Lashing and securing deck cargoes
- 1. UK P&I CLUB Carefully to Carry SEPTEMBER 2006 Lashing and securing deck cargoes “The carrier shall properly and carefully For the purposes of this article, the reader’s attention is drawn to the load, handle, requirements of the IMO Cargo Securing Manual Regulations and the IMO stow, carry, Code of Safe Practice for Cargo Stowage and Securing. keep, care for and discharge the goods The IMO cargo securing manual carried.” Regulations VI/5 and VII/6 of the 1974 SOLAS Convention require cargo Hague Rules, units and cargo transport units to be loaded, stowed and secured Articles iii, Rule 2 throughout the voyage in accordance with the cargo securing manual (CSM) approved by the administration and drawn up to a standard at least equivalent to the guidelines developed by the International Maritime Carefully to Carry Organization (IMO). Advisory Committee This report was produced by the Carefully The guidelines have been expanded to take into account the provisions of to Carry Committee – the UK P&I Club’s advisory committee on cargo matters. the Code of Safe Practice for Cargo Stowage and Securing (the CSS The aim of the Carefully to Carry Code), the amendments to that Code, the Code of Safe Practice for Ships Committee is to reduce claims through Carrying Timber Deck Cargoes, and the codes and guidelines for ro-ro contemporaneous advice to the Club’s vessels, grain cargoes, containers and container vessels, and ships Members through the most efficient means available. carrying nuclear waste and similar radioactive products. Such individual publications are subject to amendments which need to be carried into the The committee was established in 1961 appropriate section of the cargo securing manual as they occur. and has produced many articles on cargoes that cause claims and other cargo related issues such as hold As from 1 January 1998, it is a mandatory regulation for all vessels, other washing, cargo securing, and ventilation. than exempted vessels such as dedicated bulk solid, bulk liquid, and gas- The quality of advice given has carrying vessels, to have onboard an approved and up-to-date cargo established Carefully to Carry as a key securing manual. Some administrations may exempt certain cargo-carrying source of guidance for shipowners and ships of less than 500 gross tons and certain very specialised ships, but ships’ officers. In addition, the articles such exemption should not be assumed in the absence of a formal have frequently been the source of expertise in negotiations over the exemption certificate. settlement of claims and have also been relied on in court hearings. It is a mandatory requirement for masters and ships’ officers to be In 2002 all articles were revised and conversant with the CSS Code and the CSM Regulations, to understand published in book form as well as on disk. their applications for the vessel in which they are serving, and to be capable All articles are also available to Members of deploying correctly the hardware which goes with it. All securing of on the Club website. Visit the Carefully to Carry section in the Loss Prevention area cargo units shall be completed before the ship leaves the berth. The CSM of the Club website www.ukpandi.com and its associated hardware are subject to port state control inspection. for more information, or contact the Loss Violation of the CSM requirements may give rise to vessel detention and/or Prevention Department. prosecution of the master and owners.
- 2. The CSS Code and CSM Regulations and their such losses fall into the following random categories amendments contain much sound and well-tried which are neither exhaustive as to number nor mutually advice, and should not be treated lightly. There are, exclusive in occurrence: however, a number of anomalies, and in some instances the applied text is difficult to reconcile with safe practice ● Severe adverse weather conditions. and sound seamanship. It is hoped that these ● Lack of appreciation of the various forces involved. shortcomings may be rectified by future amendments. In the meantime, the following suggestions may be ● Ignorance of the relevant rules and guiding found useful by ships’ officers, loading recommendations. superintendents, supercargoes, surveyors, and the ● Cost limitation pressures to the detriment of known like. safety requirements. What is a deck cargo ● Insufficient time and/or personnel to complete the The phrase ‘deck cargoes’ refers to items and/or necessary work before the vessel leaves port. commodities carried on the weather-deck and/or ● Dunnage not utilised in an effective manner. hatchcovers of a ship and thereon exposed to sun, wind, rain, snow, ice and sea, so that the packaging ● Inadequate strength, balance and/or number of must be fully resistant to, or the commodities lashings. themselves not be denatured by such exposure. Even in ro-ro vessels, many areas above the actual ‘hold’ space ● Wire attachment eyes and loops made up wrongly, can reasonably be considered as ‘on deck’ even including incorrect methods of using bulldog grips. though not fully exposed to the onslaught of wind and ● Lack of strength continuity between the various sea. The combined effects of wind, sea and swell can securing components. be disastrous. Where damage and loss occur to cargo shipped on deck at anyone’s risk and expense, the ● Taking lashing materials around unprotected sharp shipowners, the master and his officers, and the edges. charterers, must be in a position to demonstrate there ● Incorrect/unbalanced stowage and inadequate was no negligence or lack of due diligence on their part. weight distribution. Deck cargoes, because of their very location and the ● The perversity of shore-based labour when required means by which they are secured, will be subjected to to do the job properly. velocity and acceleration stresses greater, in most instances, than cargo stowed below decks. When two ● Securing arrangements, both supplied and or more wave forms add up algebraically a high wave approved, not fully utilised on the voyage under preceded by a deep trough may occur; this may be consideration. referred to as an ‘episodic wave’: a random large wave – noticeably of greater height than its precursors or This last point is particularly true of ISO freight successors – which occurs when one or more wave containers and timber cargoes carried on the weather- trains fall into phase with another so that a wave, or deck, and of large commercial vehicles carried in ro-ro waves, of large amplitude is are produced giving rise to vessels. sudden steep and violent rolling and/or pitching of the ship. These are popularly – and incorrectly – referred to All interests involved in the lashing and securing of deck as ‘freak’ waves; they are not ‘freak’, however, because cargoes should bear in mind that high expense in the they can, and do, occur anywhere at any time in the purchase of lashing materials is no substitute for a open sea. The risk is widespread and prevalent. The simple design and a few basic calculations before stowage, lashing, and securing of cargoes therefore lashing operations commence. Other than in ro-ro and require special attention as to method and to detail if purpose-built container operations where unnecessary risks are to be avoided. standardisation of gear and rapid loading and turnround times pose different problems, ship masters Causes of losses should be encouraged – on completion of lashing operations – to make notes of the materials used, to Unfortunately, despite all the loss-prevention literature produce a representative sketch of the lashing system, available, there is a continuing incidence of the collapse to insist upon being provided with the test/proof and/or loss overboard of deck cargo items. Losses certificates of all lashing components involved, and to continue of large vehicles, rail cars, cased machinery, take illustrative photographs of the entire operation. steel pipes, structural steelwork, packaged timber, These, at least, will be of great assistance to the freight containers, hazardous chemicals, boats, vessel’s interest in the event of related future litigation. launches, etc. When investigated fully, the causes of
