Heavy Lift PDF [PDF]

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Table of Contents

Prefac€...............................rrr...o......r.....i.o...........

1

Shiptypes,Crangsand Derricks...................... 5 Stability calculationsin gengral..................... 11 Lashingequipment................... o............. ......... 2l

Planningof Heavy-tift..................................... 35 Lifting/Loadifl$....................................... 49 .........

Lashingand securitrg,Cargo SecuringManual and Documentatio[ .........rr........o..................... 55 During the voyage...........o...................o. .......... 67 AbbreviationS ..................... oo..r........................ 69 r LaW

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OMalstalNavigationsskole Septenber' 04

1

Introduction

Heavy indivisible loads may be defined as those weights which, becauseof their mass and/or their shapecannot be handledby the normal gear availableon board ships or on the quay alongside.On traditional ships, equippedwith 5 tons or maybe even 10 tons denicks or cranes, the handling of a loaded 20' container may be regardedas heavy lift, while the same container on ships with specialist gear, i.e. container feeder ships, are handled swiftly and as merely routine. The definition of heavy lift is therefore very much dependingon the type of ship, the gear on board and not least the facilities on the quayside.The range starts, as mentioned, at around 10-15 tons up to several thousand tons on semi-submersible heavy lift ships. Physical dimensions are often a more limiting factor than the weight for transportationover public highways, why ship borne transportation often is the only choice As the result of the need to transportvery heavy indivisible loads by sea, fabrication facilities have over the years been developedcloseto water. The indivisible part of "Heavy indivisible loads" will very often be the limiting factor, which necessitatesthe choice of transport by sea and not by road or rail. Odd sized indivisible equipmentvery often cannot be transportedby road due to restrictions laid down by authorities, or physical restrictions, i.e. bridges, road corners, high voltagecablesoverheadetc. Most countries have very strict legislation on the width and height of loads that may be transportedon public highways.The basedimensionsof the load also governthe number of axles, which can be placed under it, and hence the axle loading transmitted on to the ground. In the off-shore business Heavy Indivisible loads are defined as those loads weighing in at more than 150 tons orbeing of a size not suitablyfor public roads.

OMarstalNavigationsskole September 04

Loading arm for oil terminal. Whereas transportation of large equipment for long distancesover land requires special permission for each and every stretch of road to be used, police escort and maybe even alterations to the landscape (trees cut down, signs and light poles temporarily removed), the transport by sea is vinually free of obstructionsif you can get the equipment safely on board and off again. This existing state of things has led many producersof large indivisible equipment or very heavy loads to locate in port areasfor easyand logistically simple accessto transportation. An often seen feature is shipyards switching to producing large heavy industrial items rather than ships. It could be units for the off-shore oil exploration or production or it could be towers for windmills. "Heavy lift" as a term covers a wide range of cargo units. With the containerisationof the break-bulktrade,handling of relatively large and heavy items - up to 12 metreslong and 36 tons in weight - has become commonplace in maoy ports and on many ships. Stepping back 40 years in time, handling of a loaded 40' container would clearly have been considered heavy lift. Nowadays even the smallest container feeder ship, loads and discharges40 feet containerswith her own gearat commendablespeed. Loading a 50 tonnes dump truck may in some ships be heavy lift and requiring a fair amount of plaruring and possibly alterationsto cranesor the rigging of the derricks, while other - even smaller - ships will be able to load the truck with relative ease; one crane and no changes necessary.So defining heavy lift as all lifts abovea certain limit is simply not possible. ln modern heavy lift tonnage loads of over 1000 tonnes can be handled. 500 - 700 tonnes can be commonplace. Conventionalship tonnageis now extensivelyfitted with heavy lift facilities of wide application, apart from those vessels especially built to carry exceptional loads, requiring particularhandling and ballastingfunctions.

@Mantal Navigationsskole September04

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The range of "heavy lift" cargo can well be of the order of 100-800tonnes.

Trade Features

A specializedtrade exists, and is growing, which calls for specialized lifting and carrying facilities, the demand for which arising from the need to transportheavy indivisible load units from point of manufacture to place of installation, with the least amount of intem-rption in their passage. Loads such as refinery, chemical, electrical, mechanical and transportationunits, for example, cover some of the cargoes involved. All are of extremely high tonnage and size; most are in a stage of construction as will permit direct installation, at site; all require transportation applicableto their design. The trade is therefore competitive, primarily becausethe site installations are in countries and areas, which'are developing their industrial capacities,not only quickly, but also, frequently, away from deep-water ports without suitableconnectionland routes.For this reason,alone,the transportation of these heavy units, while possible by conventional purpose built heavy lift ships, creates economicand carrying problems,which the smallervessel can reduce, or overcome by transporting "direct". lndeed, the trade, in some circumstances, is introducing a completely integrated consortium of road and maritime transport, the former "rolling" on to, and off the latter, the ship being an incorporated part of the exercise. ln other cases, the ship operates within the market demands and offers facilities of its designacceptableto shippers'needs.

@Marstal Navigationsskole September04

Another example of this trade is the project cargo sector, where contracts of transportation of complete industrial installations, power plants, windmills or other large installations involving large volume andy'orheavy loads. The contract will often also include the transport of all the smaller parts of the installation. The shippers of these complex and often very expensive items will generally prefer "door-to-door" transport without undue trans-shipment,as any such extra operation will increase the possibility for structural or technical damages.

