t8-1-tavakoli.pdf

7/30/2019 t8-1-tavakoli.pdf

1/17

Mohammad Saeed Seif,Assistant Professor, Sharif University of Technology, Tehran, Iran,Mohammad Taghi Tavakoli,Research Assistance, Sharif University of Technology, Tehran, Iran,

NEW TECHNOLOGIES FOR REDUCING FUEL CONSUMPTION INMARINE VEHICLES

Summary

This paper reviews different methods used for reducing the fuel consumption of marinevehicles in recent years. Methods for optimizing hull forms, use of microbubbles and newcoating, weight saving and improvement of propulsion system efficiency are discussed.

Moreover, different components of resistance and methods of drag reduction are investigated andnew hull forms are presented.

Key words: Fuel Consumption, Advanced Marine Vehicles, Drag reduction

NOVE TEHNOLOGIJE SMANJENJA POTRONJE GORIVA MORSKIHPLOVILA

Saetak

Ovaj rad obrauje razliite metode koje se posljednjih godina koriste za morska plovila.Obraene su metode optimizacije formi brodova, upotreba mikromjehuria i novih premaza,utede teina i poboljanje korisnosti propulzijskih sustava. tovie, istraene su razliitekomponente otpora i metode smanjenja otpora, te su predstavljene nove forme brodova.

Kljune rijei: potronja goriva, napredna morska plovila, redukcija otpora


2/17

XVI Symposium SORTA2004 New technologies for reducing fuel consumption in marine vehicles

FSB Zagreb t8-1: 2

1. Introduction

The fuel costs are the second largest item (after salaries) on a big vessels budget. The fuelconsumption for a large ferry ranges between 1000 and 5000 liters per hour. This means that theship consumes more oil per hour than a one-family house does for one whole years heating. Theannual fuel budget for a ferry running 20 hours per day is in the order of millions of dollars.Even small reductions of a few percent in the fuel consumption mean considerable annualsavings.

Following are some of the most important factors that affect the fuel consumption of aship:

Ship-specific parameters such as form of the hull, weight, type of main engines, propellers.

Number of engaged main engines.

The ship speed. Water currents (direction and speed).

Water depth under the keel.

The ships draft (depends on the cargo).

Wind and waves (direction and strength) [1].

There are several techniques to achieve fuel consumption reduction on marine vehicles(Fig. 1). In general, most methods are focused on reducing drag and some others try to increaseefficiency of the propulsion system and operation

The speed and power of a ship in a seaway depends on the ship's resistance, the action ofpropeller, engine, and the behavior of the ship in waves. These are discussed in the following

sections.

Fig. 1 Methods of fuel consumption reduction

Slika 1. Metode smanjenja potronje goriva

Method of FuelConsumption Reduction

Improvementof ro ulsion

PowerPlants

Fuelimprovement

NewPropellers

Operation

Ship Routing Maintenances

Weight Saving

Newmaterials

OptimumDesign

Drag Reduction

Hull formsoptimization

Airlubrication

Polymer andCoating

ModernHull


3/17


FSB Zagreb t8-1: 3

2. Resistance definition

As the resistance of a full scale ship cannot be measured directly, our knowledge about the

ships resistance has to be gathered from model tests. The measured calm water resistance isusually decomposed into various components, although all these components usually interact andmost of them cannot be measured individually. The concept of resistance decomposition helps indesigning the hull form as the designer can focus on how to influence individual resistancecomponents. Fig. 2 gives an overview of resistance decomposition.

Fig. 2 Components of ship resistance

Slika 2. Komponente otpora broda

The total calm water resistance of a new ship hull can be decomposed into different

components. The main items are explained below: Friction resistance

Due to viscosity, directly at the ship hull water particles cling to the surface and move withship speed. The integral of the shear stresses over the wetted surface of ship yield the frictionresistance.

Viscous pressure resistance

The form of the ship induces a local flow field with velocities that are sometimes higherand sometimes lower than the average velocity. The average of the resulting shear stresses isthen higher. Also energy losses in the boundary layer, vortices and flow separation prevent an

1.1. Total resistance

Residual resistance Skin friction resistance

(Equivalent flat plate)

Form effect on skin friction

Friction resistancePressure resistance

Viscous pressure resistanceWave resistance

ViscousWave breaking resistanceWave making resistance

Aerodynamic

resistance

Added resistance

in wave

Calm water resistance


4/17


FSB Zagreb t8-1: 4

increase to stagnation pressure in the after body as predicted in an ideal fluid theory. Full shipforms have a higher viscous pressure resistance than slender ship forms.

Wave resistanceThe ship creates a typical wave system, which contributes to the total resistance. The waveresistance cannot be properly estimated by simple design formulae. It is usually determined inmodel tests. Although efforts to compute the wave resistance by theoretical methods back tomore than 100 years, the problem is still not completely solved satisfactorily [2].

