Methodology of SHIPMA use

SHIPMA relies on the use of an autopilot, which also includes a tug and thruster allocation algorithm. The choice for using an autopilot rather than hands-on steering by a pilot or Master allows the engineer to clearly judge and compare the results of different simulations on technical and physical aspects. The use of an automatic pilot in desktop simulation assures repeatability and a consistent nautical assessment procedure. The hands-on mode often seen in other models (actively steering the ship over a chart displayed on a screen) would put a civil engineer in a position where he is in fact playing the role of a pilot or Master. Alternatively, one could ask a pilot to do the runs, but the chart display offered to him is rather different from his normal sailing practice. This will jeopardise the result of the manoeuvres. Furthermore, runs have to be repeated to guarantee consistency.

SHIPMA input and output

The input of the SHIPMA model is organised through the Graphical User Interface. The Shipma GUI organises all data for a project in a hierarchical tree. A Shipma project tree consists of a number of subordinate “nodes”, each defining some aspect of the project: 
  • A set of nodes containing a description of the manoeuvre, desired track, setting of autopilot, time step, starting position, tugs etc. 
  • A set of nodes in which the ship is represented by dimensions, mass, windage area, etc. and the manoeuvring characteristics of the ship, to be expressed in hydrodynamic derivatives 
  • Nodes to describe several external conditions such as bottom level, current pattern, wind field, wave field.
Note that for this type of data Shipma offers the possibility of choosing for a simple set-up with constant wind, waves or current or to import self prepared environmental grids in which the number of grid points is practically unlimited.

The main output consists of:
  • track, position, course and heading of the ship 
  • course deviation and distance to the desired track 
  • rudder angle and number of propeller revolutions 
  • for wind and waves: direction, velocity/height and forces acting, on the ship 
  • water depth at the centre of gravity 
  • current velocities on the ship 
  • bank suction forces 
  • tug forces
The track and the output data can be plotted using D3D-Quickplot.

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