Lashing Cargo [PDF]

Zitiervorschau

1.

Securing

1.1

Securing principles

1.1.1

Definitions

The following terms and definitions are used in this chapter. They are mainly based on the IMO CSS-Code. Kilo Newton (kN)

suitable unit of force under the SI-System for securing considerations; it replaces the traditional tonne or kilogram, which should be used for the mass only; the force of 1 kN corresponds to about 0.1 tonne or 100 kg, taken as weight or force in the old fashion

securing element

single piece of securing equipment like a deck ring, shackle, turn buckle, chain, wire, wire clip or securing point on the cargo unit

securing device

suitable combination of securing elements forming a lashing, a shore or a welded stopper

homogeneous securing device

consists of elements having the same values of MSL

securing arrangement

a suitable composition of securing devices

homogeneous securing arrangement

consists of securing devices of suitably adapted strength and geometrical configuration to achieve, that in case of an extreme external load all the devices carry their share and are not loaded beyond their MSL

breaking load (BL) or breaking strength

nominal force at which a securing element will break; information to be supplied by manufacturer or chandler; for some securing materials BL is available by rules of thumb

Annex 13 method

calculation method for evaluating a securing arrangement supplied in the Annex 13 to the IMO CSS-Code; latest edition from 2003, MSC/Circ. 1026

maximum securing load (MSL)

maximum acceptable force in a securing element or securing device; the Annex 13 shows a table with MSL as percentage of BL for different materials

calculation strength (CS)

MSL reduced by a factor of safety; figures of CS for securing devices are only used in balance calculations according to the Annex 13 CS = MSL / 1.5 for the standard method CS = MSL / 1.35 for the alternative method

cross-stowage

stowage pattern where the cargo is tightly stuffed

side-stowage

single stowage 1.1.2

between and supported by the ship's sides or other fixed structures like longitudinal bulkheads; minimal securing effort necessary in general; securing against longitudinal forces required in fore or aft holds, because friction may be reduced due to temporary vertical forces; compacting of surface of cargo may be required if units may jump out support against transverse forces is given by fixed ship's structure from one side only; there is a need for transverse securing to the other side and also longitudinal securing stowage pattern applicable to single cargo units stowed on deck or in the hold; unit needs securing from all sides

Information from the shipper

For securing a heavy cargo unit on board against movement and breaking loose in heavy weather, the following information in addition to those listed under chapters 1.1.2 and 2.1.2 is required from shippers:    

The position and MSL of securing points on the unit. Limitations of the direction of forces to securing points on the unit. Alternatively, information on securing areas where loop lashings may be attached. Sensitivity of the unit against racking deformation.

1.1.3

Planning essentials and documentation

The securing of heavy cargo units in ships requires proper pre-planning for the prevention of sliding and tipping in transverse and longitudinal direction. With units of weak construction also racking should be prevented. A securing plan shall be prepared indicating the lashings, shores and welded stoppers as appropriate. The plan shall be supplemented by a list containing the MSL figures for each securing device, the lashing angles and additional information necessary in order to assess the securing arrangement by means of the Annex 13 method. An appropriate calculation shall be made using the Annex 13 method, either by manual calculation or using a recognised computer program1, in order to verify sufficient protection against  

transverse and longitudinal sliding, transverse tipping and also longitudinal tipping if applicable.

The securing plan and the calculation sheets shall be filed in the cargo operations log on board the ship. 1.1.4

External forces

Forces acting on cargo units on sea-going vessels are resulting from three main sources: 

1

Gravity forces with their components in the transverse and longitudinal direction of the ship's co-ordinate system due to rolling or pitching. e.g. LashCon by DNV

 

Inertia forces on cargo units due to accelerations of the ship, which is the physical reference system for the cargo. Impact forces resulting from the impact of wind or heavy water spray on cargo units stowed on deck.

Forces from the above sources act as a combined vector within a three dimensional coordinate system of the ship. This vector varies permanently. For ease of comprehension and valuation, the three components of this vector are considered separately. The three components are: Fx = longitudinal force, Fy = transverse force, Fz = vertical force. Although ships tend either to roll heavily or to pitch heavily, there may be simultaneous motions in both ways. Therefore, peak values of forces in the transverse direction may appear in combination with up to 60% of peak values in the longitudinal and the vertical direction and vice versa. However, peak values in the longitudinal direction and in the vertical direction may appear together with 100% each, because of their common sources from pitching and heaving motions of the ship.

Figure 3.1.1: Rolling and pitching motions of ships The magnitude of forces to be expected during a voyage depends on a number of circumstances and parameters. These are explained as follows: Weather, wind and sea conditions cannot easily be predicted over a period of more than a couple of days although some certainty may be given through the knowledge of typical conditions in distinguished areas and during certain seasons of the year. Duration of the voyage has a general influence on the probability of meeting unfavourable weather and sea conditions. In a short voyage this risk is smaller and can be better controlled by observing the weather forecast. Behaviour of the ship can be classified by size of the ship, her stability and her speed.  

Large ships do not find a sea condition producing violent motions as often as do small ships. In large ships there is a reduced risk of severe forces to the cargo. Ships with high initial stability and shorter periods of roll meet "resonant" wave encounters and large roll amplitudes with greater probability than do ships with a low initial stability. In addition, "stiff" vessels produce higher transverse forces through their shorter periods of roll and higher angular accelerations.



