Tanker Ships

16.11.2012

CHALMERS UNIVERSITY OF TECHNOLOGY

ASSIGNMENT 1: TANKER SHIPS

Marine Structural Engineering MMA167 | Bergmann, Ludwig, Robic

Bergmann, Ludwig, Robic

Assignment 1: Tanker Ships

MMK221

Summary This report provides an overview of the most common tanker type: Oil tankers. After an introduction, which treads the historical development of oil tankers and provides a classification of today's used oil tankers, the report focuses on the structural arrangement of oil tanker. A general overview and a short description of structural elements of a tanker ship is given, where else baffels are explained in more detail. These elements minimize the effects of sloshing, which can be described as movement of liquid cargo, which can cause considerable forces on a vessel. Future trends is the last chapter, which provides possible solutions to deal with problems of saving energy and a vessel's environmental footprint.

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Bergmann, Ludwig, Robic

Assignment 1: Tanker Ships

MMK221

Table of contents Summary ................................................................................................................................................. 1 Table of contents ..................................................................................................................................... 2 Introduction............................................................................................................................................. 3 1.

Structural design.............................................................................................................................. 4 1.1

General arrangement .............................................................................................................. 4

1.2

Structural arrangement of a double hull oil tanker................................................................. 5

2.

Liquid sloshing in oil tanker ships .................................................................................................... 6

3.

Future trends and developments .................................................................................................... 7 3.1

Air lubrication systems ............................................................................................................ 7

3.2

Super hydrophobic hull surface............................................................................................... 7

3.3

Use of wind power and solar energy....................................................................................... 7

3.4

Traility - Ship of the future ...................................................................................................... 8

References ............................................................................................................................................... 9 List of figures ........................................................................................................................................... 9 List of tables ............................................................................................................................................ 9

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Bergmann, Ludwig, Robic

Assignment 1: Tanker Ships

MMK221

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Bergmann, Ludwig, Robic

Assignment 1: Tanker Ships

MMK221

1. Structural design 1.1 General arrangement In general, a tanker ship can be divided into three subsections (see Figure 3): the fore end, the cargo area and the aft end. An important aspect of the fore end is its fluid dynamic optimized shape to keep the water resistance as low as possible. The cargo area contains the oil tanks. The machinery room, the fuel tank, the pump room and the super structure of the tanker vessel are located at the aft end. The following description focuses on the midship structure because this is the highest loaded area of the vessel. [3]

Figure 3: General side view of an oil tanker [3]

Despite the fact that many rules are set by the classification societies for designing the hull structure of a ship, several structure designs exist. Figure 4 illustrates some examples.

Figure 4: Typical tanker structure arrangements [6]

Most of the tankers in service are designed with a double hull (see Figure 4) which contributes to increase safety in case of collision, grounding or other mechanisms which damage the hull.

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Bergmann, Ludwig, Robic

Assignment 1: Tanker Ships

MMK221

1.2 Structural arrangement of a double hull oil tanker This section aims to give an overview of the different components of the structure of a typical double hull oil tanker. An example is shown on Figure 5.

Figure 5: Structural arrangement of a double skin crude oil tanker [7]

• Transverse framing and floors Transverse plates and floors are primary members of the ship structure which take the majority of the loads and distribute them to secondary members like longitudinal stiffeners. • Longitudinal framing The purpose of the longitudinal frames is to increase the stiffness of the ship hull over its length and to prevent the plating from buckling. The longitudinals at the deck and bottom of the ship have the largest dimensions because there occur the highest stresses. The scantlings of the side shell longitudinals increase form deck to the bottom where they reach the dimensions of the bottom ones. The longitudinals are continuous over the ship's length. • Girder Girders are the connection plates between the two hulls of a double hull tanker to ensure a constant distance between them and transmit forces. • Bulkheads Longitudinal and transverse bulkheads are used to divide the inner ship space into several watertight tank compartments. Bulkhead plates are supported by stiffeners to prevent from buckling. • Hatchways In general tanker ships have a closed cross section which is interrupted by hatchways. Hatchways are oiltight openings which provide access to the oil tanks from the deck.

