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1. A lightweight material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2. Diversity of semi-finished products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262.1 Castings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262.2 Rolled semis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262.3 Extruded semis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272.4 Special products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

3. Ease of processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

4. Resistance to corrosion in marine environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

5. Impact on the environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

6. Recycling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

7. Innovation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

C h a p t e r 2A L U M I N I U M ’ S A D VA N TA G E S

21

SOMETIMES the obvious must bestated: the first advantage

of aluminium is that - like steel - itis a metal.

The rules used to calculate thestrength of metal materials can beapplied without difficulty becausesemi-products made from alu-minium alloys are isotropic andhomogeneous in the mass. Themechanical properties of the alu-minium alloys used in shipbuildingare stable over time. There is nophenomenon of “ageing” of thematerial’s internal structure asmay be the case with “plastics”.

By applying the rules and prac-tices of classical sheet metalworking and fabrication, it is pos-sible to construct ships and torepair or fit them out with no par-ticular difficulty and in any climaticconditions (1).

Like most everyday metals, alu-minium is ductile in the sense thatit can sustain strains that remainelastic so long as the stresses donot exceed the proof stress.

If the stress accidentally exceedsthis limit, the permanent set (due

to the plasticising of the metal)absorbs the energy proportional tothe hatched area in the curve inFigure 6.

The result is that, in the event ofan impact, all or part of the impactenergy is absorbed by the defor-mation of the metal depending onthe intensity of shock and themass of metal at the point ofimpact. The fact that deformationis possible before rupture occursis a factor of safety.

However the continuous develop-ment in the marine uses of alu-minium since the Nineteen Fifties,

especially shipbuilding, is explainedby the specific advantages whichaluminium offers:

■ its lightness of weight,■ the availability and diversity offunctional semi-finished products,■ its formability,■ its resistance to corrosion inmarine environments,■ its environmental compatibility,■ its cost-effective recyclability.

It is for these reasons that alu-minium contributes so much tothe development of high speedships and numerous marine appli-cations.

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2 . A L U M I N I U M ’ S

22

FRPRp0,2

5086 H116

Steel E24

•

A %

σ

Figure 6

UNIAXIAL STRAIN CURVES

(1) Provided the rules of welding in acontrolled atmosphere are obeyed, cf.Chapter 6.

FEDERICO GARCÍA LORCA

A D VA N TA G E S

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1.A LIGHTWEIGHTMATERIAL

Aluminium is the lightest of thecommon metals (table 3), its densityof 2.7 being one third that of steel.Structures made of aluminium alloywill therefore always be lighter thantheir steel counterparts.

In theory, aluminium and steelcan be compared using three cri-teria (table 4):

■ at equal thickness, for structuresnot subjected to stress, the ratioof masses is equal to the ratio ofdensities:

such that one tonne of steel isreplaced by 340 kg of aluminium,resulting in a saving of 660 kg or 66% compared with a steel structure,

■ at equal rigidity, the ratio ofYoung’s moduli is 3, and the ratio ofthicknesses of the sheets willdepend on the following relationship:

For a unit area of 1, the ratio ofmasses:

is such that one tonne of steel isreplaced by 500 kg of aluminium.The saving in weight is 50 % com-pared with steel.

■ at equal stress, for sheets, andon non-welded structures, theproof stress being 220 MPa forSealium® and 355 for EH36 steel,it must be verified that:

The ratio of mass:

is such that one ton of steel isreplaced by 570 kg of aluminium.The saving in weight is 430 kg, or43 % compared with steel.

23

THE SPIRIT OF ONTARIO

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In practice, when we take intoaccount:■ the level of mechanical proper-ties of the aluminium alloys usedin marine applications (2), ■ the fatigue limit of welded jointsfor structures subject to variableload (3), experience shows that the weightsaving on an aluminium structureis 40 to 50 % compared with anequivalent structure made fromE24 steel and 30 to 40 % withsteel with a high proof stress [1].

