buttock angle ?

Discussion in 'Boat Design' started by frank smith, Mar 31, 2011.

  1. frank smith
    Joined: Oct 2009
    Posts: 980
    Likes: 14, Points: 28, Legacy Rep: 185
    Location: usa

    frank smith Senior Member

    I notice a great variation in buttock angle of sail boats . It look as though there are trends that change with time. There is the obvious consideration of making a smooth transition from midships section to the stern . And this will change with the water plane shape and draft.

    What are some of the things that effect
    the buttock angle.

    Thanks Frank
     
  2. TeddyDiver
    Joined: Dec 2007
    Posts: 2,589
    Likes: 125, Points: 73, Legacy Rep: 1650
    Location: Finland/Norway

    TeddyDiver Gollywobbler

    Fr number and Cb for instance.. Smaller buttock angles are typical for semiplanning and planning hulls and then also the other "numbers" related to speed of particular design change accordingly..
     
  3. frank smith
    Joined: Oct 2009
    Posts: 980
    Likes: 14, Points: 28, Legacy Rep: 185
    Location: usa

    frank smith Senior Member

    So a shallow draft hull with a high Cp will end up with a steep buttock angle ,
    unless the aft sections are very wide ?
     
  4. daiquiri
    Joined: May 2004
    Posts: 5,373
    Likes: 255, Points: 93, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    You also have to consider that, besides being determined by purely hydrodynamic or internal accomodation considerations, trends in sailboat hull shapes have been heavily influenced through years by various handicap rating systems and by designers' efforts to carve a maximum advantage out of them.

    You can find a nice summary of how these rules have changed the shape of hulls from 19th century to present days in this site: http://www.sailtexas.com/handicaparticle.html
     
  5. frank smith
    Joined: Oct 2009
    Posts: 980
    Likes: 14, Points: 28, Legacy Rep: 185
    Location: usa

    frank smith Senior Member

    daiquiri , thank for the link. My reason for the question is an interest in a shallow hull with high initial form stability , like the junk or barge type boat. In particular I am looking at the work of Bolger , Griffiths , Hunt, and also the presto type sharpie.
     

  6. jehardiman
    Joined: Aug 2004
    Posts: 3,097
    Likes: 595, Points: 113, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    Where are you looking to measure the buttock angle?....

    A barge could be said to have low buttock angle or a high buttock angle depending on where you take the measurement.

    As Daiquiri said, buttock angles have much more to do with the intended use of the hull than with the age of the hull. So a low capacity shallow water sharpie may have a 2-4 degree buttock angle at the aft waterline, where as a high capacity canal boat of the same length may have a 90 degree one at the aft waterline.
     
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.