Floating crane design. The following report presents an over view of a floating crane design that based on a small laboratory pontoon. The model pontoon is to represent the floating crane. Starting from the experiment to observe the circumstances under w

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Contents

Aim.........................................................................................................

Objective.................................................................................................

Apparatus................................................................................................

Method....................................................................................................

Theory.....................................................................................................

Results and analysis...............................................................................

Prototype crane design...........................................................................

Evaluation...............................................................................................

Appendix.................................................................................................

Aim

The following report presents an over view of a floating crane design that based on a small laboratory pontoon. The model pontoon is to represent the floating crane. Starting from the experiment to observe the circumstances under which a floating body is unstable then to compare the observed results with the theoretical prediction. Then collecting the data through the laboratory tests to determine the location of the cg of the unloaded pontoon and finally designed a full size (prototype) crane to a linear scale of 50.

Object:

  1. To investigate the stability of a floating vessel.
  2. To compare the observed results with theoretical predictions.

Apparatus:

The apparatus consists of an open metal pontoon (‘barge’) which floats in water and carries a mast figure1.a plumb-bob suspended from the mast provides a means of measuring the angle of inclination of the barge. The vertical position of the centre of gravity is controlled by a weight WV which may be moved to different heights on the mast. The horizontal position of the centre of gravity is controlled by a second weight WH (weight of sliding jockey =P) which may be moved to different horizontal positions on the barge. The following information is necessary: length of pontoon length l= 0.360 m, pontoon width b= 0.203 m and pontoon height = 0.0765 m. Total weight of pontoon assembly used= 2830 g which is equal to

2830/1000 =2.83 kg                                              

2.83 × 9.81 = 27.7623 N

pontoon

                                          Vertical movable weight                   Jib        

                                                                               figure 1             plumb-bob                                               jockey                  water tank

Method:

  • Fill the tank with water and insert the floating body (pontoon).
  • Utilising a known movable weight positioned on the deck at approximately the middle of the longitudinal centreline and a pendulum hanging inside the vessel.
  • The weigh(jockey) W is moved from the centreline a known distance (δx)towards the side and this moves the centre gravity of the pontoon from centreline to a new position
  • This causes the vessel to tilt,the angle of tilt (δθ) is being measured by the pendulum.

In order to obtain a good accurate laboratory readings

  • Centralized jockey weight correctly, the plumb bob line was central and the bob was not snagging on the scale.
  • When the jockey weight moved by each X distance two students measured the length and three students measured the resulting angle of inclination θ on the scale to minimize the error causes as a result of different eye sight and took the mean of the reading.
  • During the experiment two students plot the graph and another two rechecked it in order to make sure the graph is linear.

Theory:

The floating object is stable when the metacentric height MG is positive, i.e., the metacentre is located above the centre of gravity; else it is unstable.

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The distance between the centre of gravity and the point of intersection of line of action of buoyancy and symmetry axis, is a measure of stability. The point of intersection is referred to as the metacentre, M, and the distance between the centre of gravity and the metacentre is called the metacentric height MG

 google image (figure 2)

The position of the metacentre is not governed by the position of the centre of gravity, it merely depends on the shape of the portion of the body under water.

The metacentric height is computed from measured dimensions as:

MG = MB ...

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