Bulbous bows, ship design, etc.

Discussion in 'Boat Design' started by TollyWally, Sep 12, 2009.

  1. TollyWally
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    TollyWally Senior Member

    All this stuff about hull dynamics fascinates me. Displacement hulls, planing hulls, high speed, low speed all of it is interesting. So...

    "Ships are long relative to the wave length of the generated waves and they are relatively deep. Block coefficient is more important here, Ships are also designed for a constant Service speed and are easier to optimize. Consequently there is a lot of effort in the design of a carrier as a pressure source and a sink separated by a long parallel mid body, the relative wave generation at bow and stern are chosen carefully along with bulb design (produces a wave train out of phase with the main hull). Then there’s wake…."

    "If you’re interested there’s a lot of material we could dive into here but probably better in a new thread. There are some very good books on modern ship design."

    I'm interested, care to expand on this a bit?
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    Expand on what?...too many topics raised all at once!
     
  3. TollyWally
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    TollyWally Senior Member

    Ad Hoc,
    You're right. I quoted MikeJohns in my post, I guess I hoped he'd pick up the ball and run with it after he mentioned the thought of another thread.


    Looking back at my first post I think that, as you mentioned, I made it too open ended. I guess if I had my druthers I'd pick a discussion on bulbous bows.
     
  4. willfox
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    willfox Junior Member

    For source and sink information try and find a book on Hydrodynamics. These are mathematical models which explain the velicities of the water around the hull of the boat. The bow being the source and the sink being the stern. Such a book is Theoretical hydrodynamics by Louis Melville Milne-Thomson.

    The bulb design is important because it needs to generate an out of phase bow wave to its stern wave at the operating froude number. It is interesting to see when tank testin at a range low froude numbers (0.2-0.3) (V(m/s)/Sqrt(Lwlxg), and plotting these against resistance, a fairly subtle wobbly line is created obviously increasing with speed on the whole. These are known as resistance humps and hollows. A hollow is a smaller resistance for that Froude number. This is what a ship designer must design to to get maximum efficiency for the ship which is obviously hugely important. Humps and hollow could be found in principles of yacht design by Lars Larsson.

    As for the Block coefficient im not sure why this is more important. I guess it would be very similar to the Prismatic as the ship hull at midships is roughy a rectangle. Maybe its because it is more sensitive when designing such a full hull?

    I hope this helps a little. It is really interesting stuff.
     
  5. ivor Bittle
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    ivor Bittle Junior Member

    Bulbous bow

    I am an engineer not a naval architect. I had a look at the bulbous bow from an engineer's perspective on my website at www.ivorbittle.co.uk

    It all made sense to me.

    Ivor Bittle
     
  6. TollyWally
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    TollyWally Senior Member

    Ivor,
    I remember your site from a few weeks back. For what ever reason I still can't get the pictures to come up. It's a great pity because your site looks fascinating. I've briefly read the text but without the pictures it isn't as clear as it could be. You are to be commended for your efforts. Please feel free to comment here on this thread.

    As an aside perhaps someone wise in the ways of the internet could explain to me what it means when there is a little red x in a box in the upper left hand corner of a "ghost" picture on the net.
     

  7. ivor Bittle
    Joined: Feb 2008
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    ivor Bittle Junior Member

    Bulbous bow

    Tolly Wally,
    I am sorry to hear that you cannot get the pictures on my website.

    You will get nothing from Firefox.

    If you open using either my name or www etc. you should get the frames with three coloured dots in squares etc. in them. If you have, and you wait, the site will fill the frames.

    These artcles go up in two files, one for the text and one for the graphics. The text is opened first and then the graphics. Pictures are big files and take time to download.

    Best of luck with it.

    Ivor Bittle
     
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