HIGHLIGHTS

A NEWSLETTER PUBLISHED BY SSPA SWEDEN AB 3/2000

Contents The ferry in Muong Khoa 2 Twin-skeg VLCC in restricted waters 4 CFD a key to lower fuel costs 6 Short comments 8

PART OF OBAN TRIPTYCH BY KUNIYOSHI. BY COURTESY OF THE MUSEUM OF FAR EASTERN ANTIQUITIES, STOCKHOLM, SWEDEN.

The ferry in Muong Khoa

SSPAs staff is used to travel, being a consultant means that you work where the client asks you to work. Although our business is related to marine engineering and marine transportation in a very general sense it still usually implies that our clients have some close relation to the sea. In a recently completed project, however, the mission took our consultant to a remote mountain area in a landlocked country in the Far East - to Laos. This is the story why. Laos or Lao Peoples Democratic Republic which is the formal name, is a landlocked country between Thailand and Vietnam. It also shares it borders with Cambodia, Myanmar/Burma and China. Compared to its over-populated neighbours Lao has only about 5 million inhabitants on an area almost equivalent to half the area of Spain. It is also an ancient civilised country which in the 20th century has suffered from occupation, civil wars and political pressures with the result that Laos today is one of the least developed countries in south east Asia. A sparsely populated country with large mountain areas, no railroads, no open sea connections and only limited air fields. A country which has to rely on the roads for transport and communication.

Solving the problem in Muong Khoa

Laos national road #2 starts in Pak Beng close to the Thai border, passes through the regional centre Oudumxai and continues through the northernmost province Phongsaly to the Vietnamese border and the city Dien Bien Phu. Since the road is one of only a limited number of roads crossing the mountain ridge between Vietnam and Laos, it is of great importance not only for the communication between the two countries but also for the possibility of opening up business connections, trade markets and provide communication to people who have lived in a very isolated community. In the village of Muong Khoa in Phongsaly province the road crosses the Nam Ou river, a major tributary to the Mekong. Originally there was a cable ferry connection in Muong Khoa, but during a severe flooding in 1994, when the water rose about 20 m above normal levels, the cable was torn apart. Since then the ferry connection is maintained using a small tugboat, which pushes the ferry barge across the river. The main disadvantage with this system is that the tugboat cannot operate during the rainy season, when the river is too strong. As the rainy season lasts for about 5 months (June October) this means that no trucks or cars can traffic the road beyond Muong Khoa for almost half a year.

Forecasts are tricky especially regarding the future!

Forecasts can easily be destroyed by political eruptions or nervous financial reactions. Still some signs are too strong to be eliminated in that way. Asia is gaining momentum again, and it means changes for all of us. Asia has ten times as many inhabitants as Europe or North America. This area moves very fast, especially some large countries like China. China trade import/export in 2000 grew some 35% relative to the year before. Size and speed are starting to impact world scale economy and ecology. Japan and Korea led the way some years earlier, and from my ice-bear point of view its time to realise that the worlds point of gravity is moving east! At the same time the need for transportation will grow, and since most world inhabitants live along shores and inland waterways it means business for us. It is a challenge to find ever more efficient marine transportation concepts focusing on economy, ecology and customer satisfaction providing appropriate technology. Lars Afzelius

Build-up of infrastructure
To improve the infrastructure Laos has also received significant support from various countries. The new airport in the capital Vientiane was built by Japan, Thailand is planning a railroad connection over the Mekong river, the European Union supports irrigation projects and several countries like the USA, China and Sweden support different road construction projects. Sweden through Sida (Swedish International Development Cooperation Agency) and their project managers, HIFAB International, has in co-operation with the World Bank taken the approach to support national and regional road administrations in Laos with advisors in road maintenance projects. Two of these road advisors had independently a similar problem how to establish a reliable road connection across a river without building a bridge.

uring the rain season landslides are frequent along highway #2 causing severe interruptions. 4WD cars are imperative despite the national road status.

ational highway #2 in Phongsaly province.

