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Marine Operations January 5, 2025 12 min read Capt. Chris Baker

2 or 3

Rig Moving: Boats, Anchors and Redundancy

15 January 2025, Abu Dhabi, UAE: Jackup oil rig and platform supply vessel staying in harbor in calm water with cloudy sky

Introduction

When an Offshore Unit of any description is to undertake a location shift for operational reasons, the primary considerations must always be SAFETY OF PERSONNEL, SAFETY OF THE ENVIRONMENT and SAFETY OF PROPERTY AND EQUIPMENT.

In order to achieve this, many considerations and mitigations are employed together with procedures and analyses of soil conditions, environmental limitations and other factors involved to evolve a complete operational procedure that reduces risk to a minimum level.

Modern times and economic factors however have forced the industry to make savings across the board and one of the biggest changes to affect the rig moving process is the acceptance of using only 2 tugs as the normal operating requirement as opposed to the previous accepted practice of employing 3 boats for the same operation.

Why is this practice now prevalent?

Sadly the truth is a contradiction of the entire ethos of "SAFETY IS PARAMOUNT".

The fact of the matter is that this practice is the direct effect of economic pressure. i.e. it is cheaper.

This is due to several different factors, including but not limited to:

  1. Reduction of Charter costs by one third.
  2. Reduction of fuel and consumables costs by one third.
  3. The waiting time for boat availability is reduced.

The advocates of this practice will always argue that since it is largely a successful and wide spread methodology with no related increase in serious incidents during rig moves, it is acceptable. The same people, usually more involved with financial decisions than operational ones will therefore, argue that it is a safe and proven success whilst reducing economic costs at the same time.

A Contradiction of Logic

At the top end of the Offshore Marine Technology scale we have the very expensive and very advanced DP Semi-Submersible Rigs and Drillships.

The station keeping capabilities of these units depend on very advanced computerized propulsion management systems and since their inception, the word REDUNDANCY has been the all important factor in both their capability and their classification.

Millions of dollars have been spent in the technological advances that have been necessary to achieve the levels of REDUNDANCY required for these units to do their job in an acceptably safe manner.

Why then, if the industry is so obsessed with REDUNDANCY at one end of the equipment range, and seemingly uncaring of the costs involved, are they equally obsessed with reducing REDUNDANCY and saving costs at the other end?

Make no mistake, using 2 tug assist boats instead of 3 has a serious impact on REDUNDANCY and therefore by definition, SAFETY.

Examples: Positioning Configurations

Example 1: Three Tug Configuration (Optimal)

Anchor 2 -------- Platform -------- Anchor 3
Stern Tug -------- Jack Up -------- Stern Tug
Bow Tug
Anchor 1 -------- -------- Anchor 4

As illustrated above, a jack up rig manoeuvring into final position alongside a platform using the following towing/winching set up has full REDUNDANCY in every plane of movement required, including Emergency stopping, to achieve the proper operational position SAFELY.

Any Risk Assessment conducted pertaining to this arrangement will conclude that all reasonable measures have been taken to mitigate the risks involved with final positioning.

THIS IS THE SAFEST WAY TO MANOEUVRE A JACK UP UNIT INTO AN OPERATING POSITION ALONGSIDE A PLATFORM - THIS IS NOT AN OPINION.

Example 2: Two Tug Configuration (Reduced Redundancy)

Anchor 2 -------- Platform -------- Anchor 3
-------- Jack Up -------- Aft Tug
Bow Tug
Anchor 1 -------- -------- Anchor 4

In example (2), by removing one of the stern tugs, the REDUNDANCY of the Unit's capability of transverse movement (i.e. from port to stbd) has been reduced by 50%.

Should either of the stbd side anchors fail, the entire process of final positioning would need to be put on hold, probably by soft pinning until the one and only available stern tug can change position.

This not only causes delays in the process but also introduces the risk of the footprint produced by the soft pinning process disturbing the soil make up and possibly degrading the quality of a secure footing in the final position.

Equally, should there be a deterioration of the environmental conditions, the one and only available stern tug may well not be able to secure a proper towing connection on the opposite side of the rig. Once disconnected from the unit, the inability of the tug to reconnect due to weather or current conditions would leave the unit with absolutely no REDUNDANCY for transverse movement at all.