This saving in weight becomesmore important when the proper-ties and specificities of aluminiumare taken into account by design-ers and constructors. Experienceshows that a “literal” transpositionof steel structures producesresults that are average tomediocre.

Using extrusions (and aluminiumalloy castings) is an excellent wayof reducing the weight of sub-structures, enhancing the fatiguestrength of welded joints and opti-mising appearance, as figures 10to 17, pp.28-29 & figures 48 to 50,pp.66-67 illustrate.

A comparison of the weights oftwo high speed ships with alength of 110 metres shows thatthe saving in weight by an all-alu-minium vessel is 214 tonnes or 34% compared with an equivalentsteel ship [5] (table 5):For an equal speed, this reductionin weight translates as a saving onthe cost of the propulsion unitwhich requires 20 % less powerthan for the equivalent vesselmade of steel. The saving on fuelconsumption will also be in theregion of 20 %.

The lightness of aluminium has anumber of additional benefits:

■ during manufacture. At the shi-pyard, sub-structures made fromlighter aluminium alloys are easierto handle and require less power-ful handling/lifting equipment thanis needed for steel. Some shi-pyards with substantial liftingequipment will take advantage ofthis weight reduction to fit out inthe workshop sections of largeships that are subsequentlyassembled in the dry dock (4),

24

REDUCTION IN WEIGHT OF ALUMINIUM ALLOY STRUCTURESComparison Criterion Aluminium Steel Potential SavingEqual thickness Density 2,7 7,8 66 % Equal rigidity Young’s modulus 70 000 MPa 210 000 MPa 50 % Equal stress Proof stress 215 MPa 355 MPa 43 %

Table 4

Property 5086 5083 Sealium® 6082 6005A Steel Steel Stainless CopperH111 H111 (**) T6 T5 E24 E36 Steel Annealed

Z7CN18-09 M20Annealed

Density (kg.m-3) 2 660 2 660 2 660 2 710 2 700 7 820 7 820 7 900 8 940Fusion interval (°C) 585/640 574/638 574/638 570/645 607/654 1400/1530 1400/1530 1375/1400 1083Coefficient of linear expansion20 à 100 °C (10-6.K-1) 23,8 23,8 23,5 23,5 23,6 11,7 11,7 17,5 16,5Modulus of elasticity (MPa) 70 000 70 000 70 000 70 000 70 000 210 000 210 000 200 000 115 000Yield strength, Rp0,2 (MPa) 120 125 220 260 260 240 360 300 70Tensile Strength Rm (MPa) 240 275 305 310 285 410 550 660 235Elongation A % 15 15 10 10 12 24 20 54 45 (*) The mechanical properties indicated in this tale are mean values given for guidance only. Table 3(**) 5383 H116.

PROPERTIES OF SELECTED ALUMINIUM ALLOYS AND METALS IN CURRENT USE (*)

(2) Cf. Chapter 3, table 18.(3) Cf. Chapter 4, figures 48 to 50.(4) Welding zones will be carefullyprotected by covers positioned toprevent air currents disturbing the gasesthat protect the arc.

2. ALUMINIUM’S ADVANTAGES

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■ for the nautical properties of theship. The reduction in the weightof the ship’s superstructure (whe-ther its hull is made of steel or alu-minium alloy) will improve the ves-sel’s stability (5) and make it possi-ble to reduce its beam, producingships that are more slender andhence faster,

■ in operation. The saving inweight of an aluminium ship trans-lates as a significant fuel saving forthe same speed. This is true wha-tever the size of the vessel.

This fact was confirmed by a com-parative study conducted in 1990by the Naval HydrodynamicLaboratory of the ‘Ecole Centrale’of Nantes. The study looked attwo trawlers with equivalent catchcapabilities, i.e. the same holdcapacity, the same propulsionand the same fishing equipment.

One was made of aluminium andthe other of steel (table 6).

