Keel Bulb Design Software

Discussion in 'Sailboats' started by Adam16, Nov 6, 2020.

  1. Adam16
    Joined: Nov 2020
    Posts: 5
    Likes: 0, Points: 1
    Location: Brisbane

    Adam16 Junior Member

    Hi

    I saw that there was a software section but thought this might be more appropriate to my requirement. I am looking for a some sort of design software that can determine the weight in lead for a particular bulb shape. I have a project on that requires a bulb of around 75kg but I am not sure how to go about designing a bulb and calculating the amount of lead required for the particular shape. Hopefully there might be some software that allows you to draw up or import a drawing that can calculate what weight it would be.
    TIA
    Cheers Adam
     
  2. messabout
    Joined: Jan 2006
    Posts: 3,086
    Likes: 257, Points: 83, Legacy Rep: 1279
    Location: Lakeland Fl USA

    messabout Senior Member

    Excuse the Imperial measure, if it is helpful 2.4 cubic inches of lead weighs one pound. 75 kilograms comes to about 165 pounds. So.... 2.4 times 165 suggests that 402 cubic inches of lead will do the job. (6587 cubic cm.......I think) The shape of the bulb is a whole other matter.

    If the bulb is in the shape of a streamline then the starting wild guesses is that the area of the largest section times the length amount to about two thirds the volume that you need.

    You can do the calculations manually by using Simpsons rule. Divide the length into an even number of spaces. That means that you will have an odd number of sections to fiddle with. Find the area of each of the stations, If it is a round shape the square of the radius times pi is the area of the section. Make a chart of the sections such as 1, 2, 3, etc. Place the area of the sections in the chart. Now multiply that area, of each of the sections as follows. . The first multiplier will be One the second will be four, the next will be two. continue to use the two and four multipliers until the next to last one which will be four, the last one will be one.. Your multipliers will look something like this..............1,4,2,4,2,4,2,4,2,4,2,4,1 Take the sum of all the multiplications. Multiply the sum by the distance between the sections. Divide that product by the constant three. The equivalent will tell you how many cubic inches or cubic centimeters of volume that you have measured.

    Forgive my clumsy explanation please. Doing the arithmetic is not nearly as complicated as it sounds. Easy with a hand held calculator. I think it is fun, but then some think that I am a nutcase. If you have access to a program such as Solidworks, or similar, you can do the math in a few seconds. Otherwise do it the hard, fun way, like the old time NAs had to do.
     
    Rumars and jehardiman like this.
  3. jehardiman
    Joined: Aug 2004
    Posts: 2,803
    Likes: 365, Points: 83, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    Not so much wild guesses if you use Pappus's Second Theorem. Draw the half shape for the bulb you want. Find the area (A) and the centroid (c) from the axis of revolution. Volume = 2*pi*Ac. For "most" streamline shapes A= 0.707 rl, where r is the radius and l is the length and c = .42 r. So Volume = 0.59*pi*r^2*l...give or take for the first turn around the design spiral. The largest section is pi*r^2 and the largest section*length is pi*r^2*l; then messabouts's "wild guess" is 0.66*pi*r^2*l.....near enough.

    Edit corrected.... no "2*" in the calculation of messabout's volume...
     
    Last edited: Nov 6, 2020
  4. jehardiman
    Joined: Aug 2004
    Posts: 2,803
    Likes: 365, Points: 83, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    Wait... did I just fark that up?
    ....yes, but no...
    Largest section is pi*r^2...but messabout (and my math) is correct... Volume = 0.66*pi*r^2*l
     
  5. jehardiman
    Joined: Aug 2004
    Posts: 2,803
    Likes: 365, Points: 83, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    Ok people...let this be a lesson...don't drink and text...
     
    Ad Hoc likes this.
  6. Earl Boebert
    Joined: Dec 2005
    Posts: 378
    Likes: 49, Points: 28, Legacy Rep: 302
    Location: Albuquerque NM USA

    Earl Boebert Senior Member

    The Q and revintage like this.
  7. Adam16
    Joined: Nov 2020
    Posts: 5
    Likes: 0, Points: 1
    Location: Brisbane

    Adam16 Junior Member

    Hi Due to illness I have not got back to this since I first posted, I would like to thank all for your posts on this matter. Now to start working through the solutions, Oo

    Thank you guys
     
  8. Adam16
    Joined: Nov 2020
    Posts: 5
    Likes: 0, Points: 1
    Location: Brisbane

    Adam16 Junior Member

    Thank you
     
  9. Adam16
    Joined: Nov 2020
    Posts: 5
    Likes: 0, Points: 1
    Location: Brisbane

    Adam16 Junior Member

  10. Adam16
    Joined: Nov 2020
    Posts: 5
    Likes: 0, Points: 1
    Location: Brisbane

    Adam16 Junior Member

    Thank You
     
  11. Rumars
    Joined: Mar 2013
    Posts: 858
    Likes: 333, Points: 63, Legacy Rep: 39
    Location: Germany

    Rumars Senior Member

    As messabout said, your bulb needs a volume of 6.6 liters. If you want it the really old fashioned way without math, make a wire frame of the shape you want (steel wire), cover in cling wrap, fill with water. Modify until it holds 6.6l.
    Otherwise, any software that can calculate the internal volume of the desired shape.
     
  12. Ad Hoc
    Joined: Oct 2008
    Posts: 6,641
    Likes: 649, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    :rolleyes::rolleyes::rolleyes:
     
  13. Howlandwoodworks
    Joined: Sep 2018
    Posts: 72
    Likes: 16, Points: 18
    Location: Columbia MO

    Howlandwoodworks John Howland


  14. The Q
    Joined: Feb 2014
    Posts: 162
    Likes: 15, Points: 18, Legacy Rep: 21
    Location: Norfolk, UK

    The Q Senior Member

    That article along with this.. Keel and Rudder Design Methodology – Vacanti Yacht Design LLC (vacantisw.com) scan down and click on the pdf.. Were what I used to design my keel. Both the Star and my boat have limited draft, so taking advice from the articles, the latest Mader 8300 shape gives more useful aero foil on the keel and less "torpedo".

    Is my keel successful? I have no idea, first launch next spring covid and life permitting..
     
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.