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The ferry in Muong Khoa

Natural propulsion
The restored ferry connection will consist of a wire cable suspended across the river valley about 25 m above the water. A trolley will run on the wire cable and from the trolley there will be two wires mooring the ferry barge to the cable. To operate the ferry, the aft of the two wires is slackened a little from a winch giving the ferry a slight angle relative the river current. The current will then push the ferry across to the other side. The ferry is thus operated without any power except for the man pulling the winch.

during a year. Despite the absence of oceans and ports Laos also has to request maritime transportation knowledge to improve their road systems. At the same time SSPA got a glimpse of a different kind of infrastructure development. Pontus Clason

ontus Clason, M.Sc., Project Manager at SSPA. He received his masters degree in Naval Architecture at Chalmers University of Technology in 1981 and was then employed at the offshore fabrication yard Gtaverken Arendal until 1989. He then worked with design and development of floating offshore platforms for GVA Consultants. In 1997 he joined SSPA as a project manager for marine operation projects. Besides occasional ferry evaluations he is mainly engaged in simulation studies and simulation based training programmes. Telephone: +46 - 31 772 9121 E-mail: pontus.clason@sspa.se

The ferry in Mahaxai

In the village of Mahaxai in Khammouan province in southern Laos there is another ferry connection. Also this ferry is important for transports to and from the remote mountain villages to the regional capital Thakek at the Mekong. In Mahaxai the problem is different from that of the ferry in Muong Khoa. In Mahaxai the ferry exists and is fully operable with an electric winch pulling the ferry across the river. Here the problem is heavy truckloads. Forestry is, besides farming, an important activity in this area, and a lot of timber is hauled on trucks through the village. The timber usually consists of large logs, and the trucks carrying the logs are frequently overloaded, weighing up to 50 tons. The roads are rapidly worn down by the heavy trucks and need constant maintenance. Even the ferry suffers significantly from the heavy truck traffic. In a longer perspective it is questioned whether the ferry is suitable to carry these trucks or if it should be replaced by a bridge an expensive alternative.

he ferry landing and harbour at Moung Khoa. During the rain season the Nam Ou river may rise 510 m above normal level, on rare occasions it may rise up to 20 m.

Bridging gaps in technology

In both these projects SSPAs ship knowledge and expertise was requested to evaluate the suitability of the ferry barges for further operation and to review upgrading alternatives in order to extend the ferries service period

he speedboat offers fast services for modern people. With Japanese high performance engines and surface piercing propellers these boats travel at 3540 knots. Life jackets and ear protection are mandatory.

he Muong Khoa ferry is made of steel pontoons and has capacity for two trucks or four cars at a time. The safety standard can be improved.

ice fields dominate in the Mekong river valley in central Laos.

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Twin-skeg VLCC in restricted waters

A new efficient ship design has been developed. The Stena V-MAX is designed to transport large oil cargoes safely through narrow and confined fairways and with extremely competitive transport economy. SSPA was deeply involved in the development work, which resulted in a design where the cargo intake is increased by 2040% compared with conventional VLCCs. A typical VLCC of today is about 320m long LPP, 5860m wide, has one propeller and a draught of 2123m while carrying 2 million barrels of oil. The V-MAX has the draught of a Suez-max tanker (1617m) but with a full VLCC deadweight, which is achieved by increasing the beam. the common 14.516 knots. The vessel complies with DNVs rules for RPS (Redundant Propulsion and Separate) which e. g. means keeping more than 6 knots in 8 Bft head wind and corresponding waves with only 50% of the power.

Superior manoeuvring performance

The twin-skeg concept normally provides better coursekeeping characteristics than a conventional arrangement, see diagram below. These characteristics are often quantified by the so called stability lever, which represents the axial difference, given as a fraction of the ship length, between centre of pressure due to turning and centre of pressure due do drift. A typical value for an unstable tanker can be 0.15, while for a typical stable container vessel it can be 0.10. Twin skeg vessels are normally marginally unstable or stable, i. e. the stability lever is between -0.05 and 0.05. A twin-rudder/twin-propeller arrangement provides control characteristics, which are far better than for a conventional VLCC. Laboratory manoeuvring tests were performed, also with high-lift rudders as an option. Mathematical manoeuvring models for simulations were based thereon.

ans Liljenberg, Project Manager at SSPA. He graduated (M. Sc.) from Chalmers University of Technology in 1968 and was then for some years employed at the shipyard resundsvarvet. In 1971 he joined SSPA and has since then been working mainly with hull form optimisation of merchant ships as well as high-speed mono- and multihulls. Telephone: +46 - 31 772 9031 E-mail: hans.liljenberg@sspa.se

Hydrodynamic considerations
The hull dimensions ended up as LPP=320m B=70m Tdesign=16.76m (55') D=25.6m The lenght/beam ratio and hull slenderness are much lower than what is common for VLCCs. A single screw might have been possible for propulsion but had demanded a slender aftbody, and reduced payload accordingly. Instead the twin skeg/twin gondola concept was chosen, with two separate propellers, rudders and steering gear. It improves propulsion and course keeping, gives a short engine room and accordingly a longer cargo section within a given length. Also manoeuvrability and propulsion redundancy are improved and consequently the safe handling of the ship. A twin-skeg form allows a more aft LCB propulsively by which the forebody can be made slenderer to reduce resistance. Much effort was put on the hydrodynamic design of the hull shape. Most important was the optimisation of the speed and the consumption ratio. A number of hull shapes were tested during two years time in the search for refinement. Good guidance was given by SSPAs longtime experience in developing twin-skeg shapes. Our statistics tell that twin-skeg vessels of CB above 0.80 in general have 6% lower relative propulsion power than single screw ships of the same capacity. For once improved propulsion and vessel arrangement, reduced fuel consumption/exhaust gas pollution, manoeuvrability and safety go hand in hand.

