Ama designs that create lift

Discussion in 'Multihulls' started by rapscallion, Nov 18, 2007.

  1. rapscallion
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    rapscallion Senior Member

    "planing" amas are being talked about more and more. I think I posted a patent link to them once already; but I was hoping to hear from some people out there about them.

    I know doug likes his foils, but I kinda wanted to focus on the hull shape itself creating lift, like the patent discusses.

    I'm still learning freeship; after I get the ama rendered I'm going to take it into open foam and try to figure it out.

    I was wondering if anyone else was playing with this
  2. Doug Lord

    Doug Lord Guest

    Planing Amas

    Actually, my Ultimate 18 concept uses stepped planing ama's for high top end speed with foils just used for pitch control(similar to Parlier's cat).
    See Jim Antrim's 40(I think) where he discusses his use of planing ama's.EDIT: It's his 30+:
    Antrim 30+
    Address: Changed:12:17 PM on Friday, September 30, 2005
    See the Ultimate 18 thread in this forum and the rough model pictures here:
  3. Fanie
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    Fanie Fanie

    Yes, what's with all the millions and millions of claimed patients clogging up the net all of a sudden. Some of the stuff already exist and has been in use for a long time yet along comes an idiot and claims a patient for it. What ? He thinks he's going to get rich all of a sudden from it ?
  4. Chris Ostlind

    Chris Ostlind Previous Member

    I can't believe we are going to do this dog and pony dance again regarding planing amas... especially as they apply to claims, as perceived by others, to have been made by Jim Antrim in his SNAME article regarding trimaran design.

    For any of you who wish to read about the previous discussion and the ground it covered in the past, here's the link to that thread: speer antrim's planing amas

    Antrim does not state that his amas plane. He states that they have planing shapes and that they benefit from the shape by creating dynamic lift. Jim very precisely skirts the planing claim issue regarding his ama forms and if you wish to split tiny hairs, he does allude to the possibility. Still, he does not cross the line on the exuberance of that style of claim regarding his design work.

    There is a very distinct and purposeful style to the prose, as selected to describe this function. Further, Antrim goes to great lengths to describe the beneficial purpose of the ama forms as being much more directed to reducing windage, rather than an effort to make a planing claim. Now, why would a designer of Antrim's skill and experience, refuse to make a direct claim for planing amas if he had it within his grasp all along... and knew it?

    All hulls, the second they begin to move through the water, create some degree of dynamic lift. Does this mean that we can now begin to make planing claims for any hull in existence, simply because the designer says that the hull is of a dynamic lifting type?

    Some folks see what they want to see, rather than critically examine what is actually there. When it is necessary to put words in the mouth of the designer in order to create a substantive foundation for ones conceptual wish list, one has done a disservice to the designer, as well as to himself or herself.

    Take a long look at the writings of Antrim on the issue from the perspective of a scientist and not a marketer who is looking for a place from which to leverage a large and foamy claiming position.

    An example: If I were to make claims that my recent trimaran's spreaders are shaped just like a wing from a commercial jet airplane, would it also be construed that I am suggesting that my boat can actually fly like a jet airplane? (I mean, there they are, those bitchin' aircraft shaped spreaders, up there in the windstream about to lift my boat and seriously reduce my wetted surface area...?) The answer is: Of course not. This is true mostly because I did not say that the boat could take-off and fly. I simply said that the spreaders were jet aircraft-like in their designed shape and construction... and that is all. A very big difference and one that should be observed with some measure of care.

    If you really want to know what Antrim thinks of the planing claims of his uniquely shaped amas, why not write him a letter at the address at his website and ask him. I'd love to see the answer you get and if Jim makes the direct claim, then I'll be happy to acknowledge that fully planing amas were, in fact, his original design intent.

    Conversely, if he says they do not plane and makes no claim to that fact, then please post that response here as well.

  5. Doug Lord

    Doug Lord Guest

    Planing Amas

    In any reasonable interpretation of the language in Mr. Antrims description of those ama's he has ALREADY said they plane. They "use planing geometry". They "develop dynamic lift". Case closed.
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    BOATMIK Deeply flawed human being


    All hulls are lifting. But some are more liftier than others.

    That is the part that most people don't grasp - just how nebulous and undefined the whole idea of planing and lift is.

    Lift starts as soon as the boat moves - Excellent!