Ships running at high speed will more easily take heavy shocks from waves than will do slow ships. Thus, forces increase with speed in general.

Location of stowage of a particular cargo unit has a significant influence on the magnitude of forces expected during the voyage.    

Longitudinal forces increase from lower hold to stowage high on deck. Transverse forces increase from lower hold to stowage high on deck and from a position at about 45% of the length towards the forward and aft end of the ship. Vertical forces (in addition to the omnipresent gravity component) increase from a position at about 45% of the length towards the forward and aft end of the ship. Stowage positions on the weather deck or hatch top are subject to impact forces by wind and sea sloshing.

Mass of the cargo unit gives a proportional effect to gravity forces and to inertial forces, following Newton’s Law. Dimensions of the cargo unit have an influence to impact forces which are proportional to the affected area of the unit. This will of course only apply to deck cargo.

 0.8 g

 0.6 g  0.5 g

 0.8 g

 0.4 g

 0.6 g

 0.3 g

 0.1 g

Figure 3.1.2: Approximate accelerations to the ship 1.1.5

Basic securing principles

Practical securing of cargo may be categorised as follows: Direct securing means to apply lashings, shores or locks in order to transfer external forces directly from the cargo to the ship's structure. This is achieved most efficiently if the direction of the lashing, shore or lock is as close as possible to the direction of the force which is to be counter-acted. That means, a lashing intended to prevent transverse sliding should run in the transverse direction at a low angle or parallel to the deck. Friction securing means to apply and pre-tension lashings in a way to increase the vertical force to the stowage area. The appropriate lashing will therefore be set in a close to vertical direction. This principle is less effective than direct securing by two reasons. The first reason is that the helpful additional friction force is equal to the pre-tension in

the lashing multiplied by the friction coefficient of 0.3 with timber. Thus only 30% of the lashing force is used. The second reason is that the force in the lashing will only depend on its pre-tension effected by a tightening device. This pre-tension will not last very long due to settling effects. But there is also one advantage. Friction securing, if effective, acts into any direction, i.e. to fore and aft, to port and to starboard. The main reason for applying friction securing may be limited space on board or lack of suitable securing points. A typical example for nearly pure friction securing is found with timber deck cargo stowed from side to side. Also cargo on road vehicles and roll trailers is quite often secured in this way, but this is usually insufficient for sea-transport. Compacting means to apply securing material in order to compact a bulk of cargo units. There is no direct or indirect transfer of forces to the ship's structure. Thus compacting must necessarily always be combined with a reliable stowage pattern like cross-stowage. A typical example for compacting is the securing of steel coils in lower holds. Heavy project cargo units and similar sensitive cargo must be secured by direct securing only. If a direct securing arrangement also implies friction increasing and compacting, this is a welcome side effect. 1.2 1.2.1

Arrangements for direct securing Securing against sliding

Cargo units must be secured against transverse and longitudinal sliding in the first place. Good friction between the foot print of a cargo unit and the stowage area is the most economic way of providing a primary resistance against sliding in all directions. Friction must be improved by placing timber or rubber mats under the cargo unit. If steel beams are used for bedding, timber boards or rubber mats must be placed both between cargo unit and steel beams as well as between steel beams and the stowage area, unless the beams are effectively secured to the stowage area by welding or shoring. As a general first estimation, the overall securing effort for a particular cargo unit should be distributed into 40% both to port and to starboard, and 10% both to fore and aft. Taking the rule of thumb in the Annex 13 to the CSS-Code into account and the usual size of vessels operated by Beluga Shipping, the above estimation may be expressed in terms of MSL as follows:  MSL to starboard  MSL to port side  MSL to forward  MSL to aft

= 70% of the weight of the unit, = 70% of the weight of the unit, = 18% of the weight of the unit, = 18% of the weight of the unit.

 MSL = 18% W to fore

 MSL = 70% W to port

weight W

 MSL = 70% W to stbd

 MSL = 18% W to aft

Fig. 3.2.1: Distribution of lashing strength Transverse securing must be up-graded against the above estimation, if the ship is considered as "stiff" with a rolling period of less than 13 seconds. Longitudinal securing must be up-graded against the above estimation for stowage locations on deck forward of 0.7 Lpp. Longitudinal sliding in the lower hold and tween deck between 0.3 Lpp and 0.7 Lpp will generally be prevented by the friction of steel on timber alone. In any case of doubt, the securing arrangement must be assessed by the advanced calculation method and upgraded accordingly. 1.2.2

Securing against tipping

Securing against transverse tipping must be considered in general, if the height of the centre of gravity of a unit above the deck is greater than 60% of the width of the transverse base of the unit. port

stbd c.o.g. h w

Figure 3.2.2: Risk of transverse tipping with h > 0.6  w In the case of an asymmetrical arrangements of the centre of gravity and/or the tipping axis a thorough analysis of the necessary tipping resistance of the securing arrangement must be carried out in accordance with the advanced calculation method.

port

c.o.g.

stbd a b

tipping axis

Figure 3.2.3: Analysis of tipping with asymmetrical conditions Securing against longitudinal tipping will be limited to rare situations where the height of the centre of gravity of a unit above the deck is greater than 120% of the length of the longitudinal base of the unit.

aft

c.o.g.