Aerodynamic resistance

The aerodynamic resistance of a high performance vessel becomes a significant componentof the total resistance at high speeds. Full-scale trials of modern sport fishing boats with andwithout full towers indicate an aerodynamic component on the order of 9 percent at speeds of 32to 35 knots.

The hull and deckhouse can also produce significant aerodynamic drag at high speed,while the external shape of the superstructure may be streamlined to reduce drag.

Added resistance in waves

Added resistance in waves is for sea conditions stated for the vessels operationalrequirements. Model testing is helpful in determining this resistance component and there arealso some numerical methods for evaluation of this component [3].

3. Drag reduction

3.1. Hull form optimization

The Navy and maritime communities depend on our accumulated hydrodynamic expertise

for enhancing vehicle performance, reducing operating costs, and meeting the changing Navymission, which often demands dramatic hull form and propulsor variation.

The objective of such research was to investigate Optimization techniques for dragreduction in view of the enhancement of ship design procedures, specially applied tohydrodynamics. It was thus necessary to find approaches that ensure the global validity ofoptimal design approaches, and that allow more dedicated and refined hydrodynamic designoptimization.

The alternative approach consisted of making a complete optimal design available. Onemajor innovative feature is the ability to deal with several, possibly conflicting objectives, andcome to a set of best solution from which the designer can extract the trade-off that best suits hisneeds. Finally, some work was initiated on the methodologies towards the involvement of

optimal design technologies in a concurrent design approach, including several teams with partlyoverlapping sets of design variable and conflicting objectives [4]. These methods are mostlybased on CFD modeling and final results are tested in Towing Tank for better evaluation.

3.2. Polymer and coating

The addition of a small amount of polymer to a turbulent Newtonian fluid flow can resultin a drag reduction, which appears in a number of flow fields, and has received considerableattention since the initial publications of Toms [5] and Mysels [6].

During the past three decades, vast numbers of papers have appeared on polymeric dragreduction, which can be roughly divided into three categories [7]. The first category includes


5/17


FSB Zagreb t8-1: 5

studies on drag reduction from a molecular perspective. The behavior of polymer molecules invarious model flows (e.g. simple shear, pure strain, etc.) was examined. One of the mostthorough literature reviews of the dynamics of polymer molecules in turbulent flows was writtenby Lumley [8]. He reported a consensus option that drag-reducing polymer molecules inturbulent boundary layers are stretched by the flow, resulting in an increase in the total increasein the local fluid viscosity. A recent theoretical study was conducted by Rabin & Zielinska [9].They examined the effect of polymer molecules on the vortices distribution in elongational flowsand argued that there will be a shift in the turbulent energy from high down to low wavenumbers. The second category includes studies on the effects of polymers on the time-averagedturbulence statistics. One of the best examples of this type of research was done by Virk [10].They measured streamwise velocity in a drag-reducing pipe flow with different molecular weightpolymers and different solvents. This work produced the well known Virk asymptote for dragreduction as a function of polymer concentration. With advances in instrumentation andvisualization techniques, the third category arose, in which changes in coherent turbulent

structure due to polymers are examined.Next technology is directed, not at reducing friction drag, but rather at trying to maintain

the level of drag associated with a smooth surface through the use of anti-foulant coatings. Thesecoatings can negate the increase in drag associated with marine fouling, but they offer noimprovement over a clean smooth hull surface.

Sea-Slide coating is a typical coating that reduces friction between hull and water and canbe used over most anti-fouling paints. This is a unique coating with excellent drag reduction andcan be used on personal water craft to improve speed and handling; on boats to improve speedand fuel consumption; on any other craft where reducing the drag through the water is important.

3.3. Air-lubricated ships

Air cavity, Micro Bubble Drag Reduction and Air film, are three methods which aregenerated by air injection to super water repellent (SWR) coated ship. All techniques haveproven to deliver a net drag reduction; net in this regard means that the propulsive power of thevessel was more reduced than the required additional power for the air supply. The achievedreductions are in excess of 5%, in other words, hardly any other existing technique offers somuch potential to reduce either the power demand of sailing crafts or to let them sail faster withconstant power. Most suitable for ships sailing at one particular target speed turned out to be theACS concept, which is delivering the highest net reduction in a very narrow speed range.

Air cavity is based on the successful usage of bottom ventilation aimed at reducing frictionresistance. Air is supplied under the specially profiled bottom, so that a steady air layer is formed

separating a considerable part of the bottom from the contact with water. Fig. 3 shows an imageof the SeaCoaster. SeaCoaster, an air assisted catamaran is a hybrid of a standard catamaran andhovercraft design. Total power requirements including blowers is only 60 percent of aconventional catamaran [11].