Tests in dock showed that the tow-ing resistance of the hull belowthe waterline and the correspon-ding power are significantly lessfor the aluminium trawler than forthe steel trawler (figure 7). Thetotal gain in the performance ofthe aluminium trawler increasesappreciably with the vessel’sspeed, and these figures also rep-resent savings on fuel consump-tion per mile:■ at 8 knots the gain is 28%■ at 9 knots the gain is 39%■ at 10 knots the gain is 50% (6)Above 100 kW, we find that thegain in speed is 1 knot with thealuminium trawler for the sametowing power.

This improvement in performanceis due to a combination of two

effects, the direct effect of theweight reduction and the indirecteffect brought about by aluminiumwhose light weight is utilised todesign a narrower hull below thewaterline. If we decouple these twoeffects, we find that hull slender-ness accounts for half of the gain at8 knots but 80% at 10 knots.

In addition, propulsion tests haveshown that the slenderness of thehull of the aluminium trawlermakes a net improvement in thewake at the propellor that canresult in a 3 to 5 points increase inefficiency.

25

CHARACTERISTICS OF TRAWLERS

Table 6

Characteristic Steel Trawler Aluminium TrawlerLength over all (OA) 15,30 m 17,50 m Length on waterline (LWL)) 13,70 m 16,00 m Beam on waterline (BWL) 5,80 m 5,48 m Draft 2,05 m 1,78 m Ratio of LWL to BWL 2,36 2,52 Nominal displacement (when leaving port) 81 t 74 t

COMPARISON OF THE WEIGHTS OF 110 METRE HSSIN STEEL AND ALUMINIUM (TONNES)

Aluminium Ship Steel Ship (*)Hull 280 504 Superstructure 70 70 Sub-total 350 574 Insulation 60 40 Paintwork 5 15 Total 415 629 Saving in weight 214

(*) Steel hull and aluminium superstructure. Table 5

TOWING POWER300

200

100

02 4 6 8 10 12

kW

V (Knots)

Steel : length = 15,3 m, displacement = 81 tAluminium : length = 17,5 m, displacement = 74 t

Figure 7

(5) A weight saving of 100 in the upperworks translates as a saving of 700 onthe hull. (6) If indeed the steel trawler can attainthis speed.

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Regarding composite materials,aluminium alloys can only be com-pared with FRP (7) as this is thematerial most commonly used forutility boats (fishing, work boatsetc.). Its density is in the region of2.5. With this type of boat, thegreater the length, the greater isthe weight disparity between FRPand aluminium (figure 8).

2.DIVERSITYOF SEMI-FINISHEDPRODUCTS

Compared with normal metals,aluminium is unique in offering awide range of semi-finished prod-ucts (semis) that are:■ cast in a foundry,■ rolled, plate, sheet and strip,tread plate (8), pre-coated sheetand strip,■ extruded, standard or customi-sed; it is possible to make inex-pensive tools (dies) that produceshapes designed for a specificuse.

2.1Castings

Since 1950, most of the parts ofthe superstructure fitted to leisurecraft are made from aluminiumalloys with 3 or 6 % magnesium:51100 (A-G3T) or 51300 (A-G6).

In a foundry it is possible to makestructural components with com-plex shapes in small productionruns and even one-offs, fromalloys such as 42100 (A-S7G03)and 42200 (A-S7G06) whosemechanical properties are per-fectly adequate for structural appli-cations. These alloys are weldableand can be joined to 6000 seriesshapes.

Castings can simplify assembliesthrough being adapted for well-defined functions in the three spa-tial dimensions.

2.2Rolled semis

Rolling mills are able to supplyshipyards with thin sheet (lessthan 12.7 mm thick) for skins, bulk-heads etc., as well as thicker prod-ucts for bilges, keelplates andother structural elements requiringvery thick materials.

The rolling tools in our processingplants have the capacity to pro-duce sheet up to 3 metres wideand 15 metres long. The maxi-mum dimensions depend on thematerial temper; by way of exam-ple, table 7 shows the possiblesizes for 5083 and table 8 forSealium®.

The finishing equipment can beused to supply sheet or plate thatis levelled and sawn to dimen-sional tolerances that meet thedemands of shipbuilding, espe-cially for the fitup of faces readyfor welding, a factor of prime

importance for the fatigue strengthof welded joints (9).