fwd

h l

Figure 3.2.4: Risk of longitudinal tipping with h > 1.2  l Securing against tipping may be effected by the same lashings intended for the prevention of sliding, provided the lashings act with a suitable lever with regard to the relevant tipping axis. 1.2.3

Direct securing by lashings only

Vertical lashing angles  should not exceed 60° for the prevention of sliding. Horizontal lashing angles , i.e. deviation of transverse lashings from the transverse direction or the deviation of longitudinal lashings from the longitudinal direction, should not exceed 30°. In an ideal case the cargo unit is equipped with a sufficient number of securing points at about half the height of the unit and of sufficient strength. If all lashings have permissible deviations from the transverse direction, equally to fore and aft, no extra lashings against longitudinal securing are required. If all lashings have sufficient levers c to the appropriate tipping axis, no extra lashings are required against transverse tipping.

fwd

levers c

 aft







tipping axis

Figure 3.2.5: Ideal securing arrangement against transverse and longitudinal sliding and transverse tipping 1.2.4

Direct securing without securing points on the cargo

Quite often heavy cargo units are delivered for shipment without having dedicated securing points. In those cases loops of lashings have to be put around the whole body of the unit in a suitable way on order to prevent sliding and tipping. Pure vertical loops, although preferably used in road transport, are insufficient for sliding prevention of heavy units on ships.

f r i c t i o n l o o p s

Figure 3.2.6: Heavy unit secured to a flatrack by friction loops Additional lashings must be applied in the form of half loops for the prevention of sliding.

friction loops

horizontal half loops

Figure 3.2.7: Transverse sliding prevention by additional half loops Cylindrically shaped units without securing points tempt the lasher to place lashings around the body of the unit and fasten the ends to both sides. These so-called "silly loops" are not able to secure a cargo unit against sliding, because the turn around the body does not provide sufficient friction to counteract a load of the magnitude of MSL of the lashing.

s i l l y l o o p s

Figure 3.2.8: Inadequate transverse securing by silly loops The adequate solution of securing such a unit is to use vertical half loops from both sides. Each half loop is counted as two lashings.

vertical half loops

Figure 3.2.9: Proper transverse securing by vertical half loops

Another option for fastening direct lashings to a cargo unit without dedicated securing points is the fitting of head loops. This may be used for longitudinal securing of a cylindrical unit, where longitudinal half loops are not feasible. head loops

Figure 3.2.10: Longitudinal securing by direct lashings fastened to head loops For securing a heavy wooden box against sliding, horizontal half loops should be kept low to the rigid part of the box. If there is a risk of tipping, head loops should be used to fasten lashings to the top of the box. head loops

horizontal half loops

Figure 3.2.11: Securing a wooden box by half loops and head loops 1.2.5

Direct securing by lashings and stoppers

Occasionally, lifting fittings on heavy cargo units may also be used for securing. However, there are often restrictions with regard to the permissible securing direction or available space or amount of securing points on the ship, so that a combination of lashings and stoppers or lashings and timber shores must be used. Figure 3.2.12 shows a compact unit with lifting trunnions, bedded on double steel beams with rubber mats underneath. The shown longitudinal stowage does not allow securing to the trunnions against transverse sliding, which is prevented by robust timber shore constructions. The lashings attached to the trunnions prevent transverse tipping and longitudinal sliding.

Figure 3.2.13 shows the same unit in transverse stowage. The lashings attached to the trunnions prevent transverse sliding. Transverse tipping appears not to be critical at all. Longitudinal sliding is prevented by stoppers welded to the steel beams, which are placed on rubber mats.

port

stbd

Figure 3.2.12: Heavy unit secured against transverse tipping and longitudinal sliding by lashings and against transverse sliding by timber shore constructions

port

stbd

Figure 3.2.13: Heavy unit secured against transverse sliding and tipping by lashings and against longitudinal sliding by welded stoppers 1.2.6

Homogeneity of mixed securing arrangements

The elasticity of different securing devices plays an important role in the performance of a complex securing arrangement. The Annex 13 to the CSS-Code includes a safety factor of 1.5 as a divisor to the MSL for arriving at the smaller figure of CS. This safety factor is

mainly intended for compensating different elasticity's of the various securing devices. But it shall also cover small deviations from the ideal securing direction and other variations. This safety factor is certainly serving the purpose as long as no extreme differences of elasticity exist, but may be insufficient for situations where, e.g., a large unit or a huge pile of pipes is partly fixed by welded stoppers or stanchions and partly secured by long wire rope lashings. If the discrepancy of elasticity's is extreme, then the only reasonable solution is to dimension the stiff securing devices so that they can avoid sliding alone, while the more flexible securing devices may be left for the protection against tipping or for compacting purposes.

Figure 3.2.14: Unsuitable combination of different elasticity's In such a situation it is useless to try to solve the problem by a high pre-tension of the flexible securing device, e.g. wire rope lashings. As the high pre-tension must be applied to both sides, the pre-tension forces compensate each other. Any additional external force must be counteracted by the stiff devices, e.g. stoppers, alone, because they restrict the movement of the unit and prohibit any additional loading of the lashing. If the unit is liable to racking deformation, the lashing will certainly prevent undue racking. 1.2.7

Desirable pre-tension in lashings

The obtainable pre-tension in a lashing depends on the technical means and on the engagement and physical strength of the lashing workers. For usual turnbuckles in wire rope lashings a pre-tension of 30 kN (3 t in the old phrasing) is the reasonable maximum. For chains with lever tensioners plus extension the same figure may be obtained. The pre-tension shall be kept as high as possible but must never exceed 50% of the MSL. In practice, a pre-tension of 50% MSL is scarcely achievable. So there is hardly a risk to overdo with pre-tensioning. It is reasonable to apply pre-tensions in lashings of different elasticity's deliberately in a way so that devices with a high elasticity get a high pre-tension and vice-versa, in order to obtain a more homogeneous load distribution in an extreme load condition. There is always a slackening of lashings observed when the ship is at sea. After some hours at sea re-tightening is indispensable, with due re-tightening wire clips first.