6/17


FSB Zagreb t8-1: 6

Fig. 3 SeaCoaster is hybrid of a standard catamaranand hovercraft design [11].

Slika 3. SeaCoaster je hibrid standardnog katamarana[11]. Fig. 4 The Seiun Maru Ship - air ejection ducts [13]

Slika 4. Brod Seiun Maru ventili za ispuh zraka [13]

One of the advantages of an air cavity ship is that low air consumption requiredmaintaining the cavity (ten times less than for SES). Experimental trials show that spending only3% of the power from main propulsion system gives 25% drag reduction [12]. The idea of themicro-bubbles came for skin friction reduction of ships. Some specialists in Japan studied micro-bubble effect on resistance of displacement ships. They estimated that by use of micro-bubble atthe bottom of ships, 5% of ship drag is reduced. One reason for that study is that displacementship skin friction resistance component occupies about 80% of the total resistance. Numerouslaboratory experiments have shown that microbubbles are very effective in skin frictionreduction. Research Committee performed a full-scale experiment using the Seiun-Maru inSeptember 2001 (Fig. 4). The Seiun-Maru is a training ship that belongs to the National Institutefor Sea Training, Japan [13]. Fig.5 shows an example of its skin friction reduction effect. Thedata was taken in a circulating water tunnel, where the bubbles were injected at the top flat walland skin friction was measured by a skin friction sensor placed downstream of the injectionpoint. The horizontal axis shows the amount of injected air and the vertical axis shows the ratioof reduced skin friction to that at non-bubble condition. This figure shows that, as the amount ofinjected air increases, skin friction reduction effect by microbubbles increases up to 80% [14].

Fig. 5 Measured skin friction reduction bymicrobubbles [14]

Slika 5. Izmjerena redukcija trenja oplate zbogmikromjehuria [14]

Fig. 6 Thrust increase by microbubbles [15]

Slika 6. Poveanje poriva zbog mikromjehuria [15]

Plate


7/17


FSB Zagreb t8-1: 7

Another vessel explained here is a SES Catamaran (made in USA) fitted with micro-bubbledrag reduction (MBDR) system. This vessel uses two micro-bubble injections from the verticalhull sides. The model tests showed this MBDR system achieved an overall resistance reductionof 5-15%. Also the full-scale trials recorded a 2.5-3% speed increase at 40-45 kn [16]. Thesurvey of Latorre and Bablenko [17] showed the reduction in the local skin friction is sensitive tothe bubble orientation on the surface.

Fig. 6 shows the results, in which the bubbles were ejected from ejection ducts, with themaximum compressor power (ALL MAX) and one Half of the maximum power [16].

3.4. New hull forms

New hull forms have been successful in altering the character and reducing the level ofresiduary drag of hull forms. The past two decades have witnessed a multitude of developmentsfor fast and unconventional marine vehicles for various applications, notably navy applications,fast ferries and racing boats/fast yachts. These vehicles are frequently referred to as high-performance marine vehicles (HPMV) or high-speed craft (HSC). The term HPMV is morepopular with navies, while HSC is adopted by various rules of IMO (International MaritimeOrganization) and classification societies. This review of assorted HPMV draws on previouspublications. Papanikolaou [18] focuses in his HPMV review rather on the commercial market,ANEP [19], Azcueta and Bertram [20], on HPMV as naval platforms. The technologicalfeedback from the racing scene into military and commercial fast vessels often is considerable,e.g. Acampora [21].

Fig. 7 shows main methods for decreasing resistance of boats and ships in new hull forms. At thepresent, there are many high-speed crafts, which are designed and constructed according to thesemethods. Some of the advanced marine vehicles have the displacement volume above the water surfacee.g. planing crafts, ACV and WIG. This can be achieved by combination of hydrostatic, hydrodynamic,

aerostatic and aerodynamic forces. The others have the displacement volume below the water surface, e.g.SWATH and SLICE. In the following sections each of these types are described briefly and then relativeadvantages of these types are compared with each other [22].

Fig. 7 Methods of drag reduction

Slika 7. Metode smanjenja otpora

Fig. 8 Slice reduces wave-making resistance at highSpeed [23]

Slika 8.

Hybrid

Multi Hull

PlaningshiHydrofoil

OtherConce ts

HighB

L

SWATH

AirCushion

Methods ofDrag

ReductionWing inGround


8/17


Multihull Ship

Increasing the speed of a conventional displacement ship is only possible to a certain

extent. At Froude numbers approximately Fn>0.4, wave resistance increases disproportionatelywith ship speed for most ship hull forms. One approach for fast ships, particularly thoserequiring or benefiting from considerable deck area, are multihulls allowing very thin waterlineentrance angles while ensuring sufficient stability. The most popular multihulls are catamarans,Jansson and Lamb [24].