    It is generally said that conventional multihull hulls "don't plane", but I have never seen that said with the slightest shred of analysis or acknowlegement of how much they actually do lift - the volume of the hollow in the water behind the boat at speed is evidence that they do.


    Some of the hollow will be wavetrain, some is from wake interference, but some is from separation at the transom - that particular hollow implies lift.

    It is one of those things that go round and round on the web an other places like "slot effect" and "low drag teflon coatings".

    Certainly you can design a hull with more lift but it doesn't mean the others are not lifting.

    There are downsides too - when I first saw Hydroptere my thought was that the stepped amas are going to be very draggy in winds too light to get foilborne. This will be something that dogs most designs based around getting more lift.

    I believe they are changing the shapes of the amas on Hydroptere - but I don't know whether it is for the reason of excessive light wind drag.

    Thanks for the contribution
  7. Chris Ostlind

    Chris Ostlind Previous Member

    Jim's a pretty technical guy, Doug. How much dynamic lift does he say they produce? Does he claim they produce enough lift to fully plane when pressed to half their buoyancy by the full weight of the rest of the boat? Does he make the simple and direct claim that they plane? Or, is he simply alluding to the shapes as of the type, so that they may provide a benefit to the design overall, rather than simply resisting the heeling moment?

    Don't you find it just the least bit troubling that Jim does not make the planing claim outright?

    People make allusions to issues all the time, Doug, without actually going over the line to make a hard and fast claim. Allusions, though, are not even closely related to illusions... which seems to be the real topic as you have presented it.

    Write to Jim and see if he answers your query about his writings. Share that response with us.

  8. waikikin
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    waikikin Senior Member

    Chris, man you gotta patent those bitchin' lifting spreaders cos if there as cool as you say every one will just have to have them & like fit some alerons? too so you can tune the lift! Nice points Chris. Regards from Jeff.
  9. Doug Lord

    Doug Lord Guest

    Planing Ama's--- Yes,in fact, they do plane!

    Chris, you're comments about Jim Antrim's planing ama's were way off base as they usually are on this subject. No responsible designer would use the terms "planing geometry" and "dynamic lift" regarding one of his designs if it didn't plane. Here is what Jim Antrim said today:

    E-mail message

    From:*Antrim) Date: Mon, Nov 19, 2007, 11:42am (EST-3) To: (Doug Lord) Subject: Re: 30+

    Thanks for the compliment,
    Jim Antrim
    Doug Lord wrote:
    Jim, I've been a big fan of your work for some time. I'm curious: do the amas on the 30+ actually plane?
    Thanks very much.
    Sail Fast, Doug Lord
    ************Antrim Associates, Naval Architects
    4018 Archery Way, El Sobrante, California 94803 USA phone 510-223-9680 * * * * * * * * fax 510-262-0303 * *
  10. Chris Ostlind

    Chris Ostlind Previous Member

    Well, Doug... it looks like you've caught Jim on a "Yes" day when it comes to answering simply phrased questions about planing, be it amas or vakas, or otherwise.

    Because the topic is so fraught with unknowns, boisterous claims and vague concepts... and it is especially so when it comes to describing planing conditions for multihulls, you are just as likely to get a totally different answer from Jim, or any other designer of substantive merit, depending on the day and their mood.

    As a way of offering an example on this response of mine, here's what Jim had to say to me on the topic... "Does the ama on the 30+ lift significantly in the water due to dynamic pressure? Yes. Is the entire underwater surface at a positive angle of attack, as it would be on a full planing hull? No"

    Keep in mind that I've known Jim for a fair bit of time professionally, as he's been instrumental in helping me to develop my skills. I've also had some reasonably in depth discussions with him, as well as being the beneficiary of his design skills on my own projects as I've plodded along the design student's curve of life. I owe him a great deal in that regard and would much rather err on the side of cautious interpretation of his suggestions, than to run-off with a wild hair between my teeth because of an indication he may have suggested in his writings.

    He did say a lot more on the topic of planing amas and vakas, but I'm not going to quote additionally from this recent letter, or any previous letters on the topic, any more than I have. The info was personal in nature and it stays that way.

    If you wish to continue your rant... be my guest, Doug. It's fairly well established by now that there are some very good minds at work on this thread that run counter to your position, so by all means, keep the faith, my friend.

