Bulk Carrier Update No. 1 2011

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Guideline on fuel saving measures

Return on investment tool

Practical example

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FUEL SAVING MEASURES

No 01 2011

CONTENTS

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Photos: front cover ŠGetty Images pages 8–9: Mewis Duct from Becker Marine Systems Propeller Boss Cap Fin – MOTech, Mitsui O.S.K Techno-Trade, Ltd. Pre-swirl Stator – Daewoo Shipbuilding and Marine Engineering Propeller nozzle – SDARI Contra-rotating propeller – Wärtsilä and IHI Marine United Propeller rudder transition bulb – ENERGOPAC from Wärtsilä Pre-duct – WED from Schneekluth

bulk carrier update WE WELCOME YOUR THOUGHTS! Published by DNV Global Governance, Market Communications. Editorial committee: Michael Aasland, Business Director, Bulk Carriers Magne A. Røe, Editor Lisbeth Aamodt, Production Design and layout: Coor Service Management/Design Dept. 1104-011 Print: Grøset Trykk AS, 6,000/05-2011 Please direct any enquiries to DNVUpdates@dnv.com Online edition of bulk carrier update: www.dnv.com/bulkupdate

GUIDELINE ON FUEL SAVING MEASURES FOR BULK CARRIERS...........................................................4 SCOPE OF GUIDELINE ........................................................8 RETURN ON INVESTMENT TOOL ..................................10 HOW TO USE THE GUIDELINE FOR FUEL SAVING MEASURES AND THE RETURN ON INVESTMENT TOOL ..................................14 VALIDATION ON FUEL SAVINGS ....................................18 2 | BULK CARRIER UPDATE NO. 1 2011

DNV (Det Norske Veritas AS) NO-1322 Høvik, Norway Tel: +47 67 57 99 00 Fax: +47 67 57 99 11 Š Det Norske Veritas AS www.dnv.com

››

EDITORIAL

COST OF FUEL

Michael Aasland Business Director, Bulk Carriers Michael.Aasland@dnv.com

The cost of fuel is increasing. Although we will most probably see large fluctuations in the future, most indicators point towards even higher fuel prices in the long term. Fuel costs already make up a large percentage of ship owners’ operating costs, and this percentage will most likely grow in the future. Our industry is currently facing difficult times, with an oversupply of tonnage in the market depressing charter rates. The very large order book will further increase the supply side, so most analysts predict low to moderate rates in the short

to medium term. In this situation, it will be even more important to reduce costs. Much has been said about the importance of saving fuel from not only a financial but of course also an environmental point of view. However, we recognise that it is not easy to save fuel – if it was easy, it would have been done already! Research has shown that the use of so-called propulsion efficiency devices has a great fuel-saving potential. However, even in this area there is a lot of confusion. How do the various devices actually work? Which devices will work together?

What is the estimated effect of the device? And, most importantly, how can the return on the investment in such a device be calculated? Some ship owners do not have the necessary resources to investigate these complex issues. SDARI and DNV have worked together to address these complex issues. In a joint project, we have prepared a comprehensive guideline covering fourteen fuel-saving measures which are highly relevant today. For each measure, we have discussed how the measure or device works, the range of expected fuel savings and

the approximate cost of each device. We have also developed a unique return on investment calculator into which ship owners can enter possible future developments in fuel costs and interest rates as well as data for the relevant device and thus easily calculate the predicted cost effectiveness of each device. We believe this guideline and the return on investment calculator will be useful in endeavours to save fuel and reduce shipping’s environmental impact, and we therefore offer it free of charge to our clients.

Executive summary Fuel is one of the major cost elements for a ship owner/ operator and by reducing fuel consumption an owner/ operator will reduce both his costs and the environmental impact from his ship. The use of devices that increase propulsion efficiency has been shown to have a great potential to save fuel, however such devices are still not very common due to limited knowledge about them and their cost-effectiveness. SDARI and DNV have worked together to prepare a guideline and a return on investment tool to deal with this issue. The guideline addresses how the devices work, their compatibility with other devices, the complexity of manufacturing and the classification requirements. It also gives ranges of expected fuel savings and indicates the price ranges for each device. Various scenarios for fuel prices, interest rates, payback times, estimated fuel savings and costs can be entered in the return on investment tool in order to easily calculate both the environmental impact and the cost/benefit.

