West of England Club: How to avoid contact damage during STS operations

STS Planning and Preparation – Fendering – Mooring – Unmooring

ship to ship transfer
The West of England P&I Club has issued Loss Prevention Safety Alert on STS Transfer Operations – Incidents Resulting in Contact Damage to highlight the principal causes of recent incidents, and to focus on the safeguards that should be considered to reduce the likelihood of contact damage during STS mooring and unmooring operations.

The Club has experienced an increasing number of claims involving contact damage during ship to ship (STS) transfers, mainly during manoeuvring operations. Some of the incidents were serious. Following a claims review it appears that the majority of these cases took place in conditions that may have been unsuitable for the activity undertaken.

Contributory factors generally included one or more of the following:

  • Adverse weather conditions such as high winds, heavy seas, strong currents and/or tidal streams. In one case a daughter vessel, which was moored alongside an anchored mother vessel, made contact when trying to unmoor in a Force 8 wind. A significant number of other incidents occurred in winds of Force 6 or more.
  • Lying beam on to a long swell while lightering a vessel which was partially aground. The swell increased during the operation, causing both vessels to roll up to 10° and hit each other.
  • Poor communications and misunderstandings between vessels.
  • Excessive speed either moving ahead or during the approach while both vessels were underway.
  • Pulling ahead or falling astern of the other vessel and attempting to steer away while still in close proximity, failing to take account of the negative transfer that may cause the manoeuvring vessel to head the opposite way at the start of the turn.
  • An insufficient number of fenders, or fenders of an inappropriate type or size. Also poorly positioned fenders in the vicinity of the shoulder or quarter regions of the hull, or a complete absence of fenders in these areas.
  • Not enough crew in the mooring gang. A daughter vessel was forced to hold station alongside an anchored mother vessel for a prolonged period of time in poor weather while the mooring gang moved from one end of the vessel to the other to let go the lines. The vessels eventually collided.
  • Attempting to moor against an anchored mother vessel on the same side as the anchor in use, contrary to best practice.
  • Unsatisfactory use of tugs. A tug was instructed to pull the bow of a daughter vessel away from an anchored mother vessel that was yawing in high winds, rather than using the tug to hold the mother vessel steady. The mother vessel swung and struck the daughter vessel causing significant damage.

Mooring and unmooring should always be conducted in accordance with the STS Operations Plan, the Safety Management System, any local, national and/or flag state requirements that may apply and the guidance contained in the latest edition of the following publications:

  1. ICS/CDI/OCIMF/SIGTTO Ship to Ship Transfer Guide for Petroleum, Chemicals and Liquefied Gases (“Ship to Ship Transfer Guide”)
  2. IMO Manual on Oil Pollution, Section 1 Prevention, Chapter 6 – Ship-to-ship transfer of crude oil and petroleum products while underway or at anchor.

How to reduce the likelihood of contact damage

STS Planning & Preparation

STS operations may take place while both vessels are underway or with one vessel at anchor. When both vessels are underway it is customary for the larger vessel to steer a steady course and maintain a constant speed, usually around 5 knots, keeping the wind and sea on the port bow while the smaller vessel moors on the starboard side. The vessels may then carry out the cargo transfer while underway or may stop and drift in order to do so. Local conditions may sometimes require an alternative arrangement.

A risk assessment should be conducted prior to every STS transfer. For routine STS operations a generic risk assessment may be used. However, if any unusual conditions or factors are anticipated, a more detailed risk assessment should be carried out. In addition to covering the transfer of cargo (which is outside the scope of this safety alert), the risk assessment should address all aspects of the approach, mooring, unmooring and departure.


Appropriate fendering must be used to prevent contact during mooring and unmooring, and to keep the vessels apart during the transfer. The fenders should be of adequate size, correctly positioned and sufficient in number. Primary fenders should be placed between the hulls to provide protection and separation while the vessels are moored together.

Secondary fenders should be positioned at the shoulder and quarter to shield the areas that are most exposed to contact damage during manoeuvring operations. Typically the fenders are deployed by the manoeuvring vessel to minimise the risk of damage if it lands against an unprotected section of the other vessel’s hull. The fenders are normally positioned by service craft employed by the appointed STS service provider.

The quantity, type and position of the fenders needs careful thought. The general information set out in the Ship to Ship Transfer Guide may assist in this respect. Specific advice on fendering arrangements for particular vessels and/or operations may be obtained from fender manufacturers and providers.


Both vessels should be upright and suitably trimmed for the operation. Nothing should project overboard on the berthing side. If it is necessary to carry out the berthing operation at night the main deck should be lit and, where possible, the fenders illuminated. When placing the lights, care should be taken to ensure that they are not directed towards the other vessel’s bridge.

The engines, thrusters, steering motors and navigational equipment of both vessels should be in full working order and tested prior to the approach. Both vessels should check that they can communicate with each other well in advance of the operation

All navigation lights, shapes and sound signals as required by the International Regulations for Preventing Collisions at Sea (COLREGS) should be displayed and sounded as appropriate, including manoeuvring signals and requirements for vessels restricted in their ability to manoeuvre when conducting STS transfer operations underway. A mooring plan should be agreed before commencing the operation.

The number of mooring lines and where they are situated will depend on several factors including the size of the vessels, their freeboards, the weather conditions and the location and relative positions of their mooring fairleads. The usual practice is for the mooring lines to be passed by the manoeuvring ship to the vessel maintaining its course and speed or laying at anchor, as appropriate.


Prior to departure any projecting obstructions on the side closest to the other vessel should be stowed inboard and checks should be made to ensure that the fenders are still properly positioned and secured. All engines, thrusters, steering motors, navigational equipment and communications (both internal and between vessels) should be tested beforehand.

The unmooring operation should only proceed if everything is found to be in full working order. The order of releasing the lines should be agreed in advance as part of the unmooring plan. The mooring party on the manoeuvring vessel should wait for instructions from the bridge before slackening the lines. Personnel on the other ship should only let go when told to do so by the mooring party on the manoeuvring vessel.

The use of quick release toggles, as described in the STS Transfer Guide, may be used to minimise the risks. Some STS service providers may supply quick release hooks for this purpose.

Learn more by reading the following Safety Alert by the West of England P&I Club


Source: The West of England P&I Club

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