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Bergmann, Ludwig, Robic

Assignment 1: Tanker Ships

MMK221

• Ballast tanks These tanks provide space for ballast water to ensure that the ship has always enough draught. This is important to keep the efficiency of the propeller even in unloaded conditions. During loading operations ballast water is added or removed from the ship to minimize bending moments. • Oil discharge boilers Oil discharge boilers are used at the unloading process to heat the stored crude oil and therefore to lower the viscosity of the oil. This makes it easier to pump the oil out of the ship. • Pumps for loading operation: These pumps are situated in a pump room from which pipes are leading to the oil tanks. [18]

2. Liquid sloshing in oil tanker ships First tanker ships suffered from stability problems due to the free surface effect from liquids contained in the tanker. If the ship is partially filled, sloshing of oil from one side to the other side occurs and could cause capsizing. Sloshing is one of the most important issues when a tanker ship is designed because it can influence the stability of a ship and damage the structure. Due to this fact and that a lot of investigation are carried out to understand the relationship between baffles and the liquid cargo this chapter focuses on this part. When the acceleration of the ship is too high or when the external excitation frequency is closed to the frequency of the oil in the tank, violent oscillations of the liquid inside the tanker may occur (see Figure 6 a-d). Local high pressure loads on walls are induced by sloshing liquid and can damage the structure of the tanker. [10] The first design improvement was to separate the tanker into several smaller areas like is now common on every tanker ship. Another practice used to prevent violent sloshing on today’s tankers is to install additional plates inside the oil compartments. These plates contribute to lower the amplitude of the liquid’s oscillations as it can be seen on figure 6 A-D and thus to reduce the impact forces on the structure. Typically, the stringer decks (number 15 on Figure 5) are used to reduce the effects of oil sloshing on the structure. Many studies have tried to simulate the influence of such components in tanker ships. Modelling liquid sloshing coupled with ship motion is a complex problem which has to be resolved to increase the safety of tanker ship. [12],[11] Figure 6: Simulation of a violent liquid sloshing in a tank without baffle (a-d) and with baffle (AD) at different times [12]

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Bergmann, Ludwig, Robic

Assignment 1: Tanker Ships

MMK221

3. Future trends and developments Rising oil prices and environmental issues force oil transporting companies to improve their fleet performance and to develop new types of ships. To fulfil the growing demand of moving oil all over the world, the size of tanker ships increases constantly leading to ultra large crude carriers ULCCs. To minimize the environmental footprint of ships the "Marpol" convention was created in 1973. Marpol is an international agreement to protect the maritime environment. This convention has been constantly modified and updated over the last decades and over 136 countries have already signed it. Due to the fact that this and also other regulations get more and more strict, the following developments and studies are carried out. [13]

3.1 Air lubrication systems Mitsubishi industries announced to investigate a system to significantly lower the friction between the ship bottom hull and the sea water by using a layer of bubbles (see Figure 7). Currently the system is tested on a module carrier but after the study it is supposed to be also used on tanker ships. The company expects a reduction of CO2 emissions of ten percent by using this system.[14]

Figure 7: Mitsubishi air lubrication system[2]

3.2 Super hydrophobic hull surface A lot of research and development is carried out at the moment to create a new hull paint for ships which is hydrophobic and therefore has a lower friction coefficient. Inspired by nature the surface of this paint consists of tiny hairs which trap small air bubbles. At the moment the main problem of this bionic technology is to keep this hydrophobic surface stable over time.[15]

3.3 Use of wind power and solar energy Tanker ships are predestined for using wind and solar energy because they have a lot of free space on deck (see Figure ). Therefore many design studies were made to estimate the benefit of this so called "hybrid" technology. A reduction of the fuel consumption and CO2 emission of ten to twenty percent is estimated.[16]

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Bergmann, Ludwig, Robic

Assignment 1: Tanker Ships

MMK221

Figure 8: Tanker ship using wind and solar energy[16]

