Better by design

Ship design has come a long way since in the last 10 years or so with a plethora of computational design tools now available on the market to help designers improve the efficiency of their designs. While most Asian shipbuilders are concentrating on offering standard designs with long series runs, the majority of European yards and designers are working on ship designs that will number in single figures.

As Inge Bøen, Rolls-Royce vice president of merchant ship technology and systems points out: “European designers today are in a position where we do not design a long series of vessels. Designs are very often tailored to a specific operation or specific requirement from the shipowner. This is the case with the Nor Lines project where we worked with the owner to develop the project over many rounds of meetings and several iterations, both in terms of the function side, but more importantly the cargo solution. They want the vessel to be efficient as possible and designed to fit their own requirements.”

Rolls-Royce won the Next Generation Ship Award at this year’s NorShipping event for its Enviroship design and has received its first order for two vessels from Nor Lines in Norway The two NVC 405 cargo vessels will be built at the Tsuji Heavy Industries ship yard in Jiangsu, China and are scheduled to enter service from October 2013, operating along the West Coast of Norway.

“In this specific project for Nor Lines, CFD was used in developing the hull lines at an early stage,” explains Bøen. “CFD is a very new tool that is becoming more user-friendly and more powerful. So the input to the model tank is usually based on a few rounds of CFD iterations, optimising the hull design as far as possible before you go to model test. You then take the results of your model test back into your CFD model.”

Ed Dudson, technical director at BMT Nigel Gee, well known for its fast ferry designs and for the Pentamaran concept agrees saying: “Generally, an owner will come up with a set of requirements and those requirements along with any constraints are the input into us providing a solution. So, for example, it might be how many passengers or how much cargo, or how fast - those are the sort of requirements they might have. The restrictions might be cost, practical constraints like draught and harbour restrictions and that type of thing. There also might be some design drivers like low wash or low fuel consumption. That's where we start, with a full understanding of the requirements with regard to the limitations, and then we generally put all that together to provide a design.”

The detail in the original design works "is very much dependent on the project,” says Dudson. “Some things are fairly obvious going forward and it is not necessary to do everything in a huge amount of detail, but in others, if our design criterion was excellent sea keeping and you were actually looking at meeting a particular target, then we could go into quite a lot of detail, ultimately including doing calculations, or even a model test to prove that:- a) we could meet certain criteria, and b) what the difference was between various options. It is very much dependant on the complexity of the project.”

However, whilst the capabilities of modern software are powerful, Dudson has some words of caution: “You can develop designs much quicker than you used to, but I would say that the computer taking over the design process is some way off. If you are building a bigger vessel on Tribon you can very quickly develop a new design for a ship that is 2m longer and 0.5m wider, but if you were looking to make your bulker go five knots faster that requires a very human interface in there to make it work. What is changing is the speed - your programs run so much quicker - and we can develop visualisations for customers in a couple of days while it used to take a few weeks. But it is more in the visualisation process rather than the science, I would suggest.”

He told The Motorship: “If you know the limitations of the software you can use is quite well. We have done extensive CFD analysis on the pentamaran but have limited it to optimising the shape of the centre hull and it can do that. As soon as you start trying to put the side hulls on, that is beyond its limit. It will still give you answers but they need to be interpreted.”

Tank testing required

This means that tank testing is likely to continue in the future as Bøen explains: “I think that if you look at the next five years, we will continue to use tank testing because shipbuilding is pretty conservative in the way that they want to verify computer model testing. So even if we say that it is not necessary there is still the yard or owner that thinks model testing is the only answer.”

Dudson agrees saying: “Test tanks come into the equation for a number of reasons, the first of which is to get a very high level of confidence in performance. We, together with the shipyard, are frequently up against liquidated damages for ship performance over speed, so you need to be very confident of making speed.”

Liquidated damages are the predetermined estimate of loss to one party when the other party has delayed or failed to meet some contractual deadline or achieve certain performance criteria. In respect of speed, a well crafted clause will indicate the trial conditions under which the main propulsion machinery should perform.

“In a towing tank you can not only determine the resistance but look at propeller design and propulsion coefficients and so forth,” explains Dudson. “You can then get a full understanding of the requirements and then we also do extensive sea-keeping tests. Whilst we have great software for doing predictions, it is another level of confidence step up.”

“Also, if you look at the cost of model testing compared with the cost of the project, why shouldn't you do it,” asks Bøen. “It offers the chance to double check your calculations and verifies the performance. And you get the chance to test the model of the propeller against the specific hull design.”

When the results of the CFD analysis on the ships for Nor Lines were compared with those of the tank testing they were found to be fairly accurate. "But you still see some areas where you can go back and make some improvements in the model test when it comes to movement in sea states,” says Bøen.

The company is continuing its R&D work on improving vessel performance in a seaway with Marintek in Norway. “This is what we need to live off in the future - new technology and new developments,” Bøen told The Motorship. “So the improvements need to continue and as a company we invest a huge amount of money into hydrodynamic research - probably in the range of a couple of million pounds a year only to study vessel operations in a seaway. So there will be improvements in the future, research and development will lead to further improvement both in terms of our hull designs right down to component level on the propulsion gear.”

Alternative design

There are times when design needs to be taken ‘outside the box’, and a good case in point is when innovative ship design concepts require technical and functional solutions which may conflict with the prescriptive requirements implicit in the current rules. A number of provisions have been made in SOLAS to allow the development, evaluation and approval of such solutions, referred to as ‘alternative arrangements’.

