a better tiki 21

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

  1. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    Guzzis3,

    What improvements can you see making to the Tiki 21?
     
  2. guzzis3
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    guzzis3 Senior Member

    The short answer is to do to polynesian style catamarans what Gary Dierking did with small proas. I don't know if you have his book but is a thing of beauty. Every detail is perfectly thought out and explained. He shows how each boat can be made many different ways and you can mix and match almost every element between the designes.

    For the tiki 21 specifically the first thing I'd do is apply 3 full sheets to each hull side. Yes this will cost a bit of ply but it will give a LOT more headroom below plus a MUCH dryer bridgedeck. The second thing is I'd eliminate as many of those fiddly detail bits that I could. Why do you make intricate hatches for the chain lockers ? You don't need to cover them at all, but if you do you can do it much more easily than that. I'd pay more attention to the nesting and materials use.

    Then I'd ditch the rig. Looks pretty but it's a pig of a thing to make and those luff pockets have issues. Try dousing that sail in a hurry when it's wet for example. I'd definitely want a downhaul.

    Take the mast as an example. I can't remember the details but Wharram gets you to build a square with triangular section timber in each corner. Then he gets you to plane off the corners and gradually plane it round. Sounds fine until you remember it's 21' long. How many hours are you going to spend on that ? Turning timber you just bought into shavings ? If you MUST make a timber mast get some poly pipe and glue some cedar strips around it until you have a half circle, infill with thickened epoxy. Take it off and build another half round. Glass the inside of each and join them. Plane and sand the outside and glass it. Done. Lighter, cheaper, easier.

    But...you'd be mad to make a timber mast. Buy a section of aluminium. Cheap light instant.

    But... the mast is about 21 or 22' long. You can get a beach cat mast that size around here for about $50-100. Use a second hand jib and have a big head battened mainsail made. Won't be MUCH dearer than the gaff sail. Rig in dyneema (my preference) and you'll have a faster boat with an easier rig to step and sail. Personally I'd use a double mainsheet and single tiller extension but again that's me..

    And those beams....those beams....

    There are all sorts of savings like that all over the boat you could make while still retaining the style.
     
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  3. guzzis3
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    guzzis3 Senior Member

    The Selway boats are extraordinarily heavy for their length. The 19 is quoted at 544kg!! What did they do ballast the keel ?

    The 254 uses a flat bottom to get more hull beam with the torturing which is a good approach, I was just thinking using a thinner ply to get more double curvature and then glassing would make a simple quick cheap rugged hull in a soft V.

    IMO the 19 is no more stylish than Mr Woods Janus or even Acorn. Personally I'd build the Woods boat before the SF boat but that's me...
     
  4. guzzis3
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    guzzis3 Senior Member

  5. RAraujo
    Joined: Apr 2010
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    RAraujo Senior Member - Naval Architect

    Best part: it says "valued at $ 23000!"
     
  6. Angélique
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    Angélique aka Angel (only by name)

    The advertiser might be a boat broker or a trader, as right now he has 14 boat ads on Gumtree.
     
    Last edited: May 28, 2019
  7. waterbear
    Joined: Mar 2016
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    waterbear Junior Member

    Adding freeboard to the Tiki hull adds more beam and less headroom than you may have imagined. I made a little diagram below to illustrate this. If you use full width panels on the hull sides while maintaining the angle of the V, the beam of each hull becomes >4ft (see #2 below). This means extra weight, and only 3.75 feet of headroom as drawn (assuming a 10 inch wide floor). If we reduce the V angle to narrow the beam (#3), we have even more wetted surface area and less headroom.

    By comparison, Janus' (#4) flat floor allows for a more efficient interior cross section, with less wetted surface area, less weight, and more useable headroom vs #2. I think this is in part why Wharram went to a chined hull with Mana (#5). FYI the Mana hull section is a very rough guess based on what I've seen in pictures. The other cross sections are to scale.


    [​IMG]
     
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  8. Angélique
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    Angélique aka Angel (only by name)

    For angle plus width and height estimations some Mana 24 parts from the many build pics....

