Trimaran Design Concept with longer foils than the main hull

Discussion in 'Multihulls' started by boradicus, Jun 3, 2013.

  1. jamez
    Joined: Feb 2007
    Posts: 500
    Likes: 27, Points: 28, Legacy Rep: 231
    Location: Auckland, New Zealand

    jamez Senior Member

    There is quite a bit of material on Malcolm Tennants float-forward designs in this thread (and what looks like the germ of an idea for Gary's SID). http://www.boatdesign.net/forums/multihulls/nz-trimaran-demon-tricycle-25170-2.html

    The Wild Thing was probably Malcolms most well known tri design, following on from earlier experiments with Demon Tricycle and Firebird (built around a GBE hull). He designed a bunch of more conventionally configured tris as well, but was best known for his GBE, Tourisimo and Bladerunner cats.

    http://www.tennantdesign.co.nz/index.php?page=wild-thing
    The Australian wild thing looks to have had the float bow overhang removed or re-shaped (its hard to tell if the overhang is still there from the pic) - maybe someone can confirm what was done?? Pic of Careless Intent for comparison. The boat under sail is the NZ built Firebird.
     

    Attached Files:

  2. upchurchmr
    Joined: Feb 2011
    Posts: 2,898
    Likes: 100, Points: 63, Legacy Rep: 579
    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    It would be very interesting to know why the red Wild Thing might have had the bows shortened.
    Some quirk of handling?
     
  3. boradicus
    Joined: May 2013
    Posts: 171
    Likes: 2, Points: 0, Legacy Rep: 10
    Location: USA

    boradicus Senior Member

    Welcome, Jamez :)

    Those are some great pictures :)

    I think the forward amas concept is interesting. Sid has some smaller amas and I wonder if their placement has something to do with manoeverability and handling. One thing I happened to notice about tricycle land vehicle designs is that usually the most stable design is to have the two outlying wheels forward.

    I suppose the design is the same for land and sea in that respect because you have road frictional resistance on tires and water frictional resistance on your amas and your primary hull and the forward motion is the same.

    I wonder if placing the middle hull closer aft would have a positive correlation to better handling?

    UpChurchMr: It could well be that the difference in hull length caused him to change his design. That makes me wonder, if you could save mass and water-plane area by having a forward dagger for control. I have seen sails set forward of hulls, so I suppose it can be done...?
     
  4. jamez
    Joined: Feb 2007
    Posts: 500
    Likes: 27, Points: 28, Legacy Rep: 231
    Location: Auckland, New Zealand

    jamez Senior Member

    Hi Bora,
    I wouldn't over analyse what was really just an attempt to increase the diagonal stability of what were (for their size and time) very light racing designs, to enable them to be pushed harder in a breeze. I (regretfully) have never sailed on one, but Careless Intent has been sitting on the hard at Orakei for about 3 years now. Still looks like a mean machine.

    The designers thoughts re. handling are attached to post 18 in the Demon Tricycle thread.

    Sids floats only need to be big enough to support the boat in light winds - then the foils take over.
     
  5. boradicus
    Joined: May 2013
    Posts: 171
    Likes: 2, Points: 0, Legacy Rep: 10
    Location: USA

    boradicus Senior Member

    Foils and floats

    I didn't realize when I was reading about Sid that he had foils as well. Are the foils on the amas and on the body?

    I didn't realize it until I began reading it, that the first few of chapters of the Marchaj are basically leading up to the fact that due to several factors, such as decreased WSA and decreased heeling angle, that multihulls are both less resistant to drag and can carry more sail due to increased stability (already intuitively known). But it is kind of nice to see the theory behind the stability. This brings up an interesting question of which is more detrimental to speed, WSA or heeling angle (which also increases WSA as downward force is applied - and lost as forward moving force - while heeling).

    One one hand, you have trimarans that have vertically angled amas, so that on a heel, one side lifts out of the water and reduces WSA, but it looks like on the designs where there is little angle, that there is more possibility for wave resistance hitting the hull even if it is lifted up - not sure. Intuitively, I would think that the force lost from heeling angle would cause less speed reduction than increased WSA..

    The other question would be how much sail can you carry using short floats versus full length hull amas (or longer) due to increased stability. It would seem that forward floats, would increase the stability diagonally on broad reaches and on runs, but a full hulled ama would make up the difference on beating windward, etc, I suppose...?

    Proas seem to do well, and I wonder if this is due to not needing a lot of bouyancy on the ama to resist downward heeling force; therefore, the lighter, smaller, but longer than a float proa ama can maintain good resistance to heeling and therefore lateral stability and greater sail carrying power, while keeping the mass of the vessel and the WSA very low.

    The other factor seems to be that WSA has less resistance longitudinal to the direction of motion than it would due to lateral currents, but since you can't control the latter with respect to the wind, in actuality it probably doesn't even matter.

    Perhaps with a shorter main hull, you will have greater resistance to heeling force from the ama, and more sail carrying advantage as a result (except perhaps on a run). But in order to take advantage of this, it would seem that you would have to compensate by keeping the mast vertical with respect to the angle of heel. I know that masts cause turbulence in themselves, but I wonder if anyone has designed a rig that has low mast turbulence and at the same time has a vertical wire off of the mast to which the leading edge of the luff is attached and can be controlled so that it remains perpendicular to the angle of heel?

