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S A Malliaroudakis Maritime Ltd Tables and curves (MS Excel) Shallow water signs
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Signs that a ship has entered shallow water conditions can be one or more of the following: 1. Maximum Ship Squat increases. 2. Mean bodily sinkage increases. 3. Ship will generally develop extra trim by the bow or the stern. 4. Wave-making increases, especially at the forward end of the ship. 5. Ship becomes more sluggish to manoeuvre - To quote a pilot, “almost like being in porridge.” 6. Draught indicators on the Bridge or echo-sounders will indicate changes in the end draughts. 7. Propeller rpm indicator will show a decrease. If the ship is in 'open water' conditions i.e. without breadth restrictions, this decrease may be up to 15% of the Service rpm in deep water. If the ship is in a confined channel, this decrease in rpm can be up to 20% of the Service rpm. 8. There will be a drop in speed. If the ship is in open water conditions this decrease may be up to 35%. If the ship is in a confined channel such as a river or a canal then this decrease can be up to 75%. 9. The ship may start to vibrate suddenly. This is because of the entrained water effects causing the natural hull frequency to become resonant with another frequency associated with the vessel. 10. Any Rolling, Pitching and Heaving motions will all be reduced as ship moves from deep water to shallow water conditions. This is because of the cushioning effects produced by the narrow layer of water under the bottom shell of the vessel. 11. The appearance of mud could suddenly show in the water around the ship’s hull say in the event of passing over a raised shelf or a submerged wreck. 12. Turning Circle Diameter (TCD) increases. TCD in shallow water could increase 100%. 13. Stopping distances and stopping times increase, compared to when a vessel is in deep waters. 14. Effectiveness of the rudder helm decreases. 15. Width of the wake increases considerably. |
