catamarans vertical clearance

Discussion in 'Boat Design' started by Brian.Lin, Nov 27, 2017.

  1. Brian.Lin
    Joined: Aug 2006
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    Brian.Lin Junior Member

    dear Sir,
    how to decide the catamarans vertical clearance between waterline and wetdeck?
    I try to search information on www.
    I find following simple formula.
    a. DNV rule. HL=0.22*Lwl*(0.3-0.0008*Lwl)
    Ⅰ、Displacement catamarans : t=(0.045…0.060)L
    Ⅱ、Planning catamarans: t=(0.02…0.03)L
  2. jorgepease
    Joined: Feb 2012
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    jorgepease Senior Member

    Everyone always says don't compromise bridgedeck clearance but I see some big names at around 30" while other performance cats above 47" regardless of length.
  3. goodwilltoall
    Joined: Jul 2010
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    goodwilltoall Senior Member

    Min. 1'-0" clearance (no obtructions) for every 10'-0" Beam OA.
    fallguy likes this.
  4. JSL
    Joined: Nov 2012
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    JSL Senior Member

    A guide I got from a well known multihull designer (power and sail) was minimum of
    Disp. hull = 6 1/2% of the DWL (ie: 30' DWL = 1.875')
    Planing hull = 3 1/4% of the DWL

    As a check I looked at a 65' power cat (225 passenger tour boat, semi-disp hull form- cruise 8-10 knots) I did several years ago. Wet deck freeboard was 3.0' on a 60' DWL = 5%. Boat does harbor tours so water is usually calm.
    Last edited: Nov 28, 2017
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    These formulae are a guide, I suppose, but other factors affecting the calculation would be area of operation, slimness of hulls, vertical taper of hulls, shape of intersection of hulls with the wet deck, and provision of wave breakers. Or at least, I "imagine". :cool:
  6. JSL
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    JSL Senior Member

  7. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    They are a guide indeed, there is no rule that requires a minimum value of the air gap but, depending on the navigation area, Lwl, ... and the air gap you will have to reinforce more or less the wet deck.

  8. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Depends on the type of catamaran, its duty, role, location of operations, what is it: yacht, passenger, crew boat, fast ferry, and of course sea conditions...etc etc
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