BULK CARRIER UPDATE NO. 1 2011 |

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GUIDELINE

Guideline on fuel saving measures for bulk carriers DNV presented MACC trend curves at Nor-Shipping two years ago. They showed a large fuel saving potential, which could be achieved by, for example, improving the hull and propeller design, using various fuel saving devices and optimising machinery and outfitting. To point out a great savings potential a is good start, but it must be followed up by providing the means to achieve change. TEXT: OLAV ROGNEBAKKE, DNV

‹‹ Olav Rognebakke

A NEED IN THE MARKET A joint project between Shanghai Merchant Ship Design & Research (SDARI) and Det Norske Veritas (DNV) is ongoing with the objective of providing an overview of relevant fuel saving measures for bulk carriers to be built in China, and of developing a framework for return on investment calculations. This provides a practical approach to meet the needs of the cost-aware bulk carrier owner, as well as of designers and yards. Implementing fuel saving measures can be challenging. The bulk carrier is the workhorse of the sea, and its design and outfitting are based on a long history of focusing on cost and optimisation. Bulk carriers are also traditionally relatively ‘low tech’ and even small investments are scrutinised. However, the lower rates and high

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HFO price predicted for the next couple of years will make cost reductions even more important. The typical bulk carrier owner is also reputed to be conservative; he requires a relatively short payback timeon any investment and accepts a limited risk. On the other hand, a typical bulk carrier with a traditional aft ship, propeller and rudder will have a large potential to save fuel by adding different devices. There is also an increasing trend for new bulk carriers to install fuel saving devices. For example, Mitsui claims that it has installed more than 1,700 of its Propeller Boss Cap Fins. However, the owner has a variety of fuel saving devices to choose from, and selecting the appropriate one is a challenge. It is sometimes possible to combine

different devices, but they need to be compatible to provide a total saving that is significantly larger than that from each individual device. Other factors further complicate the picture, and a number of questions need to be addressed: What will be required from the yard in order to install the fuel saving device? What will be required from classification in way of approval? How much fuel is the device estimated to save? What are the maintenance needs? And how much will the device cost? Some owners have limited technical resources to evaluate these issues, and may need assistance to choose the right means to save fuel. Finally, the cost/benefit of the investment in a fuel saving device may be difficult to calculate. Which factors

GUIDELINE

›› Mewis Duct. Courtesy of Becker Marine Systems

should be taken into account and how? Although saving fuel will naturally have a positive impact on the environmental footprint, the decision to invest must still be based on sound return on investment calculations. A CONTRIBUTION FROM SDARI AND DNV To address this perceived need for objective information and guidance, SDARI and DNV defined a project aiming to: Provide ship owners with advice regarding the available technology and cost-effectiveness of fuel saving measures which are relevant for bulk carriers to be built in China. The project has two main deliverables: Q A guideline on fuel saving measures Q A return on investment tool for

calculating the cost/benefit of the investment This project benefits from the complementary knowledge and experience of SDARI and DNV. SDARI mainly provides cost estimates and explains the manufacturing complexity. DNV is responsible for the detailed description of each fuel saving measure, including compatibility issues, classification requirements, the range of expected savings and the expected maintenance during operation. DNV is also responsible for the return on investment tool. OVERVIEW OF THE GUIDELINE The scope of the guideline is to provide a ship owner with an overview of the most

relevant fuel saving measures available for bulk carriers to be built in China. The guideline provides the necessary input for a return on investment analysis of selected fuel saving measures. This document is available upon request from SDARI and DNV, together with the return on investment tool. The guideline starts out with a general description of the selected evaluation parameters. A basic introduction to ship resistance and propulsion helps the reader understand more about how each measure works. Different ways of validating savings are also discussed. The bulk of the guideline consists of sections giving a detailed evaluation of the various fuel saving measures. Each section describes the measure, including

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GUIDELINE

›› Propeller (PBCF). Courtesy of MOTech, Mitsui O.S.K Techno-Trade, Ltd

compatibility issues, lists classification requirements and discusses manufacturing issues. The range of expected fuel savings is an important point which, together with the expected investment and maintenance costs, creates the basis for a cost/benefit analysis. Finally, the fuel saving and cost factors for the fuel saving measure are listed in a table. The compatibility between different fuel saving devices is also presented in a matrix.

