Bollards stressed beyond capacity
Iain MacIntyre outlines how bollard capacities around the world are being stressed by rapidly-increasing newbuild ship sizes and considers the view from insurers
Wharf bollard capacities around the world are being challenged and, in some instances, exceeded by the rapid recent increase in newbuild sizes, with concerns consequently
raised about the adequacy of processes to inspect, test and maintain such key infrastructure.
The issue came to the fore in New Zealand in February 2017, when high winds led to the 41,865-GT cruise ship Seabourn Encore tearing mooring bollards off the wharf at PrimePort Timaru, with the vessel's stern then swinging across the harbour and colliding with a bulk cement ship.
A Transport Accident Investigation Commission investigation found that the bollards failed because their fastenings to the wharf and underlying wharf structure could not take the force from the ship's mooring lines. Among other observations, it stated that: “Safe and effective mooring of ships depends on port companies knowing the safe working loads for their mooring infrastructure.”
Mott McDonald Australia, New Zealand and Asia maritime practice leader Sam Mr Harris reports a “real mixed bag of responses” to the issue. “Some ports have taken a very proactive response to the changing nature of shipping and other factors, while others are more reactive to changing mooring requirements as those problems emerge,” he told Port Strategy.
“This is quite understandable given the complexities often encountered for upgrades and an increasingly cautious approach to investment in infrastructure improvements in advance of demand. With such a rapid increase in vessel sizes globally over recent decades, predicting future requirements becomes increasingly difficult to anticipate.
“Often the need for channels/berths to accommodate the physical dimensions of larger vessels - for example, deeper draught and greater ship-to-shore crane outreach - is quite
obvious. Enhanced mooring requirements are sometimes less obvious and more complicated to assess and address any shortcomings.”
AECOM ports and marine technical director James Mr Hutchison says all ports seeking to cater for larger vessels must now have assessment of their infrastructure “front and centre of their decision making”.
“The majority of port owners will commission studies to ensure that these larger vessels can be accommodated,” he says. “This may include condition assessments of existing
infrastructure but also structural capacity assessments to accommodate the larger berthing and mooring forces from these larger vessels, as well as whether dredging of berth
pockets is required. The strength of wharf bollards is just one component of the port's infrastructure that needs to be considered when larger vessels are contemplated.”
Further complicating matters, many older ports will have bollards for which there is no design load data, observes Beckett Rankine director Tim Mr Beckett.
“Even for new bollards the actual capacity can be less than the rated capacity due to quality control defects - it is not common for new bollards to be proof-tested,” he says.
“It is not just the bollard and its fixings which are critical but also the structure to which the bollard is attached. There have been several cases of sheet-piled wharf frontage failures due to the load from a bollard overstressing the wall's anchorage ties.
“I am also aware of a mooring dolphin at an oil terminal berth where the steel supporting piles failed in tension at their junction with the concrete dolphin cap under mooring line loading.”
Determining the strength
Assessing mooring strength requires appreciation that this infrastructure comprises a system of elements, configuration and operation, says Mr Harris. “The strength of the system is only as strong as the weakest link,” he states, before adding that the range of aspects that consequently need to be understood fall within the following parameters:
- What infrastructure is in place now?
- What are the design mooring conditions?
- What are the future requirements?
- What practical measures can be adopted to address any
shortfall in mooring capacity?
“Knowing the strength of bollards is important, however it only provides partial context. It is possible to proof-test the strength of bollards, but it is very expensive and can cause
significant operational disruption. Sometimes this is the only course of action though.”
Mr Beckett says that although the majority of ports “generally know” the rated capacity of their bollards, particularly on berths accommodating larger vessels, it is less common that they will know the degree to which their aging bollard capacity might be reduced by corrosion.
“In the past bollards were tested by the pull from a tug, but this method has gone out of favour as a failure under test could do significant damage to the tug.
“There are a number of firms which offer to test bollards using a hydraulic rig that tensions one bollard against its neighbour. This is much safer in the event of a failure, but it does not necessarily test a bollard for a line pull in the direction that a ship would apply it, especially for a large ship which may have very steep line angles. It is, however, very much better than no test.
“Stressing one bollard against its neighbour is not suitable for bollards on isolated mooring dolphins or for mooring hooks which have a limited range of swivel. I understand that there has been some experimental work done on testing bollards and their fixings using ultrasound or similar.”