Among the special sheets that areused in large quantities in ship-building (for floors, stair treadsetc.) we should mention the treadplate that is available in 5083,5086 and 5754 (figure 9).

26

WEIGHT OF HULL IN ALUMINIUM AND IN FRP

16

12

8

4

011 12 13 14 15 16 17

Length (metres)

Hull weight(tons)

FRP

Aluminium

From Alumiage n° 97, Autumn 1984, Japan Light MetalAssociation

Figure 8

Figure 9

TREAD PLATE PATTERNS

(7) Fibre-reinforced plastic.(8) Still called “chequer-plate” or “floorplate”.(9) Cf. chapter 6, section 7.

Two bars

Diamond

Barley seed

Five bars

2.3Extruded semis

Unlike steel, aluminium lendsitself readily to forming by meansof extrusion. Whereas steelshapes which are made by hotrolling have only very simpleforms (angles, ‘Tees’, bulb flats),aluminium shapes, both solid andhollow, can assume highly com-plex forms that are ideally suitedto their intended use.

Aluminium is extruded on extru-sion presses whose powerdepends on the form and dimen-sions of the shape and on thealloys used. This is a discontinu-ous operation using billets whosediameter will depend on the sizeof the final shape.

Most shapes which are intended foruse in shipbuilding and marineapplications belong to the 5000 and6000 series. Following extrusion,they undergo finishing operations(straightening, cutting to length etc.)and are heat treated if required.

The form and geometry of theshape are determined by an extru-sion die through which the metalis forced. Each shape must haveits own dedicated die (which ismade from special steel).Contrary to common misconcep-tion, its cost is not excessive andit can easily pay for itself throughsavings in weight and assemblyproductivity.

Shapes up to 700 mm wide canbe extruded with equipment thatis currently available.

Aluminium shapes are coming tobe used more and more in ship-building given the eminent extrud-ability of aluminium, an attributeunique among the common met-als. They offer significant advan-tages in terms of weight reduc-tion (10), time savings and assem-bly precision [3].

2. ALUMINIUM’S ADVANTAGES

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27

EXAMPLE OF SPECIFICATIONS OF SHEET IN SEALIUM®

Thickness (mm) Width (mm) Length (mm)3,8 ≤ t ≤ 4 1 830 15 000 4 ≤ t ≤ 4,2 2 100 15 000

4,2 ≤ t ≤ 4,5 2 260 15 000 4,5 < t ≤ 5,5 2 400 15 000 5,5 < t ≤ 8 2 438 15 000 8 < t ≤ 10 2 438 12 500

10 < t ≤ 12,7 2 438 10 350 Table 8

EXAMPLE OF SPECIFICATIONS OF 5083 SHEETAND PLATE

Thickness (mm) Width (mm) Length (mm) Temper4 ≤ t ≤ 8 2 500 15 000 F, O, H111, H112 8 < t ≤ 10 2 500 12 500 10 < t ≤ 12,7 2 500 10 350 3,8 ≤ t ≤ 4 1 830 15 000 H22, H32, H116, 4 ≤ t ≤ 4,2 2 100 15 000 H3214,2 ≤ t ≤ 4,5 2 260 15 000 4,5 < t ≤ 5,5 2 400 15 000 5,5 < t ≤ 8 2 438 15 000 8 < t ≤ 10 2 438 12 500 10 < t ≤ 12,7 2 438 10 350 4 ≤ t ≤ 6,35 2 000 15 000 H24, H34 6,35 < t ≤ 8 2 300 15 000 8 < t ≤ 10 2 300 12 500 10 < t ≤ 12,7 2 300 10 350 6 ≤ t ≤ 8 2 500 à 2 800 8 000 F, O, H111,

2 800 à 3 050 6 000 H112, H22, H24, 8 < t ≤ 10 2 500 à 2 800 9 000 H34, H116,

2 800 à 3 050 8 000 H 32110 < t ≤ 12,7 < 2 500 12 000

2 500 à 2 800 11 000 2 800 à 3 050 10 000

> 12,7 ≤ 3 050 12 000Sheets are sheared for thickness ≤ 8 mm and for length up to 15,000 mm. Table 7Sheets and plates are sawn for thickness > 8 mm and length up to 12,500 mm.