    [​IMG] [​IMG] [​IMG] [​IMG] [​IMG] [​IMG]
     
    Last edited: May 28, 2019
  9. Angélique
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    Angélique aka Angel (only by name)

    Gary Baigent just posted about tortured ply hull side thickness 3 - 4 - 4.5 - 6 mm, and glassing plus carbon reinforcements, on the thread Historical Multihulls in post #1327.
     
    Last edited: May 28, 2019
  10. redreuben
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    redreuben redreuben

    Gary Baigent is a tortured ply artiste !
     
  11. guzzis3
    Joined: Nov 2009
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    guzzis3 Senior Member

    Hi,

    Thank you for the diagrams. I am not sure what you are saying in some of it so I'll go into more detail and we can sort out what I am confused about.

    Chined dory rounded hulls all have lower wetted surface. I assume that is a given. V hulls are not a good choice for a fast boat. I have been thinking about V hulls just to keep somewhat close to the Wharram idea and particularly the belief that a V hulls is easier to build.

    So specifically what I envisaged was higher hull sides with about the same 3' beam. I had thought of straight hull sides like Hinemao, no rounding at all, but I was also wondering about moving to thinner ply more glass and as much bend as you could get to make the floor wider and maybe wetted surface less.

    However lets just look at the taller straight V.

    4' sides and 3' beam yields an angle of 44 degrees. Earlier Wharram boats like Raka and Tane used this narrower angle because Wharram thought 45 degrees would produce a faster boat than 60 degrees. Eventually he dumped it realising the 60 degree boats were about as fast. So at 12" draft the width at the waterline is about 14" at 60 degrees. I'm not going to do a proper displacement calculation as I don't have time atm but the cross sectional area is 84 sq inches. Quick calculation same area requires 14.4" depth at 44 degrees, so 2" deeper. That will increase skin friction but it will also make the effective area of the keel bigger for leeway prevention. You get about 44.5" vertical from keel to shear. So another 10" of cabin and you have 4'6" full sitting headroom. Obviously you can add a floor although I wonder if 10" is necessary ? but as you say any width of floor will be higher in the narrow V.
     
  12. guzzis3
    Joined: Nov 2009
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    guzzis3 Senior Member

    I really need to sit down one day and read that historical multihulls thread. I have always been interested in the evolution of the modern multihull, especially some of the dead ends people went down. I love the obscure...

    Your posts on CSK are really interesting. That boat "foamy" ? looks smaller than any CSK I have seen before.

    On the freedom 8 yes I think he's a broker. He has listed it on ebay australia with a low starting price so it will be interesting to see where it gets to. I would think that boat in that condition is maybe a $10k proposition but what would I know...

    As many have said here before building hull skins is a small part of a total boat build, but it seems to balk a lot of people. If you want to build a tiki 21 size cat and make it a nice thing I'd probably not go for V hulls. In fact I wouldn't go for ply at all. At that size I think I'd look at strip plank. You could make beautiful hulls relatively quickly with really no compromises, then get on and build the rest of the boat, but I was thinking of trying to keep it as similar to the Wharram starting point as I could. Maybe the perception of simplicity is more important than actual simplicity.

    Anyway just random thoughts.
     
  13. Angélique
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    Angélique aka Angel (only by name)

    The 1960 CSK Pattycat is listed 27' (8.23 m), that's the smallest one I saw on their site, except maybe the ‘‘Foamy’’ that Warren Seaman was building . . ?

    [​IMG]
    CSK 27' Pattycat, 1961 pic
     
    Last edited: May 29, 2019
  14. Angélique
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    Location: Belgium ⇄ The Netherlands

    Angélique aka Angel (only by name)

    Couldn't resist to post, 1965 - 43' (13.12 m) CSK World Cat launch...

    [​IMG]
     

  15. redreuben
    Joined: Jan 2009
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    redreuben redreuben

    “Apparently “ CSK boats hobbyhorse as much as Wharrams do so your really only stepping sideways.
    I think the solution could be to restyle a Woods boat to the Wharram look. Naked women optional.
     
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