Brazilian ore giant Companhia Vale do Rio Doce (VALE) has placed an order for 12 very large ore carriers (VLOCs) with China’s third largest shipbuilder, Jiangsu Rongsheng Heavy Industries – all vessels to DNV class.
Each of the vessels will be 400,000 dwt, making them the world’s largest ore carriers. They will be built to the highest standards for safety and efficiency – both DNV’s CSA-2 notation and the latest Easy Loading notation EL-2 have been specified for all vessels. They will also be environmentally friendly, with a carbon footprint 34 per cent lower than that of traditional Capesizes.
The world’s largest dedicated ore carriers are currently being designed in China. The 400,000 dwt vessels will be 360 metres long, 65 metres wide and 30.4 metres high. They will transport iron ore from Brazil to China and will achieve more than 30 per cent reduction in fuel consumption and CO2 emissions for each tonne of cargo carried compared to the equivalent capacity in Capesize vessels.
Wärtsilä engines will power the world’s largest ore carriers – RT-flex82T low-speed engines will power all 12 vessels. These engines features 7-cylinders, each with 820 mm cylinder bore, and a contracted maximum continuous power of 29,400 kW at 76 rpm. It combines the benefits of both the electronically-controlled RT-flex common-rail system and up-to-date parameters to deliver optimum propulsion plants for ships such as these very large ore carriers (VLOC). More specifically, the RTflex common-rail technology brings direct benefits in terms of great flexibility in engine setting for lower fuel consumption, lower minimum running speeds, smokeless operation at all running speeds, and better control of other exhaust emissions. The RT-flex common-rail technology will also play a key role in meeting the need for tighter emissions control under the forthcoming IMO regulations.
Safe and efficient
The vessels are arranged with seven cargo holds, each operated with single-panel, side rolling type. The hatch openings will be very wide to allow unobstructed access for loaders and grabs for discharge operations – the so-called ‘dead spots’, the space inside the cargo holds that cannot be reached by grabs during discharge, will be reduced to a minimum.
Classed using DNV’s new Easy Loading notation, potential hull loading stress problems are being carefully evaluated and dealt with at the design phase to ensure optimal operational efficiency and lifetime safety. Designed in accordance with the EL-2 notation, each of the seven cargo holds will be able to be fully loaded in a single step, and this will allow for loading times radically lower than normally achievable for such vessels.
The radically reduced loading time will give a critical advantage as the waiting time at Brazilian iron ore ports has been an average of 6–8 days during 2006–2008. Often 12 per cent of the global fleet are waiting in ports around the world at any given moment.
The current industry-wide request to accept a terminal’s nominal loading rates, at least as a potential maximum, has caused concerns as far back as the 1980s. At that time, tragedy struck when several bulk carriers were lost at sea without an easily identifiable cause. This led some people to question the safety of the very high loading rates of ores, typically over three tonnes per cubic metre, which are delivered from a position high above the cargo hold.
The International Association of Classification Societies (IACS) investigated the issue and concluded that the problem could not be directly attributable to loading rates, but instead recommended monitoring and synchronising loading and de-ballasting operations to avoid dynamic local and longitudinal stresses which could, over time, harm the structural integrity of the hull. Subsequent IMO and class initiatives led to IMO’s ‘Code of Practice for the Safe Loading and Unloading of Bulk Cargoes’, the so-called BLU code, and SOLAS Chapter VI, Part B covering these issues.
The issue can be resolved during the design stage of the vessel. Synchronising is recommended, but it is a fact of life that it is frequently not done in the loading sequences defined in the loading manual, and hence many vessels may not be fitted with adequate de-ballasting capacities. This is one of the main features of the Easy Loading notation, and which will now be incorporated into the new 400k dwt VLOC design for VALE – ballast pumps and piping dimensions appropriately sized to handle the workload to allow synchronized de-ballasting and loading or unloading operations.
In addition, the vessel will be designed with additional longitudinal and local strength, and fitted with a remote tank sounding and draught reading system with an on-line interface into the software of the onboard loading computer. Altogether, these measures will ensure vessels which are both safer and more efficient than conventional design. For the ship Master this should be good news – his vessel will be designed with a higher safety standard and loading flexibility, and with well documented, realistic loading sequences incorporating the check of both global and local strength. He will also benefit from more automated control of the critical parameters, which will be fed directly into the on-board loading computer to support easy re-calculation of global and local strength at any time.
One other feature of the so-called ‘Chinamax’ design is the use of separate ejector pumps and ballast stripping system. This will ensure the vessels may perform simultaneous de-ballasting by pumps or by gravity stripping of nearly empty tanks.
The VALE VLOCs can cope with an average loading rate of 13,500 tonnes per hour delivered to each of the holds in a single pour – each cargo hold is able to carry almost the same cargo volume as a small Panamax carrier! Hence the design will undergo a careful evaluation of both longitudinal and local strength, including a detailed Finite Element Analysis.
Ore carriers are generally tailor-made for a particular trade, and should be carefully evaluated for fatigue strength on the relevant route. Alternating between fully loaded and ballast conditions, VLOCs may also be subject to low cycle fatigue.
Recently, DNV has established that heading into harsh weather on return, ballast runs may effect heavily on hull fatigue life through so-called wave-induced hull girder vibrations, also called springing and whipping. DNV has undertaken several years of research on this phenomenon in co-operation with the Norwegian University of Science and Technology, using both model testing and full-scale measurements. A new guideline has been developed and recently released by DNV to take this additional fatigue load into account.
The VALE VLOCs will be designed with special attention to these effects, and by specifying that the vessels should be designed according to the requirements mandated by DNV’s CSA-2 class notation, VALE has set a new standard for safety assessment of ore carriers.
DNV – the leading Class for ore carrier design
Currently more than 40 per cent of the world’s VLOCs are under DNV class. The VALE VLOCs will supersede the Berge Stahl, also to DNV class, as the largest ore carriers in operation. At 365,000 dwt, Berge Stahl represented, back in 1986, a new generation of large ore carriers.
Through its dominant position in the ore carrier market, DNV has helped ship owners protect their assets through a greater awareness of structural integrity issues, which will also be incorporated into VALE’s ground-breaking, new design for the world’s largest ore carriers.