OMarstal NavigationsskoleSeptember04

Ship types,Cranesand Derricks ln generalfour typesof heavy-lift shipsexist.

The traditional 'tween-deckvessel

l.

The traditional tween-deck vessel equipped with a single heavy-lift derrick,

2.

The containerfeedervesseloften equippedwith two cranes each capable of being rigged up to lift say 100 tons.

3.

The specialized heavy-lift I project cargo vessel. These vesselscan have numerousdifferent features apart from specialist cranes or derricks, such as ramps for rolling cargo or supportinglegs to land on the quay.

4.

Semi-submersiblevesselsfor loading very large and heavy floating objects;oil-rigs, ships,bargesetc.

On conventional 'tween-deckbreak bulk cargo ships the normal cargo lifting equipmentconsistsof numerous5 or maybe even 10 tons derricks, which clearly restricts this type of vessels capabilities in the modern world of transportation - containers and the like. These ships werelare often equipped with a single heavy lift denick situated by the largest cargo hold. Some derricks, as the Stuelcken Mast and Denick describedin the following, are capableof working two holds. Not simultaneously,but the derrick can fairly easy be swung around to work both hatches.

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6

The Stuelcken Mast

and Derrick

Prominent in the area of heavy lifts on conventionalships is the Stuelcken mast and derrick arrangement,a patent of Blohm & Voss A.G. of Hamburg,Germany. A considerablenumber of these masts and derricks have been fitted into ships of varying tonnageand nationality, with S.W.L capacitiesranging from 25 tons to 350 tons. The ranges between 60-80-100 tons indicate the tendenciestowards conventional tonnage; those upwards of 350 tons being illustrative of the more specialist tonnage. The manufacturers, Blohm & Voss A.G., claim the following main advantagesin the Stuelcken masVderrickcrane cargo fittings.

The main advantages of the Stuelcken Mast compared with other cargo gear arc: 1.

Absence of all guys and preventersfor slewing the derrick;

2.

No tackle work, even when swinging the derrick through the posts or when cllanging to smaller loads;

3.

Swinging the derrick through the posts allows hatchways, both forward and aft of the masts to be served:

@MarstalNavigationsskole September 04

n I

The containerfeeder vessel

4.

The winches - and hence also the derrick - can be operated by one man by means of controllers or by remote control:

5.

The whole denick maintenance-free:

6.

The speed of cargo handling can be substantially increasedby using suitablepoweredwinches;

7.

Ordinary light cargo gear (union purchase) can be attached to the posts and operated on one side simultaneouslywith the heavy lift denick operating on the other side;

8.

So far the Stuelckenmast is built from l5 tons SWL. up to 525 tons SWL., but there is no limit to the capacity of this cargo gear, provided, however, that the vesselhas sufficient loading stability;

9.

When installing two Stuelckenmasts,for exampleto handle 260-ton loads with two equal 130 tons derricks.it is not necessaryto use a traverse.

installation

is

largely

This type of ship is most often equipped with two hydraulic operatedcranes mounted clear of the hatcheson one of the ship's side to facilitate easy loading and unloading of large items, i.e. containers, from an unobstructedcargo area. This positioning of the cranes makes it possible to constructthese ships with very large hatch openings.Smaller vesselsmight only have one hold with a hatch opening of maybe 50 metres in length. This makes it possiblefor thesevesselsto load even very large structures in one piece. With qanes with a normal capacityof 36 to 40 tons will easily handle goodsup to 80 tons without any alterations of the cranes. Some cranes have the possibility to alter the rigging to accommodate even large loads. Moving the crane'shook inwards on the jib and increasing the number of sheavesused on the runner normally does the job. After altering the rigging, the cranes capacity will often have doubled but the outreach reduced with the same factor. Extremely long and stiff objects might still be within the reach of both cranes at the same time, but shorter or less rigid objects will now require a lifting yoke in order to be lifted by the two cranes at one time. It is of course a time consuming and labour intensive - and thereby costly - project to alter the rigging of one or two cranesfor a single lift, but unless a floating crane is available in the port area it is the only 'tween-deck possibility. An often seenfeature is that the if the vesselhas any - is adjustablein the vertical position or can be removed altogether.

@Marstal Navigationsskole September04

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The specialistheavy tift / project cargo vessel

The smaller specialistheavy lift / project cargo vesselwill often be equipped with two very large derricks, again positioned on one side of the cargo area, enabling the vessel to load - and unload - very large objects over the opposite side of the ship, on to the totally unobstructed deck area or down in the - again - very long and box shaped cargo hold. The derricks can be of differenr rypes, i.e. Velle system,"inverted" Stuelckenmast / denick and others,with capacitiesin the range of 300 tons to 500 tons each, giving a combined lifting capacity of up to 1000 tons. The hatch covers will often be of the pontoon type and be flush with the main deck. ln combination with a bow- (or stern door, depending of the position of the accommodation) + ramp, this feature will enable the vesselto load rolling cargotoo. The bigger specialistheavy lift / project cargo vesselcan be of similar type as the smaller ones just enlarged.But often the cargo area will be divided into two ore more holds and the lifting gear can very well be three or more cranes. The total lifting capacity will again be in the region of 1000 tons.

