Hollow Sections aft On Planing Hull

Discussion in 'Powerboats' started by CADProjects, Mar 22, 2018.

  1. CADProjects
    Joined: Jun 2011
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    CADProjects Marine Design Services

    Last edited: Mar 25, 2018
  2. DSR
    Joined: Mar 2017
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    Location: Michigan

    DSR Junior Member

    Hi CADProjects,

    Just my 2 cents as an enthusiastic novice, but I was thinking that "stepping" the hull would be a more appropriate solution for your situation.
    Not only would you receive the reduced buoyancy aft that you're needing for static trim, you would also gain the benefits that a stepped hull provides in efficiency on plane that you would not get with the concave tunnels your suggesting (unless your using jet drive, of course..... :))

    Just a thought.....

    Last edited: Mar 22, 2018
  3. baeckmo
    Joined: Jun 2009
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    baeckmo Hydrodynamics

    I cannot see any aft tapering in the drawings; in what and where did you introduce taper? Concave shapes like the ones you show aft, are prone to hard slamming and should be avoided. Now, the proportions of your hull are a bit odd, and I wonder about the SOR. For instance, why is chine immersion a prime requirement as such?

    One issue with wide transoms and forward CG position is that when the CG is forward of the center of the waterplane area, there will be a nose-down dynamic trimming moment when the boat is "coming down" in a wave through, which will cause dangerous broaching. The rounded buttocks in the forward quarters will suffer from negative dynamic pressures at low angles of incidence, further increasing the problem. Take a good look at the old series 62 hulls and their "offsprings". There are versions designed both for foil applications with quite extreme forward CG, and with different bottom angles.
  4. TeddyDiver
    Joined: Dec 2007
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    TeddyDiver Gollywobbler

    Back to drawing board as it sounds as something's wrong with SOR.?

  5. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    A full plane mode hull form will not have dry chines at the transom and this is one of the most basic perimeters of understanding you should grasp at the beginning of the design phase. At this point you should have a pretty good idea what the Cp should be, a general idea about the CG and maybe a midship section shape, based of performance expectations, etc. Considering things such as concave aft sections would be discounted out of hand for obvious reasons, though if not so obvious, you need to start farther back and establish a solid SOR, develop a reasonable GA and masses schedule, so you know what type of hull you might need, instead of just guessing.
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