Deck cranes receive risky diagnosis

by | 30th August 2016 | News

Home News Deck cranes receive risky diagnosis

The Naval Architect: September 2016

There are not many problems with crane designs themselves, says Dyson, but there are wider issues that implicate design factors in crane failures. These can include irregular crane controls, the inadequate use of existing regulations, and a conflict of interest between shipowners and yards that can lead to inappropriate crane selection.

The advent and widespread implementation of software-controlled equipment is taking a toll on the functionality of cranes, which are adapting to the technological shift. Simple, direct systems have been replaced by more complex, computer-controlled crane systems in an effort to improve safety and efficiency, but they may be unnecessarily complicating the process at a premature stage in their development instead, says Dyson. In this sense, lack of synchronisation and incorrect software operating profiles can lead to premature wear on mechanical components and ultimately failure, for example of gearbox assemblies.

Control problems have led to interlinked system failures where the relationship between software and mechanics has failed, and Dyson ultimately believes that in a number of cases the systems have not been tried and tested to the level of older systems.

Efforts to improve the design of cranes with double-layered winch drums have also backfired, explains Dyson. The initial intention was to reduce the necessary size of the winch and so reduce costs; however, this change has commonly had the effect of accelerating wire rope wear because of the way the rope is wound back on itself in the opposite direction on the second layer. For such an arrangement, commonly used basic left and right hand lay ropes are no longer ideal and are likely to sustain premature wear. More elaborate and expensive ropes are consequently required that increase an owner’s operating costs for the crane in service – although even these ropes may still wear prematurely. As a result, “someone has advanced the design, but not for the better”, says Dyson.

The premature roll-out of new models by manufacturers is also having an impact. Insufficient testing time has meant that ships are being used as test cases. Dyson says that while only a small fraction of cases may lead to failures, it can be a big problem, putting lives and a lot of money at risk, not to mention the auxiliary cost associated with a crane’s loss of use.  

Fitting the bill
It is unlikely that shipowners have the expertise to ensure that they take delivery of the most suitable cranes for their vessels’ operating profiles, explains Dyson.

They may have an idea, but they are ultimately reliant on the contracted shipyard and provide only loose specifications. This reliance is problematic as the yards themselves are not crane experts and will turn to an approved list of manufacturers that may or may not offer the best solution for the shipowner.

A conflict of interest then worsens matters as it is often the case that “shipyards wish to go with the lowest cost they can get away with, but the owner is goaled towards a long term satisfaction of needs,” according to Dyson.    

In consequence, shipyards get what they pay for, while owners seem to be unaware of exactly what they’re getting for their money. The fact owners can commonly have no direct contact with manufacturers is a corollary issue.

Dyson proposes that more detail should be included in the specification agreed between   shipowners and the shipyard to remedy the situation, specifying three key points for consideration:

  1. A crane’s safe working load and outreach must be assessed and suitable for desired trade.
  2. The required lifecycle use of the crane should be carefully defined.
  3. Design rules and guidance should be correctly stated and specified for intended use. 

He also adds that there should be consistency and transparency at the contractual stage, between the cranes specified between owners and the shipyard and those ordered from the manufacturers by the shipyard, to ensure the two are compatible.

Making regulation work
At present, cranes are generally type approved.  However, the approvals are commonly generic in nature and concern only basic structural requirements.  In this respect, type approval does not ensure that a crane is suitable for a specific required service task or lifecycle. 

Class approval is largely peripheral for regulating cranes because the crane (above the fixed pedestal) is likely to fall under flag or statutory standards and not to be directly considered as a class item at build. Class can be involved, but it is rare for them to supervise the build of a crane as their interest effectively stops above a crane’s pedestal in most cases. 

Owners may request the input of a regulatory body approved by the flag administration.  However, this is commonly applicable to the latter stages of the build, immediately prior to delivery, when the vessel is registered to a flag state. Flag states also commonly adopt ILO standards with regards to cranes, which are seen as the lowest common denominator and are all too often administered by organisations whose own standards fall below those of classification societies and their rules. It is therefore often considered that ILO standards represent the lowest accepted level of regulation, says Dyson. This means that all sorts of organisations are approved to regulate cranes that are not as capable as the class societies, which have greater expertise and capabilities.

Class societies are happy to certify on behalf of the flag state, and the shipowner can ask for a higher level of assurance by having the vessel’s classification notation include that for cargo handling appliances, says Dyson. However, the reality is that these measures are rarely put to use. 

“All the measures to improve things are there, but they aren’t taken up”, says Dyson. This, he explains, is commonly because of the additional costs involved, especially against the backdrop of a depressed economic shipping climate that makes both owners and yards alike supremely cost-conscious. People are spending less money initially and are ultimately missing out on the best long term solutions, which may in time lead to failures and additional costs.

When asked if it would be simpler and more efficient for cranes to be included as a class item, Dyson said: “It probably would be better to apply class requirements by means of including notation for cargo handling appliances from build, as it would remove the worst people able to certify.”

Dyson also believes that more thorough tests and inspections should be conducted of cranes and their wires (the most prevalent cause of failure) in order to reduce negative outcomes. Current operational and visual tests carry little meaning, he says, because they only really test if the crane is working at that moment and not the crane’s ongoing condition i.e. the state of its component parts.  “It is a practical reality that the present regime of annual and quinquennial surveys administered through the flag states falls well short of ensuring the continued reliable operation of a ship’s cranes during the periods between inspections,” concludes Dyson.

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