+3 votes
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Ship-FSO-FPSO Motions Illustration

asked Jul 24, 2014 in Offshore-Upstream by josvanden (3,240 points)

The attached may give some ideas to the motions to new folks entering the offshore industry. Hope it helps.

 

commented Jul 24, 2014 by esjensen (2,720 points)
Thanks for sharing. It really does help when referring to to motions for an offshore container.
commented Jul 24, 2014 by pasmith (3,320 points)
Great illustration. Thanks.

3 Answers

+3 votes
answered Jul 24, 2014 by wozniakmic (3,460 points) | selected Jul 25, 2014 by odadmin
 
Best answer

There is a description of six degrees of motion for a ship available in wikipedia if anyone interested in learning what each means.

This is a quote from wikipidea:

  • Heave: The linear vertical (up/down) motion
  • Sway: The linear lateral (side-to-side) motion
  • Surge: The linear longitudinal (front/back) motion
  • Pitch: The rotation of a vessel about its transverse (side-to-side) axis. An offset or deviation from normal on this axis is referred to as 'trim' or 'out of trim'.
  • Roll: The rotation of a vessel about its longitudinal (front/back) axis. An offest or deviation from normal on this axis is referred to as list or heel. Heel refers to an offset that is intentional or expected, as caused by wind pressure on sails, turning, or other crew actions. List normally refers to an unintentional or unexpected offset, as caused by flooding, battle damage, shifting cargo, etc.
  • Yaw: The rotation of a vessel about its vertical axis. An offset or deviation from normal on this axis is referred to as deviation or set.

 

0 votes
answered Jul 25, 2014 by Normandy (21,040 points)
A little extra information on ship motions.

Motions that a ship experienced typically come from forces from wind, waves, and current. It is also subjected to forces generated by the ship's engines.

The ship's motions are created by reacting to these forces in order to control the ship’ stability.
0 votes
answered Jul 25, 2014 by pasmith (3,320 points)

Heaving: Heaving is the liner movement of the ship through the Z axis. It can be observed during rough weather. When large wave comes under the bottom of the ship, the whole ship will lifted up bodily, when the crest strikes & the whole ship will be lowered down bodily, when the trough forms. The ship will oscillate in liner direction. It is an involuntary non-rotary movement.

Swaying: Swaying is the liner movement through the Y axis. When a crest of wave strikes the starboard side of ship, ship will be pushed bodily in the direction of wave to port side. When a trough of wave forms at starboard side, the ship will be pulled bodily towards starboard side. Vice versa will happen if the crest strikes the port side. The ship will oscillate in liner direction. It is an involuntary non-rotary movement.

Surging: Surging is the liner movement through the X axis. When a crest of wave strikes the one end of ship, ship will be pushed bodily in the direction of wave. When a trough of wave forms at one end of the ship, ship will be pulled bodily towards the trough. The ship will oscillate in liner direction. It is an involuntary non-rotary movement.

Pitching: Pitching is the rotary movement of the ship around the Y axis. If the ship is floating in calm water, during that time the centre of gravity & centre of buoyancy are in a vertical line. If a wave crest strike the ship on bow area, the underwater volume of that particular side will increase. The centre of buoyancy, being the centre of the underwater volume it will shift to forward side.  But centre of gravity will not change because there is no change in weight so at this particular instant centre of buoyancy & centre of gravity are not in a vertical line thus creating a lever. This will cause the ship to incline to stern. When the wave crest passes to stern side vice versa will happen. It is an involuntary rotary movement.

Rolling: Rolling is the rotary movement of the ship around the X axis. If the ship is floating in calm water, during that time the centre of gravity & centre of buoyancy are in a vertical line. If a wave crest strike the ship on starboard side, the underwater volume of that particular side will increase. The centre of buoyancy, being the centre of the underwater volume it will shift to starboard side.  But centre of gravity will not change because there is no change in weight so at this particular instant centre of buoyancy & centre of gravity are not in a vertical line thus creating a lever. This will cause the ship to incline to port. When the wave crest passes to port side vice versa will happen. It is an involuntary rotary movement.

Yawing: Yawing is the rotary movement through the Z axis. When a crest of wave strikes the bow on starboard side, bow of the ship will be pushed in the direction of wave to port side. When a trough of wave forms at bow on starboard side, the ship will be pulled bodily towards starboard side. Vice versa will happen if the crest strikes the port side. The ship will rotate around Z axis. It is an involuntary rotary movement.

 

 


I read a very detailed description regarding vessel motions from Daniel Prasana so I repost it here. Credited to Daniel Prasana

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