1.3 1.3.1

Securing material Material approved by Beluga-Shipping

Beluga ships are generally equipped with a standard outfit of securing material, which is listed in the Lift/Lash Material Inventory. The MSL-figures declared by Beluga Shipping are partly smaller than those allowed by IMO in the CSS-Code, Annex 13 due to higher safety factors used by Beluga Shipping. Item Wire rope grommet Shackle green pin Shackle yellow pin Turnbuckle eye-eye Link chain Lashing plate

Standard lashing 10 ton MSL dimensions 22 mm , 1, 2.5, 5, 10, 15, 25 m 28 mm  28 mm  44 mm , 457 mm take up 20 mm , 1.5 m 200 x 110 x 20 mm, 35 mm 

BL MSLBeluga MSLIMO 263 kN 98 kN 118 kN 500 kN 125 kN 250 kN 500 kN 125 kN 250 kN 623 kN 156 kN 311 kN 488 kN 122 kN 244 kN -- kN 98 kN -- kN

The MSLIMO-figure for the wire rope grommet has been obtained as 30% of BL with factor 1.5 for narrow bend of the double wire. The MSL Beluga-figures are generally obtained by dividing the breaking strength by a safety factor of 4. Item Wire rope grommet Shackle green pin Shackle yellow pin Turnbuckle eye-eye Link chain Lashing plate

Standard lashing 8.5 ton MSL dimensions 22 mm , 1, 2.5, 5, 10, 15, 25 m 28 mm  28 mm  32 mm , 457 or 305 mm take up 20 mm , 1 - 1.5 m 200 x 110 x 20 mm, 35 mm 

BL MSLBeluga MSLIMO 263 kN 98 kN 118 kN 500 kN 125 kN 250 kN 500 kN 125 kN 250 kN 340 kN 85 kN 170 kN 488 kN -- kN

122 kN 98 kN

244 kN -- kN

Other equipment Item Lashing chain & lever Lashing belt & tensioner Turnfoot D-ring LE 3 Galvanised wire rope Wire rope clips

dimensions 13 mm , 6 m 50 mm width, 8 m

BL MSLBeluga MSLIMO 200 kN 100 kN 100 kN 50 kN 25 kN 25 kN

16 mm  (on coils of 220 m) for 16 mm wire rope

353 kN 141 kN ---

176 kN 80 kN ---

176 kN 99 kN ---

The MSLIMO of the galvanised wire rope is taken as one-way material with 70% BL. 1.3.2

Assessment of other material

If for any reasons additional securing material must be purchased abroad, it is important to obtain a document from the chandler or manufacturer stating the dimensions and the

nominal breaking load. It is, however, prudent to check the information given for plausibility. The overview below shows securing material that is commonly used for securing break bulk and project cargo, based on information supplied by the Annex 13 of the IMO CSSCode. It should be noted that these figures are not applicable for containers in standardised stowage, where classification societies may use other safety factors, adapted to their system. Material shackles, rings, deck eyes, turnbuckles of mild steel fibre ropes web lashings wire rope (single use) wire rope (re-useable) steel band (single use) chains of high tensile steel timber

MSL 50% of breaking strength 33% of breaking strength 50% of breaking strength 80% of breaking strength 30% of breaking strength 70% of breaking strength 50% of breaking strength 0.3 kN per cm2 normal to the grain

For checking the information of the breaking load, as supplied by the manufacturer or chandler, a set of rules of thumb are given in the following table, together with some supporting remarks. The rule of thumb figures should be used for securing calculations only in those cases where the supplied information appears uncertain or no information is available. For high tensile steel material and for synthetic fibre material rules of thumb are not available. Note: The diameter d in these rules of thumb must be entered in cm. Material / Elements Polypropylene rope Polyester rope Fibre belts Wire rope of 6 x 19 + 1 FC or 6 x 37 + 1 FC Wire rope of 6 x 12 + 7 FC or similar Shackles of mild steel Turnbuckles of mild steel Deck rings of mild steel Elements of high tensile steel Chains of high tensile steel Conifer timber shores Conifer timber shores Welded seams Welded seams Steel band

BL [kN] 12  d2 15  d2 document 50  d2

MSL [kN] 33% of BL 33% of BL 50% of BL 70% of BL 30% of BL 70% of BL 25  d2 30% of BL 2 50% of BL 20  d 2 50% of BL 20  d 2 50% of BL 20  d document 50% of BL document 50% of BL 1 kN/cm2 0.3 kN/cm2 8 kN/cm2 11 kN/cm2 document 70% of BL

Remarks turn sticks for tightening must be secured against re-winding knotting of belts is prohibited one-way use (IMO permits 80%) re-usable material one way use (IMO permits 80%) re-usable material measure bolt diameter measure thread diameter measure steel diameter of ring shackles, turnbuckles , D-rings long link & short link chains in line (parallel) to the grain normal (vertical) to the grain for shearing load for tension load not to be used for project cargo

