Adding strakes to the soft bottom inflatable hull

Discussion in 'Boat Design' started by decrepit, May 9, 2016.

  1. decrepit
    Joined: May 2016
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    decrepit New Member

    I'm a layman with boat terminology and I only vaguely understand the definition of fluid dynamics. However, I've noticed a difference between RIB inflatable boat hulls and SIB inflatable boat hulls, which is that SIBS don't have strakes. The SIB hull has higher drag because it's made of rubbery fabric. The surface of the bottoms are quite smooth (not the pvc tubes themselves, as they're a bit rough), so aside from the non-rigidity, the surface is high drag, and I'm under the impression that the purpose of strakes is to reduce drag. I'm wondering:

    1) Do strakes have to be rigid to perform?
    2) Can the SIB hull be improved with strakes glued to the hull?
    And 3) if so, how essential is shape? There are rubbing strakes glued along the keels on these boats, and I assume they'd cut drag. If trimmed and glued in the position of the strakes on RIB boats, would they function?

    I'm also referring to the inflatable boats with inflatable keels, as in the link - not the completely flat bottom ones. The inflatable keels create the v hull shape, so I don't see why you couldn't add strakes to the bottom and have them do what strakes are supposed to do.

    Thank you for your opinions.

  2. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    No, the lifting strakes won't help on a soft bottom. Ribs are deep vee bottom boats with tubes on the sides. They are designed completely differently than soft bottom boats.
  3. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    The boat is basically too flat bottomed for the strakes to work, anyway (in reducing wetted area), even if it were a rigid bottom.

  4. SukiSolo
    Joined: Dec 2012
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    SukiSolo Senior Member

    Those small inflatables are better with the slot in internal ply panels holding the beam and reasonable air pressure in the keel part AFAIK. Much better than the true flat and unsupported versions....;)

    Check the inflatable keel pressure, as usually it is a bit higher than the side tubes, to help hold the profile. If your going to use it for 'high' speed work (relatively speaking for a small inflatable), a proper small RIB with glass or aluminium bottom would be a better choice. Some are remarkably small - 2 meters or so. Any stuck on strakes, on a 'soft' version, would be interesting when you fold it up for the winter....;) let alone retaining any (necessary) accuracy when actually moving on the water.

    BTW strakes on the hull that direct water flow are NOT rubbing strakes which would be protective edging on the outermost part of the tubing.
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