@MarstalNavigationsskoleSeptember04

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The semisubmersiblevessel

The semi-submersiblevessels are not usually equipped with heavy lifting gear,but rely on being able to submerge the deck below the unit to be lifted. With the ability of these vesselsto raise and lower their cargo decks, rolling devices and skidding techniques may also be used for loading and discharging units from the quayside on to thesevessels,if floating on or off is not viable.

04 OMantal Navieationsskole September

10

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OMarstal Navigationsskole September 04

l1

Calculation of the Metacentric Height, GMt As loading and unloading in Heavy Lift operationswill often include ballast operations,and as GMt is important for the calculation of the angle of heeling due to the transverse moment about the Centre line plane, the following text will give you alternative methods of calculatingthe GMt after shifting, loading or unloadingof weights, without doing a complete calculation of the momentsaboutthe baseline. Even though most calculations can be done with the computer based loading programmes,it is still important to be familiar with the basicprinciples. GMt is the differencebetweenthe height abovethe keel of the metacentreand the centre of gravity.

(1)

GMn - KMh- KGt

The height of the centre of gravity above the keel in condition l, KGr, is calculated from the total moment aboutthe baseline for the fully loadedship.

(2)

Mkt KGt=:;

KMtr is taken from the hydrostatic particulars for the given displacementor draught. When loading and discharging, the new height of the centreof gravity can be calculatedfrom formula (3)

(3)

KGz =

Ar.KGr+Iq.Ks A,Z

KMtz is taken for the new displacement.Now GMt2 can be calculatedfrom formular (1). Example

1

Arktis Ligh is in a condition with Ar=6410 t. and KGr-5,93 m. Ballast tanks 3 s+p are to be filled with seawaterand a weight of 35t is to be loaded on rhe rop of the hatch with the centre of gravity at a height above the keel (Kg) of l4m. CalculatingKG2 og Gmtz ! From the capacityplan you can seethat tanks 3s+p have a capacityof 155,7t.with a Kg of 0,64m. The new displacementwill be: Az | 55,7+35+64 70=6600,7t

OMantal NavigationsskoleSeptember04

T2 And from formula(3) KGz =

. 0,64+ 35.14 + 155,7 6410.5,93 = 6600,7

5,85m

With A2 ]ou can readKMt2 ='7,065m, and from formula (1) youhave: =1,22m GMtz =7,065-5,85 The change in the GMt The changein the GMt is found asthe differencebetween the changein KMt and the changein KG.

(4)

DGMI=DI(MI-DKG

The new GMt can now be found

(5) Weights

Shifting

GMtr= GMtr +aGMt

Shiftingof weights(i.e. Ar = LD doesnot causeany changein the KMt, consequently: 6KMt =0 The changein KG can be calculatedfrom the changein Kg for the weightsshifted:

(6)

l,q.dKs dKG-T

and now ,

(7)

GMtz=GMtr

\o axs T

Rememberthat the changein Kg is positive when shifting weight upwards, and negative when shifting the weight downwards. Example

2

If we go on with example I and shift the contents from tk. 3 P+S to the forepeak tank (All centres of gravity as mentionedin the plan of capacities) The changein the Kg is found from the plan of capacities DKg-Kg2 -Kgr = 4,94-o,64=4,30m and now from (6),

'4'30 = o,lom dKG=155'7 6600,7 and from (4),

=-0,10m. aGMr=0-0,10 eKMt =0 bYshifting @Marstal Navigationsskole September04

l3 and from (5),

GMt3 = I,22+(-0,10)=l ,LZm. Loading and unloadingWhen loadinganddischarging you musttakethe KMt for both condition 1 and condition 2 and then calculatethe change in KMt:

(8)

SKMI = KMtz - KMtt

The change in KG is determined from KG1 og Kg on the loaded or unloaded weight q. Positive weight for loading and negative for discharging.

(e)

F 8KG= L/'

q. (ke ' " - KG) A,z

Finallyyouhave: (10)

GMtr = GMtr+(KMt2 - KMtl) -

Lq'6s - KG) L,Z

Attention should be paid to the fact that the centre of gravity for the lifted weight is the top of the derrick or crane, when you are loading with own gear.

Example 3

If we go back to example 1, and want to improve the stability by filling another set of bottom tank , DB 2 S+P (q=158,7t with Kg=0,65m)we have: giving KMs - J,0J6m., A I = 6600,7+158,2=6758,9t., and from (10),

158,2.(0,65-5,95) = GM* = 1,22+(7,076-7,065)1,35m. 6758,9 And now from (1) = 5,726m. KG: - 7,o76-1,35

The effect of free surfacesof liquids

The effect of free surfaces will increase the solid KG to the fluid KGc, and reducethe solid GMt to the fluid GMc. The effects of the free surfaces are listed in the plan of capacities for each tank., and the reduction can now be determinedbv.

F rvr

(11) a - L /

The reducedGMc can be calculat,ideither as,

(L2) GMc = GMt-6

OMarstal Navieationsskole Seotember 04

l4

or.