3.4 Traility - Ship of the future "Traility" is the name of a conceptual design study currently made by the Det Norske Veritas. Compared to a conventional tanker ship the Traility has a V-shaped hull which removes the need for ballast water and it has a propulsion system which is powered by liquefied natural gas LNG. The more V-shaped hull is necessary to increase the lightship draft and therefore to keep the propeller and the bow into the water when the ship is unloaded. To avoid high bending moments during the loading operation the ship structure is designed as five longitudinal sections with one center tank, two intermediate tanks and two side tanks (see Figure 9). For this reason the ship has four bulkheads instead of two as normal tankers have. When the ship is loaded or unloaded no longitudinal bending moments occur because the section is over the entire length of the ship filled or emptied. However, the sections have to be filled or emptied simultaneously on each side and also equally over the length. Because of these modifications the ship emits much fewer CO2, NOX, SOX and it needs 25 percent less energy. Although the Traility will be more expensive to build, it will still pay off due to the much lower operating costs. The LNG will be stored on deck in front of the superstructure and will be also used for the oil discharge boilers.[17]

Figure 9: Traility - Ship of the future[17]

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Bergmann, Ludwig, Robic

Assignment 1: Tanker Ships

MMK221

References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]

[12] [13] [14] [15] [16] [17] [18]

D. J Eyers, G.J Bruce, 'Ship construction', 7th Edition,Butterworth-Heinemann, Waltham, 2012, 978-0-08-097239-8 http://en.wikipedia.org/wiki/History_of_the_oil_tanker(07.11.2012) http://en.wikipedia.org/wiki/Tanker_(ship)(07.11.2012) http://www.globalsecurity.org/military/systems/ship/tanker-history.htm(07.11.2012) http://en.wikipedia.org/wiki/Glückauf_(1886)(07.11.2012) http://www.aukevisser.nl/german/id95.htm http://www.shipwrecksofegypt.com/images/shippages/murex.html http://www.shippipedia.com/ships/ship-types/tanker/(08.11.2012) http://en.wikipedia.org/wiki/Oil_tanker#cite_note-s6-1 Dongming Liu, PengzhiLin,Three-dimensional liquid sloshing in a tank with baffles Ocean Engineering 36 (2009) 202–212 M.A. Goudarzi, S.R.Sabbagh-Yazdi,Analytical and experimental evaluation on the effectiveness of upper mounted baffles with respect to commonly used baffles Ocean Engineering 42 (2012) 205–217 Mi-An Xue, Pengzhi Lin, Numerical study of ring baffle effects on reducing violent liquid sloshing, Computers & Fluids 52 (2011) http://www.dnv.com/industry/maritime/servicessolutions/statutoryservices/marpol/ (13.11.2012) http://www.gizmag.com/mitsubishi-air-lubrication-system/21196/(13.11.2012) http://www.gizmag.com/bionic-coating-could-help-ships-to-economise-on-fuel/14995/ (13.11.2012) http://wordlesstech.com/2012/02/17/aquarius-project-eco-tankers-of-the-future/ (13.11.2012) http://c0182999.cdn1.cloudfiles.rackspacecloud.com/TOJanFeb2011web.pdf (13.11.2012) http://en.wikipedia.org/wiki/Oil_tanker (14.11.2012)

List of figures Figure 1: Picture of Glückauf which means 'good luck' in german.[6] .................................................... 3 Figure 2: Comparison of Knock Nevis, the world largest tanker with well-known large buildings [2] ... 3 Figure 3: General side view of anoil tanker ............................................................................................. 4 Figure 4: Typical tanker structure arrangements [6] .............................................................................. 4 Figure 5: Structural arrangement of a double skin crude oil tanker [7].................................................. 5 Figure 6: Simulation of a violent liquid sloshing in a tank without baffle (a-d) and with baffle (A-D) at different times [12] ................................................................................................................................. 6 Figure 7: Mitsubishi air lubrication system[2] ......................................................................................... 7 Figure 8: Tanker ship using wind and solar energy[16]........................................................................... 8 Figure 9: Traility - Ship of the future[17] ................................................................................................. 8

List of tables Table 1: Classification of tanker ships. DWT=deadweight tonnage ........................................................ 3 Page 9 of 9