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Difference between "Brake Holding Capacity" & "Brake Rending Point"

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  • Difference between "Brake Holding Capacity" & "Brake Rending Point"

    Can anyone help me with this? We just went through a pre-CDI meeting onboard and only I could provide a half correct answer (regarding BHC but not rendering) as far as the Capt was concerned.

    Thanks in advance.

  • #2
    I'm not 100% sure of Rending Point, but to rend means to tear. I suppose that means the holding capacity is the maximum safe load it can hold and the rending point is the amount of force you can apply to it before it can be damaged.



    • #3
      Brake Holding Capacity

      The value of the brake holding capacity in relation to the size of line is important; there would be little point in a mooring system where the line parts at a load less than the brake holding acpacity. Brakes should have a holding capacity of about 60% of the breaking load of the wire, which will permit slippage before the wire breaks.

      This factor should be considered when renewing lines and reference should be made to the ship’s specification or appropriate drawings.

      It should be remembered that the brake holding power is always greater than the heaving power, and that once the brake starts to slip (render) it is impossible to heave in unless the forces causing the slippage are reduced.

      Render and Heave

      Whatever the power source, all mooring winches will be affected to a greater or lesser degree by a characteristic known as “Render/Heave Ratio”. The term “Render” is defined as the force required to turn the winch in the opposite direction when set to heave with the driving force applied.

      With hydraulic and electric driven winches, the render value is constant but with steam winches the render value varies.

      It should be noted that the heaving power is always less than the render force and it is thus impossible to heave in after a winch has rendered unless there is a change in the forces acting on the moorings.

      Many ships are equipped with self-tensioning winches with the intention of eliminating the need for line tending. These are designed so that a specified line tension can be pre-set, and the winch will render (pay out) when tension in the line exceeds this value, and will recover (heave in) when it is less than this value.

      However, experience has shown that the use of such winches whilst the ship is alongside is not a safe practice because the winch restraint is limited to its render load, which is small compared to what it can hold on the brake. It is possible for the winches at opposite ends of the ship to work against each other when an external force caused by either wind or current or both is applied to one end so that the ship could ‘walk” along the jetty. In the simple illustration given by Fig. 2 a ship is shown moored by one line at each end.