(13) GMc = KMt-KGc, Where the increasedKGc is found as

(14) Example4

KGc -

Mk+lrsu A

When shifting water from double bottom tanks 3P+S to the forepeak tank in example 2 , you must calculatewith free surfaces in both tanks. From the plan of capacities you seethat FSM for 3 P+S is 220 mt. and 195 mt. for the forepeak tank. Therefore from (1 1)

--- =0.06m. ^ 220+195 d---6600,7 andfrom (12)

m. GM"t =1,12-0,06=1,06 Regardless of type of ship working with heavy lift operations,it is recommendedto reduce free surfacesin tanks to an absoluteminimum. Start the operation with only empty or totally filled tanks and only work with a single pair of tanks when the ballast is used as a counterweight.

Determinationof the angleof heel

The angle of heel in the below formulas must not exceed 10 degrees. Ballast and loading operations will result in a moment about the centre line plane. The resulting moment Md, is defined as positive giving a heeling to starboard, and negative,giving a heeling to port side. The moment of heeling is found by summation of the weights multiplied by the lever to the centre line plane, Dg. Positive to starboardand negativeto port side.

(1s) Md.=la'ns The angleof heelcannow be calculated,

(16) 0 = Arc tan-

Md

L,'GMc

At a given list, the heelingmomentabout the centreline planeis determinedby,

(17) Md = L^'GMc'ane

@Mantal Navigationsskole September 04

15 The angle is positive for starboardlists and negative for port lists. By changesin weight, the changeand the new moment are found by,

(18) dMd=la. Ds and

=d z + l a . n s (1e) M d . zM and by shifting weights

(20) dMd=la.aDs

(2I) Mdz= Mdt+ I q.dDs 6Dg is positive when shifting a weight to starboard and negative when shifting a weight to port . If the angle of heel is more than 10 degreesit rnuri b" determined using the curve of the righting levers (GZ curve). Seefig. 1

Y=Md/A

0

Fig. I By a sudden and fast hoisting the situation is dynamic rather than static, and the heeling will reach its maximum at the dynamic equilibrium at the angle b. There will be dynamic equilibrium when the area above the GZ-curve and below the Y-curve equals the area above the y-curve and below the GZ-curve at the angle b, After rolling there will be a static equilibrium at the angle a where the GZcurve cuts the y-curve. Of course both Dg and MD will-change with increasing angle of heel, but without importance for practical purposes.

@MantalNavisationsskole Seotember 04

t5 By easy and slow hoisting the angle of heel will exceedthe angle a in static equilibrium.

Kg

Dg

F i g .2 In Fig.2 you see Dg and Kg, the distanceof the centre of gravity for the weight from the centre line and the keei respectively. Note that the centre of gravity is at the derrick top during the hoisting operation. Of courseKg and Dg will changea little with the angle of heel but can be calculated with a god approximation keeping both constant.

Example5

Now from example 3 , with Lt =6758,9t., Km6 =7,076m. and KG3 =5,726m. The port side of the ship is alongside, and you are to hoist 40t With the crane in lifting position there is an angle of heel of 3" to port , The top of the crane is 34m above the keel and the centre of gravity of the weight is 20 m from the centreline plane.

OMarstalNavigationsskole Seprembcr 04

17 There are free surfacesin Wing Tanks 1 S+p, which also can be used as heelingtanks during the operation. What is the angle of heel when the weight is hanging in the runner? The fluid GMc is calcularedfrom (11) and (12)

a-

27 =0,O04m. 6759,9

GM":=1,35-0,004-1,35 The heeling moment for the 3 degreeheeling to pofi ls determinedby (17)

Mdr =6758,9.1,35.tan(3")=-47 8,2 mt. When the weight is hangingfree in rhe runner A+ = 675g.9 +40=6798,9t.and KMta =7,078m. From (10)

GMt +=7,35+ (7,078 - 7,076) -

40(34-5,726) 6798.9

= l,l86m.

and from(l2)

GMca =1,186

)' '1 =1.182m. 6799,9

Thenewheelingmomentis foundfrom (18) Md2 =-478,2+40(-20)=-47 8,2-800=1278,2mr. Now the angleof heelcanbe foundfrom (16) -1278,2 0 = ArcTan

- -9 ( i.e. at port ) 6798.9.r.182

Note the very little effect of the free surfaces in Wins tanks I S+P. The fact that makes them useful as heeling tanks during ballastoperations.

Generalintact stability criteria for all ships

The criteria recommendedby IMO in res.749,chapter3 The following criteria are recommendedfor passengerand cargo ships Recommendedgeneralcriteria. The areaunder the righting lever curve (GZ-curve) should not be less than 0.055 metre-radianup to e = 30" angle of heel and not less than 0.09 metre-radianup to 0 = 40o or the angle of flooding 0l if this angle is less than 40". Additionally, the areaunder the righting lever (GZ-curve) betweenthe anglesof heel of 30o and 40o or between30o

@Marstal Navigationsskole September04

18 and 0f, if this angle is less than 40" , should not be less

than 0.03 metre-radian. The righting lever GZ should be at least0.20 m ar an ansle ofheel equal to or greaterthan 30o The maximum righting arm should occur at an angle of heel preferablyexceeding3Oo.butnot lessthan 25 degrees. The initial metacentricheight GMt should nor be less rhan 0 . 1 5m .

