consideration of the CATZOC within the UKC calculation

CATZOC values should be considered for paper charts and for ENCs as well because:

Firstly, according to VIQ 7

4.5 Are the deck officers’ familiar with the operators Under Keel Clearance policy, able to demonstrate satisfactory UKC calculations for the last voyage and is the policy comprehensive?

Under keel clearance can be affected by several factors and the underkeel calculations should include, but not necessarily be limited to;

• The predicted height of the tide;
• Changes in the predicted tidal height, which are caused by wind speed and direction and high or low barometric pressure;
• Nature and stability of the bottom - i.e. sand waves, siltation etc.;
• Accuracy of hydrographic data, (References to reliability is often included on charts or in the form of CATZOC on ENC's)* ;
• Change of water density and the increase in draught due to fresh water allowance;
• The vessel's size and handling characteristics and increase in draught due to heel;
• Wave response allowance, which is the vertical displacement of the hull due to heave, roll and pitch motions;
• The reliability of draft observations and calculations, including estimates of hogging and sagging;
• Reduced depths over pipelines and other obstructions.

*consideration of the CATZOC should be captured within the UKC calculation or policy.

Secondly, in the case of paper charts, to asses the reliability of paper chart bathymetry data mariner shall have a look at a Source Diagram.