SWATH and SLICE

Early SWATH (Small Waterplane Area Twin Hull) ships are semi-submerged catamarans;prototypes have been built as technology demonstrators for the US navy and the Japanese navy.Most SWATH ships were designed for speeds lower than 25 knots. The SWATH concept is atype of catamaran that features two fully submerged hulls, each connected to a structure by oneor more relatively thin struts.

The innovation lies in the arrangement of the Slices buoyancy while a standard SWATHhas two Coke-bottle-shaped hulls running the full length of the ship. As shown in fig. 8, theSLICE advantage can reduce propulsion power, required to achieve the same speed, by 20% to35% or for the same power, increase the speed by 3 knot [23]. Slices short hulls are able to pushthrough the wave "hump" much more quickly. Slice has the same stable ride as a SWATH, butcan go faster with the same horsepower [25]. Adding to these benefits, SLICE has higher speed,reduced wake, better range, endurance and fuel consumption, and is built utilizing conventionalshipyard practices, including design, construction, materials and equipment.

Monohulls (High BL )

The wave-piercing principle can also be applied to displacement monohulls like the

German MTG project of a 7000 t frigate. Kvaerner Masayards and Guy Design Group in Finlandteamed up to develop the Euroexpress design, a futuristic wave-piercing fast ferry design, Fig.9. The craft has a long slender hull shape with two large chines to generate lift and dynamicstability. The designers feel the craft will be capable of reaching speeds in the 40-60 knot rangewith a length to beam ratio of about 9:1.

Fig. 9 Euroexpress of Kvaerner

Slika 9. Kvaernerov Euroexpress

Fig. 10 Typically resistance curves for a catamaran and aplaning craft

Slika 10. Tipine krivulje otpora za katamaranske iglisirajue forme


9/17


Planing Craft

They have a simple hull structure. The numbers of planing crafts in the world are very high

and have been used for passenger transportation, military purposes, racing, and pleasure and soon.Planing boats are designed to rise up on top of the water. They can go very fast, but needmore power to get up on top of the water. The heavier the boat, the more power required to get it"on plane." At high speeds it rises from water, which almost 80% of weight will be supported byhydrodynamic forces. Fig. 10 shows typical resistance curves for a catamaran and a planing craftof the same displacement. Catamarans have low resistance at low speed and perform better thana planing craft in preplaning region. However at planing speeds the advantages return to planingcraft.

Hydrofoil crafts

Hydrofoils, similar to airplanes, use wing surfaces to generate lift (Fig. 11). Since waterdensity is much greater than that of the air, the area of hydrofoil surface can be very small

compared to airplane wings. Hydrofoils can be either surface-piercing hydrofoils (SPH) or fullysubmerged hydrofoils (FSH). Fig.12 shows effect of Sea State on hydrofoil speed for asubmerged-foil hydrofoil ship in actual sea conditions. The curve shows only a modest reductionin speed as wave heights increase. The principal disadvantage of the hydrofoil craft is the limitedpayload capability and large draft [26].

Fig. 11 Jetfoil fully submerged hydrofoils

Slika 11. Jetfoil potpuno uronjeni hidrokrilci

50-knot hydrofoil operating envelope

0

10

20

30

40

50

0 1 2 3 4 5 6

Significant Wave Height(meters)

Speed(knots)

2 6543

Sea State

Fig. 12 Effect of Sea State on Hydrofoil Speed Curve [26]

Slika 12. Utjecaj stanja mora na krivulju brzine hidrokrilca [26]

Air Cushion Vehicles

The amphibious hovercraft is supported totally by its air cushion, with an air curtain (highpressure jet) or a flexible skirt system around its periphery to seal the cushion air. Theoutstanding features of ACV's or Air cushion vehicles are their ability to operate at very high

speeds, their low vulnerability to underwater explosions, their small draft and underwatersignatures and foremost their amphibious capability.[27].


10/17


Fig. 13 Atlantis I WIG project [28]

Slika 13. Atlantis I WIG projekt [28]

0

5

10

15

20

25

30

35

0 0.1 0.2 0.3 0.4 0.5 0.6

h/c

L/D

Fig. 14 The influence of ground effect on lift-to-drag ratio [29]

Slika 14. Utjecaj dubine na odnos uzgon otpor [29]

Another type of vessels which operate like an ACV are commonly known as SES (surfaceeffect ships), SES is a catamaran type vessel which contains an air cushion between both side

hull structure at the forward and aft ends.Wing-in-Ground

A WIG (Wing-In-Ground Effect) craft can be seen as a vessel between an ACV and anaircraft. The principle of the WIG craft is based on a phenomenon called the "GROUND" effect(Fig. 13). If the wing approaches to the ground, the lifting force of the wing increase, fig.14illustrates as the wing approaches to the ground, the lift increases significantly while the dragvaries little, resulting in a higher lift-to-drag ratio and transport efficiency becomes better [29].