- 3. General guidelines The values given for the coefficient of friction between dry timber and dry steel vary from 0.3 (17o) to 0.7 The Merchant Shipping (Load Lines) (Deck Cargo) (35o), and between steel and steel sliding can occur at Regulations 1968 (United Kingdom Statutory angles of inclination as small as 6°; but until some years Instrument No.1089 of 1968) set out some of the ago there appeared to be no published data relating to general ideas to be followed when securing deck the coefficient of friction between timber dunnage and cargoes. The list of requirements is not exhaustive but the painted surface of steel decks or steel hatchcovers. provides a realistic base from which to work, and reads, Carefully controlled experiments were carried out in inter alia: Liverpool under the author’s supervision, using 9in x 3in “2. Deck cargo shall be so distributed and stowed: x 8ft sawn pine deals, some of which had earlier been allowed to float in water; others had been stored in 1) as to avoid excessive loading having regard to covered conditions so as to conform to normal the strength of the deck and integral supporting atmospheric moisture content. The experiments were structure of the ship; carried out on hinge-opening hydraulic-powered steel MacGregor hatchcovers in clean painted condition free 2) as to ensure that the ship will retain adequate of any unusual roughness and/or obstruction. stability at all stages of the voyage having regard in particular to: The tests used dry timber on dry covers; wet timber on a) the vertical distribution of the deck cargo; dry covers; dry timber on wet covers; and, lastly, b) wind moments which may normally be wet timber on wet covers. The lowest value – 0.51 (27o) expected on the voyage; – occurred with wet timbers on wet covers; the c) losses of weight in the ship, including in highest value occurred with wet timber on dry covers – particular those due to the consumption of 0.645 (33o). fuel and stores; and On the basis of such results the lowest value of 0.51 d) possible increases of weight of the ship or (27o) should be accepted as relating to the most deck cargo, including in particular those due common condition likely to be found on the weather- to the absorption of water and to icing; deck of a sea-going ship, i.e., wet timber on wet decks. 3) as not to impair the weathertight or watertight Hence, with inclination, only, and without any effects integrity of any part of the ship or its fittings or likely to be introduced by velocity and/or acceleration appliances, and as to ensure the proper stresses due to rolling and pitching, timber dunnage protection of ventilators and air pipes; alone will start to slide of its own accord at angles of inclination of 27o. Thereafter, sliding will continue at 4) that its height above the deck or any other part of progressively smaller angles. It follows that, when the the ship on which it stands will not interfere with vessel is rolling and pitching and timber dunnage is the navigation or working of the ship; unsecured, it will begin to slide at angles of inclination considerably less than 27o. 5) that it will not interfere with or obstruct access to the ship’s steering arrangements, including From such results it follows that the normal practice of emergency steering arrangements; utilising timber dunnage and of keeping downward- 6) that it will not interfere with or obstruct safe and leading lashings as short and as tight as possible efficient access by the crew to or between their should be continued and encouraged. A near vertical quarters and any machinery space or other part lashing is of great benefit in resisting the cargo item’s of the ship used in the working of the ship, and tendency to tip; a near horizontal lashing will greatly will not in particular obstruct any opening giving resist sliding forces. Do not overload lashing terminals access to those positions or impede its being and/or shackles. Think in terms of the ‘effective readily secured weathertight.” strength’ of a lashing – its ‘holding power’. Balance the ‘slip-load’ of an eye in a wire with the strengths of a Dunnage shackle, a bottle-screw and a chain. A lashing is no stronger than its weakest part. If all deck cargo items could be structurally welded to the weather-deck using components of acceptable strength this would remove the necessity to consider Spread the load coefficients of friction between the base of the cargo Point-loading and uneven distribution of cargo weight and the deck or dunnage on which it rests. Such is the can, and frequently does, cause unnecessary damage large range of deck cargoes which do not lend to decks and hatchcovers. Unless the weather-deck themselves to such securing, however, that an has been specially strengthened, it is unlikely to have a appreciation of the sliding effect naturally raises the maximum permissible weight-loading of more than 3 subject of coefficients of friction. tonnes/m2. Similarly, unless hatchcovers have been
- 4. specially strengthened, it is unlikely they will have a Good dunnage must be used to spread the load, and it maximum permissible weight-loading of more than 1.8 is always good practice to add 5% to the weight to be tonnes/m2. The ship’s capacity plan and/or general loaded before working out the dunnage area. For the arrangement plan should always be consulted. If the 30 tonne weight, for instance, 31.5 tonnes would be information is not there, try the ship’s stability booklet. used and the dunnage area would go from 12m2 to In the event that specific values are not available 12.6m2. onboard the ship, allow no more than 2.5 tonnes/m2 for weather-deck areas; and no more than 0.75 tonnes/m2 Dunnage timber is often no more than 6"x1" (150 x for hatchcovers in small vessels; 1.30 tonnes/m2 in 25mm) rough planking; but where weighty cargo items vessels over 100m in length. (The word tonnef used are involved dunnage should not be less than 50mm later in this article means tonnes force.) (2") thickness x 150mm (6") width, and preferably 75mm (3") x 225mm (9"). It is acceptable, however, to The adverse effects of point-loading are not always fully use two dunnage planks nailed together securely to appreciated. On the one hand, a 6 tonne machine with make up the thickness. A dunnage width greater than a flat-bed area of 3m2 will exert a down-load of 2 150mm is always acceptable – 225mm (9") to 305mm tonnes/m2 (Fig 1a). (12"), for instance; but where the thickness goes to 75mm (3") care must be taken to choose straight- grained timbers of as great a width as possible, and to ensure that they are laid with the grain horizontal and parallel with the deck. There have been incidents in the past where what appeared to have been a soundly dunnaged and well-secured item of deck cargo broke adrift and was lost overboard due to a