At a time when companies are downsizing, with periods often ensuing where there are few if any semisubmersible design and construction projects underway, the need to support the industry with knowledge retention is a key requirement.

This has acted as a driver for the recent publication of a procedure for the strength and fatigue assessments of semisubmersible units as well as updates to Lloyd’s Register’s “Rules for Offshore Units,” which cover classification requirements for semisubmersible units.

This year’s depressed offshore market also has produced a situation in which double digit numbers of semisubmersible drilling rigs have been unable to pick up profitable contracts and are being cold-stacked as a result. What will become of these units in the future?

Alternative uses
The semisubmersible unit lends itself well to change of use because ship motions are favorable and there is a good amount of deck space to work with. Drilling units can become floating production units, accommodation facilities and dive support vessels.

In the future more alternative uses are likely to be seen such as floating chemical processing plants, desalination plants and power plants. Who knows if the next generation of semisubmersible units will be the return of the recent cold-stacked units into service, perhaps redesigned or modified, some with new owners and some with different roles?

What the industry can be certain of is that when the growth returns, there will be a new generation of naval architects that will work on these projects. By publishing best practices, the industry can make sure that they have access to its lessons learned.

Lloyd’s Register also has been looking at ways in which it can standardize its design review of semisubmersible units going forward. The industry has to adapt to delivering these projects in a low oil price climate. This means being more time-efficient, and having more prescriptive requirements will help achieve this.

Bigger picture
But it is important not to lose sight of the bigger picture.

Every time a new standard comes out there is the danger that it will reduce the safety review to a tick box exercise. There is the possibility that things that fall outside of what the standard was originally intended for get overlooked. There is the tendency to say, “Well, it meets the standard; therefore, it must be safe.” As such, Lloyd’s Register’s main goal is actually not to produce standards but to manage the knowledge necessary to ensure that designs are safe.

Producing standards is a great way to deposit knowledge, but they need to be accompanied by training and case studies so that the practitioners understand where the requirements came from, what the limits are and how to approach designs from first principles when necessary.

A recent fatality on a semisubmersible has highlighted a need to bring more attention to designing for wave impacts. Lloyd’s Register has introduced new rule requirements for model test specifications and reporting to bring more rigor to this part of the design stage where wave impacts can be identified.

Model testing
Model testing is an area where Lloyd’s Register saw great opportunity to standardize and offer best practice to the industry. Some of the longest reports the company receives to review are model test reports—the longest one so far being 15,000 pages. Although this was an exception, upward of a thousand pages is quite commonplace. Therefore, Lloyd’s Register wanted to look at a more efficient way of reviewing these reports.

Further investigation found that there was quite a difference in the level of testing and reporting between projects and test facilities. This is not to say that some tests were good and others not, quite the contrary. In fact, every test had its own merits, but it was clear that there was the opportunity to combine the best aspects of several case studies together into standardized rule requirements that
not only could be better than any individual effort but would also allow time savings for reviewing the reports.

Real projects
The new procedure focuses on answering questions the company has been asked by designers on real projects.

Designers are looking to have their design approved first time, so Lloyd’s Register has put a lot of detail into the procedure in order that this is achievable. What typically causes delays in the assessment phase is the need to revisit how the structure has been modeled, agreeing fatigue factors of safety and adding additional load cases to ensure that the most critical load combinations that could occur in service have been assessed.

A lot of detailed requirements have been added to mitigate delays in these areas. Specifically regarding the way structures are modeled, this affects the accuracy of the results, which is something that often is underestimated.

Lloyd’s Register has found that for every hour spent designing the hull, another hour is spent designing the interfaces with that hull. Therefore, the procedure has taken an all-inclusive approach, covering requirements for the interfaces in as much detail as for the hull. By covering both within the same procedure, Lloyd’s can ensure that consistent design methods and assumptions are used between the hull and interfaces. This is an area where there often is a disconnect as a result of the hull and interfaces being designed by different teams or even different companies that are not always in communication with each other.

Detailed documentation
There is also a lot of emphasis on what documentation needs to be seen. At first glance it is easy to think that it is excessive, but the greater the level of detail, the easier it is to identify errors, which ultimately leads to a safer design.

In addition, what is not always appreciated at the design phase is how highly sought-after documentation becomes in later years when the basis of design needs to be revisited for upgrades, modifications or investigations. Sometimes vessels are sold, and design documents are not always passed on to the new owners.

Similarly, once a vessel has been built, the responsibility for it might change hands within the company from the design team to the operations team. In most cases there is a handover of design documentation, but Lloyd’s does not take this for granted. Lloyd’s Register, in effect, mitigates the risk of loss of data by retaining very detailed documentation independently.

Comments