It has a very high transport efficiency compared to airplanes expressed as the amount offuel used per passenger per km. [30] Further studies and developments in these types of vesselsare going on in Germany, USA, China, Japan and some other countries.

Hybrid FormsSeveral hybrid designs combine buoyancy, hydrodynamic and other forms of lift force.

The HYSWAS (hybrid small water plane area single hull) is a mental version with a deeplysubmerged torpedo-like buoyancy body and hydrofoils giving 30%-70% of the required liftforce.

The HYSUCAT is a hybrid of a catamaran hull fitted with a hydrofoil system, whichcarries part of the craft's weight at speed resulting in a most economical high speed craft. This isaccomplished through dynamic lift, which reduces the wetted area of a catamaran in water. Liftcreated by hydrofoil reduces the resistance of the craft up to 45%. The craft consequently ispropelled with lower power input at reduced fuel consumption. Several types have been built aspatrol boats reaching speeds up to 50 knots. Notice that the foil design is sensitive and requires

tailoring towards specific design conditions [31].High Aspect Ratio Twin Hull (H.A.R.T.H.) is still a basic displacement hull. It does not

use horsepower to lift, or rise, it above the waves like hydrofoil. It does not have gyros, shiftingballast, or trim tabs, to make it ride level, and remain straight and true, in high seas. Buoyancyholds it up, and the well-understood physics of hydrostatic pressure, keeps the hull straight andtrue. According to the developer, if the power is lost in seas, HARTH ships are designed forstability, with a geometry that assures dynamic wave averaging. HARTH ships are still at theprototype testing stage and not all information related to this technology is available. Fig. 15shows an artist concept of a 360-passenger ferry [11].


11/17


Other conceptsAmong the many other types of hybrid craft and unconventional hull forms no discussed in this

short overview due to time and space limitations, are:

Fast monohull by Blohm+Voss, a displacement hull with the hull volume as deepsubmerged as possible.

Deep-V monohull with excellent calm water performance and payload, acceptableseakeeping.

Fast catamarans, usually planing or almost-planing hulls.

Weinblume, are catamarans with staggered hulls excellent wave resistance at moderatespeeds, acceptable seakeeping, and low washing [27].

Fig. 15 HARTH ships, concept of a 360 passengers ferry [11]

Slika 15. HARTH brodovi, koncept za trajekt za 360 putnika [11]

Fig. 16 Typical water jet

Slika 16. Tipini vodomlazni propulzor

4. Improvement Propulsion System

The demand for reduced fuel consumption in marine transportation challenges thedesigners to select propulsion system that meets performance requirements economicallythroughout different operational profiles. The combined hydrodynamic characteristics of hull andpropulsors result in a speed-thrust relationship for the environment in which the vessel operationtakes place.

4.1. Propeller system

Most vessels utilize fixed-pitch submerged propellers. Surface propellers are fitted tovessels which operate perform at very high speeds or to those with an operational draftlimitation. Waterjet propulsors are utilized for increased frequency demand on larger vesselswith high-speed operational profile [3].

Water jetThe concept of waterjet propulsion dates back to 1661 when Toogood and Hays firstproposed this form of propulsion. Its use in the intervening years has been confident principallyto small high-speed pleasure and work boat situations where high maneuverability is requiredwith perhaps a draught limitation. It is only in recent years that the waterjet has been consideredfor large high-speed crafts. This propulsion is simpler, lighter and more efficient than screwpropellers. A typical form of a waterjet propulsion system is shown in Fig. 16 [32].

Surface Piercing Propeller

At present, supercavitating propellers and waterjet propellers are popular propulsivedevices for high-speed crafts. But surface piercing propellers have more possibility of high-speed


12/17


performance. Fig. 17 shows approximate efficiency of different propulsion types. Surfacepropellers also known as partially submerged propellers, are special propulsive devices, whichhave the following excellent advantages:

1) High propulsive efficiency

2) Shaft resistance and hub resistance avoidance

3) Low probability of Cavitation occurrence

It is found that propeller efficiency in high speed range of SPP is higher compared to othertypes of propellers and even addition of appropriate horizontal rake angle increases propellerforward efficiency. But SPP equipped crafts are a few in spite of high performance. The reason isthe lack of well-organized data of SPPs because of their intricate phenomena. Another reason islack of quantitative researches on excepted weak points as mentioned below.

1) High level of bearing forces and moments, or vibratory forces and moments

2) High level of blade stress3) Reduction in performance [in back ward motion [33]]. Fig. 18 shows a typical form ofSPP.

Fig. 17 Approximate efficiency of propulsion devices

Slika 17. Priblina korisnost propulzijskih ureaja

Fig. 18 Simple sketch of surface piercing propeller

Slika 18. Jednostavna skica

4.2. Prime Movers

Nowadays, research and development in the field of main engines have resulted in muchbetter fuel consumption.