sequence of events commencing with the collapse of 3"x 3" dunnage timbers along the curved grain used on its edge, followed by consequential slackness in otherwise adequate lashing arrangements, followed by Fig 1a. The 6 tonne weight is exerting a down- loading of 2 tonnes/m2 increasingly accelerated cargo movement and finally breakage of the lashings. On the other hand, a lady of 60kg weight in evening- shoes with heel areas 50mm2 (0.00005m2) will exert a Because of the random nature of grain configurations in point-loading of 1200 tonnes/m2 if, when dancing, she the thicker dunnage timbers it is acceptable to achieve stands on your toe with all her weight on one heel (Fig thicknesses by nailing planks together. A 2" thick 1b). Which is why our ladies are often more dangerous dunnage timber can be made up using 1" thick planks, than machines! and a 3" thick dunnage timber can be made up using 2" and 1" thick timber planks, all securely nailed together. To a large degree, this will correct the tendency for separation in timber with a badly-aligned grain. And remember, it will be as important to install good lower-level foot lashings as it will be to install downward-leading lashings if load-spreading dunnage is to remain fully effective. Fig 1b. The heel of the lady’s shoe is exerting a point-loading of 1200 tonnes/m2. Fig 2. The use of foot lashings with a twin-tier stack When exceptionally heavy weights are to be carried, it may be necessary to shore-up the weather-deck from below; but, again, care must be taken to spread the load on the tween deck so as not to overload that plating. In the not so dense range of cargoes, units of 20 to 40 tonnes weight are common today, and stacking of unit weights is widespread. If a piece of machinery weighing, say, 30 tonnes with a base area of Good dunnage boards nailed together to 6m2 is placed direct on the weather-deck the point- support corner castings loading will be 30/6 = 5 tonnes/m2. If, however, the deck plating has a maximum permissible loading of 2.5 Foot lashings well-secured to, and tonnes/m2 then the minimum area over which that 30 tautened at, each corner casting in equal balanced manner tonne load must be spread is 30/2.5 = 12m2.
- 5. Rolling periods Rule-of-thumb for lashing strength It is not the purpose of this article to deal with ship The seaman’s basic rule-of-thumb for securing cargoes stability aspects, so far as those aspects may be with a tendency to move during a moderate weather avoided. voyage is simply that the sum of the minimum breaking- loads of all the lashings should be not less than However, it is worth repeating a few established and twice the static weight of the item of cargo to be relevant stability facts. For instance, the roll period of a secured. That is, a single item of 10 tonnes weight ship is the time taken to make one complete transverse requires the lashings used to have a total breaking-load oscillation; that is, from the upright position to starboard of not less than 20 tonnes – on the positive assumption inclination, from starboard inclination back to upright that the lashings are all positioned in a balanced, and through to port inclination, thence back to upright. efficient, and non-abrasive manner. This rule may be Hence, if the roll period is 15 seconds and if the roll to adequate, or even too much, below decks – though not starboard is 10o and the roll to port is 11o, the total necessarily so in all instances – but it will not be ‘sweep’ within the 15 second roll period will be 10o +10o adequate on the weather-deck in instances where calm +11o +11o = 42o . seas and a fair weather passage cannot be guaranteed. When a ship rolls the axis about which the rolling takes place cannot generally be accurately determined, but it In circumstances where, for any time during a voyage, is accepted as being near to the longitudinal axis winds of Force 6 and upwards together with associated passing through the ship’s centre of gravity. The time wave heights are more likely to be encountered, the period of the roll is generally independent of the roll increased stresses arising therefrom are those here angle, provided that the roll angle is not large. Thus, a considered, allowing for 30o roll angles with not less vessel with a 15 second roll period will take 15 seconds than 13 second roll periods. (And see Tables 3 and 4, to make one full transverse oscillation when the roll herein, taken from the CSS Code and the CSM angle (to port and to starboard) is anything from say 2o to Regulations.) 30o. The crux, from a cargo lashing viewpoint, lies in realising that a roll angle of 2o and a roll period of 15 In such cases, the sailor’s rule-of-thumb – the ‘3-times seconds involves a ‘sweep’ of no more than 8o, whereas rule’ – tends to be that the sum of the safe working load a roll angle of 20o and a roll period of 15 seconds of all the lashings shall equal the static weight of the involves a ‘sweep’ of 80o (ten times the arc) in the same cargo item to be secured; the safe working load being time. The first will be barely noticeable; the second will arrived at by dividing by 3 the minimum breaking-load/ be violent and will involve large transverse slip-load/holding power of the lashings. In other words, acceleration stresses particularly when returning to the if the breaking-load/slip-load/holding power of all the upright. lashings is 30 tonnes, then they can safely hold an item whose static weight is 10 tonnes – again on the Equally important is consideration of vertical assumption that all securing arrangements are acceleration as the ship pitches and scends. Calculation deployed in a balanced, efficient, and non-abrasive of this force is not so simple, but measured values give manner. The author is not aware of any failures of results varying from 0.5g amidships to 2g at the far lashings/securing arrangements or loss of deck cargo forward end of the ship. where this ‘3-times’ rule-of-thumb has been applied in a sensible manner. A ‘stiff’ ship is one with a large GM (metacentric height); difficult to incline and returns rapidly to the It is not arbitrary, however, because it is derived from upright and beyond, sometimes with whiplash effect. the International Load Line Rules within which This imposes excessive acceleration stresses on cargo framework the United Kingdom Department of lashings. A ‘tender’ ship is one with a small GM; easy to Transport, in earlier Instructions to surveyors, gave the incline and returns slowly to the upright, sometimes following guidance, inter alia: even sluggishly. Although acceleration stresses are small the inclined angles may attain 30o, and the simple “When severe weather conditions (i.e. sea state gravitational effects of such angles and slow returns may conditions equal to or worse than those associated impose equally excessive stresses on cargo with Beaufort Scale 6) are likely to be experienced in lashings. Try to avoid the extremes of either condition. service the following principles should be observed And it is worthwhile working on the assumption that, if in the design of the deck cargo securing deck cargo is to remain safely in place during severe arrangements: adverse weather conditions, the lashing arrangements (iv) Lashings used to secure cargo or vehicles should be sufficient to sustain 30o roll angles associated should have a breaking load of at least 3 times with 13 second roll periods, and 5° pitch angles the design load, the design load being the total associated with not less than 1g vertical acceleration.
