Consider following factors in UKC assessment:

• Tide- Predicted height
• Changes in the predicted tidal height, caused by:
  • wind speed and direction
  • high or low barometric pressure
• Bottom - Nature and stability – i.e. sand waves, siltation etc.
• Hydrographic data - accuracy (often included as notes on charts)
• Water density - Change of water density and the increase in draft due to freshwater allowance
• Vessel’s size and handling characteristics and increase in draft due to heel.
• Wave response allowance - Vertical displacement of the hull due to heave, roll and pick motions.
• Draft observations and calculations - Reliability
• Hogging and sagging - Estimates
• Underwater Obstructions - Reduced depths over pipelines and other obstructions
• Bow Cushion/ Bank Suction Effect - See ‘FOM 3.30 – Shallow water effects’ for details
• ‘Smelling the Ground’ Effect - See ‘FOM 3.30 – Shallow water effects’ for details
• Squat – See ‘FOM 3.31 – Squat for details

Master shall carefully appraise the chart, nautical publications, weather, sea conditions and its effect on vessel’s hydrodynamics for above listed factors. An appropriate correction may be applied to draft if effect of above listed factors is significant.

Under Keel Clearance is required to be calculated for each leg of the passage and recorded in NAV Form 001 – Passage Plan.

NAV Form 002 shall be used for ‘UKC Calculations’ for:

• Each arrival and departure, for all ports and passage under pilotage.
• Any course leg where the depth is less than 2.5 times the vessel draft.

For vessels fitted with ECDIS:

• Check accuracy of chart data (reliability) for UKC calculation.
• Use CATZOC Consideration sheet in NAV form 002 and corrections due to reliability of survey.
• Source of Information:
  • Get latest sounding information and the nature of the bottom from the local authorities or terminal well before arrival.
  • Cross-check against other available sources such as Charts, Guide to Port Entry and Sailing Directions.

Notify Marine Superintendent to seek office approval as per FOM 3.32 for any conditions stated below:

• Vessel is unable to comply with company’s minimum UKC policy.
• CATZOC waiver is required after CATZOC calculations.
• The calculated air draft is less than 2 meters.
• Any other concerns prior undertaking the passage.
• Additional risk mitigation measures are required.

Following supporting documents are required:

• Completed NAV Form 002 - Under Keel Clearance calculation.
• Risk Assessment.
• Other supporting documents e.g., email communication from agent, port authorities, and relevant extract of nautical publications for depth data.

Include following in the cargo plan:

• UKC calculations based on depth at the berth at lowest predicted tide.
• If the height of the tide is required to maintain the minimum UKC.
• Estimate of the expected berthing window relative to the tide.
• Calculations to determine safe limits for any other restrictions such as air-draft, water line to manifold, UKC etc.

Calculate UKC for max laden draft alongside berth at High Water / Low water every day.

Cargo watch officers shall write down the actual UKC experienced in the above form at the HW and LW.

Master shall sign this form once every day.

Where the depth for a certain port is suspected, or when calling Port where UKC is less than company standard requirement:

• Take due precautions to constantly check and record the same.
• Take Manual Depth sounding at the first instance after berthing and during various stages of loading.
• Take extra precaution during final stages of loading operations.

When a ship is required to load or discharge cargo at a berth, which offers insufficient depth of water to permit the ship to lie safely afloat in the loaded or part loaded condition at or near low tide:

• The operation should be planned in such a way that company’s UKC criteria always remain in compliance.
• Liaise with the local agent and commercial operator to ensure that terminals with such draught limitations and significant tidal variations have procedures in place if discharging or loading operations over the tide are to be permitted.
• Exercise due diligence to ensure that depth data and tidal information is correct.
• Effects of squat must be anticipated due to strong tide / current when loading / discharging with small UKC clearance.
• Vessel is maintained upright and on even keel when the vessel’s draft is close to the minimum UKC. Small angles of list on wide vessels can result in large increases in draft.
• Echo sounder should always be kept ON and UKC regularly monitored.
• During final stage of loading / closing to Low water drafts to be visually monitored.
• De-ballast as soon as possible while loading and take minimum ballast while discharging to ensure maximum UKC.
• When the vessel is alongside the berth, carry out manual check of depth at six points around the vessel and verify this with the charted depth.
• Discuss with the agent and terminal representatives the contingency measures to leave the berth in case of any unsafe situation during the vessel’s stay at berth.
• Main engine should be kept standby for operation at short notice.
• Carry out a Risk assessment for the planned operation.

When discharging over tide:

• Properly estimate the time required for start of cargo operation after berthing and expected discharge rate to ensure that draft is reduced sufficiently before the low water.
• Keep contingency plan in place for removing the vessel from berth in sufficient time in case of delay in start of cargo operation or if the discharge rate is below the required rate.
• Ensure vessel is always brought bodily up taking minimum ballast i.e. even-keel to have sufficient clearance at all points.

• Be aware of and counter the effect of “SQUAT” in shallow waters.

Allow following for Squat calculations:

• expected maximum speed
• vessel-specific block co-efficient

Shallow water and Squat effects are largely dependent on the ships speed. To minimize these effects, reduce ship’s speed.

Draw up and post a table of Squat Values on the Bridge.

See ‘FOM 3.31 – Squat’ for details on the principle of Squat.

General

Minimum air draft clearance required for passing under bridges or overhead cable is:

2 metres

If calculated air draft clearances are less than 2 meters, notify Marine Superintendent to seek office approval. Following documents are required:

• Completed NAV Form 002A – Air Draft Calculation
• Risk assessment
• Other supporting documents e.g., email communication from agent, port authorities, and relevant extract of nautical publications for air draft data

High Voltage Cables

Minimum air draft clearance below High Voltage cables:

• Is decided upon by the local authorities
• Normally ranges between 2 to 5 meters
• Depends on the voltage rating of the cable.

• NAV Form 001 – Passage Plan
• NAV Form 002 – Under keel clearance calculation
• NAV Form 002A – Air draft calculation
• NAV Form 002B – UKC monitoring during cargo operation

• FOM 3.30 Shallow water effects
• FOM 3.31 Squat
• FOM 3.32 Guidance to Master for UKC and Air Draft compliance