    This would be interesting, because if a flexible rod were also attached to the top tip of the mast, a Gunter rig could be set (more efficient from what I am reading) and furled flat. Toward the top of the sail this would seem more feasible to accomplish due to the fact that there is less sail area to resist vertically against, and therefore a smaller, bendable mast section would be more feasible.

    But there would also be the important lever action of the trimaran to consider with the main hull acting as the fulcrum. So, there would seem to be a need for the greatest bouyancy at the point of the fulcrum in order to benefit from larger amas; so in essence what you would have would be a cat with a center fulcrum, which would largely be unmanned and used solely as the fulcrum. If this is the case, it might be interesting to look at lighter, leaner mid mull, but not necessarily a shorter one. A cat with an inflatable mid fulcrum hull??? Hmm.
     
    Last edited: Jun 17, 2013
  6. Gary Baigent
    Joined: Jul 2005
    Posts: 2,966
    Likes: 105, Points: 63, Legacy Rep: 509
    Location: auckland nz

    Gary Baigent Senior Member

    Bora, Sid has very short, low buoyancy floats/amas with J foils to provide the foil assist.
    The Three Devils sketch (see jpeg) is an extrapolation of Sid but with long float amas, two beams, shallow ama freeboard, almost semi-circular in cross section, plus foils. Just an idea. Nothing "concrete" has been done.
    Both these designs are unrelated to the Tennant overlong float, Wild Thing/Demon Tricycle type of trimaran.
    Two sailing mates, Jacques de Reuck and Andrew Bogle, have sailed/owned a Wild Thing design named Taranui (built in the Bay of Islands by Max ? - sold to Australia now) - Jacques commented that doing a Coastal Classic on Taranui, he thought the float freeboard was too shallow, not enough buoyancy because it was always hard pressed. My thoughts are the overlong and needle shaped ama bows, didn't/don't actually stop the overloaded ama bow from being pressed under or slowing down a pitchpole. Okay, will help a little. IMO, needs foils to lift and steady the platform. Foils are God. This will piss many off - that's why I posted it.
    But remember Malcolm designed these boats long before the high buoyancy float tris appeared from France - and the French designs all carried foils as well. So he was first to do it - and he also put asymmetric daggers, (but vertical) in the floats. All that was required was to angle them 30-40 degrees and Wild Thing would have really made a reputation for itself then.
     

    Attached Files:

  7. boradicus
    Joined: May 2013
    Posts: 171
    Likes: 2, Points: 0, Legacy Rep: 10
    Location: USA

    boradicus Senior Member

    That's interesting about Wild Thing. I would not have guessed that the longer amas would be shallower, but it might be that they are carrying more weight as a cat would carry it but not designed to do so. The French have a lot of innovations. Their navy was a close rival to GB's back during the Napoleonic Era, but of course they were no match for a sea faring nation like GB. If you live on an island, you're more likely to have many hours at sea over and above nations with less coast line for the land area. At least you would think this - and apparently it is true. The Philippines have their proas, which are decently advanced, and they are mostly islands.

    I still like my lever action cat idea =)! Anyway, I don't mind casual coffee shop conversations - as long as they are fun =) Have a cuppa =) ! ! !
     
    Last edited: Jun 18, 2013
  8. boradicus
    Joined: May 2013
    Posts: 171
    Likes: 2, Points: 0, Legacy Rep: 10
    Location: USA

    boradicus Senior Member

    It seems very quiet in the forums these days. I have not posted a lot recently myself due to the fact that I have been studying more than posting. I am still not ready to create a hull to simulate the theoretical design that I was interested in uncovering more about, but I have been adding to my base of knowledge so that I can eventually investigate this design further. Right now I am going back to study some math that I missed along the way. My next mini project is to create a small program to spline points together with a polynomial that I can then calculate the distance for. I have the algorithm, but I need to buld a GUI to enter the point into. I think it would be cool to use some slider controls for the x-coordinates of the points and use a uniform distance for incrementing the y-coordinates along the y-axis. Anyway, I certainly have enjoyed this forum, even despite some argumentativeness - that as someone pointed out earlier is paltry in comparison to what has happened in threads other than this one. Nevertheless, it is too bad that people don't seem to be as active as they once had been - well at least on my subscription threads.. Has anyone begun any new project boats (a bit off topic)?
     
  9. redreuben
    Joined: Jan 2009
    Posts: 1,688
    Likes: 80, Points: 48, Legacy Rep: 349
    Location: Beaconsfield Western Australia

    redreuben redreuben

    Well bora you might get a better response to the above from the software forum ?
     

  10. boradicus
    Joined: May 2013
    Posts: 171
    Likes: 2, Points: 0, Legacy Rep: 10
    Location: USA

    boradicus Senior Member

    I just found the software forum and posted something :) I guess I was a little sad at seeing the thread get cold - thank you for your suggestion! :)
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.