Superstructure design factors

Discussion in 'Boat Design' started by Radenpm9, May 29, 2018.

  1. Radenpm9
    Joined: Jun 2015
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    Location: UNITED KINGDOM

    Radenpm9 Junior Member

    Hi all,

    I am curious about the factors influencing the superstructure design.
    According to the Ship Resistance and Propulsion book by AF Molland, Stephen R Turnock and Dominic A Hudson, the superstructure shape will contribute to the air drag/resistance (Ra) that expressed by:
    Ra = (1/2) ρ Cd Ap (Va^2)​
    where ρ : air density
    Ap : projected area perpendicular to the relative velocity of wind to the ship
    Va : relative wind velocity
    Cd : Drag coefficient (please see attachment for each shape, credit to the book authors)​
    Drag superstructure.jpg

    I often find the superstructure design of fast craft has forward slope (no.4 on Cd image) that produce larger resistance than backward slope (no.2, 3 & 5 on Cd image), if I assume the other factors are the same.
    For example the daughter craft (DC) design from Palfinger Marine and Delta Power while I also find backward slope from Delta Power (white circled, image credit to manufacturers).
    PALFINGER_MARINE_Daughter Crafts_FRSQ850_A_Series.jpeg
    IMG_1304.jpg

    Delta Arctic Phantom DC.JPG

    Anyone has thought why did the designers choose forward slope rather than the backward one? Moreover they chose it for fast craft that requires less resistance.
    Any other factors contributing the design choice of superstructure?
    Thank you.

    Kind regards,
    Raden
     
  2. Ad Hoc
    Joined: Oct 2008
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    Location: Japan

    Ad Hoc Naval Architect

    Hi Raden

    The choice of rake (angle), as it is called on the front tier of either the deckhouse, superstructure or wheelhouse is dictated, ostensibly, by 2 main factors:-

    1) Regulations.
    Some clients refer to local regulations,where wheelhouse windows are to be raked between 15-25 degree fwd - to prevent glare etc. (You can see this in the MCA Workboat code).
    2) Fashion
    Everyone has their own wave of the pencil over the front of the vessel to create a "style".

    That's pretty much it.

    Although on rare occasions, it may be dictated by a structural reason.
     
  3. Radenpm9
    Joined: Jun 2015
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    Radenpm9 Junior Member

    Hi Ad Hoc,

    Many thanks for the correction, rake, I will remember it. :)
    Also, thank you for your insight. Learning the code soon

    Style - this is the thing that I still don't quite understand and sure how to cover the subject since I learn engineering. To the best of my knowledge many design studio employs industrial designer/interior architect/architect. It is also interesting for me to learn the design style. Have you got any suggestion?

    Kind regards,
    Raden
     
  4. Ad Hoc
    Joined: Oct 2008
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    Location: Japan

    Ad Hoc Naval Architect

    Start designing and sketching...different size vessel...monohulls and catamarans. Then see how the lines, the style, the 'shape'...plays a role.

    Just pencil and paper is sufficient...and by design, i mean...shapes...not number crunching.
     

  5. Radenpm9
    Joined: Jun 2015
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    Location: UNITED KINGDOM

    Radenpm9 Junior Member

    Interesting, I will do my best!

    Thank you
     
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