Heavy lift operations

All ships can be regarded as heavy lifters in relation to size and derricks. Every ship is only limited by its size and type of cranes and derricks. For most ships it is possible to use their loading programmesto determineballast operations,angle of heel and angle with the horizontal for the derricks in heavy lift operations. The vessel concernedwill have its own suidelinesfor the operations. The following is from a ship of DW 5860t, Lengrh 82.I2m., Breadth 17.0m. and draft 8.26m. and equipped withal00tderrick Notes regarding handling heavy cargo hoisting gear ln order to avoid unexpected movements of cargo being hoisted, or accidents of other kinds, it is recommended that the following precautionarymeasuresbe taken. 1. The heavy denick is to be used in an angle of 45 degreeswith horizontal. ?

The maximum list angle should be 10 degrees.

3.

All tanks, bunkers as well as ballast tanks should be either completely full or empty. Slack tanks must be avoided.

4.

Upper forepeak should always be empty.

5.

Ballast tanks acting as counterweight should be filled or emptied one by one during slewing and hoisting.

6.

When filling and emptying the double bottom ballast tanks, it is to be ensuredthat there always remains a list of about 5 degreesto the hoisting side,during the time the heavy load is not between the hatch coamings. Only between the hatch coamings guys from the hoisting side deliver their full capacity. For examples of loading and unloading conditions seeconditionsmarked "a".

7.

@MarstalNavigationsskole September 04

T9 Generally you must always be careful to avoid heavy accelerations and decelerations with the hoisting gear causedthe strongforcesinvolved. Heavy lift operationscan with advantagebe carriedout by ballast operations. You can use the ballast as a counterweight slowly reducing the heeling moment causedby the heavy weight. When the weights equal each other the crane itself can be used for the rest of the operation.The ballast now being used to reduce the heeling until the weight is well on board. Take care that there is almost no list when the weight has to be landedon board. Every type of derricks and cranes have their own specificationfor maximum list, angle with the horizontal and limitations for weight Many vessels have special heeling tanks with muck capacity and often a small FSM, to reducethe fluid GMc during the lifting operation. Generally it must be recommended to reducethe number of slack tanks as much as possible.

Example No. 6

The vesselis lying as in example No. 5, but now lifts the weight by shifting ballast from WT 1 P to WT 1 S. The distance athwart ships between the centres of the wing tanks is 14 m.. How much ballast must be shifted before the weisht is lifted? The weight will be lifted when the change in the moment about the centre line plane equals that of the counterweight 6Md=-478,2-(-127 8,2)=800mt.From (20)

800 ' t 4 There will be no changein stability comparedto example No. 3, as it is a shifting of weights between tanks with identical centresof gravity.

OMantal Navigationsskole September 04

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04 September OMarstalNavigationsskole

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LASHING EQUIPMENT The following text containsa short descriptionof various stowage and securing materials and elements in order to provide an overview on availabledimensionsand strength. It is desirable that manufacturers and ship chandlers deliver with such material appropriate documents on the nominal breaking strength and elasticity properties. There is however no world wide standard asreed on such information. If no breaking load (BL) values are available or those given are doubtful, the text containssome rules of thumb which may be usedto estimatethe breakingstrength.

Fibre ropes

Natural Fibre ropes are made of the materials manila, hemp, sisal and manila-sisal-mix.Natural fibre ropes will not normally be used for lashing heavy indivisible loads, but is mentioned for information only. If not otherwise declared the breaking strength can be estimatedby: BL = 6* d2 kN (d = rope diameterin cm) Synthetic fibre ropes are considerably stronger. If the nominal breaking strength is not supplied by the manufacturer or chandler the followine rules of thumb may be used: BL = 12* d2 kN For polypropyleneropes BL = 15* d2 kN For polyesterropes BL = 20x d'z kN For polyamideropes All the above fibre ropes are not recommended for the securing of critical cargo units, such as heavy units, becauseof their high elasticity and the tendencyof knots to slip open.

Conventional wlre rope lashings

Material: Steelwith a nominal BL of around 1,6 kN/mm2.

Typicallashingwire typesare: 6*9+1FC,(FibreCore) 6 x 1 9+ l F C 6 * 3l + 1 FC (runnertype) If no BL informationis availablethe rule of thumbreads: BL=50* d-'tN Speciallashingwireswith high flexibility- andeasierto work with for the lashinggang- havea highernumberof

OMarstal Navigationsskole September04

22 fibre coresand thereforelessBL and Maximum Securing Load (MSL). Thetypicalmakesare:

6 * 9 +7 FC 6*12+7FC 6*15+7FC

If no BL information is availablethe rule of thumb reads: BL=25 x d2 kN It is clear that those more flexible wires require the double effort of lashing work and material for getting the same result althoughthe handling may be more convenient.

