a better tiki 21

Discussion in 'Multihulls' started by guzzis3, May 7, 2019.

  1. 23feet
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    23feet Junior Member

    Nice design. If it was 23 feet it would be my next boat.

     
  2. rwatson
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    rwatson Senior Member

    It looks like Wharram has already designed a better Tiki, the Mana 24.
    It has a whole lot of better ideas, including more internal room, all CNC cut with tabbed building connectors, skeg keel, solid deck, better outboard pod

     

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  3. guzzis3
    Joined: Nov 2009
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    guzzis3 Senior Member

    I have had a chance to look at someone else's T21 plans. At first glance I Thought Wharram had done a better job but as I looked harder I started to see all the same problems. It is true the hull sides are easy to make but then it descents into chaos. Many little parts to make, and yes each is simple but there are lots of them. A good example is the mast since you mention the rig. Trust me there are easier ways to make a mast. Wharram himself mentions on the drawing that he tried to avoid the proper use of a plane. and the Gaff! The beams have already been mentioned above. Take a good careful look at the Woods approach and the Wharram approach. Mr Woods achieves a stiffer and more durable beam with far less effort material and skill.

    James Wharram has reputedly sold more plans than any other multihull designer. He has also been at it longer than just about anyone so that helps the total. I am in no position to argue that completion rates are higher, I don't know. What I do know is a vast number of Wharrams have rotted away, that many were built not to plan and many of those were properly awful boats (you can't blame the designer for that I guess, although wharrams seem to attract more of that than other designers). Even those built to plan are disappointing boats with terrible resale.

    My GUESS is people PERCIEVE Wharrams as easier to build and so have a go. I am confident however if you did a proper time and motion study building a Wharram and another good similar cat design you would find there is pretty much nothing in it.

    It is true you can save a lot of money on a home built rig compared to a factory built new one, but second hand masts and sails are cheap. Here for cats under 30' I can buy second hand spars for less than the materials to make a mast out of timber.

    As I have said before the trick to a great boat design isn't in the hull lines. Anyone can draw a hull that works. The real trick is in the details both for build-ability and use.

    Someone previously said the nesting in the 21 was good. I heartily disagree. There is a significant amount of ply wasted AND things like the aft decks are 2 pieces joined. There were no nesting programs in 1984, in common use anyway, but you can do the same thing with paper templates. I would of course take a slightly different approach and use a few more sheets of ply to make a higher boat. Slightly more cost but a MUCH more comfortable result, and virtually no extra labor. I believe the T21 isn't that low because he wanted to minimize ply sheets. It follows his long held practice or building cats with really low freeboard. He has a fascination with windage and no concern about the bridgedeck being awash.

    Anyway I'm drawn into Wharram bashing again and I didn't really want to do that. They are what they are and if people want to embrace that great. I just thought that with some consideration the Tiki 21 could be improved.
     
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  4. guzzis3
    Joined: Nov 2009
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    guzzis3 Senior Member

    Except it is only available as an outrageously expensive kit, not plans. Have a look at the prices!
     
  5. Angélique
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    Angélique aka Angel (only by name)

    The Mana 24 keeps popping up here, see eg. post: #2#4#5#10#13#77#79#80. . . .
     
  6. Angélique
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    Angélique aka Angel (only by name)

    It might be too far off for this thread, so I've posted some info and links about Choy Design and C.S.K cats on the thread Historical Multihulls in post #1324. They're based on Polynesian style voyaging canoes, and in the 1940s Choy Design/C.S.K cats were in existence way before Wharram started selling cat plans in the late 1950s. If anyone knows or find a Choy design/C.S.K that suits this thread, please post it here, as I don't know how small they went...
     
    Last edited: May 26, 2019
  7. Noel Fuller
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    Noel Fuller Junior Member

    Back in the day when everyone here in Auckland with a multihull actually knew me a bit, quite a few people in search of more accommodation built multihulls without the prescribed daggerboards and of course found their boats were 'dogs' to windward, poor to tack and heavy on steering. For these I prescribed plates fixed to their kelsons, with lots of fairing so they stayed put, situated below the centre of pressure of the sails, and not so long as to make going about difficult again. In every case owners who did this reported noticeably better performance to windward, in going about and easing the load on the rudder. As they also saw this plate as a shoe to sit on and worried a bit over sitting on a stone, they tended to make them narrower than I thought best. Anyway a 24 ft Wharram got results, the owner said, from faired planks about 3 ft long, about 2 inches thick, extending little more than 2 or 3 inches either side of the kelsons. I was never in a postion to observe or measure change in performance for myself but owners said these boards work. It's an easy improvement to make. As far as I know no one actually did experiments to optimise the gain in lateral resistance. I even saw a few years back a large Crowther with a full length skeg and a full length plate which I consider was overdoing things a lot and suspected would be rather hard to put about. I don't know what he thought when I introduced myself and suggested shortening it!
     
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  8. redreuben
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    redreuben redreuben

    Keelson plates sound like Bernd Koehler’s vortex generators.
    I’ve yet to see any really convincing evidence that this approach works at any degree of efficiency
     
  9. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    How would you improve it, lengthen it?
     
  10. Angélique
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    Angélique aka Angel (only by name)

    In post #82 as I understand it Noel talks about added horizontal plates extending 2" ~ 3" to both sides on both keelsons, Bernd Kohler's anti-vortex panels are
    triangular and upward angled mounted on only on the inside of the flattened V bottoms on both hulls.