A single weld leg should have a thickness a = 5 to 6 mm. Thus the MSL shear = 4 kN per cm welded seam and MSLtension = 6 kN per cm welded seam. 1.3.3

Inspection and maintenance

Inspection and maintenance of both fixed and portable securing gear should be carried out under the responsibility of the master. Reference is made to Chapter 2 of the approved Cargo Securing Manual. Visual inspection of all components being utilised should be completed at intervals not exceeding six months, aside from the usual inspection during loading/unloading. Defective components must be immediately and effectively taken out of service, i.e. placed into a scrap bin. Components not being used after completion of work must be collected into a dedicated storage place and protected from corrosion by salt water. Actions of inspection and maintenance of the ship's cargo securing equipment must be documented in the appropriate Annex to the Cargo Securing Manual. Threads of turnbuckles, shackle and bearings of twistlocks shall be regularly greased. Wire rope grommets of the re-usable type shall be given conservation with wire rope grease. Parts showing significant abrasion, corrosion or signs of cracks, or parts which are bent must be discarded. If repair appears feasible the parts should be transferred to an authorised workshop or otherwise put into the scrap bin. Discarded or missing parts must be replaced by equivalent parts. Appropriate manufacturer's declaration documents must be received from the chandler and kept with the Cargo Securing Manual. Great care has to be taken, that securing elements, which have bee taken ashore inadvertently during unloading, are returned immediately and be not replaced by other non-identical elements. Damage to fixed cargo securing elements must be repaired by an authorised workshop and reported to the next classification society survey. Discarded material as well as used one-way material must be disposed at a scrap yard. The receipt of such disposal must be kept on board. Disposal of such material over board at sea is not permitted on Beluga ships. 1.3.4

Welding standards

If deemed necessary for the safe securing of cargo, additional securing points or stoppers or buttresses may be welded in appropriate positions under the strict observation of hotwork procedures with the master's permission. Such welding shall be carried out by skilled persons only. Reference is made to Chapter 2 of the approved Cargo Securing Manual. Any welded attachments to the ship's deck, hatch cover, cargo hold plating, tank top or tween deck pontoons must be aligned to stiffeners below the welding surface using an appropriate weld area for absorbing the intended load.

Eye plates or lugs shall be aligned to the direction of the intended load. D-rings of high tensile steel shall be welded to the deck or vertical structures in the ship by a full penetration weld of several weld legs on both sides of the saddle in order to obtain the nominal securing capacity. Preferably low hydrogen electrodes (lime basic electrodes) should be used. Stoppers must be welded to the deck or hatch cover in a way that welded seams are not subjected to excessive torque. Welding at or in close vicinity of fuel tanks is prohibited. 1.4

Determination of MSL of securing devices

Any calculated assessment of a securing arrangement, either by a simple rule of thumb or by an advanced calculation method must be based on a sound input from the strength capacity of the securing devices. It is therefore indispensable to obtain a clear picture of the available MSL figures of the individual lashings, shores or stoppers. 1.4.1

Beluga standard lashings

The 10 ton standard lashing has an MSL = 98 kN, while the 8.5 ton version provides an MSL = 83 kN. However, it is important also to assess the securing points at the cargo unit in order obtain the final MSL of a particular Beluga standard lashing. 1.4.2

Securing points on cargo units

If the shipper has given the breaking strength BL of securing points on cargo units, the MSL may be taken as 50% of this BL. If the shipper has given strength information in figures of SWL for securing, then these should be directly taken as MSL-figures. If lifting fittings in form of trunnions, plates or rings shall be used for securing and their strength is supplied in figures of SWL for lifting, the MSL for securing may be taken as twice the lifting SWL. If no information is given, the rules of thumb under chapter 3.3.2 should be used. 1.4.3

Conventional wire rope lashings

Types of wire ropes for lashing purposes Mainly two types of wire rope should be used with regard to cost and ease of handling. These are the flexible constructions of six strands with one or seven fibre cores. If not otherwise specified by the manufacturer or chandler, the rules of thumb for the breaking load in chapter 3.3.2 above should be used. The left type in Figure 3.4.1 with seven fibre cores is quite flexible and easy to use, but has only about half the strength of the more common type with one fibre core.

d

d

6 x 12 + 7 FC 2 BL = 25 x d

6 x 19 + 1 FC 2 BL = 50 x d

Figure 3.4.1: Suitable wire ropes for lashing purposes Narrow bends and sharp corners If a wire rope is guided around narrow bends or, moreover, around sharp corners, its strength will be considerably reduced. The table below shows the residual strength as percentage of the strength of the straight rope. It is important to note, that the strength reduction is more severe if the rope is slipping in the bend. ratio b/d 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 rope steady in the bend 50% 65% 72% 77% 81% 85% 89% 93% 96% 99% rope slipping in the bend 25% 50% 60% 65% 70% 75% 79% 83% 87% 90% Example:

b/d = 2.0

Total MSL of the double wire is 2 x 0.77 = 1.54 x MSL of the single wire steady in the bend

b

d

Figure 3.4.2: Residual strength in a narrow bend Sharp corners are much more aggressive to a wire rope. As a rule of thumb, the residual strength after a 180° turn with sharp corners is 25% of the single straight wire rope, if steady in the turn. If slipping at sharp corners, the strength is nominally reduced to zero. In certain cases there is no other choice than using bolt holes or frame notches for fastening lashings to a cargo unit, with the permission of the shipper. The MSL should then be carefully established using the mentioned rule of thumb.