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PHYSICAL EFFECTS Most of the fuel saving devices work by reducing the energy loss from the propeller. There will be losses due to friction on the propeller blades and the generation of hub and tip vortices as well as axial and rotational losses. The effective wake is the velocity field in the plane of the propeller, and the characteristics of this wake influence the propeller efficiency. In addition, some devices improve the wake. The 22nd International Towing Tank Conference (ITTC) issued a document entitled “The specialist

committee on unconventional propulsors”, which categorises energy saving devices as “pre-swirl”, “post-swirl” or “pre- and postswirl”. These devices create one or more of the energy saving mechanisms in the following list: Q Pre-rotation to the propeller inflow Q Improve propeller inflow Q Alleviate flow separation Q Recover rotational energy from downstream Q Decrease viscous loss after propeller cap Q Decrease eddy after propeller cap

GUIDELINE

›› Mewis Duct. Courtesy of Becker Marine Systems

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Produce additional thrust

PUTTING NUMBERS ON FUEL SAVINGS It is necessary to present ranges of expected fuel savings, since the actual reduction in the required engine power for a fixed speed depends on the ship size and the design of the hull, propeller and appendage. A highly optimised design will have less margin for fuel savings. Another topic is the individual adaptation of the chosen measure. The performance generally increases with the amount of effort put

into the design of a fuel saving device. Typically, a supplier operates with an item cost as well as a design package cost. The latter will only be incurred once for a series of identical vessels. THE IMPORTANCE OF VALIDATION The validation of the expected fuel savings is important and challenging. Ideally, validation should be based on a comparison between two ships that are identical except for the fuel saving measure in question. However, even two sister vessels

straight out from newbuilding dock may experience a few per cent difference in required power, which implies great uncertainty in a savings estimate. An alternative is to conduct model tests in which the towing tanks have long experience in conducting accurate repeatability tests in accordance with the guidelines issued by the ITTC. In recent years, computational fluid mechanics has become a viable validation option. }

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SCOPE OF GUIDELINE

Scope of guideline The guideline contains a detailed description of 14 different fuel saving measures, briefly described here. There are many other good candidates for fuel saving devices. This selection consists of popular ones intended to be representative of typical main categories. TEXT: OLAV ROGNEBAKKE, DNV

Mewis Duct

Rudder profile

The MD is a combination of a vertically offset mounted duct positioned right in front of the propeller and an integrated asymmetric fin arrangement. For full-form slower ships. Combines the effect of a wave equalizing duct and pre-swirl fins.

Thinner rudder profiles have less drag but are more likely to develop separated flow and cavitation. The twisted leading edge rudder from Becker Marine Systems is a more refined profile. High lift profiles can give significant power savings.

Propeller Boss Cap Fin The PBCF consists of small fins attached to the propeller hub. The number of fins equals the number of propeller blades. The aim is to reduce the energy loss due to hub vortices.

Pre-Swirl Stator The PSS is a set of blades positioned right in front of the propeller, with an asymmetric configuration. It works by introducing pre-swirl ahead of the propeller to reduce rotational losses and thus improve propulsion efficiency.

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Propeller design The main propeller characteristics determining the open water efficiency are the diameter, rotational speed, pitch ratio, number of blades and blade area ratio. The main parameters may be optimised and selected on the basis of experimental data from propeller series such as the Wageningen B-series. High efficiency is achieved by a large diameter, low number of blades, low blade area ratio and low RPM.