As with aluminium castings, it ispossible to build particular func-tions into an extruded shape (butin one direction only), for example: ■ masses of inertia. The ease withwhich aluminium alloys can beextruded is such that it is possibleto distribute masses very finely soas to optimise the unit weight ofthe shape (figure 10),■ backing strips allow shapes tobe welded to each other or tosheet. As shown in figure 11, in ashape that has a permanent bac-king strip it is possible to replacea fillet weld (case a) by a butt weld(case b) which has a higher fati-gue limit. It is possible to combinebacking strips and stiffeners in ashape (figure 12),

■ locating or aligning points (fig-ure 13),■ local bulges (bulbs) that balancethe masses that are to be welded(figure 14)

Shapes can be used to ‘move’welds to zones of less stress (fig-ures 15, 16 and 17), significantlyimproving the fatigue strength ofwelded joints as a result.

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SHAPEWITH OPTIMISED INERTIA

➤

➤

➤

➤

➤

➤

SHAPEWITH BACKING STRIP

Case a : welds on lap joints

Case b : offset flange on extrusion

SHAPE WITH INTEGRAL BACKING STRIP AND STIFFENERS

Backing strip

SLOTTED EXTRUSIONS FOR WELDINGTO SHEET COMPONENTS

Plate Plate

BULB ON EXTRUDED FLANGE FORIMPROVED WELDABILITY

Profil

Bulb

Plate

➤

Figure 10

Figure 12

Figure 13

Figure 14

Figure 11

(10) Cf. chapter 4.

Optimised sections for bestweight and inertia distribution

Optimised shapes for betterfatigue life

Wide tee bottom for best welds

Rounded edges for easier coatingand better point adhesion

➤ ➤

2.4Special products

These are not semis in the strictsense, but aluminium alloy prod-ucts shaped to a greater or lesserdegree.

This category includes honey-comb sandwich panels. Theseproducts are used in shipbuildingas interior panels, curtain walls,partitions etc. [12, 13].

The panels (Figure 18) are madeusing cladding sheets betweenwhich the “honeycomb” - alsomade from aluminium alloy - issandwiched (11). Their construc-tion makes them extremely rigid,and under identical service condi-tions they can save as much as 30% in weight compared with con-ventional aluminium alloy panelsto which stiffeners are welded.

These products cannot be weldedowing to the slenderness of theconstituent parts of the honey-comb and the presence of theadhesive. They must therefore beconnected to their conventionalsubstructures by means ofscrews, rivets etc.

2. ALUMINIUM’S ADVANTAGES

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STRESSES IN FABRICATED I-BEAMS

➤

➤

Fillet Fillet

➤

➤

I-profile of flat plates I-profile of two Tee extrusionsand 1 plate

Formed Channel Extruded Channel Extruded top hat

➤ ➤ ➤

I-BEAM FABRICATED FROM SHAPES AND/OR SHEET

BA A

C

A : ShapesB : Fillet weld in lap jointC : Extruded plate or rolled sheet

Figure 15

Figure 16

Figure 17

Adhesive

Cladding sheet

Honeycomb

Cladding sheet

Adhesive

HONEYCOMB SANDWICH PANEL

(11) The parts are bonded together withan organic adhesive. Before they can beused in shipbuilding these structuresmust pass the fire resistance testsaccording to IMO resolution A.754.

Figure 18

OPTIMISING STRESS DISTRIBUTION

3.EASE OFPROCESSING

Provided we obey certain rulesthat are specific to aluminiumalloys, and which are discussed inthe following chapters, we canprocess them by the normal prac-tices of shaping and forming -bending, sheet-metal working,drawing and machining - as areused for other everyday metalssuch as normal steel, stainlesssteel etc.