Comparison of manoeuvring characteristics of V-MAX and conventional VLCC

The twin-skeg concept offers more options in manoeuvring. The standard turning circle does not differ very much. The normally better course stability characteristics provide a larger turning radius at the same time as the better steering capacity reduces it. The superior characteristics are, however, demonstrated in a zigzag manoeuvre. Especially at lower speeds, the advantage of a twinrudder/twin-propeller system is evident. A force, on the stern of the ship, can be obtained in an arbitrary direction, by an individual control of propellers and rudders.

eter Ottosson, Project Manager at SSPA. He graduated (M. Sc.) from Chalmers University of Technology in 1976 and has since then been employed at SSPA. He has developed many of SSPAs simulation programs, especially in the areas of manoeuvring and seakeeping. Telephone: +46 - 31 772 9074 E-mail: peter.ottosson@sspa.se

iagram of zigzag manoevres of a twin-skeg and a conventional arrangement.

Optimised propellers
The influence of propeller size and rpm was studied, which eventually led to a geared propulsion train (with clutches for engine maintenance) to keep the propeller rpm down and increase efficiency. The initial propeller design achieved expected efficiency and had very good cavitation properties. This tempted us to improve its efficiency further, balancing against cavitation and vibration performance. The installed power is higher than normal in VLCCs, giving a service speed of 16.9 knots at 90% MCR against

Heading and rudder angle

Time

Twinskeg

Conventional

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Twin-skeg VLCC in restricted waters

n order to meet Stenas demands for a more flexible current model, work was started on a new model in PORTSIM, shown to the right. In this new model the current situation is based on an arbitrary number of specified points, each of which is defined by velocity and direction. The current, at the bow for instance, is in the simulation process continuously obtained by an intelligent interpolation between the predefined current points. Each point is weighed differently depending on the momentary distance to the point. By studying, in the same way, also the current at the stern, effects from current gradients are considered.

V-MAX operating in strong current

Since manoeuvring was an important task, when developing the V-max, a number of simulations were made already at the design stage. In order to study these matters, simulations were carried out at SSPA, but also by Stenas own personnel, which was made possible by Stena purchasing SSPAs general manoeuvring and seakeeping program PORTSIM. Stena could then, via their captains, perform real-time simulations, in respective approach fairways, among them the Delaware River up to Philadelphia. Hans Liljenberg / Peter Ottosson

eakeeping was studied with emphasis on avoidance of green water on deck. Raised forecastles were investigated in sea state 8 (significant waves of 10 m) and a best compromise was chosen.

he Stena V-MAX VLCC was designed with three primary requirements in mind, namely restricted draught increased safety competitive fuel consumption

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CFD a key to lower fuel costs

Every shipowner, every sea captain, every shipyard engineer is well aware of the essential significance in the connection between the hull resistance and the ships fuel consumption: the lower resistance the bigger reduction of fuel consumption. Hull resistance is however a question containing a lot of variables e.g. to choose the design with the lowest wave resistance will not always be the most judicious. SSPA has long experience, stored in a hull form data bank, of designing LNG and LPG vessels. At the initial design stage, SSPA offers speed-power calculations, and in the hull optimisation phase SSPA gives recommendations regarding fuel saving/speed increasing modifications. Final predictions are given based on scale-model tests in SSPAs towing tank. Appropriate ship trial corrections are applied based on SSPAs ship-model speed trial statistics. A good example of the complexity, but also of the possibilities, was given during the optimisation phase of an LNG tanker, ordered and built by a Korean shipyard a few years ago. Two versions of the LNG hull were computed using the CFD-code SHIPFLOW. For the validation of the CFD-calculations model tests were performed to reveal the accuracy and the flaws of the computations.

enrik Andreasson. Project Manager and Ph. D. student at SSPA. He received his M. Sc. degree in Naval Architecture in the spring of 1999 at Chalmers University of Technology. After graduation he continued his thesis work on drag reduction surfaces at the department of Naval Architecture and Ocean Engineering. At the end of 1999 he was employed at SSPA as a researcher. He is mainly working with projects related to CFD and ship manoeuvring. Telephone: +46 - 31 772 9072 E-mail: henrik.andreasson@sspa.se

ave profile at a distance of 25 m from centreline. Hull A has an overall higher wave profile than Hull B, which indicates a higher wave resistance for Hull A. The position of the origin is at the fore perpendicular.