    On Bernd's KD 860 the anti-vortex panels were first the only leeway resistance option he offered for this cat, but now on the KD 860 page 1 it says, plus a pic from page 2 ...

    ‘‘ . . . . For windward performance the boat has, depending on your choice, anti-vortex panels, a single dagger board in the port hull, and my favored solution a center dagger board under the bridge deck. . . . . ’’

    ‘‘ . . . . The dagger board can be equipped with an automatic, so that these turns back to prevent damage to the hull. . . . . ’’ - ? ?

    Maybe it's an pivoting centerboard, or a dagger with a replaceable/resettable shear construction, maybe on the aft side of its casing . . ?

    [​IMG]

    If the anti-vortex panels worked well to generate leeway resistance, then I'm wondering why Bernd added the daggerboard options to the KD 860 plans.





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    For reference Bernd Kohler's vision on anti-vortex panels and lift theory as published on the K-designs website at the download section.

    PDF Bernd Kohler K-designs Anti-Vortex Panels

    [​IMG] thump from page 8 of 11 in the above PDF

    PDF Bernd Kohler K-designs How Boards & Rudders Work - Lift Theory

    [​IMG] pic from page 1 of 14 in the last above PDF
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    As I understand it in post #82 Noel talks about added horizontal plates, 2" ~ 3" extending to both sides on both keelsons, of which the outside of the leeward plate might be working as a chine runner, as supposed to be on Matt Layden's small shallow draft flat bottomed monos...

    Blog: Building an Enigma 460 - Chine Runners on

    [​IMG]

    P.S. - I've reshuffled the text a bit, and added some.
     
    Last edited: May 26, 2019
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  11. Noel Fuller
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    Noel Fuller Junior Member

    Absence of evidence is not evidence of absence. However, a dagger board is more effective for sure, I've perused the literature on Bernd Koehler's approach since you mentioned it. At the time when I considered endplates for lateral resistance at a point of balance, wings on keels had been introduced by Aussies in the America's Cup and the AYRS had featured shallow water sailing in a Tornado cat with Tee boards in the daggerboard slots. Another eample I can give involves a block of flats bridging a couple of Tennant U section hulls with the dagger boards not included. The owner asked my advice on balancing his rudder as he always had enormous weather helm. I told him his rudder was already balanced and in danger of breaking because of being the only point of lateral resistance. However, the boat had two tiny skegs in the right place. I suggested he make endplates about 5' long and about a foot wide with fillets to improve attachment to the skegs. He did make boards for testing. While at anchor in a small harbour a diver went down and fastened the boards to the skegs, not very securely, for the windward leg back to Little Shoal bay just west of the harbour bridge in the Waitemata Harbour. They set off in a fresh SW and were amazed at how high they were sailing relative to the past and the absence of weather helm. Partway back one of the boards detached very suddenly. The boat immediately lost 5 degrees of heading and had weather helm again. They were convinced.

    My little foiler, Sabrina, also designed for mudflat sailing was not suited to this approach. An end plate on one of the Bruce foils increased lateral resistance that side but reduced righting moment effectively disabling the boat. For amusement I include a cartoon suggested by me and rendered by artist David Barker that depicts the Block of flats to the right, its skipper being the bloke with the axe on the committee boat. Gary Baigent with his then cat is depicted centre left. I'm shown in one of the research models I made, while a small Wharam is heading off to sea. This was the notice of the Annual General Meeting of the Auckland Multihull Sailing Association (AMSA) July 1979. IMG_20190527_104001 (2).jpg
     
  12. Angélique
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    Angélique aka Angel (only by name)

    I'm guessing the outside of the leeward improvised end plate on the LAR keel did most of the leeway resistance work, was that the one that broke off . . ?
     
    Last edited: May 26, 2019
  13. Noel Fuller
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    Noel Fuller Junior Member

    I have it in my mind that was the board but the weather board was by no means inactive bearing in mind the mass of the cat. It stayed on.
     
  14. guzzis3
    Joined: Nov 2009
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    guzzis3 Senior Member

    Excellent contribution but I have never seen a CSK much smaller than 30'.

    I don't mind what people want to discuss but I'm reluctant to wade into leeway resistance after THAT thread on bridgedeck centerboards. :D

    Say you wanted to torture the hulls and get a rounded V what do you all think about using 4mm ply and skinning it both sides in say 400 gsm 45/45. You could tape the hulls outside, sheath inside, torture then sheath outside. ok 4mm is less than ideal thickness as core but the hull skins should be stiff enough ? You could probably get away with a rot resistant exterior grade ply... just a random thought...
     

  15. Angélique
    Joined: Feb 2009
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    Angélique aka Angel (only by name)

    The kinda extreme tortured ply Selway Fisher 26¼' Cat 254 (post #14) is build with 6 mm hull sides...

    [​IMG] - [​IMG]

    ‘‘ . . . . The pre-shaped sides are simply stitched to the bottom and epoxied at a set angle. The 6mm sides are then pulled up producing a round sectional shape. This gives a very light but stiff hull which simply uses bunk tops and shelves as longitudinal stiffening. . . . . ’’

    The Selway Fisher Cat 19 might be a competitor for the Tiki 21 already . . ?
     
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