How to do Ship Stability Calculations successfully

You will learn about different conditions of stability.

You will learn how to calculate the GM of a vessel, how to calculate list for single and multiple weights and how to calculate free surface effect. You will also learn how to interpret GZ curves.

This online training for Deck Cadets is aligned with the Standards of Training, Certification and Watchkeeping (STCW) and the UK MCA / Scottish Qualifications Authority (SQA) Level 7 Ship Stability: An Introduction unit.

This learning can be used to study and prepare for:

  • Ship Stability: An Introduction assessment
  • SQA Stability and Operations assessment
  • UK MCA Orals assessment
  • Interview preparation.

You can see the contents of what is contained in this unit in the contents list below, and subscribe here.

  1. Draught Calculations
  2. How Loadlines Work
  3. How to Complete a Load Line Calculation
    1. Subscriber Content
  4. Loadline practice questions
  5. Transverse Stability
  6. Calculating KG and GM when loading, shifting and discharging weights
  7. KG and GM practice questions
  8. Suspended weight Calculations
  9. Suspended weight practice questions
  10. Calculating List on a Vessel
  11. Single Weight Shift Problem
  12. Single Weight Loading Problem
  13. Calculating List for Multiple Weights
  14. List practice questions
  15. Free Surface Effect
  16. Longitudinal Stability
  17. Change of Draught for a Single Weight Shift
  18. Change of Draught for a Single Weight being Loaded
  19. Change of Draught for a Single Weight being Discharged
  20. Multiple Weight Problems
  21. Trim practice questions
  22. Ship Stability Definitions
  23. UK MCA & SQA Ship Stability Booklet
  24. UK MCA & SQA Ship Stability Formulae Sheet
  25. The Different Conditions of Stability
  26. Interpreting GZ Curves
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Draught Calculations

To complete draught calculations, we need to use the ship’s hydrostatics to find MCTC, LCF and LCB.

MCTC is the trimming moment that is required to change a vessel’s trim by 1cm. It is found in the vessel’s hydrostatics and it is the amount of trimming moment that is needed to change the vessel’s trim by 1cm, but not the draught.

How Loadlines Work

When a vessel is going to sea, a vessel must be loaded to the loadline that corresponds to the region she is in. When she is loading in dock water, she can submerge these lines, as when she goes out to sea, her draught will decrease as she rises up in the denser water.

The diagram below shows the different load line marks, as well as the formulae to be used and the measurements. Note that the centre ring should be in line with the Summer load line.

Load line marks are measured from the top of each load line to the next. If a calculation starts at the bottom of the load line mark, you need to add on 25mm.

Ship’s load line, showing fresh and salt water marks for tropical, fresh water, winter and winter North Atlantic. There are also calculations to show how to calculate between each of the different load lines.

How to Complete a Load Line Calculation

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