a better tiki 21

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

  1. Manfred.pech
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    Manfred.pech Senior Member

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  2. oldmulti
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    oldmulti Junior Member

    This is interesting. Pitching is a problem with all boats but some have less than others. Fine ends are a problem on fatter hulls but according to Hugo Myers once you have length to beam above 15 to 1 fine ends are ok. With a small simple multi you need wider waterline beam to fit EG bunks and carry the loads. As Lock Crowther found out fuller ends and wider waterline beams generally ended up with a better riding boat that could achieve the same speed for a cruising boat. As long as the boat had some asymmetry fore and aft it also helped reduce pitching. The other trick was to have a wide stern but in the form of a step or scoop stern of low buoyancy that would sink into a wave in a following sea if running downwind in large seas. It has the same effect as a canoe stern downwind. But upwind a wide low buoyancy stern hull has a lot less pitching. It also helps to centralize weight. Have a look at the Tiki 25 in Sea People magazine issue 1 november 1983 page 14. (available for free on the PCA web site). It started to head in this direction but Wharram did not pursue it.
     
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  3. Angélique
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    Angélique aka Angel (only by name)

    Thanks Old Multi for the info, here's the PDF link.
     
  4. redreuben
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    redreuben redreuben

    Those two 25’ Tikis are for me the most interesting boats in the whole Wharram catalogue.
    Except they aren’t in it.
    I read the racing column till it petered out about issue 5, such a shame it all went nowhere.
    Do you think the lightweight boat was 4mm ply ?
     
  5. oldmulti
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    oldmulti Junior Member

    Redreuben. All other wharrams around this size have 6 mm ply. There is a TIKI 21 built in the Philippines with quality 4.8 mm ply skins, but the standard is 6 mm ply. The Haiti 17 is the largest Wharram that has a 4 mm ply skins. But taking the advice of Gary, experience of Tennant Bamboo Bomber and Richard woods Strider 24 (racing version) cats, a 4 mm ply skin with some compound curves and a light glass sheathing looks very possible.
     
  6. Manfred.pech
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    Manfred.pech Senior Member

    oldsailor ?
     
  7. jamez
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    jamez Senior Member

    Heres a clip of my old Hinemoa taken just before the start of the Coastal Classic back in 2008. I had just sailed through the fleet (of 239) and was trying to get a couple of klicks upwind of the start to get a grandstand view of it. Hit a big wake (there were heaps of spectator boats and the water was fairly churned up) which you can see half way through the clip. To me this demonstrates the lack of pitch dampening that is inherent with this shape (heavily rockered, double ended hull).


    This is not limited to Wharrams though. Great Barrier Express catamarans have a fairly low prismatic, heavily rockered, well rounded V hull with a transom. In certain conditions; like a sloppy steep head sea they tend to hobby horse while similar size cats with higher prismatic coefficient, less rockered hulls pitch noticably less and sail away from them.
     
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  8. Angélique
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    Angélique aka Angel (only by name)

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  9. Manfred.pech
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    Manfred.pech Senior Member

    oldmulti = oldsailor ? Welcome back home ?
     
  10. redreuben
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    redreuben redreuben

    Oldmulti and oldsailor aren’t the same guy.
     
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  11. Manfred.pech
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    Manfred.pech Senior Member

    Thank you, redreuben !
     
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