25% 25% MSL = 50% MSL of single wire

Figure 3.4.3: Residual strength in a bolt hole with sharp corners Doubling the wire rope at the sharp corners will be beneficial to the residual strength, as shown in the figures below.

2 x 25%

2 x 25%

2 x 25%

2 x 25%

MSL = MSL of single wire

MSL = MSL of single wire

Figure 3.4.4: Doubling the wire at the sharp corners of a notch

Figure 3.4.5: Spreading the load to two notches

Application of wire rope clips The reliable holding capacity of a wire rope clip depends on the tightness of the nuts. A well done clip must press a visible dent into the wire with its U-bolt. The U-bolts should, as far as possible, be placed on the dead end of the wire rope. In order to obtain the proper tightness of a clip, the nuts or threads must be greased before tightening. A clip attached in this manner may be attributed a holding capacity of about 10% of the breaking load of the wire rope. Figure 3.4.6 shows the load transfer from the loaded part to the dead end of the rope under the above assumption that the load in the bend is reduced by 40% of the force at the beginning of the bend. The situation is well balanced with a load transfer of 10% BL per clip. 0% BL

10% BL

20% BL

30% BL 20% BL friction

80% BL

70% BL

60% BL

50% BL

Figure 3.4.6: Transfer of loads with 10% BL per clip The correct assembly of a wire rope lashing must take into account:    

Wire rope clip size should fit to the rope diameter, U-bolt of clips should be attached to the dead end of the wire, Number of clips should be at least as shown in Figures 3.4.7 to 3.4.9, Nuts of clips must be greased before tightening,

 

Distance between clips should be at least 6-times wire diameter, Dead ends must be secured against tangling open.

There are many ways to assemble a wire rope lashing in terms of forming an eye or loop, include a turnbuckle and connect it to the ship and the cargo. In any case, the clipped connection should be placed at a bend. Therefore, the following three types of wire lashings have proved as reliable options.

double wire in bend

large bend diameter

Figure 3.4.7: Type A wire rope lashing Type A is the favourite lashing type. It can be assembled and tightened in a convenient working position. The strength of shackle and turnbuckle should be consistent with the strength of the double wire. If the upper bend has a diameter of less than 5  d, a reduction of strength of the double wire must be considered. This also applies for the Type B wire lashing.

double wire in bend large bend diameter

Figure 3.4.8: Type B wire rope lashing Type B wire lashing should be used, if only turnbuckles of less strength are available. A good pre-tightening before setting the wire clips is necessary because the turnbuckle has to pick up the slack of both parts of the wire. It should be noted that in this option no shackle is necessary and only 5 clips must be set in total.

double wire in bend

Figure 3.4.9: Type C wire lashing Type C wire lashing must be used with a stronger wire than in type A. It is the preferable type for long lashings and for half loop lashings, which run over a unit and come back to the same side. A widespread mistake is to attach the wire clips in the open length of the wire lashing without using a bend in between2.

" L a P a l o m a " l a s h i n g

Figure 3.4.10: Lashing with indeterminable MSL The overall MSL of a wire rope lashing is the least MSL of the elements: wire rope, shackle, turnbuckle, deck ring and the fitting on the cargo unit.

2

This lashing has been given the name "La-Paloma" lashing in memory of the lucky sailor presented by the performer and vocalist Hans Albers.

Figure 3.4.11: Correct assembly of Type A wire rope lashings

Figure 3.4.12: Wrong clips setting and MSL reduced due to single lay at sharp corners

Figure 3.4.13: "La Paloma"-lashing with indeterminable MSL

Figure 3.4.14: Too large angle of wires and "La Paloma"-connection 1.4.4

Chain-lashings and fibre belts

Chain-lashings with lever tensioners and fibre belts with ratchet tensioners are readymade lashings with an approved breaking strength and a documented MSL. But as with the Beluga standard lashing it is important also to assess the securing points at the cargo unit and also on the ship in order obtain the final MSL of the chain- or fibre lashing. While chains are pretty stiff and fibre belts are highly flexible, an in-series combination of both may be a suitable way to create a lashing with acceptable flexibility and persisting pre-tension.

Figure 3.4.15: Chain lashings

Figure 3.4.16: Web lashings 1.4.5

Welded stoppers

Beluga Shipping uses standardised stoppers, which are in majority simple stopper plates acting against sliding of a cargo unit. In certain cases such stopper plates are modified to also fulfil a clip function, i.e. secure the foot plate of a cargo unit against lifting and in this way to prevent tipping of the unit. When using stoppers a face plate shall be inserted between cargo and stopper. The face plate shall be tag welded to the stopper.