Hull shape The hull lines and ship speed determine the lower limit of the vessel’s resistance. Traditionally there has been a large focus on design speed in the optimisation of hull lines, but new flexibility requirements mean that a vessel must perform well over a range of drafts and speeds. For low Froude number bulk carriers, a high block and maximum draft help reduce the dominating viscous resistance. Detailed aft ship optimisation that takes the propeller into consideration is required to achieve maximum performance.

SCOPE OF GUIDELINE

Propeller nozzle

Openings – arrangement and design

An efficiency improving propeller nozzle changes the flow field in and around the propeller and divides the thrust force between itself and the propeller. A nozzle can also be used to improve cavitation and noise properties.

ContraRotating Propeller A CRP is a highly efficient means of propulsion, but is also complex and costly. A two-digit improvement in efficiency is possible compared to a traditional propeller.

Propeller rudder transition bulb There is a variety of solutions involving bulbs fitted to the rudder in order to reduce hub vortex losses. Such solutions are typically a central part of a modern high efficiency rudder.

Pre-duct A pre-duct is fitted to optimise the propulsion properties by improving the flow into the propeller. It can also improve manoeuvrability and reduce hull vibrations. Some pre-ducts also produce thrust.

Openings in the hull are needed for sea chests and bow/stern thrusters. The detailed configuration of these openings is important for resistance and possibly noise and vibration. The efficiency of the thrusters depends on the shape of the tunnel.

Main engine Generally, larger bulk carriers have two-stroke diesel engines installed. The most common type of engine is mechanically controlled, while electronically controlled engines are becoming more common for newer vessels. Typically the de-rating of the main engine, engine control tuning for electronically controlled engines and low load optimisation using the variable turbine area and exhaust gas bypass can be done to reduce the specific fuel oil consumption (SFOC).

Auxiliary engine Auxiliary engines on board bulk ships that are not geared usually mainly supply electrical power to the accommodation and machinery systems when under way. The most common setup is to have three auxiliary engines of the same size. This allows one engine to be out for maintenance while still complying with the redundancy requirements. Generally all the measures that may be applied to the main engine in order to reduce the SFOC may be applied to the auxiliary engines.

Waste heat recovery system Waste heat recovery has the largest potential to improve the efficiency of traditional two-stroke engines, but there are challenges related to exploiting this potential. Both the complexity and cost of the system have made these types of systems rare on bulk carriers.

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ROI TOOL

Return on investment tool – a tool to analyse the cost effectiveness of fuel saving measures TEXT: EIVIND NEUMANN-LARSEN, DNV

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ROI TOOL

›› Figure 1: Methodology

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FINANCIAL ANALYSIS FRAMEWORK When evaluating a fuel saving measure, several issues should be considered, such as the technical maturity, complexity of manufacturing and implementation, complexity of operation and classification requirements. These and other issues are covered in the Guideline and are not addressed in this tool, which is purely a financial tool that evaluates the cost/benefit of the fuel saving measures. Accordingly, the tool provides a framework for financial analysis, leaving it to the ship owner to enter the variable parameters into the calculation based on information included in the Guideline, as shown in Figure 1. FUEL SAVING MEASURE AND INVESTMENT PARAMETERS The starting point is to enter the investment cost and additional maintenance costs (if relevant) due

to the new fuel saving measure. Some measures are quite costly and might have an impact on the second-hand value of the vessel. In these cases, this is also to be taken into consideration. Once the initial and annual costs have been estimated, the fuel consumption and corresponding costs are calculated. Fuel price developments are a major uncertainty when calculating operational costs, but at the same time fuel costs typically amount to 30–40% of a vessel’s total running costs. The fuel price can be stated as a fixed price throughout the investment period in the tool, but different fuel price development scenarios, typically a high, medium and low price scenario, can also be analysed. In this way, it is possible to evaluate a fuel saving measure’s fuel price sensitivity and its effect on profitability.