Gas Turbine

Approaches to obtaining higher power output and improved efficiency were considered.Clearly the advanced gas turbine has [center stage] in the world for converting fuel to work. Thepower and efficiency delivered by the advanced gas turbine have made it the predominant prime

mover in the sea. The enhancement options of gas turbines are: 1) intercooling, 2) thermal[recuperation], 3) steam injection, 4) reheat, 5) closed loop cooling, 6) catalytic partial oxidationand 7) water recovery [34].

Fuel Cells

Recent advances in fuel cell technology have occurred which make fuel cells increasinglyattractive for naval ship and commercial marine applications. Fuel cell systems have beenidentified as promising power generators for both ship service power and hybrid propulsionsystems. They are among the cleanest, most efficient innovations being developed for futurepower generation. Fuel cells generate electricity and heat from an electrochemical reaction,


13/17


rather than relying on combustion. Advantages of fuel cells are their compact size, mobility,modularity, and quiet operation. [35]

Plants with combined systemModern combined plants usually comprise combinations of diesel engines, steam turbines,gas turbines and electric motors. Such plants are more commonly found in naval vessels. [Oneexample is ferry which have been retrofitted with electric motor or diesel engine poweranimating main propulsion thruster units to increase service speed and improve maneuverabilityas well. [31]. Typical modern systems of combined propulsion machinery are thus: COSAG,CODOG, CODAG, CODLOG and etc.

5. Operation

5.1. Ship routing

For the past twenty years, ships officers have been able to make use of routing advisesfrom weather routing departments, connected with meteorological institutes. With a known orexpected rough weather pattern on the ocean, an optimum ships route, with respect to aminimum traveling time, fuel consumption or risk of damage, can be found. The forecast of windand waves is a meteorological problem. The prediction of the ships reaction to wind and waves,in particular the ships speed, is usually based on routing experience with the ship underconsideration, or with similar ships. For an accurate routing of ships the routing officer needsreliable speed loss information for every sea condition. Developments in the last decade make itpossible to calculate the speed in a seaway. In 1974 the Shipbuilding Institute of HamburgUniversity published a program system with respect to this subject [36]. The Delft University ofTechnology has also published a prediction method for speed, power and motions in a seaway[37]. These computer programs can help to avoid dangerous situations, minimize traveling timeand reduce fuel consumption. The speed of a ship in a seaway depends on the ship's resistance,the action of propeller and engine, and the behavior of the ship in waves. The effect of routing onthe operational costs is to be found mainly in the fuel and lubricating oil costs. Maintenance andrepair costs are also affected, but it is very difficult to find exact data on this subject. One of theparameters on which the consumption of fuel and lubricating oil at sea is dependent is the type ofweather encountered by the ship during the voyage in a given period. In rough weather theresistance of a ship increases due to the effects of wind and waves. With the main engine set atconstant rev/min sailing through a wave field implies a speed reduction and an Increase of theengine output. Thus the time necessary to sail a distinct route increases together with the fuelconsumption over that route.

5.2. MaintenanceHull maintenance

The loss of speed or the increase in fuel consumption owing to the growth of marine weedand small molluscs on the hull is a more significant problem for marine vessel operators thanhull roughness. The rate of weed and mollusc growth depends on:

the mode of operation of the vessel;

the effectiveness of any antifouling paint that has been applied; and

Local environmental conditions, especially water temperature - the warmer the water, thefaster weed grow.


14/17


Fig. 19 Power increase due to fouling

Slika 19.

Fig. 20 Typical increase in power required to maintain vesselspeed of a fast fine ship vs increasing hull roughness

Slika 20. Typical increase in power required to maintain vessel

speed of a fast fine ship vs increasing hull roughness

Fouling will only affect the friction part of the ships resistance, for instance, an increase ofthe frictional resistance by about 30 per cent for a ship with an age of five years and a time sincelast docking of year.

The effect of fouling is much larger for tankers than for container ships. An investigationmade by the author from log data of a 200,000 tdw tanker, sailing from Europe to the PersianGulf, showed an increase of the still water resistance. For full load and ballast condition, thisincrease was as 26 to 29 per cent one year after the last docking, and 47 to 52 per cent two yearsafter the last docking. After the oil crisis these ships reduced power by 50 per cent, resulting in aspeed reduction for the clean hull of 16 to 13 knots. To maintain this speed two years after the

last docking the power of a fully loaded ship had to be increased from 50 to over 80 per cent; seeFig. 19. Estimates indicate that fouling can contribute to an increase in fuel consumption of up to7 percent after only one month, and 44 percent after six months, but can be reduced significantlythrough the use of antifouling paints [38].

