SHIP ТО SHIP TRANSFER GUIDE (PETROLEUM)

(Third Edition 1997)

For Use with Crude Oil and Petroleum Products

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Chapter 8

Unmooring

8.1    UNMOORING PROCEDURE

8.1.1  Unmooring While One Ship is at Anchor

Where STS transfer operations have taken place at anchor, under normal conditions of current and weather, unmooring may be carried out with the constant heading ship remaining at anchor. However, if in the judgement of the person in overall advisory control, weather and current conditions so require, the constant heading ship should weigh her anchor and unmooring should be carried out while making way.

 

8.1.2   Unmooring after Underway Transfer

Where STS transfer operations have taken place while underway, it is normal to bring the combined two-ship system head to the wind before unmooring, unless local conditions dictate otherwise.

 

8.2   UNMOORING CHECKS

Sufficient crew should be allocated to unmooring stations and consideration should be given to the following points:

• side of cargo transfer cleared of obstructions including derricks or cranes;

• method of disengagement and of letting-go mooring line agreed;

• fenders, including their towing and securing lines, checked to be in good order;

• winches and windlass ready for immediate use;

• rope messengers and rope stoppers ready at all mooring stations;

• fire axes or other suitable cutting equipment available at each mooring station;

• communications confirmed between ships;

• communications established with mooring gangs;

• mooring gangs instructed to let go mooring lines only when directed;

• shipping traffic in the vicinity checked; and

• Check List 5 of Appendix 1 completed.

 

8.3   PROCEDURE FOR UNBERTHING

Unmooring can be achieved by singling up fore and aft, then letting go the remaining forward mooring and allowing the bow to swing away from the constant heading ship to a suitable angle, at which time the remaining stem mooring line is let go and the manoeuvring ship moves clear. After disengaging, neither ship should attempt to steam ahead or fall astern of the other until both ships are well separated.

 

It should be noted that local conditions or vessel configurations may cause difficulties in separating the two ships and other alternative plans should be considered.

 

Because of the unpredictability of, and difficulty in assessing some conditions, it is recommended that unberthing at anchor be carried out only by persons with considerable experience in STS operations.