    With all that being said, there is still room at the Inn, so to speak, for an ama to produce a planing effect and I think you can see that potential in the design of Sam's (Frosh) boat which I think he still has in the works. For those not familiar, you can see that design in the previously mentioned link I provided a couple of postings ago. planing amas
    He's got a very interesting project going on there and he could discover some really fun things if he puts it on the water and gets that bad dude running well.

  11. Doug Lord

    Doug Lord Guest

    Just can't bring yourself to back up YOUR OWN WORDS can you,Chris?
    So now we have at least two MAJOR trimaran designers who have described that 1) the main hull planes and 2) that the ama planes yet we have a novice designer who disputes what Jim Antrim(2) and Ian Farrier(1) say.
    I'm sorry that you do not understand either concept ,Chris. Perhaps over time with some experience on the water you will. Good Luck!
  12. Chris Ostlind

    Chris Ostlind Previous Member

    Nope, Doug... There'll be no further comment in response to your issues in this matter. It's all been said and it's all contained in my post directly above.

    This leaves the field wide open for you to champion a perfectly satisfying designed and built solution. Build your boat, which I have more than supported, and prove that these potentials can be accomplished, rather than a topic of vague discussion.

    And good luck to you on the matter.

  13. Petros
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    Petros Senior Member

    I have been thinking about this for a long time, almost 25 years. Actually planing pontoons have been around for a long time, but not on sailboats, but on float equipped aircraft and powered boats. On a float plane, if the pontoons do not come up on plane, the aircraft would not take-off. Clearly long skinny hulls can be made to plane, the idea that cat hulls can not plane is total nonsense. It has also been used on powered boats for quite a while as well, there have been stepped catamaran hulls on high powered racing boats since at least 1976, if not longer. The same kind of concept can be used on a fast cat or tri sail boat but the problem is when you do not have enough speed for planing, you have a VERY draggy hull in displacement mode.

    The various so-called planing cats and tri amas I think are a compromise between a fully optimized planing hull, and a more conventional one. As someone pointed out, most hull shapes when pushed through the water will generate some lift, so it is a matter of degree. The more you optimize for planing the worse the performance at displacement speeds, and visa-versa. It is even possible on a sailboat you can not even get up to planing speeds to come up "on step" if the drag of the hull is too high. So what to do?

    I have been toying with the idea of building a small lightweight cat with a fairly conventional catamaran hull shape with retractable steps (I have been developing some drawings). This would complicate the design, but would allow for a more optimum hull shape in either sailing configuration. I think small retractable planing surfaces would have less drag than lifting foils and would not be prone to damage or fowling. If it works well I might see about getting the money together for building a larger one.

    I doubt the idea itself is patentable, except perhaps as a design patent for particular shapes that are new.
    Doug Lord likes this.
  14. rapscallion
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    rapscallion Senior Member

    I found some nice info on stepped hulls in principles of yacht design. Assymetric hulls can't be tested in michlet (from the patent). I have some data on assymetric hulls from Open foam - but I'm still a open foam newbie - I wouldn't bet the farm on the results. But they seem to agree with the material in the text. Maybe a combination of foils and a non stepped hull shape would make the most sense. It seems that bu the time the hull shape is doing it's job the foils should have already lifted the hull out of that water. I sail in light air too much for a stepped hull to work for me.

  15. catsketcher
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    catsketcher Senior Member

    Its been done

    Dick Newick did design dynamic lift amas for many of his trimarans in the 80s and 90s. Ocean Surfer had the new moon amas as did a lot of the New Zealand Echos - a 36 ft tri. The Echo I built did not use new moon amas as Dick was not as convinced then (and neither were we) that the loss of volume and the increased drag was worth it. This seems to be the case with most designers who seem to go for low drag high volume hulls rather than in hull lift devices.

    Long thin planing hulls aren't as efficient as short fat ones - look at sailboards - when the hulls are planing. However a trimaran float has to work at slow, moderate and fast speeds and be slightly, moderately and deeply depressed which makes any planing design much harder to work out than a sailboard.

    If you flick through old copies of Mutlhulls (around 1985 I think) you will find a tri that had stepped hulls to create dynamic lift. It wasn't taken up by anyone else.

    Dicks boats and other tris did use canted foils to create lift. The NZ builder sailor of a 36ft Echo really liked his canted foils and said he could feel the difference when one broke. We swapped ideas back and forth on the Echo we built but didn't put them in as we had fuller amas and didn't need the lift.


    Phil Thompson
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