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Formula 18 and Formula 20 Hull Design / Plans  Bottom

  • Hi, I have in mind to build my own cat. I grew up sailing Hobies 16 and A-Class cats and I would like to design an 18 or 20 ft. cat. Having spent some time in the boating industry, I have a reasonable understanding of watercraft design and building.
    That said, I would like to start from a good basis and modify a known design based on my needs and construction method. Question, can anyone suggest where I could find basic hull plans for something like the Nacra Infusion or Nacra 20C, as well as data such as center of buoyancy, Cp and basic dimensions. Alternatively if a member of the community owns one of these designs (or a similar alternative), I could come to visit to study their hull and take a few pictures for inspiration. I live in central NJ. Thank you very much for any help or good piece of advice.
  • One obvious idea that comes to my mind is a Taipan 4.9. They were originally garage built boats and I think you can still get plans. Granted though this boat is a bit smaller that what you seem to be asking for... Maybe scaling everything up 20% would be okay.
  • How about a wooden Tornado?

    https://content.instructa…0/FBWB03O9SMEP282LA0.pdf



    Edited by jack108136 on Nov 22, 2022 - 06:11 AM.
  • If you absolutely want to waste time and money, so please go ahead!

    The 5.5 hull will do nicely if you want to build a pair of F18 hulls, in need of some modernizing if you are up to it.

    https://www.catsailor.com…re-18-sq-fleet#Post28052

    --
    Brgds
    Lars

    Frankentri 5.8/5.5/Inter20
    Aerow trimaran foiler

    https://www.facebook.com/groups/1192604934176635
    --
  • I did buy plans for the Tornado for some initial analysis. I have also sailed one few years back. While I think the Tornado is absolutely amazing and possibly still the Queen of beach cats. Given the age of the design and that race courses were focused more on upwind legs and that gennakers were not around, my concern with that design is that the forward buoyancy is limited when compared to more modern designs. That is why I was looking to get more information on more modern designs, and I particularly like the Nacra Infusion and I think the scaling it to a 20 wouldn't bee too much of a stretch. Any ideas as to where I could find those plans?
  • Do you want to build a boat?

    Or

    Do you want to sail?

    The hulls are "easy". The rest of the boat is HARD.
  • I really want to do both. Building a boat is like therapy, except cheaper. So I enjoy the process and the reward you get from sailing the craft at the end. About the "rest" being hard, my idea is to use off-the shelf components that you can acquire in the aftermarket from Nacra of a few other builders (Mast, Rudder, daggerboards, beams, etc.
  • benediktI did buy plans for the Tornado for some initial analysis. I have also sailed one few years back. While I think the Tornado is absolutely amazing and possibly still the Queen of beach cats. Given the age of the design and that race courses were focused more on upwind legs and that gennakers were not around, my concern with that design is that the forward buoyancy is limited when compared to more modern designs. That is why I was looking to get more information on more modern designs, and I particularly like the Nacra Infusion and I think the scaling it to a 20 wouldn't bee too much of a stretch. Any ideas as to where I could find those plans?


    An idea I have thrown around is the Tornado general hull shape but with inverted wave-piercing bows and Nacra 6.0 daggerboards.

    For scaling the Infusion to 20', just find one and enter the dimensions into AutoCAD and you can manipulate numbers from there.

    --
    Scott

    Prindle 18-2 Mod "FrankenKitty"
    Tornado Classic "Fast Furniture"
    Prindle 19 "Mr. Wiggly" - gone
    Nacra 5.8 "De ja vu"
    Nacra 5.0
    Nacra 5.8
    Tornadoes (Reg White)
    --

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