a very, very light and efficient one. When it starts definitely planing, the fore-and-aft and athwartships attitudes will be different, as will the wake.

    This is where Skiff design has gone over the last 15 years; towards a boat that's moved AWAY from the conventional planing hull and towards a slim, low wetted surface, low form drag hull that (as Catsketcher says) doesn't feel like an old-style planing hull.

    It all seems to underline the difficulty of finding a suitable definition, therefore to what extent should be argue about it? Of course, that goes both ways - when planing is so hard to define, who should claim that their boat does so?

    BTW in response to earlier posts - I certainly believe that the Tri Fli and HSP tris plane but I'm not sure a Farrier planes in the same way. Having said that, while I've sailed all three I haven't spent much time on them.

    I can see that Farrier could well claim that the beamier 'planing' shape is faster FOR A RACER/CRUISER TRI LIKE A FARRIER. The fact that the shape that is best for a racer/cruiser is different from the shape that's fastest for a straight-out race machine isn't surprising.
     
  6. cavalier mk2
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    cavalier mk2 Senior Member

    The forced description is pretty common for displacement speeds exceeding 1.35 x the square root of waterline length, the windsurfer is pushing into the bow wave and stretching away from the stern. It could be described as bow wave penetrating displacement speed or semi-displacement until it begins to rise with the lift of the wave. There are plenty of boats with hulls that pierce the wave train without planing, it does take a hull designed for planing to do so and seems to be most common in racer/cruisers up to a certain size and smaller daysailors. In both cases the object seems to be to retain higher performance with more room/capacity than a thinner hull could manage.
    Planing is measurable , though the surface condition of the water can make it more challenging. Perhaps an addition of percentage of lift to the definition would help . I.E. craft must experience more than x% of lift to be called planing. The condition could then be categorized planing, semi-planing, semi-displacement, displacement as an example. The main point about any discussion is to help those interested in boat performance and design to understand that there are different approaches to design solutions when looking for performance, be it speed or elbow room, within size constraints. As you have illustrated with the evolution of skiff design achieving those goals is an ongoing process, sometimes the definitions get left behind with the stern wave.
     
  7. Chris Ostlind

    Chris Ostlind Previous Member


    The free plans went out the day I posted the offer.



    The canoe design selected already has 26 sets of plans out there being used successfully by their builders. Nothing more need be said, save that it was fun to see who would respond and how quickly they would do so.
     
  8. cavalier mk2
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    cavalier mk2 Senior Member

    Now if only you could design yourself some manners and topic relevance you might not have to give your plans away......
     
  9. Chris Ostlind

    Chris Ostlind Previous Member

    Just look at the contributions you have made over the last 13 days. You've managed to come to zero as a conclusion. You are still tossing around some iffy set of definitions as if they have solved the whole thing. Own this... the stuff you have considered hasn't made the argument any closer to being resolved than it was way back in '06. Virtually the same, not proved positions, are being bandied and you still have not drawn them out as anything even close to proofs.

    Do take the time to re-read post number 257, from 4-20-2010 and you'll see that you have not moved the needle one bit when it comes to drawing any kind of conclusion that is more correctly phrased.

    You can't make-up for poorly established arguments by being a naughty boy, Cav. Your commentary took a very definitive change in direction at post number 303, on 5-21-10, when you said,

    It was you who took the business from the friendly exchange into the zone of not having anything left to say, producing a slanging session. Now, you wish to further obfuscate the dialogue with more attempts at personalized denigration that is humorless.

    Come-on, bud... change your tune and get your comments back on track.
     
  10. Chris Ostlind

    Chris Ostlind Previous Member

    Quote from Doug Lord.

    "Problem is, bud, you don't recognize a conclusion that's staring you in the face!"



    Oh, Doug, I see it plainly. It goes something like this.

    Man with the initials, DL, suspends outhouse over a river with two hefty cables. He lets out just enough wire to hang the bottom of the outhouse in the water.

    He gets all the press down to the river bank that afternoon and proclaims loudly... "I've just built the first planing loo. You can see it there, suspended perfectly, as it rides the irregularities of the water's surface just like a planing sportboat. Now, imagine yourself as the owner of such a remarkable watercraft? You can tear it up on plane at the same time you loudly pinch a loaf.

    Now, who wants to step-up and be the first to own a craft that is surely going to be ranked among the most significant developments in competitive boating for the last 50 years?"


    A member of the national press raises his hand and asks a question...

    "Oh, the cables represent a big problem for the planing claim, you say? Well, the issues are staring you right in the face and you are simply failing to recognize them. Either the shitter planes, or it doesn't and we can all very clearly see that it does. The cables have nothing at all to do with that status."
     
  11. DennisRB
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    DennisRB Senior Member

    On F-32SR, the ultimate racing version of the F32 on the F-boat site.

    The only difficult part with the F-32SR was deciding on whether to use the narrow F-32A center hull (2.55m trailer width) or the wider F-32AX center hull (2.95m trailer width). In this regard, both the F-9/F-9AX and F-32/F-32AX have given a unique opportunity for comparison, with identical boats, the only difference being narrow or wide center hulls.
    The narrow F-32A center hull should be faster according to theory, but in reality, besides having more room, the F-9AX and F-32AX hulls also appear to be just as fast or faster. This is probably due to the higher displacement of the X versions, which means for a given weight the wider/flatter hull will be floating higher, for less drag, and will also be able to get up on the plane earlier, and stay there longer. The choice was easy for a plan based boat, just offer both options, but a decision has yet to be made for the eventual production version.