‘Alternative design and arrangements’ means measures which deviate from the prescriptive requirement(s) of SOLAS, but are suitable to satisfy the intent of those requirements. The term includes a wide range of measures, including alternative shipboard structures and systems based on novel or unique designs, as well as traditional shipboard structures and systems that are installed in alternative arrangements or configurations.

Since 1974, more than 100 approved alternative arrangements have been submitted to the International Maritime Organization. The majority of these cases relate to provisions in Chapter II-1, II-2 and III of the SOLAS convention.

Alternative arrangements can mean small changes, such as the siting of lifeboat equipment, or involve fairly major design changes, as in the case of the Silja Serenade, delivered to the Silja Line in November 1990. The ship had a revolutionary interior layout for the time featuring a promenade-street running alongside the central axis of the ship for nearly her full length. This allowed for a larger number of cabins with windows, which has been copied since by most of the recent deliveries for Royal Caribbean, including the Oasis and Allure of the Seas.

“Fire safety is one of the main aspects in which alternative design has been exploited in relation to large passenger ships,” says Luis Guarin, director of safety engineering at Safety at Sea Ltd, “for example, the size of a fire zone for a passenger ship cannot be bigger than 1600m² or 48m in length”

This was extended from 40m to 48m, to allow the main fire bulkheads to be aligned with the watertight subdivision, but was still a problem for post-Panamax vessels, as explains Guarin: “If designed with this limitation they will have important functional problems that relate to big public spaces and internal spaces, such as promenades etc. Regulation 17 was introduced in part to allow innovative design solutions to be developed despite limitations imposed by prescriptive requirements. That led to the introduction of atriums and internal promenades running along a great part of the length of the vessel. You now have the Oasis of the Seas, the Royal Caribbean vessel with what is referred to as ‘Central Park’ inside.

“This approach is probably implemented in every passenger vessel newbuilding today,” says Guarin. “An alternative design arrangement evaluation is done at the design stage to look at the rationale, the risks and implications associated with the proposed arrangements; this has led to a number of new solutions to gain approval as they meet the same safety intentions and safety goals as described in SOLAS Chapter II-2 and SOLAS Chapter III. In relation to the latter, LSA alternative design arrangements are particularly attractive for very large vessels.”

He told The Motorship: “There are also a lot of minor issues addressed through alternative design which were probably addressed through exemptions provided by class in the past. This approach has also led, through the risk assessment process, to the certification of new hazards and new problems that were not covered completely.”

Integrating engineering

Aveva launched a range of brand-new products and enhancements to its Aveva Marine solution during September and October this year. “The thrust of Aveva’s development strategy is to ensure that productivity improvements are delivered both through individual product capabilities and – importantly – through closer integration between the various applications, the data that they use, and the project disciplines they support,” explains Stéphane Neuvéglise, Aveva’s head of business management, marine systems

Aveva Engineering, for example, is an innovative solution for integrating a wide variety of schematic and tabular engineering information onto the project database. Every company has a legacy of fragmented data, held in a variety of schematic drawings and ad-hoc spreadsheets, frequently duplicating information and adding their own inconsistencies for good measure. Now it becomes possible to develop this valuable data inside a single database, bringing much more control, allowing inconsistencies to be identified and making it accessible across the entire project.

Similarly, the new Aveva Surface Manager application widens the scope of data interoperability by enabling Aveva Marine to use data created in specialist surface modellers.

Perhaps the most eagerly awaited addition is Aveva Design Reuse. This is much more than just a ‘Save As’ function; it enables all or parts of previous projects to be replicated for use on subsequent tasks by also copying the ‘intelligence’ in the originals. The potential savings in design effort can be as high as 70%, whether for sister ship designs, or for creating new ships from modular design elements. Importantly, Design Reuse does more than simply replicate hull structure; it can replicate outfitting, equipment and drawing information. Different catalogues and standards may be applied to the new design to meet specific client requirements.

When asked whether Aveva believes that this is the ultimate as far as integration can go, or are there other aspects of ship design and building that can still be integrated or improved. Neuvéglise replied: “No, we would never suggest that there is no more scope for improvement. Integrating work processes by integrating the different types of information which support them offers some of today’s biggest opportunities for increasing productivity. That’s why Aveva has, for many years, been pioneering new technologies and championing open standards for data interoperability.” He continued: “This has already created many opportunities still to be fully exploited by the shipbuilding industry, but we continue to develop new applications which add more functions and extend technology integration. In engineering, stand-alone software that cannot share data is history; today’s new applications must combine power with interoperability.”

More than CAD

Intergraph believes that a broader horizontal strategy is needed for shipbuilding that extends across engineering, business, material management, production, and life cycle management domains. The company’s SmartMarine Enterprise is an adaptable, open solution that can serve as a platform for such integration and data repository functions, where global project information can be created, managed, re-used, and controlled throughout the product life cycle.

Intergraph claims that its SmartMarine Enterprise is much more than a modern data-centric CAD system dedicated to the marine industry - it is a suite of process-driven ready-to-use software solutions for the complete life cycle which includes:-

• materials and procurement management;
• engineering project and cost control;
• hull preliminary (initial) design;
• outfitting preliminary design;
• hull and structure design modelling;
• outfitting design modelling; and
• fabrication and construction planning.

All of these are designed to offer benefits in terms of increased productivity and automation, and reduced cost and schedule.