Special plant or machinery is notneeded to work aluminium alloysin most cases. Wherever possiblehowever it is advisable to have adedicated workshop for process-ing aluminium alloys that is sepa-rate from workshops where steeland above all copper alloys areused (12).

Just like other everyday metals,aluminium alloys lend themselveswell to joining techniques suchas:■ welding,■ screw fastening,■ riveting,■ snap fitting, ■ bonding, etc.

Thanks to its good corrosionresistance, the surface of alu-minium remains clean and will notstain its handlers.

4.RESISTANCE TOCORROSION INMARINEENVIRONMENTS

Marine environments are knownto be very hostile to all materials.Like bronze, aluminium is one ofthose rare metals and alloys capa-ble of withstanding this aggres-sive environment. They belong tothe groups of materials referred to

as being “marine grade”, a labelthat indicates exceptional resist-ance to corrosion in a marine envi-ronment.

Its lightness of weight and resist-ance to corrosion - the mainaspects of which are dealt with inChapter 10 (13) - account for thegrowth in the maritime uses of alu-minium over the past half-century.

The “marine” alloys of the 5000and 6000 series combine excel-lent corrosion resistance in marineenvironments with good mechani-cal properties. They are thereforethe most suitable for marine appli-cations such as shipbuilding. It isalso not essential to protect themby painting or anodising (14).

The excellent corrosion resistancein a marine environment has anumber of important conse-quences for users: ■ the dimensional integrity ofcomponents eliminates the needto provide a corrosion “allowance”(extra thickness) on the submer-ged hull,■ the service life of installations,ships etc. can be very long. It isnot uncommon to find marina jet-ties and boats that have givenseveral decades of service. It isobsolescence rather than corro-sion which puts an end to theiruse,■ the appearance of installations,ships etc. is conserved far betterthanks to the material’s very goodresistance to corrosion. The sur-face acquires a “patina” thatblends very well into the environ-ment without detracting from itsoverall aesthetic. Because the cor-rosion products of aluminium arewhite, even if the metal suffers pit-ting corrosion its aspect does notdeteriorate as is the case withsteel, whose corrosion producesrust colours,■ maintenance is minimal evenwhen the aluminium is not protec-ted (not painted or anodised).

When it is painted, the need torepair the paint is less frequentand less urgent because theunderlying metal resists corrosion.

5.IMPACT ON THE ENVIRONMENT

The issue of environmental impactis a complex one. It depends on anumber of factors, including: ■ the constituent material,■ how the product is formed inthe workshop / shipyard,■ service conditions,■ maintenance,■ the end of the product’s life.

Before a ship or installation is evenbuilt and operated, the design ofthe project is an important stagethat will in part determine itsimpact on the environment. Byapplying design rules that areadapted to suit the material and itsservice conditions, we can reducemaintenance, enhance corrosionresistance etc. [6].

The construction of installationsand ships using aluminium alloysis based on the classical opera-tions of sheet metal working -cutting, forming, welding etc. -which are described in Chapters5, 6 and 7 (15). Advances in joint-ing techniques and tool designare reducing the impact on theenvironment.

By reducing the weight of struc-tures such as ships, aluminiumcan save fuel and can thereforehave a beneficial impact on thelevel of carbon dioxide emissions.

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30

(12) To avoid the attendant risks ofgalvanic corrosion of aluminium. (13) Cf. page 145.(14) However submerged structuresmust be protected with “antifouling”paint to prevent marine bio-incrustation.(15) Cf. pages 73 to 128.

The excellent corrosion resistanceof marine alloys eliminates theneed to paint most interior sur-faces of ships (16), coastal installa-tions or offshore structures. Theresulting savings on protectionalso greatly mitigate the environ-mental impact, as there is nosandblasting or discharge ofvolatile organic compounds(VOC).This remains true over theentire life of the vessel becausesurfaces that are not painted tobegin with never will be painted.

At the end of their working life,aluminium ships and offshoreinstallations can be readily recy-cled owing to the residual value ofaluminium scrap.