Figure 3.4.17: Stoppers with and without face plate

Figure 3.4.18: Stopper with clip function The applicable MSL-figures for Beluga standardised stoppers have been determined by means of advanced calculation programmes. The results are given in the tables below. Material used shall have a minimum strength according to S355 or GL 360, with minimum yield strength of 355 N/mm2 (equal to 35.5 kN/cm2 or about 35.5 kg/mm2). Thickness of welding seam is 8 mm. The MSL will be reduced if the thickness of welding seams is smaller. L

L

MSLtransvers

MSL

h

h

L1

h1

stopper plate with clip function

simple stopper plate

MSLvertical

Figure 3.4.19: Standardised stoppers in the Beluga fleet Ordinary stopper plate L 20 cm 30 cm

h 15 cm 15 cm

t 2 cm 2 cm

MSL 150 kN 200 kN

Stopper plate with clip function L 20 cm 30 cm

L1 15 cm 20 cm

h 15 cm 15 cm

h1 5 cm 5 cm

t 2 cm 2 cm

MSLtransvers 100 kN 150 kN

MSLvertical 50 kN 80 kN

The MSLs of stoppers of different design or clips with other dimensions of the clips shall be determined with approval from the Engineering Department of Beluga Shipping.

Figure 3.4.20: Corner stoppers made of angle profile sections

Figure 3.4.21: Beam stopper vertically mounted

Figure 3.4.22: Beam stoppers strengthened by stiffeners 1.4.6

Timber shoring arrangements

Timber shoring arrangements for securing heavy cargo units must be solid constructions, which do not disassemble in a slack condition. All elements must be well connected to each other by strong nails or cramps. Additionally, timber shores must be stabilised by nailing dunnage planks cross-wise onto the shores.

overlap of crossbeams

shore

crossbeam

steel cramps in place

crossbeam

shore

view from the top

shore shore overlap of crossbeams

Figure 3.4.23: Principle of timber shore construction The pressure transferred from the cargo unit to the ship's structure must be distributed to structural girders by means of crossbeams. Shores must be tightly fitted in and positioned on benches. Crossbeams must overlap the shores on each end. Timber shores that are intended to transfer securing forces from cargo units to rigid structures of a vessel are given a nominal MSL of 0.3 kN per cm 2. This figure applies to the crossbeams, where the force acts "normal" or vertical to the timber grain. The shores actually transfer the force along the grain with a permissible load of about 1 kN per cm 2, but the MSL must reflect the weakest part of the construction, which moreover may also be the cargo unit itself. Since timber shores are subject to pressure, the risk of buckling behaviour restricts the free length of a timber. If the external force shall be restricted to the permissible MSL = 0.3  cross-section a2 in cm2, then the free length of a shore must be limited to: lperm = 25  a

[cm]

This formula is based on the assumption that the shore is not loaded higher than its MSL. If there is doubt about this limitation, the free length should be made shorter. diagonal braces shore shore benches horizontal crossbeams

uprights

Figure 3.4.24: Shoring arrangement with horizontal crossbeams

vertical crossbeams

shore diagonal braces

shore benches

Figure 3.4.25: Shoring arrangement with vertical crossbeams

Figure 3.4.26: Timber shoring construction with intermediate stabilising members

Figure 3.4.27: Transverse and longitudinal shoring of concrete pipes

Figure 3.4.28: Shores between bedding cradles

Figure 3.4.29: Shores on benches between cargo units 1.5

Securing calculation

The 1994 amendment of the IMO CSS-Code has presented a new Annex 13 with the title "Methods to assess the efficiency of securing arrangements for non-standardised cargo". This Annex 13 enables the maritime community to use an internationally agreed approach for non-standardised cargo securing calculations, which meanwhile has been accepted worldwide by ship operators as well as in legal disputes. 1.5.1

Annex 13 Rule-of-thumb

Rules-of-thumb, as given in chapter 3.2.1 of this document, may be used for a raw estimation of the lashing effort. Another rule-of-thumb is provided by the Annex 13 that reads: The total of the MSL values of the securing devices on each side of a unit of cargo (port as well as starboard) should equal the weight of the unit. It must be noted that this rule does not take the size or speed of the vessel into account, neither her stability nor the location of stowage in the ship. It further addresses only the weight of the unit, but not its dimensions, which may become important for forces by wind and sea-sloshing. The rule ignores the effect of lashing angles and friction at the stowage place, but an explanatory text in the IMO Code reminds that lashing angles to the deck should not be greater than 60° and care should be taken for adequate friction.

On ships of the Beluga fleet the above rule-of-thumb should not be used except for small items in under deck stowage. 1.5.2

Annex 13 Advanced Calculation Method

The advanced calculation method, presented in the Annex 13 to the CSS-Code, is still a simplified model of the reality, but it has certain advantages against the various even more simple rules-of-thumb. In order to obtain reliable results from the advanced calculation method certain typical misuse practices must be avoided: -

Use of invalid MSL-figures in the balances of forces and moments,

-

Ignorance of limiting conditions, as lined out in the Annex 13,

-

Mixing with elements of other calculation methods,

-

Converting the balance formulas into target oriented equations,

-

Non-observance of SI-units.

1.5.3

Annex 13 Alternative Calculation Method

The alternative calculation method has been developed in IMO, on the initiative of the late marine surveyor Capt. Edward Boyle, NCB New York, and adopted in 2002. It contains only minor changes to the basic advanced calculation method and does not replace the latter. The changes are: -

Horizontal lashing angles are taken into account.

This is the key issue of the improvement and solves the frequent question on how to treat a lashing at, e.g 45° to the transverse direction. However, the amount of entry data to the calculation is considerably increased and it is advisable to use an approved computer program for avoiding calculation errors within the processing of the lashing data. -

Calculation strength CS = MSL/1.35.