OPERATING PROFILE AND FUEL CONSUMPTION A vessel’s annual fuel consumption is calculated based on the daily consumption in tonnes and total days at sea. However, it is also possible to define a detailed operating profile with different sailing conditions or operating states, e.g. sailing ballast, sailing laden, cargo handling in port, etc. The different operating states are specified in more detail with average engine load and specific fuel oil consumption, as shown in Figure 2. The reduction potential for each measure will vary depending on aspects like ship size, operation and engine load, and the fuel savings potential needs to be estimated for each operating state. FINANCIAL MEASURES General investment parameters must be decided upon (i.e. investment period, discount rate and

BULK CARRIER UPDATE NO. 1 2011 |

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ROI TOOL

fuel price scenario) and the given cash flow is then generated by the tool. The fuel savings are set as incomes and the initial and maintenance costs as costs. Common financial figures are calculated automatically, such as: Q Net Present Value (NPV): the present value of discounted benefits and discounted costs minus the investment cost Q Payback period: the time span required to recover the cost of an investment

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Internal Rate of Return (IRR): the discount rate at which the benefits (inflows) equal the costs (outflows) Profitability Index (PI): the present value of the future cash flows divided by the initial investment (also known as the cost/benefit ratio)

As shown in Figure 3, the expected cash flow and profit are visualised in different charts, and changes in investment

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parameters are updated instantly to allow easy evaluation of the effect. ENVIRONMENTAL BENEFITS There is currently a high focus on green ship designs, and the environmental benefits should be taken into consideration in the evaluation. It is probable that stricter environmental regulations will be enforced in the foreseeable future, and fuel savings measures can reduce the burden of such

ROI TOOL

regulations. Figure 4 shows how the tool estimates the environmental benefits due to the reduced fuel consumption, including the reduction in CO2, SOx, NOx, and particulate matter.. COST/BENEFIT EVALUATION The financial tool also has features to investigate the initial cost sensitivity, as shown in Figure 5. This is particularly relevant in order to evaluate the effect of any budget over-runs,

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potential, cost efficiencies and fuel and emission reductions, as well as the number of years needed to recover the initial costs and the measure’s sensitivity to changes in fuel price. In that way, the tool will help reduce the risk of making a wrong investment decision. }

and is also relevant when evaluating measures on a series of ships where quantity discounts may come into effect. Several fuel saving measures are promoted by different vendors and shipyards, and ship owners need to obtain a general overview and evaluate the cost effectiveness of these measures for their bulk carriers. The return on investment tool combined with the Guideline should provide an overview of the fuel saving measure’s

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›› Figure 4: Reduced emissions

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›› Figure 5: Fuel price and initial cost sensitivity

BULK CARRIER UPDATE NO. 1 2011 |

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HOW TO USE

How to use the guideline for fuel saving measures and the return on investment tool In this article, we will illustrate the use of the SDARI-DNV Guideline for Fuel Saving Measures and the Return on Investment Tool by using an example. We will in the example assume the role of a technical manager in a typical ship owner organisation. It should be noted that the values used here have been selected to illustrate the process only, and reference is made to the guideline for further details. TEXT: MICHAEL AASLAND, DNV

We assume a project under evaluation with the following initial data: Q Fuel Oil Consumption: 32 MT/day laden and 28 MT/day in ballast Q Operational profile: Laden 150 days, Ballast 150 days, Manoeuvring 10 days, Cargo Handling 40 days, Idle 10 days. First of all, it will be useful to understand the basic principles of propulsion and resistance. Chapter 2 of the guideline, “Physical Description of the Fuel Efficiency Measures”, provides an overview of the physics of ship powering and resistance and groups the issues into three areas: Q Resistance components Q Propeller characteristics, propulsive efficiencies and related losses Q Machinery All these areas are important and should be considered in detail. Chapter 5 is helpful in this respect, as it gives a detailed