Mr Hutchison concurs that most ports will have good understanding of bollard strength, but also notes that the safe working load (SWL) - typically stamped on each bollard to
indicate its rated load capacity - can only be realised if:
1. The bollard is properly connected to infrastructure to be able to transfer the loads from mooring lines to the wharf structure.
2. The wharf structure is capable of accommodating the combination of mooring line loads imposed on all of the various bollards.
“These are generally referred to as local and global capacities. Bollards are generally only tested when they are new and once they have been installed it is very difficult to actually test them. We are not aware of any ports that test their bollards with a proof load.
“Generally, if there is a concern with a bollard, they are visually inspected and assessed. It is good practice to remove the bollards to inspect the condition of the bolts at deck level, however, it is not known whether this is routinely carried out.
“A problem that has been identified in the United Kingdom involves several examples where cast iron/cast steel bollards have failed before reaching their rated load capacity.
Accordingly, designers are now recommending such bollards be concrete-filled as a precaution.
“Another issue with using existing bollards to accommodate larger or different vessels from the original design is the uncertainty as to what the original designer intended with the
horizontal and vertical angles of mooring lines. With larger vessels, these angles can change substantially and may be outside the envelopes allowed for in the original design of not only the bollards but also the wharf structure.”
Although observing that the majority of ports would have infrastructure maintenance programmes in place, Mr Hutchison says with regard to bollards specifically that it “would mostly consist of painting”.
“It is important to check the condition of the holding-down bolts - or welds if welded to a steel member - as this is critical to ensure the bollard's rated load can be accommodated.”
Mr Beckett agrees that bollards “generally receive little, if any, maintenance” within such programmes.
“Mooring hooks, being more complicated items of equipment, are generally subject to periodic strip down, inspection and servicing. This attention tends not to extend to testing of the holding-down bolts.”
According to Mr Harris, ports are becoming increasingly aware of the importance of implementing sophisticated asset management plans which are aligned with broader business
objectives, “rather than reacting to repairs and maintenance on an ad-hoc basis”.
“Compliance with ISO 55000 for asset management is increasingly becoming the norm. This extends beyond condition assessment, to taking a targeted and longer-outlook
approach to managing maintenance priorities.
“However, this often does not extend to a full assessment of the mooring system as a whole, unless an incident occurs or an upgrade requirement presents itself. We are seeing a much greater level of proactivity though."
Reviewing infrastructure in preparation for new callers
Ports with sophisticated asset management arrangements will be more readily able to flag requirements for mooring upgrades ahead of receiving larger-calling vessels due to their existing mooring limitations being better understood, continues Mr Harris.
“In many jurisdictions, we are seeing governments put an obligation on port owners to develop long-term masterplans for their assets. We have supported a number of ports though this process, which requires an evaluation of future trade and fleet requirements and how their infrastructure and operations must adopt to these changes over time.
“These plans are live documents that need to be updated regularly to respond to changing outlooks. This provides a great opportunity to identify these issues early and to put in place programmes of works to address these proactively over time in advance of the challenges of accommodating bigger ships.”
Mr Beckett notes that some ports have structured infrastructure auditing/testing programmes in place that are automatically triggered ahead of receiving a first call from a larger vessel. When undertaking a mooring assessment for an “oversized” ship, for example, he says a wind limit may be imposed in order to keep mooring line loads within bollard capacity.
Adds Mr Hutchison: “Most ports would not allow larger vessels to call in the first place until checks on capacity of their infrastructure to accommodate these larger vessels were
completed. The issue then becomes a matter of how thorough those checks should be.”
Regardless of any new technological developments in the construction of bollards, mooring loads will still need to be resisted as well as also accommodated by the wharf structure, with the bollards “simply a localised transfer point”, emphasises Mr Hutchison.
“Forces from the mooring of vessels are largely horizontal and offshore, which are the worse kind of loads to deal with. There are alternatives available, such as the magnetic or
vacuum mooring systems, which have advantages over conventional bollards such as reduced time for securing vessels alongside and associated reduction in labour costs. However, the total mooring load from a vessel remains the same and still needs to be accommodated by the wharf structure, albeit via different load paths.”
Noting “there is no silver bullet - yet!”, Mr Harris says designing bollards to accommodate a wide range of conditions leads to very expensive infrastructure solutions.