    On F9R

    The wider F-9AX center hull can also be used to build an F-9RX, which will have very similar performance to the F-9R. The F-9RX will have less wetted surface area, for the same load, so it should be faster in light airs, and the wider center hull will encourage it to plane earlier, so it could also be faster in heavier airs.

    ---------------------------------------------------------------------------------------

    I haven't read this whole thread but I sit half way on this topic. Obliviously a tri can lift its vaka out of the water supported by the amas. This is flying the center hull. But in my opinion if the center hull has "planing shapes" it will develop some lift and help it rise to the surface in addition to lift from the amas. So its sort of "assisted planing" and when it happens the boat will sail faster. Many tri sailiers report a "hump" where their boats get stuck at a certain speed requiring an extra bit of breeze to get past. But once over the hump they can continue to build speed. I think this has something do with the vaka reaching its "assisted plane".
     
  12. Gary Baigent
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    Gary Baigent Senior Member

    Good one Dennis, assisted planing - maybe we can all accept that compromise .....? - actually, on second thoughts, no, assisted is a bit too wishy-washy and PC - how about pseudo planing - yeah, that has a good ring to it.
     
  13. DennisRB
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    DennisRB Senior Member

    It seems obvious to me that there are 2 forces acting on the vaka to make it appear to plane (pseudo plane) or whatever. The actual forces that make a real planing boat plane. And the lift created by weight shifting to the amas. You cant ignore one or the other. They will both always be there.

    If one can accept this (and it appears a pretty easy thing to accept) then one might also accept that planing shapes and wider vakas will induce this "pseudo plane" earlier. It might not be a true plane. But it also isn't happening ONLY because most of the weight has shifted to the ama. Therefore it is more than just a sales tactic by Ian Farrier to sell boats as he has wider and thinner hulls to compare and this "pseudo plane" does occur differently on both vaka shapes on otherwise identical boats. It then just reduces to an argument over what the definition of planning really is. I am still yet to hear a definition people will all agree on, so its pretty hard to blame anyone for shoddy marketing if they say their vakas plane.

    I for one wont go an buy a tri just because someone says it planes. There is no relevance. If I am after speed I will look to see what design is winning more races and ignore what the designer has to say about planing. Would anyone really ignore race results and buy a tri based on claims of planing even when results show it to be slower? I doubt it.
     
  14. Doug Lord
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    Doug Lord Flight Ready

    Planing is planing is planing is planing if it is planing

    -----------------------------
    what he said(again)
     

  15. Chris Ostlind

    Chris Ostlind Previous Member

    As long as we are accepting things easily... In the instance above, one could also accept that the fatter hull, having less draft, is more easily levered to the claimed state, having fewer centimeters to raise to make it appear to be planing.

    I don't believe that any of the nice folks contesting the planing capacity of an F-boat have indicated that there isn't some dynamic lift going on as the hull moves through the water. Even the skinniest L/B ratio proa hulls demonstrate a degree of lift. The question is: can an F-boat achieve the necessary degree of lift to plane without leaning a huge majority of its weight over on the leeward ama and its subsequent lift of the vaka through mechanical means.

    Some here have tried to illuminate that there is sufficient waterplane surface for the magical event, but their calculations are always made with the craft at static rest. I would suggest that as the craft heals, the orientation of the heeled waterplane shifts further and further from the ideal as it might be described by Savitzsky. As the vaka is lifted from heeling, the waterplane is further reduced in area. Further, the transom shape and orientation on the F-boat does not add to the potential, but draws the form further from an optimal planing ideal.




    It's also equally hard for a person to make said claims in light of this non-descriptive wording. Without any substantive agreement as to the definition, that means that any claims to support said behavior can be just as easily disproved by claims that it can't.

    The question that arises, then, is... why would you want to make a claim regarding a topic that is so iffy in its nature, if it weren't more about the sizzle than the steak?




    Interesting question, Dennis. I believe that way back in the dark ages of this thread, I asked why had the equally sized F-boats been getting their butts kicked routinely by Antrim's A30+ in the San Francisco Bay area races. Ian never really addressed that directly, but as I remember it, he hauled out his usual rebuttal on the matter and referred to the typical winning trimaran in these kinds of duels as skinny and coffin-like with no creature comforts.

    Right away, that kinda creates a buzz that says, if F-boats can plane and the other, skinnier boat makes no such claims, it would seem that the F-boat would have a decided edge in boat speed. For some reason, Ian discounts this claimed advantage and instead goes right at the big fat interior creature comforts as an argument of choice. That would suggest that planing really isn't one of the hot buttons that Ian wants to push in the marketplace, but, in fact, it's all about cabin volume and creature comforts.

    So, that takes us back to the place where the F-boats got wider to provide creature comforts that they did not have in comparison to the other, equally sized monohulls in the marketplace. One could then extrapolate... Since the lack of a strict planing definition does not exist; that the claim of planing is there for the taking as a bonus to having made the F-boat hull wider.

    So you get to have your cake and then eat it, as well. There are lots of people who will never race their F-boats, but they did consider that planing claim in the marketing literature as one of the bits of spice tossed on the top.
     
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