- 6. weight of the cargo or cargo plus vehicle accelerations shall be considered to be 1.5g subjected to acceleration of: longitudinally, 1.5g transversely, 1.0g vertically up, and 2.0g vertically down. To date, the IMO have not offered 0.7 ‘g’ athwartships, an explanation as to why a tonne of radioactive waste 1.0 ‘g’ vertically and should be considered to ‘weigh’ twice as much as, say, 0.3 ‘g’ longitudinally, a tonne of tetraethyl lead or some other equally noxious substance. relative to the principal axis of the ship. The rule-of-thumb method given in Section 6 of the When sea state conditions worse than those current CSS Code amendments indicates that the MSL associated with Beaufort Scale 6 are unlikely to be values of the securing devices on each side of a cargo experienced in service, a lesser standard of unit (port as well as starboard) should equal the weight securing such items of cargo might be acceptable to of the unit, and a proposed amendment to Table 1 in approval by the Chief Ship Surveyor. Section 4 of the Code now provides MSLs as follows: The equipment and fittings used to secure the deck cargoes should be regularly maintained and Table 1. Determination of MSL from breaking strength inspected.” Material MSL To condense those recommendations into a form simple to apply, reference should be made to the Shackles, rings, deckeyes, turnbuckles paragraph enclosed within the horizontal lines above. of mild steel 50% of breaking strength Put into practical and approximate terms, and using the phrase ‘holding power’ to indicate ‘breaking-load/ Fibre rope 33% of breaking strength slip-load/holding power’, this means: Wire rope (single use) 80% of breaking strength ● The total holding power, in tonnes, of all lashings holding the cargo item vertically downward to the Web lashing 50% of breaking strength deck should be equivalent to three times the (was 70%) ordinary static weight of the cargo item in tonnes: i.e. a 10 tonne cargo item requires total lashings Wire rope (re-useable) 30% of breaking strength having a holding-down potential of 30 tonnes. ● The holding power, in tonnes, of all lashings Steel band (single use) 70% of breaking strength preventing the cargo item moving to port and to starboard should be equivalent to seven-tenths of Chains 50% of breaking strength the holding-down potential of item 1, above: i.e. a 10 tonne item requires lashings with holding power “For particular securing devices (e.g. fibre straps with tensioners preventing transverse movement of 21 tonnes. or special equipment for securing containers), a permissible working load may be prescribed and marked by authority. This ● The holding power, in tonnes, of all lashings should be taken as the MSL. When the components of a lashing preventing the cargo moving forward or aft should device are connected in series (for example, a wire to a shackle to a be equivalent to three-tenths of the holding-down deckeye), the minimum MSL in the series shall apply to that device.” potential of item 1, above: i.e. a 10 tonne item requires lashings with holding power preventing longitudinal movement of 9 tonnes. Say that a cargo unit of 18 tonnes mass is to be secured using only shackles, web lashings, chains and The IMO 1994/1995 amendments to the CSS Code turnbuckles – all MSLs of 50% breaking strength (BS). (now carried forward into the requirements for the The unit will require 18 tonnef MSL on each side, preparation of the CSM) changes the emphases of the namely, 36 tonnef total MSL (72 tonnef BS for these foregoing paragraphs as discussed hereunder: items), representing a total lashing breaking strength to cargo mass ratio of 72/18 =4. The CSM ‘rule-of-thumb’ varies as the MSL of the different lashing components, as listed in its (Table 1) Secure the same cargo unit with steel band, only. Total – shown on the next page – giving rise to five different MSL required will still be 36 tonnef (72 tonnef BS) but answers to the one problem. For the most part, vertical the MSL of steel band is nominated as 70% of its acceleration is replaced by a 1g transverse breaking strength – so this gives a total lashing acceleration, and vertical and longitudinal accelerations breaking strength of (36x100)/70 = 51.42 tonnef, are not quantified except, that is, in the instance of representing a a total lashing breaking strength to containers of radioactive wastes, and the like, when cargo mass ratio of 51.42/18 = 2.86.