14 | BULK CARRIER UPDATE NO. 1 2011

evaluation of the most common measures in the three areas: Q Mewis duct Q Propeller boss cap fins Q Pre-swirl stator Q Propeller nozzle Q Contra-rotating propeller Q Propeller rudder transition bulb Q Rudder profile Q Pre-duct Q Propeller design Q Hull shape Q Openings – arrangement and design Q Main engine Q Auxiliary engine Q Waste heat recovery system Each of these measures is evaluated with respect to the following parameters: Q Description, including compatibility Q Requirements from Classification Q Manufacturing complexity Q Range of expected fuel savings

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The device’s expected maintenance needs when in operation Rough indication of price range

In this example, we will for simplicity focus on one measure only, and we have selected the propeller boss cap fins (PBCF). The section of the guideline covering the PBCF starts off by describing how the device works, with references to further reading on the topic. The guideline also covers class requirements and finally describes the complexity of manufacturing and installing the PBCF. Based on the information provided in the guideline, it is concluded in this example that the device is of interest for further evaluation. The main reasons for this conclusion are: Simple concept, relatively common device, limited or no effect on the rest of the ship, and it does not place high demands on the shipyards’ installation capabilities.

HOW TO USE

›› Propeller Boss Cap Fins. Courtesy of MOTech, Mitsui O.S.K Techno-Trade, Ltd

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HOW TO USE

The section on PBCF goes on to describe the maintenance needs and provide ranges of expected fuel savings as well as indications of the price of the device from a number of sources. In this example, the following values have been selected with regard to the PBCF: Q Expected saving of 3% at full draught and 2% at ballast draught. These values are rough indications, and the guideline explains how they can be verified Q Cost of maintenance estimated to be USD 5,000/year Q Cost of design package estimated to be USD 28,000 – to be split between four ships – and cost of PBCF including installation, USD 40,000, i.e. a total cost of USD 47,000 per ship Q We further assume that there is no impact on the resale of the ship, which is a conservative assumption.

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The following variables are also assumed: Q Investment period of three years Q Discount rate of 8% Fuel price developments will of course have a large impact on the cost/benefit analysis of the fuel saving device. The tool allows for several alternatives: Q Using a fixed price in USD/ton for the whole period Q Using one of four scenarios: Low, Medium, High or Custom. In this example, we have for illustration purposes selected the custom scenario option, with a starting price of USD 550 and a 2% year-on-year increase (Figure 1). With the above assumptions entered into the return on investment tool, we obtain the following results (Figure 2). Based on the assumed input, we achieve estimated fuel savings of 228 tons/year due to the reduced consumption on laden and ballast voyages.

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We also achieve the following financial results presented in Figure 3. The net present value of the USD 47,000 investment is calculated to be more than USD 250,000 (Figure 4). The return on investment tool also generates plots indicating the sensitivity of the investment for various fuel price scenarios entered, as well as its sensitivity to cost overruns. The latter is very useful, since the percentage overrun can be entered and the results plotted graphically (Figure 5). Finally, the tool calculates the environmental impact of the fuel saving measure and plots the result as shown in Figure 6. In this example, we have shown how the SDARI-DNV Guideline for Fuel Saving Measures and the Return on Investment Tool can be used when evaluating the cost/benefit of fuel saving devices. }

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›› Figure 2: Fuel consumption results.

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›› Figure 3: Financial results.

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›› Figure 1: Various fuel price scenarios.

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Figure 4: Cumulative discounted cashflow.

Figure 5: Investment cost sensitivity – cumulative discounted cash flow.

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Figure 6: CO2 reductions.

Figure 7: SOx, NOx, and particulate matter reductions.

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BULK CARRIER UPDATE NO. 1 2011 |

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VALIDATION

Validation of fuel savings The ship owner would like an accurate estimate of the fuel savings before deciding to purchase. After installation, it is valuable to know the actual savings. The effect of each measure varies depending on ship characteristics like size, hull lines, speed, propeller and rudder configuration. The reduction in power usage reported by suppliers may well be validated for certain designs, but some of the fuel saving devices should be optimised for each new vessel. Optimisation requires a means to estimate savings. Validation also becomes important when different devices are combined, as compatibility issues may reduced the overall effectiveness. The performance of a fuel saving measure may be validated by full-scale measurements, model tests or numerical analyses. TEXT: OLAV ROGNEBAKKE, DNV

