Planing Trimarans II-the real thing?

Discussion in 'Multihulls' started by Doug Lord, Jun 2, 2010.

  1. Doug Lord
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    Doug Lord Flight Ready

    Planing Trimarans II-following Parlier...

    This is more a question and is not specifically related to the "meat" of the other planing trimarans thread,which was: "can the main hull of a trimaran whose ama is partially immersed plane?" That is not the subject of this thread. Nor is this question part of this thread: " Can a trimaran ,flying the main hull, and designed with planing amas, plane?"
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    This is the question I'm particularly interested in: IF a trimaran is designed to sail most of the time with the main hull flying AND IF such a boat was designed with planing amas that plane when the main hull flys-could it be faster than a tri that does the same thing(flys the main hull most of the time) with "foil assisted" non-planing, high L/B ratio amas?
    ---a. sub-question: could this boat be designed with planing amas whose wetted surface and total drag was less than the "foil assisted" ,non-planing, high L/B ratio amas when both are flying the main hull?
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    If possible, lets try to limit ourselves to the two questions above-but any and all comments-theoretical or experience based or both- are most certainly welcome! Thanks.....
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    Pix: --Parliers hull
    --my hull
     

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  2. cavalier mk2
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    cavalier mk2 Senior Member

    Without touching the drag question which I think will take testing to answer, an advantage the foil assisted high length beam ama will have is less motion in the rig do to the softer ride which should mean more drive. The surface following ama will induce more motion to the boat and sails for a more turbulent ride don't you think?
     
  3. Doug Lord
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    Doug Lord Flight Ready

    ----------------
    I'm not so sure: on ORMA tris with long narrow hulls(ama's) and "foil assist" the foils lifted a more or less maximum of 70% of the boats weight-and often less.
    They had to let buoyancy support part of the weight so the ama could provide pitch resistance.(mostly no rudder t-foils)
    Parlier said that over 20 knots drag of his planing hulls was less than an equivalent length ORMA ama-and over 40 knots something like 4 times less...
     
  4. cavalier mk2
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    cavalier mk2 Senior Member

    The pitch is the question, if you ad t-foils to the rudder it becomes a part of a needed symbiotic design relationship and the nay sayers will try to burn the heretics at the stake again. Isolating specific design elements that are meant to work in unison can be challenging. Wouldn't a full foiler be faster ? Less drag and little pitching. More data....If it needs the rudder t-foils the other ama has to be evaluated with them too for a valid comparison , if so to save the flack you might ad them to your original question.
     
  5. cavalier mk2
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    cavalier mk2 Senior Member

    I just refreshed my memory from Yves website. I remember looking at those hulls on the catamaran thinking they would be great offwind but would suffer a penalty in certain conditions to windward with the fuller bow punching into wave tops. Perhaps a longer wavetop piercing nose ? I do like the idea though I wonder about light air speed comparisons.
     
  6. Doug Lord
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    Doug Lord Flight Ready

    ===========================
    I didn't include light air considerations of the planing ama because I think I've solved that problem: look very closely at the balsa model hull in the first post.
    To work in all conditions the solution must be something like the rotating hull pictured. I figure if leadbellies can rotate the keel surely a tri could rotate the hull.
    My question(s) deliberately ignored light air considerations as if that problem was solved.
    ----------
    For the stepped hulls I propose some sort of pitch control is required. My solution is to use small lifting foils on a daggerboard in the main hull and on a rudder in the main hull which would:
    1) be somewhat smaller than foils designed to fly the whole boat,
    2) be set up to control the pitch of the ama in the water,
    3) help the main hull to fly earlier than it would without the foils,
    4) control the angle of heel of the whole trimaran automatically by using an altitude control system that would allow the mainfoil to lift up OR pull down as required.
     
  7. cavalier mk2
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    cavalier mk2 Senior Member

    Interesting concept, the challenge is the weight and strength of the rotation mechanism and the fact that the highest loading is all cantilevered. It wouldn't be as smooth for flow but it would be considerably easier and stronger to have the stern step section be able to raise and lower. With foils for pitch control the shock loading on the amas and akas is going to be higher than the high length, beam foil combo, maybe some flex and shock absorbing in the akas ?
     
  8. Doug Lord
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    Doug Lord Flight Ready

    =========================
    There is hardly any load on the rotation system on the updated version that uses a collar around the hull just aft of the step. Allows the hull to be made in one piece....
    You're right about the shock loading-it would have to be addressed...
     
  9. daiquiri
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    daiquiri Engineering and Design

    Doug, you have basically created a hydroplane hull. There is a plentiful of experimental data on planing characteristics of these hulls at NACA Technical Reports site http://ntrs.nasa.gov/search.jsp .
    You can calculate the expected planing characteristics of your hull based on these data, and compare it with calculated characteristics of a foil designed to carry the same weight. I expect that above a certain speed a planing hull will become more efficient.

    But first take a look at this video: http://www.youtube.com/watch?v=JbOr46fV4n0
    That guy was going really fast! :)
     
  10. Doug Lord
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    Doug Lord Flight Ready

    ----------------------------------------------
    Thanks ,Slavi! Great video-and I appreciate the information.
     