- 7. Do the calculation using wire rope, re-useable, and the through all the calculations required by the Sections 4 answer is (36x100)/30 = 120 tonnef: ratio 120/18 and 6 route and, more importantly, you will be able to = 6.67. For wire rope, single use, the answer is see clearly the extent to which the MSL multipliers (36x100)/80 = 45 tonnef: ratio 45/18 = 2.5, and for degrade or upgrade the generally accepted three-times fibre rope the ratio is 6. And these ratios (or multipliers) rule. remain constant for equal cargo mass. (If you do the same calculations using, say, 27 tonnes and 264 In the instance of the 18 tonne cargo unit given above, tonnes cargo mass, you will finish up with the same the lashings total breaking strength would be 54 tonnef 4, 2.86, 6.67, 2.5 and 6 ratios (or multipliers). If a when the three-times rule is applied. Simply 18x3=54 component was assigned a 66.67% MSL the result tonnef total BS, that is: would be a ratio of 3 – the three-times rule multiplier. Cargo mass x Rule number = Lashings total breaking strength The CSS Code is here changing the seaman’s commonly-held understanding of the term ‘rule-of- Correction factors thumb’ – a single multiplier easy to use and general in While the three-times rule rule-of-thumb may be application – by inserting the MSL percentages to considered adequate for the general conditions produce a range of rule-of-thumb multipliers. considered above, Section 7 of the CSS Code Amendments provides Tables 3 and 4 where GMs are Just to labour the point. If the cargo mass to be secured large and rollperiods are less than 13 seconds, and was 18 tonnes, and we use the five results obtained by those Tables, reproduced below, provide a measured using Sections 4 and 6 of the Code, the total lashing way of applying that extra strength. breaking strength required in each instance would be: 72 tonnef, or 51.48 tonnef, or 120.06 tonnef or 45 Table 3. Correction factors for length and speed tonnef or 108 tonnef – and that seems to be an enigma at odds with commonsense! Length (m) 50 60 70 80 90 100 120 140 160 180 200 Speed (kn) One way of partly rationalising this ‘enigma’ is to create 9 1.20 1.09 1.00 0.92 0.85 0.79 0.70 0.63 0.57 0.53 0.49 12 1.34 1.22 1.12 1.03 0.96 0.90 0.79 0.72 0.65 0.60 0.56 an additional column on the right-hand side of the MSL 15 1.49 1.36 1.24 1.15 1.07 1.00 0.89 0.80 0.73 0.68 0.63 Table 1, as follows: 18 1.64 1.49 1.37 1.27 1.18 1.10 0.98 0.89 0.82 0.76 0.71 21 1.78 1.62 1.49 1.38 1.29 1.21 1.08 0.98 0.90 0.83 0.78 Table 2. Determination of MSL from breaking strength, including rule- 24 1.93 1.76 1.62 1.50 1.40 1.31 1.17 1.07 0.98 0.91 0.85 of-thumb multipliers Material MSL ROT Table 4. Correction factors for B/GM <13 multiplier B/GM 7 8 9 10 11 12 13 or above Shackles, rings, on deck, high 1.56 1.40 1.27 1.19 1.11 1.05 1.00 deckeyes, turnbuckles on deck, low 1.42 1.30 1.21 1.14 1.09 1.04 1.00 of mild steel 50% of breaking strength 4.00 ‘tween deck 1.26 1.19 1.14 1.09 1.06 1.03 1.00 lower hold 1.15 1.12 1.09 1.06 1.04 1.02 1.00 Fibre rope 33% of breaking strength 6.06 NOTE: The datum point in Table 3 is length of ship 100m, speed of ship 15 knots and, in Table 4, B/ GM = 13. Wire rope (single use) 80% of breaking strength 2.50 Web lashing 50% of breaking strength A word of caution. Ships’ officers may care to ignore in (was 70%) 4.00 Table 3 any correction factor less than 1, as shown in bold italic lettering. For all those values less than 1 let Wire rope (re-useable) 30% of breaking strength 6.67 the rule-of-thumb calculation stand on its own and only apply the Table 3 factors when the values are greater Steel band (single use) 70% of breaking strength 2.86 than 1. This way the safety of the three-times rule or any other rule-of-thumb you may care to use will not be Chains 50% of breaking strength 4.00 compromised. (Compare with overall (60.67% of breaking Section 5 of the current CSS Code Amendments says: general component) strength) (3.00) “5 Safety Factor Within the assessment of a securing arrangement by By looking at Table 2 – and in respect of any cargo a calculated balance of forces and moments, the mass – you can use the multipliers without going calculated strength (CS) of securing devices should
- 8. be reduced against MSL, using a safety factor of such components inter alia to have ‘identification 1.5, as follows: marking’, ‘strength test result or ultimate tensile strength result’ and ‘maximum securing load* (MSL)’, CS = MSL all to be supplied by the manufacturer/supplier with 1.5 information as to individual uses, and/strengths/MSL The reasons for this reduction are the possibility of values to be given in kN – kiloNewtons. (To convert kN uneven distribution of forces among the devices, to tonnes force (tonnef) – multiply by 0.1019761, or for strength reduction due to poor assembly and others. a rough value, divide by 10). Notwithstanding the introduction of such safety factor, care should be taken to use securing * The CSS Code 1994/95 amendments say: elements of similar material and length in order to “Maximum securing load is to securing devices as safe working provide a uniform elastic behaviour within the load is to lifting tackle.” arrangement.” and Appendix 1 of the 1997 amendments to the CSM says: Many people were puzzled by that expression CS=MSL/1.5 appearing where it did in the text, “Maximum securing load (MSL) is a term used to define the because the phrase calculated strength appeared to allowable load capacity for a device used to secure cargo to a have no direct relationship to the Sections 1, 2, 3 and 4 ship. Safe working load (SWL) may be substituted for MSL for preceding it, nor did it sit easily with any attempt to securing purposes, provided this is equal to or exceeds the apply it to Section 6 which followed it. It can now be strength defined by MSL.” stated with some authority that Section 5 (other than the third paragraph thereof) and its CS=MSL/1.5 This latter definition is included in the proposed expression does not relate to, nor should any attempt amendment to Annex 13 of the CSS Code. ever be made to apply it to, Section 6 or any other rule- of-thumb, other than the admonition in the third There are difficulties likely to result from this mix of paragraph relating to securing elements of similar terms which raise questions about the validity of the material and length. cargo securing manuals issued and/or approved to date by the various national administrations, and the Section 5 and its CS=MSL/1.5 are wrongly placed in other approved certifying organisations. If the the text. They relate