Wire clips (butldog grips)

It is of utmost importance that wire clips are applied in correct number, direction, size and tightness. Neglecting these requirements is the main reason for the failure of wire rope lashings. Wire diameter

Clios sizemetric

l2 mm 16 mm t8 mm

t2

v2'

T6 t8 20 22 24 26

5lg"

20 mm 22mm 24 mm 26 mm

Clips size in inches

3t4" 3t4" 7t8" l'

t"

The number of clips in a simple dead eye shows a close relation to the slipping load. Numberof anpliedclios

2 J

4

Eyes- Splicesand Grips

Slinpineat ....7oof BreakinsLoad approx.25Vo aoorox.50Vo approx.757o no slippins

ln some instance lashing wires are supplied pre-cut to length and with eyes and/or attachment devices already formed in one or both ends. Such purpose-madeitems are usually sold with certificates stating the test-load and nominal break-load applicable. For general lashing pu{poses,however, the wire is usually supplied in coils and must be cut to length aboard the ship with the eyes and attachment devices formed and fitted on site as required. It is to this latter practice that the following considerationsapply. The eye may be formed by splicing the strands of the wire back into the lay of the standing part around a thimble. There are several methods of achieving this result. All are time-consumingand, even if effected with the exerciseof

@MarstalNavigationsskole September 04

23 great skill and care,they all reducethe strengthof the wire in the tucked area to about 8OVoof its nominal breakingload. In instanceswhere the eyesare formed with lessskill and care the strands may pull or slip at loads of no more than 50Voof the breaking-load of the wire. For these reasons bulldog-grips and their close cousin Crosby-clipswere invented,the use of which allows eyes to be formed quickly and securely in wire ropes by relatively unskilled personsproviding a few simple rules are followed. The correct method and the incorrect method of making eyes in wire ropes using bulldog-grips is shown in the following figures:

2

,1

Jl -"i!'li :.'rr..;' /:'i. ;:r:-,4:;:;+S":ti$S+i+il5.s.\s r,.. *:S.N.i{.\_'i.::s-i : Fig.i.O8

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Experienceshowsthat the simple most predominantfactor associated with the failure of cargo lashings is the incorrectapplicationof bulldog-grips. Seamanship and rigging books, manufacturers' information material, and many years of instructive propaganda have all promulgated the correct methods to adopt; but with little apparent beneficial results; the learning curve remains stubbornly flat, and the task of getting the work done properly is as difficult today as it must have been when bulldog-grips first came on the market. The strength of eyes formed by bulldog-grips has for years been a matter of speculation in some quarters.On the other hand, severalpublications attempt to give guidance on the subject. Empirical tests made several years ago over a range of wire-and-grip configurations - indicate that the perfect eye around a thimble, made and tested under perfect conditions, will hold at 9OVoto IOOVoof the nominal breaking-load(NBL) of the wire before slipping and/or fracturing. On the other hand, departuresfrom the ideal will result in slippageat much reducedloads.

OMarstal Navigationsskole September04

24 GROSBY@GLIPS

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$EE APPLIC.ATION AND wenrurNc TNFoRMATToN

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Basic rules for the use of Bulldog-grips for marine lashings: 1.

For all sizes of wire from 8mm to L9mm diameter, use not less than three grips at eacheye; for wires of 20mm to 32mm diameter. use not less than four grips per eye; for wires of 33mm to 38mm diameter, use not less than five grips at each eye and upwards. Using less numbers of grips than here recommended can seriously impair the holding effectiveness of the eye.

2.

Bulldog-grips have a grooved surface in the bridge piece, which is suitable for a standard wire rope of right-hand lay having six strands.Crosby-gripshave

OMarstalNavigationsskole 04 September

25 a smooth surface in the bridge piece. The grips should not be used with ropes of left-hand lay or different construction. J.

Before cutting the wire to length, whip or securely tape both sidesof the cutting point. The two cut ends will then not tend to unlay, and a good, firm eye can be madewithout wasting materialor time.

4.

The first grip must be close up to the thimble - or at the neck of the eye if a thimble is not used - and the other grips must be spacedapproximately six rope diameters apaft, i.e. 96mm apart on a 16mm diameter wire; 108mm apart on an 18mm diameter wire.

5.

The grips must all face in the same direction and must be fitted with the saddle(or bridge) applied to the workingftrauling part of the rope; the U-bolt (or bow) must be applied on the tail/dead-endof .the rope. Applying the grips in reduced numbers and in other directions can seriously impair the holding effectivenessof the eye.

6.

Ideally, all nuts should be tightened using a torquewrench so as to give tightening values in accordance with the manufacturers'instructions.This is feasible in covered workshop conditions but, on an exposed deck in the dark and rain of a winter's night, it is sufficient to take all nuts hard-up with a ring spamer. Thereafter,all eye terminations should be checked after a while and the nuts hardened-up again if necessary.This latter practice should never be neglected. The very nature of the grips and the wire means that one is compressingthe other; the flattening effect of that compressionmay continue to some very slight degreeafter the nuts have been first applied firmly.

7.

Under test, when the gripped connection starts to slip, it first goes quickly; the rate of slip then reduces, but slip does not stop until the load is removed.

8.

With three grips used in the correct manner and with the eye formed around the correct sized thimble (a hard eye) the eye will not fail or slip at loads less than90Vo of the nominal break-load.

9.

