Bow Shape

Discussion in 'Sailboats' started by SuperPiper, Aug 23, 2013.

  1. SuperPiper
    Joined: Jan 2003
    Posts: 362
    Likes: 5, Points: 18, Legacy Rep: 58
    Location: North Of Lake Ontario

    SuperPiper Men With Little Boats . .

    I did a search of threads with keywords BOW SHAPE in the title. Zero matches. Has this not been discussed here?

    Here is the question. Are plumb bows faster, or are they just faster for a given LOA? If there is no rule constraints, are plumb bows faster than sloped bows? Cruise ships are built with sloped bows. There must be some advantage. If you were designing a boat from scratch and there were no limitations, would you design it with a vertical bow or a sloped bow?
     
  2. Doug Lord
    Joined: May 2009
    Posts: 16,643
    Likes: 315, Points: 93, Legacy Rep: 1362
    Location: Cocoa, Florida

    Doug Lord Flight Ready

    I would lean toward a reverse bow depending on the boat and the purpose of the boat because I like the looks. The A Class cats pioneered reverse bows/wave piercing bows way before anyone else. In that class they've been proven to work in combination with bow volume down low. There are several threads(boatdesign and multihulls) on bow shape.
    What shape bow do you like?
     
  3. SuperPiper
    Joined: Jan 2003
    Posts: 362
    Likes: 5, Points: 18, Legacy Rep: 58
    Location: North Of Lake Ontario

    SuperPiper Men With Little Boats . .

    Not everybody thinks plumb or dreadnaught bows are in vogue.
     

    Attached Files:

  4. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 146, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    The idea of a ship designed with "no limitations" is too wide to be
    very useful.

    From a resistance minimisation point of view it might lead to weird
    knobbly shapes like Ward's Optimum Symmetric Ship (search for them on
    this site: there are some pictures in a few threads).
    Or you will get canoe-like bodies similar to long thin rowing shells.

    Or you will end up with strange multihulls or pressure distributions:
    "Diamond Tetrahull"
    http://www.cyberiad.net/waketet.htm

    Hovercraft
    Free-surface pressure distributions with minimum wave resistance
    E.O. Tuck and L. Lazauskas, ANZIAM Journal, Vol. 43, 2001.
    http://www.cyberiad.net/library/pdf/tl01.pdf

    Multihulls
    Optimum spacing of a family of multihulls
    E.O. Tuck and L. Lazauskas, Schiffstechnik, Vol. 45, No. 4, Oct 1998,
    pp. 180-195.

    Unconstrained ships of minimum total drag
    E.O Tuck and L. Lazauskas, Dept. Applied Mathematics Technical Report,
    The University of Adelaide, Dec. 1996.
    http://www.cyberiad.net/library/multihulls/multipep/multipep.htm
     
    Last edited: Aug 24, 2013
  5. michael pierzga
    Joined: Dec 2008
    Posts: 4,862
    Likes: 115, Points: 0, Legacy Rep: 1180
    Location: spain

    michael pierzga Senior Member

    If you need the longest waterline in relation to LOA, use a plumb bow, plumb stern.

    If you want a good boat you choose to shape the ends to perform a job......for instance provide bouyancy, knock down waves, increase foredeck area, handle ground tackle....

    The modern, style driven, trend of plumb bows creates a very unseamanlike boat
     
  6. SuperPiper
    Joined: Jan 2003
    Posts: 362
    Likes: 5, Points: 18, Legacy Rep: 58
    Location: North Of Lake Ontario

    SuperPiper Men With Little Boats . .

    Leo, I quickly scanned through the technical references you provided and I didn't see any bow profiles.


    That is what i suspect too, Michael. For example, when J-Boats launched the J109, they had the freedom to select any bow shape but stuck with a near-vertical bow. They could have called the boat the J110 and given the bow a more sloped entry.

    Is vertical faster?
     