“If anything, we are seeing an increased emphasis to provide refined designs for a well-defined design basis. There are plenty of new technologies though which provide exciting solutions to many problems we encounter in mooring vessels. Each solution helps manage vessel motion, although presents its own new challenges and there are not blanket
solutions for all situations.”
Mr Beckett concurs that ports will prefer to invest in bollards designed specifically for the needs of their vessel callers and will be unlikely prepared to pay for over-design of a facility.
“The development of auto-mooring systems may reduce the reliance on bollards in certain locations, but these are likely to be limited in number since auto-mooring equipment is much more expensive than bollards.
“The development we, as designers and specifiers, would like to see is improved quality assurance procedures for the manufacture of bollards, so it gives confidence that the actual capacity is no less than the rated capacity.”
In conclusion, Mr Harris implores ports to take a long-term view of the future requirements of their infrastructure. “This is not a static outlook and will evolve over time. However, a port masterplan provides an opportunity to take stock and evaluate the adequacy of your existing infrastructure to meet future needs.
“Increasing bollard capacity can have knock-on impacts though the quay structure. The whole mooring and quay wall system need to be considered together. We have seen instances where higher-capacity mooring/berthing equipment has been installed on infrastructure not designed to accommodate it and other instances where the existing bollards are not appropriate for the moored vessel conditions. Both situations should really be avoided.”
In addition to regular inspection and assessment of bollards - including removing bollards where possible to inspect holding-down bolts - assessment of the overall capacity of
wharf infrastructure should be a priority, concurs Mr Hutchison.
“It is extremely important to understand the limitations of how larger vessels can be moored alongside existing wharf structures and this is ultimately governed by the ability of the
wharf structure to resist these loads.
“Dynamic mooring assessments can be undertaken using software such as Optimoor and TermSim, which, if undertaken in consultation with port operators/pilots/shipping lines to
confirm the number, type and size of mooring lines and how these are configured through the fairleads back to winches on the vessel's decks, provide greater certainty of the mooring forces compared to conventional static-based assessments.
“These dynamic mooring assessments can target bollard limits to determine limiting wind speeds before a vessel must leave the berth. It is important to note that the largest vessel may not necessarily generate the maximum individual bollard forces because a smaller vessel with a lesser number of mooring lines may do this, hence why it is
important to check a range of vessels, not just the largest.”
Adds Mr Beckett: “Be careful where you purchase your bollards and always ensure that there is independent and dependable verification of the manufacturer's quality control.”
Allianz Global Corporate & Specialty's global head of marine risk consulting, Captain Rahul Khanna, and ports and terminals underwriter Simon Keenan, state unequivocally that ports must know if their bollards can withstand the loadings of ever-increasing vessel sizes.
While they advise this has “always” been an important area of consideration to insurers, they also note the impact of vessel sizes having exponentially increased over the past
decade or so, especially in the container and cruise ship sectors.
“A failure of bollard and consequently the mooring lines on it could result in a vessel breaking off its berth and result in a very serious casualty,” collectively advise Captain
Khanna and Mr Keenan.
“We have seen such incidents in the past and this concern is growing, especially as the consequences can be very costly, including loss of life.”
An overall observation they share is that given the infrastructure of many ports around the world was built in the pre-WWII era, records of bollard strengths are often not available.
“In many ports, the testing and regular maintenance of bollards is a low priority in spite of it being the key infrastructure of the port. This is clearly a big concern, as safe mooring of vessels depends upon understanding what loads can be safely taken by such bollards, especially in bad weather.”
Nonetheless, the pair believe insurers would generally not seek to interfere with the workings of a port by themselves prescribing programmes for auditing, testing and maintenance of such infrastructure.
“We expect them to follow good industry practices on testing and maintenance and there are implied warranties in an insurance policy.
“Having said that, insurers like Allianz, who have an in-house risk consultancy function, do make it a point to advise their clients of best practice processes and assist them in
formulating adequate procedures for checking, testing and maintenance of such structures.”
Ultimately, conclude the pair, it is vital that safe mooring practices are enforced by ports, including monitoring if the maximum number of mooring lines that can be placed on each
bollard is not exceeded.
“We have often seen this process ignored and it has resulted in bollards been uprooted in high on-shore winds. Our advice would be to engage experts to reassess the breaking strengths of all mooring structures in case of any doubt and if proper certification is unavailable. There are new non-destructive technologies available in the industry for testing of bollards and these should be used when possible.”
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