to the Advanced Calculation components are not identifiable by at least their MSLs, Method illustrated in Section 7. To make sense of they are not complying with the CSM Regulations. To Section 5 there is currently a proposed amendment to overcome this problem it has been suggested in the Annex 13 indicating that the expression should be re- relevant quarters that all aspects could be safely met by sited under paragraph 7.2.1. In Section 7 calculated attaching, with suitable wire, small coloured metal tags strength is used within a set calculation method, and it stamped with the MSL of the component, much as is is in that sense and in that context that calculated currently required for components approved for the strength (CS) should be applied. So, unless you are securing of timber deck cargoes. Responses received involved with a full advanced calculation method, just from the industry to date would give positive support to ignore CS=MSL/1.5; and note that the advanced this proposal. calculation method itself, is also under review. Readers should be alert to the likely soon promulgation of formal The Committee’s advice to ships’ officers and others amendments to these aspects; act accordingly and trying to apply the requirements of the CSM/CSS Code avoid using the advanced calculation method for the is this: if the chains, shackles, rings, and the like, time being. available to you are not clearly identified as to their MSLs (and remember, they should be so identified) use Breaking strengths the stamped SWL of a lifting shackle as required by the CSM/CSS Code, thereby using a component which Within the CSS Code and the CSM Regulations the may have a breaking strength two-times greater than is phrase breaking strength is not defined. Within the needed, but you will have complied with the letter of the context of those two documents, however, the phrase Regulations. Alternatively, it is suggested that the best breaking strength could reasonably be taken to mean method may be to multiply the stamped SWL value by 4 the point at which the component, material or element to obtain the breaking strength, and apply the can no longer support or sustain the load, pending percentages given in Table 1 to obtain the MSL – and some possible amendments by the IMO. then remove that component from any possibility of use for lifting purposes by tagging it. This should then have The CSS Code defines the values of maximum fulfilled the spirit of the Regulation without resorting to securing loads (MSL) of mild steel components for the use of massively oversized lashing components. securing purposes as 50% of breaking strength (see Table 1). The 1997 amendments to the CSM require
- 9. Wire rope Fig 4. Grips and clips It is recommended that for efficient lashing purposes wire ropes should be round-stranded, flexible and not so great in diameter as to make their use cumbersome. Full-formed tucked splice The most common of such general purpose wires is 16mm diameter (2" circumference) of 6x12 construction galvanised round strand with 7 fibre cores having a certificated minimum breaking load of 7.74 tonnef (tonnes force). This is the cheapest wire for its size, will turn easily around thimbles and lashing points, Bulldog grip Crosby clip can be spliced or bulldog gripped without difficulty and is easily handled. Other wires of different construction and of varying Bulldog grips applied correctly sizes or strength may be needed for particular lashing purposes and the certificated minimum breaking load should always be verified before taking such wires into use. The WRONG WAY to apply bulldog grips Fig 3. Wire rope The application of bulldog grips Experience continues to show that the most common cause of lashing failure is the incorrect application of bulldog grips. Tests indicate that where an eye is formed around a thimble in the correct manner the Correct method by by which to lashing arrangement will hold secure with loads up to or measure the diameter of wire rope even in excess of 90% of the nominal break-load (NBL) of the wire before slipping or fracturing, although it is usual and recommended to allow not more than 80%. Uncoiling. Correct method Without a thimble, the eye when made-up correctly, can be expected to slip at loads of about 70% of the NBL. Where the correct procedures are not followed slippage is likely to occur at much reduced loads. Under strictly controlled conditions, more than 100 tests were applied on a licensed test bed on 16mm and 18mm wire rope lashing configurations. The Unreeling. Incorrect method configurations tested were as illustrated in Fig 5 a, b and c. As a result of such tests the following recommendations are made: It should be stressed that these recommendations relate to cargo lashings only. Lifting gear and other In some instances wires intended for use as lashings statutory applications require a minimum of 4, 5 and 6 are supplied pre-cut to precise length and with eyes or grips for 16mm diameter wire and upwards, attachment devices already formed in one or both ends. respectively. It is also most important to ensure that the Such purpose-made items are usually sold with bulldog grips are of the correct size in order to certificates stating the test load and minimum break correspond with the diameter of the lashing wire. load applicable. If test certificates are not supplied then they should be requested. More commonly the wire is Recommended minimum number of bulldog grips for supplied in coils and must be cut to length onboard each eye – lashing purposes only: ship with eyes and attachment devices formed and Diameter of wire rope (mm) Wire rope grips fitted as required. Where this is the case, eyes formed Up to and including 19 3 by bulldog grips must be made up in accordance with Over 19, up to and including 32 4 the manufacturer’s instructions otherwise the eye Over 38, up to and including 44 6 terminations will tend to slip under loads very much smaller than the certificated breaking load of the wire. Over 44, up to and including 56 7