Fig. 20 shows the increase in power required and hence the typical increase in fuelconsumption necessary to maintain vessel speed of a fast fine ship (e.g. Container Liner) versusincreasing physical hull roughness.

Engine maintenance

Careful initial running-in and regular maintenance are extremely important for ensuring thereliability as well as the performance (including fuel consumption) of any engine. This appliesequally to inboard and outboard marine engines. Every engine manufacturer recommends service

intervals and these should be adhered to rigorously, especially for basic services such oil changesand filter and separator replacement.

A new or reconditioned engine needs to be run in carefully The engine manufacturer's maintenance programme must be followed Complicated mechanical work should be entrusted to a qualified mechanic

6. Weight saving

In the maritime sector, weight reduction is getting more and more important, just as in theautomotive and aerospace sector. Especially parts that are placed high on the ship have asignificant effect on the stability of the ship. Every kilogram saved on top of the ship saves three


15/17


kilograms in the keel necessary for stability. Weight reduction can have a big influence on thedraught of the ship and can therefore reduce fuel consumption.

Saving structural weight can provide the designer with trade-off leverage that will havesignificant effect upon increasing the useful load capacity and fuel consumption of a vessel. Thetrends for useful load fraction (as well as weight fractions for structure, machinery, and otherfixed weights) for four planing hulls have been studied in ref. [39]. These trends are extrapolatedto hull sizes up to 1000 tons. It is found that the useful load fraction increase with increasingdisplacement. The term useful load includes military payload, ships fuel and potable water, shipscomplement and effects, and stores [3].

6.1. New materials

Several commercially available materials and technologies can be used now to improvetoday's marine vehicle. High-strength steels could reduce weight without reducing protection,and aluminum and magnesium alloys could replace steel altogether in some components. Also,ceramic- and metal-matrix composites could reduce the weight of braking systems withoutsacrificing performance. Dry cargo ships have been affected by new design trends thatemphasize a need for lower topside weight. Heavier cargo handling gear and related machinery,and more narrow, hydrodynamically contoured, high-speed hulls have increased stabilityproblems. Thus, weight saving is required to permit more efficient hull designs.

6.2. Optimum design

Ship structural design has a large influence on issues such as useful service life,maintenance requirements, and the overall cost of operation. This influence is especiallyprominent for very large vessels. The design of structural components (bulkheads, stiffeners,plating, connections, etc.) is governed by such factors as material selection and structural

configuration requirements. The primary structure constitutes the most important aspect of anyship structural design. Currently, much of the design process is dictated by subjective experience,even for new designs, oftentimes resulting in a less-than-optimal design. The recent increase ininformation technologies dedicated to optimal design, associated with the progress of thenumerical tools for predicting ship hydrodynamic performances, allows significant improvementin ship design [40]. The possible application of mathematical optimization to design problemswas investigated early in many industrial sectors. However, in spite of the attractiveness of thisapproach, it was still rather unused in practical design applications up to recent years, for reasonsrelated with the unavailability of numerical models for product performances evaluation, or thedifficulty of operating them in a smooth way [41].

7. ConclusionMost methods for reducing fuel consumption are reviewed in this paper. There are

considerable potential for using these methods and many improvements can be made. Many ofthese methods are still investigated in the reasearch centers and conisderable studies arenecessary for their application is marine transportation.


16/17


REFERENCES

[1] Thomas Hellstrm, "Optimizing Control at Sea: The Experience of the Seapacer Project", 2002

[2] Bertram Volker, "Practical Ship Hydrodynamics", Great Britain, Butterworth-Heinemann, Reprinted 2002.[3] Blount Donald L. and Bartee Robert J., "Design of Propulsion Systems for High Speed Craft", MarineTechnology, Vol. 34, No. 4, Oct. 1997, pp. 276-292.

[4] Giassi,A. Maisonneuve,J.J. Bennis,F. Multidisciplinary Design Optimisation and Robust Design Approachesapplied to Concurrent Design, COMPIT 2003, Hamburg, May 2003

[5] Toms, B. A. 1949 Observation on the flow of linear polymer solutions through straight tubes at largeReynolds numbers. In Proc. Intl Rheological Congress, Holland, 1948, Vol._, pp.135-141.

[6] Mysels, K. Flow of thickened fluids. US patent, 1949, No.2492173.

[7] Wei, T. & Willmarth, W.W. modifying turbulent structure with drag-reducing polymer additives in turbulentchannel flows, J. Fluid Mech., 1992, Vol.245, pp.619-641.

[8] Lumley, J.L. Drag reduction by additives. Ann.Rev. Fluid Mech., 1969, Vol.1, pp.367.

[9] Rabin, Y. & Zielinska, B. J. A. Scale-dependent enhancement and damping of vorticity disturbances by

polymers in elongational flow. Phys. Rev. Lett. 1989, Vol.63, pp.512. (1967)[10] Willis & Ratliff Corporation, "Survey of Alternative Waterborne Technologies".