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FULL-SCALE MEASUREMENTS Fuel savings measured by full-scale trials might appear to provide the best validation of a device’s performance. However, full-scale measurements are subject to limited measurement accuracy, poor control of the environment, and the effect of unexpected or unknown changes to the vessel between tests. When conducting measurements, it is common to make use of the onboard sensor system. However, the quality of such a system may vary significantly. If the sensor is not intended to provide high precision measurements, the accuracy may be insufficient. Since fuel saving measures often produce small gains, this uncertainty may be enough to disrupt the identification of any fuel saving. When predicting the performance based on a sea trial, correcting for environmental effects like wind, waves and current is a challenging task. How these corrections are conducted may have a significant effect, and will probably represent a major source of uncertainty. High quality validation data are obtained from full-scale measurements by good planning and execution combined with careful post-processing and analysis.

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›› Illustration of speed power curve – measured data in blue and corrected data in red. The dots indicate the measured points while the lines are the smoothed results.

VALIDATION

MODEL TESTS The International Towing Tank Conference (ITTC) 1999 report on unconventional propulsion addresses the issue of using model tests to assess the performance of various fuel saving devices. Towing tank organisations typically use extrapolation methods based on modifications of the ITTC 1978 approach. Some have developed a new methodology for each particular type of unconventional propulsor. The report explains that extreme cases, such as

integrated ducted propulsors, cannot be adequately studied using the ITTC 1978 methodology, while for example pre- and post-swirl vanes, ducts and propeller pods have been dealt with by appropriate modifications. The standard correlation procedure fails to scale and predict the energy saving due to laminar flow on some devices at normal towing speeds. For some devices, reliable full-scale estimates of savings depend strongly on achieving the Froude and Reynolds number

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Without PBCF.

With PBCF.

COMPUTATIONAL FLUID DYNAMICS Unsteady RANS codes can now be used to accurately predict turbulent flow at realistic Reynolds numbers for ship powering applications. Computational Fluid Dynamics (CFD) has become a standard tool for yards, research institutes, designers and classification societies. Similar to model tests, CFD simulations allow for precise control of the measurements and environment. Since CFD simulations can be conducted at full scale, the scaling problem inherent in model tests is avoided. When conducting CFD simulations, it is important to have a firm understanding of the physics to be investigated. This is necessary in order to include the appropriate numerical models in the simulations. When addressing new topics, model tests should be conducted and simulations performed in either model or full scale

to confirm the physical models. A mesh convergence study and sensitivity study may also be necessary. ITTC has issued recommendations on how to perform such studies. CFD may be a cost effective means of validating savings, but typical analyses are still demanding in terms of both required man-hours and computational resources. In addition, software licences are expensive. Assuming that the hull shape is fixed and that reliable extrapolation methods exist for the fuel saving device in question, model tests may be cheaper if many parameter variations are needed. In CFD, meshing typically takes up most of the time, and this is in general required for new speeds and drafts. } All photos are courtesy of MOTech, Mitsui O.S.K Techno-Trade, Ltd

similarity. Partial ducts are reported to result in energy savings in full-scale trials, but the ITTC report concludes that this probably cannot be proven by model tank towing tests at Froude speed. Even cavitation tunnel tests at higher speeds may show uncertain trends. New testing procedures and the application of large high-Reynolds number water tunnels promise to improve fuel saving estimates.

›› Without PBCF.

›› With PBCF.

BULK CARRIER UPDATE NO. 1 2011 |

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DELIVER IN BULK SHIPPING When business conditions are tough, execution becomes the margin of difference in bulk carrier management. Making your fleet perform requires leading edge expertise in every aspect of maritime operations. DNV’s global teams of surveyors and consultants provide support along the entire vessel lifecycle, from specification review and pre-contract to operation. Through our class, advanced analytical and advisory services, we can help you deliver results in bulk shipping. Classification • Advisory services • Health, safety and environmental risk management

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