With three grips used in the correct manner but without a thimble (a soft eye), this being by far the most common configuration likely to arise in practical, on-site, lashing arrangements,the eye can be expected to slip at loads at about 70Vo of the

@Marstal Navigationsskole September04

26 nominal break-load. It would not be unreasonable to call this the "slip-load" or the ,,holdingpower,,of the eye, and it is so called throughoutthis paper.

1 0 . The practice of using half-double grommets is

widespread, but rigging gangs and ships' crew frequently assumesuch arrangementswill provide a holding power of twice the break-load of the wire. Testsproved such assumptionto be wrong. In a half_ double grommet, with six grips used correctly as illustrated below, the slip-load will be about 1Zz times the nominal break-load. The holding power naturally decreases as the number of gnps is reduced.

Il.

The practice of using bulldog-grips to join two end of wire rope together to form a single loop is to be avoided, and is not approved by the manufacturers of either wire rope or bulldog-grips. Rigging gangs and ships' crews frequently assume such arrangementswill provide a holding power of twice the break-loadof the wire. Tests also proved such an assumptionto be wrong. Bearingin mind the content of (5) above, it follows that, where an attempt is made to join two ends of wire in a loop witli the grips, there is no tailldead-endinvolved: Both parts are working/hauling pafis and so there is a failure of the mechanical principles on which the grips are designed. It is, however, appreciated that circumstancesmay demand some such arrangement, and so tests were carried out on a range of made-up loops. The results were more favourable than expectedwhen six grips were used.In a single loop, with six grips used correctly as illustratedbelow, the slip load will be about l4OVoof the nominal break_ load. The holding power naturally decreasesas the number of grips is reduced.

1 2 . In a soft eye with two grips, and with one or both used in the reverse manner, the eye can be expected to slip at loads of about half of the nominal breakJoad. These may be considered the least desirable configurations. However, if used, do not allow their holding power to be greater than half the nominal break-load of the wire.

1 3 . ln soft eyesusing only one grip the slip-load will be 0,25 NBL with the grip positioned correctly and 0,18 NBL with the grip used in reverse.

@Marstal Navigationsskole September O4

27

SOFTEYES

HALF_DOUBIE CROMMITS

MARINEIV]REROPE GALVANISED lllmm - 0 r 12 C0l{St?UClT0N aIld lSmm - I r 24 CONSIBUCIJON

SINGLE IOOPS

Slip load : NBL x

1.40

GRIPS OF BUTTDOG CORRECT APPLICATION A word of caution before deciding to use half-double grommets(at NBL*1,5) and singleloops (at NBL*1,4) as opposedto single eyes (at NBL*0,7). Remember that at one terminal end in the instanceof a half-doublegrommet, and at each terminal end in the instanceof a single loop, there is no more material than at the terminal end of a single soft-eye. For instance,say that for convenienceand time savingyou choose to use 12 half-double grommets of l6mm 6xl2 wire to secure a 46 tonne item, rather than 25 single eyes. If one of the half-double grommets fractures at a poor terminal connectionyou loose 8,257oof the total holding power - if a soft eye had failed you would have lost only 4Voof the total holding power. Lashing and securing of heavy cargoes (or other cargoes for that matter) is not an exact science.It is frequently a case of a balancedtrade-off. but-the trade-off should be basedon information and a few quick calculations.

@Marstal Navigationsskole September04

28

Correct Method Of Installing U-Bolt Wire Rope Clips

t.

Turn back specified length of rope from thimble and apply first clip one saddle width from seized dead end. Tighten nuts evenly to specified torque. Important: Seat "live end" of wire rope (load carrying part) in saddle and position U-bolt over "deadend".

z.

Apply second clip close to the thimble without binding on it. Turn on nuts firmly but do not tighten yet to recommendedtorque.

3.

Apply all other clips, equally spacedbetween first two clips.

4.

Apply light tension and tighten all nuts evenly to specified torque.

5.

Recheck and re-tighten nuts after initial load. This load should be at least equal to loads expected in generaluse. Wire rope will stretchslightly causinga reduction in diameter,which will slacken the clips. Nuts must be checked at frequent intervals for tightnessto assureefficiency of termination.

If the specified number of clips are applied accordingto these instructions, they will develop approximately 80% efficiency of right lay wire rope of classes6 x 19, 6 x 37,7 x 19. 8 x 19, 19 x 7 and cablelaid. Add at least one additional clip if thimble is not used or if clips are used on other wire ropes than those mentioned above. Check with wire rope manufacturer if in doubt. If more clips are used than specified, the amount of wire rope to be turned back has to be increasedproportionately.

Chains

Lashing chains are generallymade of high tensile steel in order to reduce their weight for the ease of handling. The most common lashing chains are class 5, class 6 and class 8. Breaking strengthof material: Class 5: 500 N/mm' Class6: 600 N/mm2 Class 8: 800 N/mm2 If no information on the breaking strengthis availablethe rule of thumb reads: BL = 80+d kN for class5 BL = 95*dzkN for class6 BL= 125*d2kN for class8 Where d is the diameter of the chain steel in cm.

04 September OMarstalNavigationsskole

29 Example: A lashing chain of 13 mm, class 8, has an BL of 725*1,3*1,3= 211,25kN. There are various systemsof chain tensionersavailableas well as specially adaptedhooks to shorten chains to the required loadedlength. Chain lashingswith lever tightener should be used as described in the manufacturer's information with particular regard to permissible lever angles,securingof the lever and re-tighteningthe lashings during the voyage.

