small catamaran plans needful

Discussion in 'Multihulls' started by pulsar, Aug 9, 2006.

  1. pulsar
    Joined: Aug 2006
    Posts: 32
    Likes: 1, Points: 0, Legacy Rep: 30
    Location: Poland

    pulsar Mechanical engineer

    Is there anybody who can tell what is better for catamarans: symetrical or asymetrical hulls?, or mayby for small cats (about 5 meters) it's not important?

    Peter
     
  2. frosh
    Joined: Jan 2005
    Posts: 621
    Likes: 14, Points: 0, Legacy Rep: 44
    Location: AUSTRALIA

    frosh Senior Member

    Symmetrical hulls or not?

    Hi Peter, you can't say that one is better than the other, just different. You need to understand the reasons for use of a particular shape.
    Tornado hulls, classical semicircular symmetry underwater is designed for racing, and minimum wetted surface area in relation to buoyancy.
    Hobie 16, very assymetrical, combined with huge keel rocker means that reasonably good lateral resistance is achieved without daggerboards. This is ideal for sailing in surf and coming and going from beach to shore.
    The Tornado has substantial daggerboard area which is essential for it's excellent windward peformance. The Hobie 16 goes upwind quite well but is not considered an all out speed machine around the race course. However it must be right for a lot of people as hundreds of thousands have been sold and it has been inducted into the sailing hall of fame in the US. :)
     
  3. pulsar
    Joined: Aug 2006
    Posts: 32
    Likes: 1, Points: 0, Legacy Rep: 30
    Location: Poland

    pulsar Mechanical engineer

    Thanks again Frosh.

    :)
     
  4. cleblanc
    Joined: Dec 2004
    Posts: 26
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Sept-Iles, Quebec, Canada

    cleblanc Junior Member

    Here is a view of a symmetrical hull with an integrated fin:

    Nacra 570
    [​IMG]

    Nacra Blast (more modern fin integration)
    [​IMG]

    I have sailed four type of beach catamaran:

    Asymmetrical hull: Hobie 16 and Prindle 16

    Symmetrical hull with integrated fin : Nacra 5.7 (see also Dart, Nacra Blast)

    Symmetrical hulls with daggerboard : Nacra 5.2 (see also A-Cat, Most F-18, F-20)

    Symmetrical hulls with rotating centerboard: Mystère 5.5 (Also Prindle 18-2, Tornado)

    On the race course, the symmetrical hull catamaran with boards have the best result.

    In everyday sailing, drag racing on a beam reach, performance is similar...

    Personally, I really enjoyed all of these boats but the boardless boat were more reliable and easier to sail.

    The major difference is on an upwind beat. Catamaran with boards will point higher and go a little faster. On a race course this makes alot of difference.

    The other difference is beaching and grounding. I have beaches very often with boardless cat and it is very easy. On a boat with daggerboard, you can really damage your boat.

    My current project is to build the P95 from K-Design. A 9.5 m asymmetrical catamaran.
     
  5. Ikarus342000
    Joined: Mar 2007
    Posts: 32
    Likes: 3, Points: 0, Legacy Rep: 47
    Location: FRANCE

    Ikarus342000 Ikarus342000

    Duo 425

    Hi,

    I am Bernd Kohler, the designer of the DUO 425. Normally I do not join in forums. But here I found it necessary to comment.
    From the DUO 425 are now 1380 plans are sold. The sail the world over.

    There was never a problem with masts "ripped out" of hulls or even a broken mast. It is a matter of sound engineering. I was sailing once for Fieste ( a place on the Adriatic sea in Italy ) our DUO in a force 10 wind. It was fast, wet, fun and the boat was still in the same shape afterwards.
    Why not compare wind surfers and catamarans ? I have had many wind surfers who where heading in an other direction, so they had not to amid they could not "catch" me.
    Do not get me wrong. The boat has a weak spot. The boat needs wind. Because in this extreme a-symmetrical configuration, the boat has a relative big wetted area. On the positive side to this, the boat can be build by a dedicated amateur in about 120 hours.
    So my advice, lay in the sun on the comfortable trampoline when there is not much wind and go sailing when others go home, because it is to much wind for them.

    Cheers

    Bernd
     
  6. svfrolic
    Joined: Mar 2007
    Posts: 29
    Likes: 1, Points: 0, Legacy Rep: 10
    Location: Annapolis, MD USA

    svfrolic Junior Member

  7. pulsar
    Joined: Aug 2006
    Posts: 32
    Likes: 1, Points: 0, Legacy Rep: 30
    Location: Poland

    pulsar Mechanical engineer

    I have bought plans of DUO 425. I have made some changes to the project. Mainly I will use one mast with 10 msq windsurfing sail. I have also changed the way of connecting hulls (beams are mount on deck). Project is very simple and take more or less as Bernd says 120 hours. I have only problems with epoxy, I haven't used it before...


    Some interesting tips I found on www.thebeachcats.com

    Peter
     

  8. Ikarus342000
    Joined: Mar 2007
    Posts: 32
    Likes: 3, Points: 0, Legacy Rep: 47
    Location: FRANCE

    Ikarus342000 Ikarus342000

    Duo 425

    Hi Peter

    The good thing in building your own boat is that , if careful done, you can make changes to your own taste. It is a pity that you have changed the rig. Because with the low centre of effort of the biplane rig the boat can be sailed with a lot more wind and as a consequence would be a lot faster. Good choice to put the beams on the deck(s). When I would re-design the boat I would do the same.
    Yes, I know to work with Epoxy is not easy in the beginning. Stay cautious when work with this otherwise great material. By the way, I posted a picture of a DUO 425 here at the boat forum from a DUO 425 who is now 15 years old.

    Cheers

    Bernd
     
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.