[11] "AIR CAVITY SHIPS" at: http://www.cco.caltech.edu/~matveev/FILE3/ACS/acs.html.

[12] Hiroharu KATO "Microbubbles as a Skin Friction Reduction Device A Midterm Review of the Research"Department of Mechanical Engineering, Toyo University and Yoshiaki KODAMA Center for SmartControl of Turbulence National Maritime Research Institute

[13] Yoshiaki Kodama1, Akira Kakugawa, Takahito Takahashi, Shigeki Nagaya1 and Takafumi Kawamura,"Drag Reduction of Ships by Microbubbles", National Maritime Research Institute of Japan.

[14] Nagamatsu, T. et al. 2002, A full- scale experiment on microbubbles for skin friction reduction using Seiun-Maru, part 2: The full-scale experiment, J Soc of naval Architects of Japan

[15] Latorre. R, Mr. Aaron Miller and Mr. Richard Philips "Micro-Bubble Resistance Reduction for High SpeedCraft", 2002.

[16] Latorre, R., Bablenko, V., 1998. "Role of bubble injection technique in drag reduction." Proc. ONR-NUWCInternational Symposium on Seawater Drag Reduction, Newport, RI, pp. 319326.

[17] PAPANIKOLAOU, A. (2001), Review of advanced marine vehicles concepts, Norwegian MaritimeTechnology Forum.

[18] ANEP (1996), The application of costing and operational effectiveness methods for the selection of hulltypes, ANEP 52, NATO.

[19] AZCUETA, R.; BERTRAM, V. (2002), High-performance marine vehicles as naval platforms, HIPER02,Bergen, pp.22-33.

[20] ACAMPORA, B. (1995), SM Racer: Design and operation of one of the worlds fastest monohulls, MarineTechnology 32/3, pp.197-208.

[21] Insel M., "Characteristics and Relative Merits of Advanced Marine Vehicles Type", Design Techniques for

advanced Marine Vehicles, February 2000.[22] Terrence W. Schmidt, "Technology for 21st century".

[23] JANSSON, B.O.; LAMB, G.R. (1992), Buoyantly supported multihull vessels, High-Performance MarineVehicles Conf., Arlington, MH1-17.

[24] "Aerohydro, Inc.," at: http://www.aerohydro.com/products/marine/navatek.htm.

[25] "Hydrofoil Basics - Characteristics" at: http://www.foils.org/basfigs.htm

[26] N.N. (2002b), Finnish hovercraft Tuuli, Hansa 139/7, pp.53

[27] LOSI, P.C. (1995), The wingship potential for strategic lift, Industrial College of the Armed Forces,Washington.

[28] http://www.se-technology.com/wig.


17/17


[29] "HYDROFOIL PHOTO GALLERY, with some specifications of high-speed crafts", at:http://www.cco.caltech.edu/~matveev/hydrofoil.html.

[30] http://www.sun.ac.za/kie/unistel/technologies/hysucat/explanat.html.

[31] Carlton J S, "Marine Propellers and Propulsion", first published, Manchester, Butterworth Heinemann, 1994.[32] Nozawa Kazuo and Takayama Naohisa, "Hydrodynamic Performance and Exciting Force of Surface Piercing

Propeller", Osaka University.

[33] Janes Jack P. E., "A Fully Enhanced Gas Turbine for Surface Ships", International Gas Turbine andAeroengine Congress & Exhibition, Birmingam, U. K., June 1996.

[34] R.M. Privette, T.J. Flynn, M.A. Perna R. Holland, R. Rahmani, C. Woodburn S.W. Scoles, R.C. Watson,"PEM Fuel Cell System Evaluation for Navy Surface Ship Applications".

[35] P. Schenzle, P. Boese and P. Blume, Ein Programm System sur Berechnung der 11 Schiffsgeschwindigkeitunter Dienstbedingungen, Institt fr Schiffbau der Universitt Hamburg, Bericht Nr. 303, 1974.

[36] J.M.J. Journe, Prediction of Speed and Behaviour of a Ship in a Seaway, Delft Ship HydromechanicsLaboratory, Report No. 427, 1976.

[37] J.M.J. Journe and J.H.C. Meijers, "Ship Routeing for Optimum Performance", Transactions IME, 21February 1980, Conference on Operation of Ships in Rough Weather.

[38] D. Savitsky and J. L. Gore "Re Evaluation of Planing hull Form", J. HYDRONAUTICS, Vol. 14, No. 2,APRIL 1980.

[39] J. J .Maisonneuve, Sirehna, "Advances in Optimal Design Technology"

[40] J. J .Maisonneuve, Sirehna, U. Vivani, " Optimal Design of Ship Hull Forms"

Documents

t8-1-tavakoli.pdf