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Under Keel Clearance(UKC)

the distance between the deepest

point of the vessels hull

and the sea bed

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The OOW shall check prior to arriving at

positions where minimum UKC is expected,that the calculated UKC is valid for thecurrent conditions.

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In determing the UKC, the following factors mustbe considered:

1. The effect of Squat.

2. Environmental conditions (height of swell, tidalheight & range, changes in the density of waters).

3. The vessels size and handeling caracteristics,and increase in draught due to heel.

4. The reliability of ships draught observationsand calculations.

5. The accuracy of Hydrographic data and tidalpredictions.

6. Reduced depths over pipelines.

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Minimum UKC for various areas of navigation:

1. Open Sea - minimum 6 meters2. Narrow Channels - 15% of the deepest draught

3. In Port Navigation - 10% of the deepest draught

4. Alongside Berth - Minimum 0,50 meter

UKC calculations shall form a part of theVoyage Plan, and the OOW shall have a copy

of the UKC calculations available when arrivingat the location where UKC considerations mustbe observed.

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Maneuveringshallow water

1. Coast Guard regulations define shallowwater as a ratio D/T of less than 2 forassessing maneuvering characteristics.

2. The shallow water depth typically refers to1.2 times ship draft.

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Signs that a ship has entered shallowwater 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 forwardend of the ship.

5. Ship becomes more sluggish to manoeuvre - Toquote a pilot, almost like being in porridge.

6. Draught indicators on the Bridge or echo-sounders will indicate changes in the end draughts.

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Signs that a ship has entered shallowwater conditions can be one or more of

the following:

7. Propeller rpm indicator will show a decrease:

If the ship is in open water conditions, this decreasemay 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 maybe up to 35%.

If the ship is in a confined channel such as a river or acanal then this decrease can be up to 75%.

9. The ship may start to vibrate suddenly. This isbecause of the entrained water effects causing thenatural hull frequency to become resonant withanother frequency associated with the vessel.

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Signs that a ship has entered shallowwater conditions can be one or more of

the following: 10. Any Rolling, Pitching and Heaving motions will

all be reduced as ship moves from deep water toshallow water conditions.

11. The appearance of mud could suddenly show inthe water around the ships hull say in the event ofpassing 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.