  7. michael pierzga
    Joined: Dec 2008
    Posts: 4,862
    Likes: 115, Points: 0, Legacy Rep: 1180
    Location: spain

    michael pierzga Senior Member

    Yes and no. When fully powered a Long water line will be the fastest. Fine entry forward will be the fastest.

    But in the end..what is fast ? And what do you want the boat to do.
     
  8. Ad Hoc
    Joined: Oct 2008
    Posts: 6,454
    Likes: 530, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

  9. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 146, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

    You need to do a bit of digging yourself to get the shapes...

    You will need to find the photos of Ward's Optimum Symmetric Ships. The
    size and location of the bulbs and other "wobbles" depend on the deisgn
    Froude number. There are some Michlet input files that have the offsets for
    one of them.

    The offsets of the diamond tetrahulls are available as an example distributed
    with Michlet. Sideviews are a trapezoidal shape; sections are unusual
    SWATH-like shapes (actually they are special cases that include Cassini ovals).

    The hulls for "Unconstrained ships of minimum total drag " have parabolic
    waterplanes, semi-elliptical cross-sections, and parabolic sideviews
    (buttocks).
     
  10. SuperPiper
    Joined: Jan 2003
    Posts: 362
    Likes: 5, Points: 18, Legacy Rep: 58
    Location: North Of Lake Ontario

    SuperPiper Men With Little Boats . .

    Hey Leo, you seem to have this stuff at your fingertips. Can you post a few images for me?

    Thanks.
     
  11. Leo Lazauskas
    Joined: Jan 2002
    Posts: 2,696
    Likes: 146, Points: 63, Legacy Rep: 2229
    Location: Adelaide, South Australia

    Leo Lazauskas Senior Member

  12. Mike Graham
    Joined: Feb 2013
    Posts: 67
    Likes: 6, Points: 0, Legacy Rep: 54
    Location: Maryland

    Mike Graham Junior Member

    Unfortunately, hull design has a lot of local minima -- drastically different characteristics and optimum designs occur for different requirements. For a lot of low speed vessels, a sloped bow can make it easier to have more arrangeable space with a smaller waterplane area with no real drawback. A bulbous bow makes sense on a large displacement hull optimized for one speed but makes no sense for a small boat. A bluff bow may increase drag greatly for one hull but drastically improve performance for many styles of planing┬╣ hulls. A very fine bow might improve drag and seakeeping, but at the cost of increased scantling weight and greenwater problems. Inverted bows and really weird bow shapes have shown to outperform others in certain circumstances.

    So the answer is "It depends". There is no optimal hull design for a given length. Speed, purpose, weight impact, operational conditions, etc. all impact the actual hull design. What is optimal in one case isn't optimal in another to a frustrating degree.

    Plumb and inverted bows are certainly underutilized. Opposition when they are hydrodynamically and space optimal often involve concerns that are mostly aesthetic or unrelated to normal operation.

    ┬╣People here are fond of pointing out the word "planing" doesn't mean anything clear, but I'm not about to let a small thing like meaninglessness stop me. The same applies to my use of "displacement".
     
    2 people like this.
  13. gonzo
    Joined: Aug 2002
    Posts: 14,265
    Likes: 584, Points: 123, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    A plumb bow and stern is the best approach for a rowing shell that will operate in flat water only. A surf-boat requires flare and rake to make it over the waves and to keep from broaching and pitchpoling on the way back to shore. It really depends on the intended operation.
     
  14. SuperPiper
    Joined: Jan 2003
    Posts: 362
    Likes: 5, Points: 18, Legacy Rep: 58
    Location: North Of Lake Ontario

    SuperPiper Men With Little Boats . .


    Good dialogue. It's starting to make sense now.
     

  15. michael pierzga
    Joined: Dec 2008
    Posts: 4,862
    Likes: 115, Points: 0, Legacy Rep: 1180
    Location: spain

    michael pierzga Senior Member

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.