Optimisation criteria of an LNG

Since the Froude numbers of LNG tankers are low, the wave resistance is only a small part of the total resistance, around 10 15 per cent to be compared with the skin friction resistance, which constitutes 60 65 per cent of the total resistance. Therefore, only a small profit is

gained by a shape modification, as an increase in the wet surface area will increase the skin friction resistance.

This is SHIPFLOW
The CFD code SHIPFLOWTM version 2.5 uses a zonal approach to solve the flow near the ship, and is as such especially adapted to calculations involving a ship. First, the flow is solved according to potential flow theory using a higher order panel method, including either a linear or non-linear surface boundary condition. To include viscous effects, the flow can be solved with momentum integral methods for thin boundary layers in the region around the fore part. For the stern region Reynolds Averaged Navier-Stokes equations can be solved. In this article emphasis is put on the potential flow solver and the thin boundary layer solver.

ave contours from above. The upper half of the figure shows the contours of Hull A and the lower half Hull B. Red colour denotes the highest wave elevation and blue the deepest wave trough. The longitudinal line indicates the longitudinal wave cut at 25 m from centreline.

Comparison of wave patterns

The two hull form concepts, denoted Hull A and Hull B, were very similar except in the bow region, where hull B had a shorter and wider bulb. The most straightforward way to compare the effect of the different bulb alternatives with SHIPFLOW would be to integrate the pressure along the hull surface, but since the potential flow simulation does not include viscous effects, the waves around the stern would be over-predicted for this kind of vessel. This will give a large error in resistance. A much better way is to compare the wave patterns in the region of interest. When comparing the contour plots, Hull A created a higher bow wave that gave raise to a wave pattern with higher waves, which took up more energy to maintain. This would naturally induce a higher wave resistance for Hull A.

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CFD a key to lower fuel costs

flow path. A straighter flow path is better, since it will give smoother pressure gradient due to less acceleration and retardation. The downwash from where the bulb meets the bow is thus the most important feature to predict.

Coupling between CFD and reality

It is important to remember that CFD simulations do not include all the physics that reality contains. There are always simplifications to make the simulation feasible. Towing tank tests are still very necessary to predict the performance of the design. However, for a skilled user who knows the theory, the drawbacks and possibilities of it, CFD can be a very valuable tool in the developing of new designs. It is one thing to perform a CFD simulation, another one to understand and interpret the result. There SSPA comes into the picture. Henrik Andreasson

pper: The towing tank experiment of the Korean LNG tanker (Hull A). Lower: Simulation of the same experiment with the CFD code SHIPFLOW.

This can also be visualised by comparing wave profiles along longitudinal cuts parallel to the centreline. The scale-model test supported the CFD result, as the measured residual resistance, according to ITTC 78, was lower for Hull B. Since the wave resistance only constitutes a small part of the total resistance, it is very important to check also that the wetted surface does not increase. Therefore it is not always right to choose the design with the lowest wave resistance.

LNG and LPG developed at SSPA Customers that recently have performed LNG or LPG projects at SSPA are Daewoo-KOGAS, Daewoo-Bergesen/ Exmar, Samsung-KOGAS, Samsung-BP/AMOCO, AESA, Daewoo-GEOGAS, Jiangnan, Gdynia Shipyard Bergesen, etc.

Streamline comparison
Another way to investigate the bulb configuration is to compare pressure distribution and streamlines. High magnitude of maximum and minimum pressure will induce higher and more energy exacting waves. The purpose of the bulb is to subdue the bow wave by its interfering with the bulb wave. Therefore a relatively high gradient over the bulb is accepted to create a bulb wave high enough. The streamlines give information about the mean

successful design of an LNG carrier, built at Daewoo.

he figures display the absolute bow region and show a comparison between CFD simulation of streamlines and a modelscale wet paint test. The colours in the CFD picture indicate the pressure distribution. Please, note that the down wash from the bulb was similarly estimated in both the wet paint test and the CFD simulation.