  11. daiquiri
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    daiquiri Engineering and Design

    Posting some interesting test reports found on my PC. Hope you will find them useful, at least from a qualitative point of view.
    Cheers.
     
  12. Doug Lord
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    Doug Lord Flight Ready

    ================
    Thanks very much-great stuff! The planing tail is very interesting.
    Have you seen Gene Clements "booklet"-I have a copy if you're interested:
    very small single stepped hulls.
     
  13. Doug Lord
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    Doug Lord Flight Ready

    2 foils + altitude control= power + safety

    Planing amas using a stepped hull similar to Parliers design require a rudder t-foil on each hull OR a single foil on a mainhull daggerboard and rudder. These foils help the boat to take off earlier, control pitch and with a manual or automatic(wand) altitude control system they can control the angle of heel of the trimaran when the main hull is flying. Further, the system can be designed to generate extra RM as well.
    What I find most interesting is that this system is not limited to planing amas-it can be used with any ama and appears to be able to work advantageously on tris from around 18' on up. The foil system can help allow a lightweight powered up tri-a beach cat killer- that permits the crew to sit just to weather of the cockpit w/o running across the boat tack to tack or having to use trapezes.
    One catamaran designer is already experimenting with this and the potential on trimarans is just flat tremendous.
     
  14. science abuse
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    science abuse Junior Member

    I'm not on par with the expertise of the professional boat builders on this site, however I do think I can add some thing that would be, at the very least, an interesting curiosity.
    When I saw the modeled planing Ama above, I immediately saw a familiar fuselage. I beleive this sort of thing has already been thoroughly tested, though it was begun about a centrury ago and involved propellers and wings. Amphibious aircraft have long been in use of lightweight, low-drag, planing hulls. Unfortunately, I haven't come up with many good shots of anything below the waterline.
    http://apma.org.au/reference/aircraft/s6/s6a_b.html
    [​IMG]



    Obviously, having wings helps planing, though that beast up there weighed 5700lb. However, many of the design hurdles facing both Tri/Cats and the seaplanes are the same. They were even raced pretty extensively, which help spurred the designs away from the usual utilitarian/miltary uses and more toward fast-and-light.
     

  15. Chris Ostlind

    Chris Ostlind Previous Member


    Of course, making claims about a system and a performance potential, for a craft that does not exist, will always be a fun game... fact is, until you begin to produce some sort of detailed drawings about how this mechanism actually would work, it's all pipe dreaming.

    There are a lot of folks here who are deeply connected to the engineering trades as well as those who have built complex machines before. Why not take the time away from the magnificent Trapwing project to generate some satisfactory, 2D, or even 3D drawings so that you can more effectively describe the system requirements for all the members?

    I see this thing working as follows:

    Crew of two are seated somewhere within cockpit environment of the craft and remain there as claimed by designer.

    The boat is sailed away from launch site with both amas in the Conventional Trimaran (CT) mode. Sails are sheeted-in and the boat accelerates, beginning to fly the windward hull.

    As immersed ama reaches its fastest, CT, potential, crew rotates the windward ama to the PA (planing ama) mode while the skipper maintains sail trim , heading, observes sea state, wind conditions, etc. to keep the boat on max CT (somewhere around 20 knots for a boat something like 20' LOA).

    With the windward ama fully rotated to the PA mode (and locked in place, of course) the skipper alerts the crew to prepare for a tack/gybe. Tack/gybe is initiated and as the boat swings through the wind, it loses significant boat speed until the sails fill again, are trimmed correctly and the boat, once again, powers-up. The loss in speed is all part of the game for super-light craft at this size.

    Once the sails are powered-up with the boat now tooling along at 12-14 knots, the crew finds that the performance envelope of the PA hull form now immersed is not optimized for full potential in the operating regime in which they reside. As a result, the boat is unduly sluggish, resistant to acceleration and throwing tons of spray from the optimized, PA form in the water.

    Realizing that they are not going to get over the hump, they tack/gybe back to the CT ama shape, return the other ama to the CT setup and spend the rest of the day having a blast.

    Summing up...

    The boat is unlikely to experience anything like full potential in anything short of a scenario in which the wind is howling at the absolute limit of the CT design and the crew can effect blistering tack/gybe maneuvers, while rotating hulls, wrist twisting of the manual flap control, trimming sails without error, expert tiller control of the boat as it describes its arc through a tack/gybe. This is accompanied by a whole host of other nice little things such as, not forgetting to lock-down the freshly rotated ama before it is immersed.

    Yes, I'd have to say that this boat shows great promise, with but a few "little things" to sort before it might become effective half of the time it is being sailed.

    In the meantime, a much simpler and less expensive beach trimaran of the same length and sail area, which launched at the very same time, has been blasting around at high speed all day long with hours and hours of enjoyable, non-fussy sailing for both crew. Their boat breaks less, has fewer parts on which to perform maintenance, cost far fewer dollars to purchase initially and has provided a much higher use-satisfaction report than the boat with the tricked-out amas ever will.


    "Simplicate and Add Lightness"


    ~
     
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