Chainwith chainlevertiehtener

The advantage of using chain resides, in some circumstances,in the fact that, under the normal loads for which it is designed,it will not stretch.Thus, if all chain lashings are set tight before the voyage and the cargo neither settles nor moves, there is no normal loading circumstanceswhich will cause the chain to lose its tautness. Hence, its widespread use in the securing of freight containers. Below are shown some illustrations of some chain types and arrangements.

OMarstalNavigationsskole September 04

30

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It is important to remember that within the CSM of Regulations set down by IMO manufacturers/suppliers lashing chains now have a mandatory duty to provide the user vessel with details of breaking strengths,Maximum Securing Load; so the table aboveshould only be used in the absence of other more precise data and when you know the chain you have is of grade8.

@Marstal Navigationsskole September 04

3I

D-rings, LashingLugs, Pad-Eyes,Etc.

Many a well-stowed, well-securedcargo started to break adrift becausethe lashing terminal points were either too weak to start with or overloadedwith too many lashings. To spend time and trouble to complete a well-balance stowage and lashing arrangement,and then to lose the cargo becausedeck terminal lashing points failed would be unfortunate in the extreme. The most unfortunate combination of events occurs where the lashing lug itself and its attaching welding are of ample strength, but the substructure to which the lug is welded is of much reduced strength.This situation arises where heavy lugs are attachedto lightweight deck plating or bulwark plating on a ship, or to relatively thin plating forming the casingof a high-valuepiece of machinery. One of the most useful deck lashing terminal points is the D-ring made of drop-forged steel, in either single or double construction.The dimensionsof such rings govern their intrinsic strength together with the length, type and depth of weld attachment.The constructions shown in the following figure for instance,illustrate that.

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A single D-ring with a l5-tonne break-loadwill haveweld-runsof 100mmldngthon eachsideof the connecting saddle.

@Marstal Navigationsskole September04

32 b.

A single D-ring with a 20-tonne break-load will have weld-runs of 130mm length on each side of the connecting saddle.

c.

A single and a double D-ring with a 36-tonne breakload will have weld-runs of 140mm leneth on each side of the connecting saddle.

noon Fig.3.55

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@Marstal Navisationsskole September 04

33 All drop forged material yield strengthwell in excessof ordinary mild steel. As mentioned above, it is not only deck terminal points that fail; the lugs on the cargo itself may fail from similar causes,so due considerationmust be given to their strength,also. The important thing to rememberwhen assessingthe weld connections for D-rings, or any other form of welded terminal, is that constructional and classification considerations require that the yield strength of the weld connectionsshall be at least equal to the intrinsic yields strength of the material welded. Ordinary shipbuilding mild steel, for instancehas a yield strengthof about 235 Nl mmz; so it follows that an ordinary mild steel lashing plate of, say, 20mm thickness should not be welded to ordinary mild steel plating of less thickness. ln other words, unless the yield strengthand thicknessof the substructure are known to be the same or better than the proposed lashing plate, play for safety. If necessary, decreasethe size and increasethe number of the lashing plates, and reinforce the sub-structure when terminal points are required to be welded to any part of a ship's structure. Lloyd's Register,for instance,recommendthat eye plates (lashing plates)used for lashing of deck cargoesare not to be welded to the upper side of the sheer strake nor, in general, are they to penetrate the strength deck plating. Deck, bulwark or other plating is to be of sufficient thickness to withstand any shear forces that may be incurred in way of eye plates (lashing plates) due to asymmetricalloading of the eye plate (lashing plate), and such plating is to be stiffened as necessary to prevent deformation under direct eye plate (lashing plate) loadings.

Fire and Explosion Hazards

The need for care, thought and planning before any welding of lashing terminals takes place cannot be too greatly emphasised,bearing in mind that the attachmentof such terminals may occur when stowage of below-deck cargo is well advanceor maybecompleted. Before any welding is effectedon board the vesselit is of "hot work permit" from the utmost importance to obtain a the port/harbour authority. Make sure that the port/harbour authorities are in possession of all relevant information relating to your ship and its cargo. Make sure the welding contractors and/or the ship's officers and crew are competent to carry out and/or adequatelysupervisethe welding work.

OMarstal Navigationsskole September04

34

f.," F * Cts{ F, - f '3i*d.

In the case of welding lashing plates to the weather-deck make sure that in the spacebelow the weatherdeck, place not less than two reliable men, each supplied with two suitable portable fire-extinguishers.ln the spacebelow the weather-deck, spread purpose-madethick suitable noncombustible sheeting immediately beneath each point where welding is being effected. Do not allow two areas of welding if only the non-combustiblesheet below can protect one area. Rig fire hoses on deck, with adjustable spray/jetnozzles,and with full water pressureon the deck "hot work", maintain a fire main. On completion of all watchman in the space below for a while. Some regulations state up to four hours as the necessaryfire watch period after welding. A ship's officer should be directed to effect a thorough examination in the spaces below before those spaces are closed and/or batteneddown. If in doubt - don't weld!

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