Short comments

PORTSIM training
In August, Captain Cynthia Smith, Master Mariner from United States Merchant Marine Academy (USMMA) in Kings Point, New York, visited SSPA. Capt. Smith teaches in Nautical Sience courses in the Department of Transportation, and she has a broad sea-going experience both from merchant and naval ships. The goal of her visit was a twoday PORTSIM introduction and training course. USMMA ordered PORTSIM already in 1993 and now it is time for an upgrading to PORTSIM 4 for Windows. The upgraded

delivery includes 15 licences and ship models from a 90-m Transport Vessel up to a 300-m VLCC. USMMA uses PORTSIM for classroom teaching as well as for the midshipmen in manoeuvring experiments. Capt. Smith expressed that a part task simulator such as PORTSIM generally provides a wider variety of ship types, thereby increasing the potential for comparative studies for the midshipmen. Thorsten Thorstensson
apt. Cynthia Smith, USMMA, and Thorsten Thorstensson, SSPA, study the new features in the upgraded version of PORTSIM.

SSPA goes aboard

In a project called Safe Fairway the Port of Gothenburg and Swedish Maritime Administration are planning a major upgrade of the ship routes in Gothenburg harbour. The main objective is to accommodate the newer and larger ship traffic better and especially the Post Panamax type container vessels. SSPA has been engaged in the

designing of the fairway alternatives and has performed an extensive simulation program. To obtain a better understanding of the complexity of navigating large ships in restricted waters, two SSPA project members joined the pilot during the take-in of a 6000 TEU container vessel from Vinga to quayside. The outcome of the study will be presented on a later occasion. Pontus Clason environment. ENSUS 2000 (Marine Science and Technology for Environmental Sustainability), 46 September, 2000. Forsman, B.: The port a risk object or a place for a picnic. Scandinavian Yearbook of Maritime Technology, 2000. Hallander, J., Bark, G.: Interaction between collapsing cavities influence on noise generation and scaling. ASME 2000 Fluids Engineering Division Summer Meeting, Boston, Massachusetts, USA, 1115 June, 2000. Kllstrm, C.: Autopilot and trackkeeping algotrithms for highspeed craft,. Control Engineering Practice, 8 (2000) pp185190. Leer-Andersen, M., Clason, P., Ottosson, P., Andreasson, H., Svensson, U.: Wash waves Problems and solutions. SNAME 2000 Annual Meeting, Vancouver, Canada, 47 October, 2000. Leer-Andersen, M., Janson, C.-E., Larsson, L.: Farfield wash wave calculation using a hybrid Rankine/Kelvin Source Method. MARNET CFD, DTU, Copenhagen, October, 2000 Torstensson, H.: Damage analysis on transport packaging, Technology, Law and Insurance, 1999 4, pp181190.

China increases the capacity for building large crude oil tankers and bulkers.
SSPA has been commissioned to carry out towing tank, cavitation and manoeuvring tests, and to support the hull form development for Dalian New Shipyard that will build five VLCC vessels for NITC (National Iranian Tanker Co.). These five vessels are the first VLCC tankers to be built in China. Jiangnan-SWS (Shanghai Waigaoqiao Shipbuilding Co.) has a new shipyard under construction in the Shanghai area with capacity for building VLCC tankers and large capesize bulkers. SSPA won the order to develop hull form and carry out model tests for first vessel, which is planned to be a capesize bulker, to be built at the new SWS shipyard. Hasse Olofsson

Maritime Safety Management course in Singapore

From November 20 December 1, Sida, (Swedish International Development Cooperation Agency) and the Ministry of Foreign Affairs of Singapore, for the first time jointly arranged a training programme, attracting 25 participants from 9 different Asian developing countries. Sida commissioned SSPA Sweden to conduct the programme on Maritime Safety Management in cooperation with the Maritime and Port Authority of Singapore, MPA. Singapore proved to be an ideal place for discussions of maritime safety issues and offered many opportunities for interesting site visits in the giant port of Singapore. Bjrn Forsman

Welcome to visit our web site! SSPA HIGHLIGHTS 1/2001 will be distributed in April 2001.

SSPA HIGHLIGHTS IS PUBLISHED BY SSPA SWEDEN AB. P.O. BOX 24 001 SE-400 22 GTEBORG, SWEDEN

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PHONE INT. + 46 - 31 772 90 00 TELEFAX + 46 - 31 772 9 12 4 E-MAIL postmaster@sspa.se WEB SITE www.sspa.se EDITOR: LI FREDRIKSON PRODUCTION: NILS LINDSKOUG GRAPHIC DESIGN: WERNER SCHMIDT PHOTO: SVEN WESSLING PRINTED IN SWEDEN ISSN 1401-3711

SSPA papers and articles

Afzelius, L.: Virtual reality tools for ship management and safety. 25th IMTA Annual Conference, Venice, Italy, 2326 October, 2000. Ellis, J., Torstensson, H.: Risks of marine transport of dangerous goods and implications for the