Desirable trim

Discussion in 'Hydrodynamics and Aerodynamics' started by muthubd14, Sep 6, 2014.

  1. muthubd14
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    muthubd14 Junior Member

    Hi all.. It is said that trim by aft is desirable for a vessel..But too much trim is undesirable too.

    Could some one help me out in determining the optimum trim fr 90 m vessel operating at Fr= 0.45....
     
  2. TANSL
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    TANSL Senior Member

    If the vessel is designed with trim = 0, the optimal trim is zero.
     
  3. PAR
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    PAR Yacht Designer/Builder

    Yep, it's that time of year again . . .
     
  4. TANSL
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    TANSL Senior Member

    It is very possible but I think that "that time" will take years for them.
     
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  5. PAR
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    PAR Yacht Designer/Builder

    Very valid point my friend . . . :)
     
  6. DCockey
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    DCockey Senior Member

    So how should "optimum trim" be determined for a new design? What is meant by "optimum trim" - trim for lowest resistance?
     
  7. muthubd14
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    muthubd14 Junior Member

    yeah... The value of trim for which better speed could be achieved..??
     
  8. TANSL
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    TANSL Senior Member

    The designer should calculate the boat with a trim that makes the boat run as smoothly as possible, when operating normally. That trim, whichever it is, is defined as zero trim.
    If the ship to operate in its normal form, acquires a non-zero trim, the designer has miscalculated the ship.
    This is my opinion and, like everything, is debatable.
    You talk of better speed. What does that mean, under what conditions will be reached?
     
    Last edited: Sep 10, 2014
  9. farjoe
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    farjoe Senior Member

    we have similar questions on a newly delivered new boat whose ratings indicate that we should be faster than what we are achieving now.

    For example his polar data indicates that the optimum VMG at 4 knots true is achieved at 2 degrees heel.

    Current techniques on most boats at this speed is to send the crew to leeward to heel the boat.

    Is the data given simply the result of were his VPP achieved balance with non movable weights or is it really the best heel (lowest hull resistance) at this wind speed?
     
  10. TANSL
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    TANSL Senior Member

    Hull resistance depends inter alia on the friction (wet surface) and the formation of waves. So the heel that makes minimal these two factors will produce the least resistance.
    I am not an expert in hydrodynamics but do not think the heel improves hull resistance. However, due to other factors, may be, I donĀ“t now, the boat heeled is faster than upright :?::?:
     
  11. Ike
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    Ike Senior Member

    You are talking apples and oranges here. The original question was for a powered vessel (I think). The quoted vessel is a sail boat. Yes it is often true that a sail boat will perform better at a specific heel angle, but not a powered vessel. So which is it?
     
  12. PAR
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    PAR Yacht Designer/Builder

    I think the point is moot Peter, as it's probable his assignment is due and he's handed in his answers to his instructor by now. Ain't the net grand . . . The worst part is 10 years from now, this guy's going to pen up a 150' ferry for someplace in southeast Asia . . .
     
  13. Ike
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    Ike Senior Member

    most likely
     

  14. farjoe
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    farjoe Senior Member

    Rereading the original question, you are probably right. My question is however still a valid valid one. Maybe I should start up a separate thread.
     
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