This is a consequence to the more precise consideration of horizontal lashing angles, which allows to reduce the safety factor. -

Small changes in the balance calculation.

The changes are insignificant, in particular if a computer program is used. The amended version of the Annex 13 contains a calculated example, which demonstrates that each lashing must be treated separately, duly distinguishing its direction of action (fore, aft, port, stbd). For each lashing two f-values must be taken from an appropriate table with the entries of the vertical and the horizontal lashing angle, and utilised within the applicable balance. 1.5.4

Computer based calculation

There are numerous versions of suitable computer programs for the application of the advanced and the alternative calculation method presented by the Annex 13. One of the most commonly used is the LashConTM by Olav Lyngstad, available from Det Norske Veritas. This program has been introduced in the Beluga fleet.

The program offers to chose between the basic advanced calculation method and the alternative method with recommendation of the latter. It provides a storage stack where a number of calculated cases can be stored. It also offers print-outs of each page. The calculated accelerations can be replaced by figures adapted to conditions in sheltered waters. However, there are several minor drawbacks, which must be known and overcome on occasion by manual calculation or by using LashCon in a dual approach. -

The program does not offer intermediate entries for the stowage levels. This may become particularly important for interpolation between the stowage levels "on deck low" and "on deck high".

-

The program does not allow to exclude steep transverse lashings from the transverse sliding balance while using the same lashings for the transverse tipping balance.

-

The program does not use tipping prevention levers "c", as proposed by the Annex 13. These levers are expressed by c = d  sin, where d is the horizontal distance from the tipping axis to the securing point on the deck. This approach appears easier to handle but fails if the securing point is not on deck but higher, e.g. on the ship's side in the tween deck or lower hold.

-

In the basic advanced method the program requires to enter a lashing a second time for checking the effect from it longitudinal component,

-

The number of securing devices is limited to 10. Grouping of devices is therefore indispensable in larger securing arrangements. This may become difficult with the alternative method.

1.5.5

Additional tipping moment for very large cargo units

The tipping moment acting on a cargo unit in heavy weather, as stipulated by the Annex 13 to the CSS-Code, is simply derived from the nominal transverse or longitudinal force Fy or Fx, multiplied with the vertical distance of the force vector from the tipping axis. However, there is an additional tipping moment resulting from rotational inertia of a cargo unit when subjected to the rotational acceleration of a rolling or pitching vessel. This moment is independent from the location of stowage in the ship. The Annex 13 to the CSS-Code does not take this additional moment into account, because it is of negligible magnitude for usual cargo units and also heavy lift units of moderate size. Only for very large units, like offshore modules, huge cranes, huge straddle carriers, this additional tipping moment should be accounted for, in particular, if tipping becomes a critical criterion. Transverse tipping The following formula determines this additional tipping moment in a rolling motion: Madd = ''max  m  ip2 [kNm] with

Madd = additional tipping moment [kNm] ''max = maximum angular acceleration of the vessel [s-2] m = mass of the cargo unit [t]

ip = polar radius of inertia of the cargo unit [m] additional tipping moment from inertia

ordinary tipping moment = Fya

transverse force Fy z tipping lever a tipping axis centre of rotation

ship acceleration

Figure 3.5.1: Additional tipping moment of large cargo units The additional tipping moment cannot be determined by means of data provided in the Annex 13 to the CSS-Code. The following tools for obtaining figures for ''max and ip are given: The angular acceleration ''max is calculated on the basis of a harmonic roll with the amplitude  and a rolling period T, which must be estimated from the metacentric height GMC by the well known formula: T 

0.78  B GM C

[s]

(B = breadth of ship [m])

The roll amplitude  should be taken as 30°. Then ''max is obtained by formula:   2      max  T    

2

[s-2]

For ease of reference the following table is offered for  = 30° roll amplitude: T [s] ''max [s-2]

8 9 10 11 12 13 14 15 16 17 128 19 20 0.32 0.26 0.21 0.17 0.14 0.12 0.11 0.09 0.08 0.07 0.06 0.06 0.05

The polar radius of inertia of the cargo unit ip depends on the cross-section of the cargo unit in the plane of tipping. There are several formulae available for estimating ip. If the mass of a square shaped unit is homogeneously distributed within the limits of length, width and height, then 1 w2  h2 ip   = 0.289  2 3

w 2  h 2 [m]

If the mass of a square shaped unit is concentrated in the shell of the unit, i.e. the unit is a hollow body, then ip 

wh = 0.289  (w + h) 12

[m]

If the mass of a cylindrical unit is homogeneously distributed within the limits of length and diameter d, then ip 

d = 0.354  d 8

[m]

If the mass of a cylindrical unit is concentrated in the shell of the unit, i.e. the unit is a hollow cylinder, then ip 

d = 0.5  d 2

[m]

h ip

ip

l

l

h w

w

Figure 3.5.2: Polar radius of inertia ip for a full square shaped body (left) and a hollow square shaped body (right) Longitudinal tipping A similar consideration for tipping in the longitudinal direction should consider a pitching period T = 0.5  Lpp seconds and a pitching amplitude  of 15°. This includes a moderate slamming shock. The additional tipping moment in longitudinal direction may become significant due to the generally short pitching periods of 5 to 6 seconds.

Figure: 3.5.3: Cargo units with large polar radius of inertia