Can a CPP be reversed permanently

Discussion in 'Props' started by philrich1979, Nov 19, 2013.

  1. philrich1979
    Joined: Nov 2013
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    Location: United Kingdom

    philrich1979 New Member

    I have just joined a 60m ex navy vessel as engineer. The vessel is now being converted into a yacht

    The boat originally had CPP units. During this refit shes has had 2 new main engines driving a reversible gearbox.

    The original propellers were kept, but locked in a full ahead position.

    I have doubts about whether this should be done, I think there may be too much thrust when engaging astern, which may cause damage to the shaft seals.

    Does anybody have any experiance doing this? Or any theories of how the vessel might handle?
  2. johneck
    Joined: Nov 2011
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    Location: New England

    johneck Senior Member

    How was it locked ahead? The thrust load may be greater since the pitch ratio is probably higher than it normally would be astern, but I doubt that is a major issue. What might be an issue is the force required to hold the pitch.
  3. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    First, what is the thrust block rated for? Then ask the KT, KQ, questions. FWIW, a CCP only has one maximum efficiency point. If the original design is not at the new RPM to load point, everything is going to be worse, and it would be better to go back to solid shafting with a new optimum fixed wheel.
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