- 10. An allowance of 150mm should be made between the Fig 6. Correct application of Bulldog grips last bulldog grip and the end of the ‘dead’ wire. It is important to ensure that the lashing wires are not cut short immediately next to the bulldog grips. The end of the ‘dead’ wire should be tightly taped. Slip load = NBL x 0.70 Fig 5. Configurations tested 6a. 6b. SOFT HALF-DOUBLE EYES GROMMETS Slip load = Slip load = NBL x 0.70 NBL x 1.50 Galvanised marine wire rope 16mm – 6x12 construction and 16mm – 6x24 construction 6c. SINGLE LOOPS Slip load = NBL x 1.40 accordance with the manufacturers’ instructions. In practice it may be sufficient to use a ring spanner although thereafter all the nuts should be checked periodically and adjusted as necessary. 5a. 5b. 5c. Single eye at Single loop ½ double each end grommet Fig 7. Soft eyes – some other representative slip loads ● Bulldog grips have a grooved surface in the bridge 7a. piece which is suitable for a standard wire of Slip load = righthand lay having six strands. The grips should NBL x 0.50 not be used with ropes of left-hand lay or of different construction. Crosby grips have a smooth surface in the bridge piece. The first grip should be applied 7b. close to the thimble or at the neck of the eye if a Slip load = 7c. NBL x 0.60 thimble is not used. Other grips should be placed at Slip load = intervals of approximately six rope diameters apart NBL x 0.50 (i.e., 96mm with a 16mm diameter wire; 108mm with an 18mm diameter wire). ● The grips must all face in the same direction and must be fitted with the saddle or bridge applied to the working or hauling part of the rope. The U-bolt 7d. Slip load = must be applied to the tail or dead-end of the rope as NBL x 0.50 illustrated in Fig 6a. If the grips are not applied as indicated, the effectiveness of the eye can be seriously affected. Galvanised marine wire rope 16mm – 6x12 construction and 16mm – 6x24 construction ● Ideally, all the nuts on the grips should be tightened using a torque wrench so that they may be set in
- 11. ● Should a connection slip under load, it is likely that Fig 9. Half-double grommets – some other representative slip loads initially the rate of slip will be accelerated. The rate may then decrease, but until the load is removed the slip will not be completely arrested. ● As mentioned earlier, if three grips are applied in the 9a. Slip load = NBL x 1.00 correct manner and with an eye formed around a thimble (a hard eye) the eye will not fail or slip at loads of less than 80-90% of the NBL. Without a thimble the eye (a soft eye) made-up correctly can be expected to slip at loads in excess of about 70% 9b. Slip load = NBL x 1.00 of the NBL. See Fig 6a. This is referred to below as the ‘slip-load’ or ‘holding power’ of the eye. Fig 8. Soft eyes – UNSAFE application of Bulldog clips 9c. Slip load = NBL x 1.00 8a. Slip load = NBL x 0.25 9d. Slip load = NBL x 0.70 9e. Slip load = NBL x 0.70 Fig 10. Single loops – some other representative slip loads 8b. Slip load = NBL x 0.18 Galvanised marine wire rope 16mm – 6x12 construction and 16mm – 6x24 construction ● The use of half-double grommets is widespread and it is sometimes wrongly assumed that the holding power will be twice the NBL of the wire. In fact, tests show that the slip-load will be only 1.5 times the NBL. See Fig 6b. The holding power also decreases as the number of grips is reduced. See Fig 9 and Fig 11b. ● The use of bulldog grips to join two ends of wire 10a. 10b. Slip load = NBL x 1.40 Slip load = NBL x 0.80 rope is to be avoided: again, it is sometimes wrongly assumed that this will provide a holding power of twice the NBL. In a single loop with six grips being used, (see Fig 6c) the slip-load will be about 1.4 times the NBL. The holding power decreases as the number of grips is reduced. (See Figs 10 and 11). 10c. ● In a soft eye, with 2 grips, and with one or both used Slip load = NBL x 1.00 in the reverse manner (see Fig 7 a, b and c ) the eye
- 12. the eye can be expected to slip at loads of about double grommet breaks adrift, you have lost more than 50% NBL. These configurations are the least twice the holding power allowable for a soft eye; so it is efficient and, as indicated, the holding power is at most important to ensure that the terminal ends are most half the nominal break load of the wire. connected by shackles or some other form of smooth, non-sharp-edged, component. ● With a soft eye using only one grip the slip-load was found to be 0.25 NBL with the grip positioned For instance: Instead of 25 single eyes, for correctly (Fig 8a) and 0.18 NBL with grip reversed convenience and time saving, you use 12 half-double (Fig 8b). grommets of 16mm 6 x 12 wire to secure a 46-tonne item of deck cargo. If one of the half-double grommets Fig 11. NOT recommended fractures at a poor terminal connection you lose 8.3% of the total holding power; if a soft eye had failed you would have lost only 4% of the total holding power. As remarked earlier, lashing and securing of deck cargoes is not an exact science: it’s frequently a case of a balanced trade-off, but the trade-off should be based on information and a few quick calculations the basis for which this article hopefully provides. Eyes and similar terminal ends in wire lashings should never be formed by the use of round turns and half hitches. Experience shows that initial slackness is seldom taken up sufficiently and that, even when it is, the turns and hitches tend to slip and create sharp nips leading to failure of the wire at loads well below those to be expected for eyes properly formed by the use of bulldog grips. When attaching wires to lashing terminals on the ship’s structure or the cargo itself every means should be taken to avoid hard edges, rough chaffing points, and sharp nips at the eye. Even where thimbles are not used the attachment of the eyes of the wire to lashing terminals may best be accomplished by using shackles of the appropriate size and break load. 11a. 11b. Single loops Half-double grommets Slip load = NBL x 0.40 Plastic coated wires Plastic (PVC) coated galvanised standard marine wire of 18mm diameter and 6x24 construction is commonly ● A turnbuckle with a thread diameter of 24mm or used for various purposes where there is a need to more can be adjusted to set up a pre-tension of avoid the risk of cutting or chafing. Such wire should be about 2 tonnes. If such a turnbuckle were attached used with caution. Tests have revealed that if plastic to an eye made up in 16mm wire as shown in Fig 8 a covered wire is used in conjunction with grips, slippage and b, full tension in the wire would not be attained is likely to occur at much reduced loads than would be and the eye would slip at the grip under the pull of the case for unprotected wire of the same size and the turnbuckle, alone. characteristics. The plastic coating should be stripped from the wire where the bulldog grips are to be applied A word of caution before deciding to use half-double and from the surface of any wires coming into contact grommets (at NBL x 1.5) and single loops (at NBL x with each other. 1.4) as opposed to single eyes (at NBL x 0.7). At one terminal end in the instance of a half-double grommet, Fire and explosion hazards and at each terminal end in the instance of a single loop, there is no more material than at the terminal end of a If lashing terminals are to be welded while or after soft eye. loading cargo, great care should be exercised. Before undertaking any hot-work it is important to obtain a hot- If a properly made-up single loop breaks adrift, you work certificate from the local port authority. The have immediately lost twice the holding power authority should also be in possession of all relevant allowable for a soft eye; if a properly made-up half- information relating to ship and cargo. The welders