Subsequent delays in positioning would quite obviously be costly in terms of both time and money and the exposure to risk of damage to the Unit and the Platform significantly increased as a revised Risk Assessment would certainly reveal.

Example 3: Traditional Towing Method (No Redundancy)

Stern Tug -------- Platform -------- Stern Tug
Jack Up
Bow Tug

Example (3) shows the more traditional approach to manoeuvring a jack up to its final operating position which is still widely used in many parts of the world today.

Although widely used, it has many disadvantages the main one of which is the complete absence of any form of REDUNDANCY in the make up of the Towing Arrangement.

Unlike the arrangements previously shown using anchoring systems, a great deal of control is removed from the Rig Mover who, although he can instruct the boats, cannot actually control them. Nor can he see what is actually happening with power settings and can only hope that his instructions are being properly followed.

In addition, the practice of using the legs and spud cans to slow or stop the unit which is still widespread, causes unnecessary environmental damage to the seabed.

There is no REDUNDANCY to deal with mechanical failures to either propulsion or tow winch machinery nor is there any REDUNDANCY in the case of a tow wire failure.

A proper risk assessment would reveal that whilst this system is still widely used, it is fraught with risk of damage to both the Unit and the Platform.

So why is it still a world wide practice?

Unfortunately the economies of the industry call the shots and this methodology consumes a great deal less time than stopping and setting up an anchored mooring system. This means that even though 3 boats are being employed the overall costs are less due to time saved.

"SAFETY IS PARAMOUNT" - is this actually a valid statement?

Manoeuvring to a Stand Off Position to Run Anchors

This particular manoeuvre has the inbuilt safety factor of there normally being around a 100 metre distance between the stand off position and the final operating position which greatly reduces the level of risk.

Whether completed with 2 boats or 3 boats, by stemming the predominant environmental conditions, a natural braking force or REDUNDANCY comes into effect which, in the case of any mishaps will move the tow away from the area of high risk.

If, however the area of operation has a high density of offshore structures or high traffic density this may actually increase the risk of damage.

The choice of 2 or 3 tugs to complete this manoeuvre is therefore very case by case specific, however 3 is always going to be preferable to 2.

Conclusion (the Author's View)

Regretfully the expression "as clear as driven snow" immediately springs to mind, however this does not seem to be the case as the snow seems to be being driven into a series of economic flurries that obscure the vision of the decision makers.

Whenever SAFETY is an issue, it is clear that more is always going to be better than less.

The word MITIGATION means to 'mollify or lessen the severity' (Chambers Dictionary) thus it should be patently obvious that the more we mitigate risk, the safer our operations offshore will be for our personnel, the environment and property.

In terms of economy which can only come a very poor second to safety, it can also be a false saving to reduce the capabilities and REDUNDANCY of an operation if that reduction results in an inability to complete the operation in a timely manner.

Delays resulting from inadequate resourcing due to unexpected changes in either the environmental conditions or equipment failure are very costly - they are also unnecessary if proper advanced planning is executed.

The protagonists will always contend that because this resource reduction has been in practice for some time now and without a significant increase in serious incidents, it is safe and OK to maintain the practice and because it saves money it becomes acceptable.

The question that needs to be asked is are we, as Marine Professionals, in the business of assessing risk and resourcing for situations where everything goes well or for situations where everything goes wrong?

We work in a harsh marine environment where things do go wrong with alarming frequency so the answer to that question is obvious.

Moreover, as professionals, we understand the sea: we understand its ability to change; we understand its strength, force and the damage it can do; we are used to dealing with the unexpected without prewarning; this is what we do.

We also understand something known as 'best Marine Practices' which most certainly does not include cutting resources to save money.

3 is always going to be safer than 2.

CB

Capt. Chris Baker

Master Mariner

MRIN.IFSMA.MSOMWS.

Founder, Siam Offshore Solutions

With 40+ years of hands-on offshore marine operations experience, Captain Baker brings practical expertise to every aspect of rig moving, anchor handling, and marine safety. Based in Songkhla, Thailand, he provides consulting, training, and problem-solving services to the global offshore industry.

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