Sailing catamaran parameters

Discussion in 'Multihulls' started by terhohalme, Apr 10, 2008.

  1. terhohalme
    Joined: Jun 2003
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    Location: Kotka, Finland

    terhohalme BEng Boat Technology

    Hi all catamaran designers,

    I added a spreadsheet of catamaran parameters. It is a collection of simple equations from physics, design books and ISO standards to "solve" a sailing catamaran. Just input some dimensions and ratios and you have all other main dimensions on one simple sheet. There are two other sheets in workbook to estimate Texel and Multi2000 ratings.

    Yes, I know there is no formula for a perfect sailig catamaran, but this leads you closer at the first shot. I tested it with many catamarans from Heavenly Twins and Wharrams to modern cruisers and to Med Club and Playstation and found decent results.

    Try, test and enjoy. Comments are wellcome (just study first...)

    Terho

    http://www.boatdesign.net/forums/downloads.php?do=file&id=42
     
  2. Nordic Cat
    Joined: Jan 2008
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    Location: South of Copenhagen, Denmark

    Nordic Cat Senior Member

    Hello Terhohalme,

    an impressive piece of work!

    I seem to have a problem changing the figures? Only the yellow fields are variable it seems. Am I doing something wrong?

    Some explanations, or even better, a sketch showing where to take the measurements would be very helpfu, as some of the designations are not clear for me, not being a proffesional designer.

    Regards

    Alan
     
  3. terhohalme
    Joined: Jun 2003
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    Location: Kotka, Finland

    terhohalme BEng Boat Technology

    Yes, you are right, only change the yellow fields, they are input. Others are calculated values. If you like to see the equations, turn off the sheet protection. The protection is on to prevent the user to distroy the sheet accidentally.

    There are some hints in shells with a red corner. Use google or books to find the terms (something to do yourself, too).
     
    2 people like this.
  4. lazeyjack

    lazeyjack Guest

    yar jar Mr Finn man
    nice, have some rep points
     
  5. masalai
    Joined: Oct 2007
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    Location: cruising, Australia

    masalai masalai

    Thanks terhohalme, downloaded for future reference
     
  6. terhohalme
    Joined: Jun 2003
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    Location: Kotka, Finland

    terhohalme BEng Boat Technology

    1 person likes this.
  7. Nordic Cat
    Joined: Jan 2008
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    Location: South of Copenhagen, Denmark

    Nordic Cat Senior Member

    Hi Terho,

    I tried inputting my design data, this is for a bi-rig cat, there seems to be some issues. Will you have a look please, and tell me what I did wrong??

    Thanks

    Alan
     

    Attached Files:

  8. terhohalme
    Joined: Jun 2003
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    Location: Kotka, Finland

    terhohalme BEng Boat Technology

    Input Bas again, it was text, not a number.
     
  9. terhohalme
    Joined: Jun 2003
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    Location: Kotka, Finland

    terhohalme BEng Boat Technology

    For bi-rig, double your J and E, not the height. If you have no jib, input foretriangle ratio to 0 %.
    Did you noticed that Length/beam ratio is (lenght of hull)/(beam between center lines)?
     
  10. Nordic Cat
    Joined: Jan 2008
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    Location: South of Copenhagen, Denmark

    Nordic Cat Senior Member

    Thanks.

    Can't input J and E,so I played around with the Rigging size ratio and boom length to include wing mast areas, and get the right total square meters in sail area.

    I must say I'm impressed! Alot of the numbers add up quite well, compared to the actual figures we are using.

    I have used the formulæ that Multihull Dynamics use to give an idea of performance relative to other designs. They calculate "performance index" and some other figures. These show a performance index of a bit more than 1,0. Your predictor is a bit lower at around but as you say, it is not the best possible speed you use. It shows 8,9 knots average in 10 knots wind.

    Are your daggerboard sizes for one or 2 boards? They seem big for only one.

    I think this is a nice tool, to get you started when designing a cat, you dial in some numbers and get an idea of where you will be.

    Thanks alot Terho.

    Regards

    Alan
     
  11. terhohalme
    Joined: Jun 2003
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    Location: Kotka, Finland

    terhohalme BEng Boat Technology

    The daggerboard area is assumed to 1.5% of nominal sail area. Perhaps 1.0 % was enough? It is corrected though by term (10/LWL)^0.5 to decrease proportional area at faster (longer) boats. Mayby this is not necessary. Any thoughts?
     
  12. Nordic Cat
    Joined: Jan 2008
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    Location: South of Copenhagen, Denmark

    Nordic Cat Senior Member

    I just redid my area calculations, yoor sheet suggests 4,4 m2 daggerboard area, and mine are 3,8 m2. My chord is 0,9 and you suggest 1,18m.
    My sailarea is quite high at 160m2 with no jib, so that may be the reason.

    I have a big deviation in rudder area because i have input the rig ratio very high to get the correct sail area. When I input actual rig height, I get comparable figures to yours.

    I have seen suggestions that rudder and daggerboard area should be around 2,5% of wetted area seen in profile. How did you get to your parameters?

    Regards

    Alan
     
  13. terhohalme
    Joined: Jun 2003
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    Location: Kotka, Finland

    terhohalme BEng Boat Technology

    If you take off the sheet protection, you can see the formula in shell.
     
  14. mallia.s
    Joined: Sep 2009
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    Location: Malta - Europe

    mallia.s Junior Member

    Parameters for single hulled vessel

    Hi,

    Could the parameters be adapted for a single hull vessel? I am currently studying a fishing boat hull (about LOA: 6-7m) and how its characteristics be altered for improved seakeeping.

    Any help would be GREATLY appreciated.

    Steve
     

  15. terhohalme
    Joined: Jun 2003
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    Location: Kotka, Finland

    terhohalme BEng Boat Technology

    Sorry, these are only for catamarans.
     
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