6.RECYCLING

Aluminium is one of the mostattractive metals for recycling inboth energy and economic terms.

The most convincing proof of alu-minium’s eminent recyclability isthe fact that you will not see alu-minium equipment or scrap thathas been abandoned or tipped any-where in the world. This appliesequally to marine environments.

Aluminium recycling requires just5 % of the original energyneeded to produce the metal.The percentage of reclaimed alu-minium has been rising con-stantly for 30 years to a levelwhere it now represents 30 % ofthe world’s consumption.

Aluminium recycling has alwaysbeen a highly organised industrialactivity (since the NineteenThirties) and is profitable becausealuminium waste is a valuableresource. In Europe, the value ofsorted waste is in the region of atleast EUR 600 per tonne, what-ever the fluctuations in the price ofthe original metal.

Aluminium is recycled at eachstage of transformation (rollingand extruding) and of usage inshipyards. All workshops thatprocess aluminium have systemsfor collecting offcuts and scrapfrom sheets and shapes which arethen re-sold (17).

The dismantling of aluminiumships is not yet a widespread prac-tice because most of these ves-sels are not very old - less than 30years - but what little experienceexists in this field indicates thatdismantling ships made with alu-minium alloys presents no particu-lar difficulty [7]. Recycling alu-minium waste should be relativelystraightforward given that thealloys used in the construction ofships are the same everywhere -they belong to the 5000 and 6000series.

7.INNOVATION

Aluminium shipbuilding benefitsfrom the innovative dynamic of thealuminium industry, whether it be:■ in the ongoing improvement inthe performance of alloys since1990. Sealium® is part of thiseffort,■ in advanced methods of assem-bly such as friction welding (FSW),bonding etc.,■ in the dissemination of kno-wledge about the uses and pro-cessing of aluminium and its resis-tance to corrosion in marine envi-ronments. As part of this endea-vour, this brochure and its prede-cessor [8] answer the needs of theprofessions involved, includingnaval architects, shipowners andyards.

Bibliography[1] “General considerations on hightensile steel versus aluminium alloy andtechnical aspects related to thealuminium construction”, V. FARINETTI,Fincantieri, Naval Shipbuilding Division,The Third International Forum onAluminium Ships, Haugesund, May 1998. [2] “L’utilisation de l’aluminium enconstruction navale”, CHRISTIAN GAUDIN,Alstom Leroux Naval Nantes, ConférenceCETIM, Senlis, November 1999.[3] “Development of value addedaluminium extrusions for the marinemarket”, J. GÖNNER, Corus AluminiumExtrusions, 4th International Forum onAluminium Ships, New Orleans, May2000.[4] “Use of aluminium profile/honeycombhybrid solutions in marine applications”,R. J. DEAN, F. RITTER, Alusuisse. The ThirdInternational Forum on Aluminium Ships,Haugesund, Norway, May 1998. [5] “Aluminium honeycomb mezzanineramps for Incat 95 metre high speedcombination Ro-Pax catamarans”, G.DAVIDSON, Incat Tasmania, M. TURNER,Hexcel Composites, Third ConferenceAusmarine, Freemantle, November 1998.[6] “Technologies for reducedenvironmental impact from ships –shipbuilding, maintenance anddismantling aspects”, B. HAYMAN, M.DOGLIANI, I. KVALE, A. MAGERHOLM FET.[7] “Research on aluminium shiprecycling”, N. ITOYAMA, Sky Alumnium CieLtd. The Third International Forum onAluminium Ships, Haugesund, Norway,May 1998.[8] L’aluminium et la mer, PechineyRhenalu, 1992.

2. ALUMINIUM’S ADVANTAGES

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(16) Only the submerged structuresmust be painted to prevent incrustationby marine organisms, cf. Chapter 11. It istraditional to paint all or part of theexternal surface of a ship in the owner’slivery, but this is for decorative purposesonly.(17) In aluminium shipbuilding, the ratioof material utilisation is around 115 %,i.e. only 115 kg of metal is needed tomake 100 kg of ship.

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HARD TOP YACHT