- 13. themselves should be properly qualified and competent Fig 12. Webbing and, if welding is taking place either on deck or under decks, a proper fire watch should be mounted both at and below the welding site. Adequate fireproof Webbing lashing with hand sheeting should be spread below welding points. On ratchet tensioner: chain deck, fire hoses should be rigged with full pressure on attachments each end the fire line. A watchman should be posted for at least four hours after the completion of welding and a ship’s officer should examine all spaces before they are finally One method of using webbing and battened down. Do not neglect these precautions. If in chain lashings doubt, do not weld. Positive action When you see something being done badly or wrongly, stop the work and have it re-done correctly. When rigging foremen, stevedore superintendents and charterers’ supercargoes insist on doing things wrongly and say they have always done it that way successfully, tell them they’ve just been lucky! Then webbing an ideal securing medium because its make them do it correctly relatively broad flat surfaces and reduced cutting nature allow it to be turned around and tightened against the One important aspect remains – ensure that the lashing pipes with short spans, producing a most acceptable points on the ship are sufficient in number and stowage. On the other hand large, heavy, crated items adequate in strength for the lashings they will hold. or high standing heavy machinery where relatively long spans may be involved require wire or chain lashings, Chain because sufficient unsupported tension is difficult to apply with webbing alone, although some of the The use of chain alone for the securing of general deck ‘superlash’ systems now available can overcome this cargoes is not widespread. Where chain lashings are problem effectively. used they tend to be supplied in precise lengths already fitted with terminal points and tightening devices. Webbing in general is manufactured from impregnated woven polyester fibre and therefore will stretch more The advantage of using chain resides in the fact that than wire rope. It is supplied in reels and may be easily under the normal load for which the chain is designed it cut and fashioned to any required length. will not stretch. Thus, if all chain lashings are set tight before the voyage and the cargo neither settles nor Webbing should not be used without clearly confirming moves, nothing should cause the chain to lose its from the manufacturer’s literature its nature, breaking tautness. Hence it is widely used in the securing of load and application. Recent independent tests confirm freight containers, timber cargoes and vehicle trailers. that good quality webbing will not fracture at loads less than those specified by the manufacturers. Tension on a In general chain for non-specific uses is awkward to hand ratchet can be obtained easily up to 0.54 tonnes handle, tiresome to rig, difficult to cut to length, and and then with increasing difficulty up to a maximum of does not render easily. For general purposes it is most 0.60 tonnes. A spanner or bar must never be used to effectively used in relatively short lengths in conjunction tighten a hand tension ratchet since recoil could with or as a part of lashings otherwise composed of seriously injure the user. wire or webbing. Webbing should be kept away from acid and alkalis and Webbing care taken to ensure that it is never used to secure The use of webbing slings and webbing lashings for drums or packages of corrosive materials or chemicals cargo securing purposes has steadily increased over which, if leaking, might affect it. All webbing should be the past years. Operational results differ widely. There inspected frequently and if re-used care taken to ensure are instances where webbing is ideal for securing deck that all lengths are free of defects. cargoes and there are other instances where it should be used with caution. Protective sleeves should be used between webbing and abrasion points or areas. For securing ISO freight Special large bore pipes made of reinforced plastic or containers use only those webbing systems designed provided with contact sensitive outer coatings make for such purpose.
- 14. Fibre rope used for general cargo lashing purposes are the D- shackle and the Bow-shackle each with an eyed screw- Ropes of up to 24mm in diameter are handy to use but pin. When using shackles it is correct to define their are more likely to be found on cargoes that are stowed strength in terms of the safe working load although, as below decks. The use of fibre ropes for weather-deck indicated earlier in this article at Table 1, et al, the CSS cargoes should be restricted to light loads of limited Code and the CSM Regulations define their volume in areas that are partly sheltered by the ship’s maximum securing load (MSL) as 50% of the breaking structure. The reason for this is that where such ropes strength; so when preparing combined cargo are used on deck difficulty is likely to be encountered in lashings always ensure that the MSL of the shackles maintaining the tautness of the lashings when they are selected is not less than the effective strength of the subjected to load stresses and the effects of wetting and eyes or other configurations formed in the wire rope drying out in exposed situations. The use of turnbuckles and similar materials. should be avoided: they may quite easily overload the rope lashing and create the very failure conditions, which Fig 14. Shackles and screws they are designed to avoid. The tautening of rope lashings is best achieved by the use of bowsing ropes and frappings. At 24mm diameter, a sisal rope has a breaking strain of 7.5 tonnes, and a polyester rope 9 tonnes. Composite rope, frequently referred to as ‘lashing rope’ is made up of wire fibres and sisal or polypropylene fibres which are interwoven thus adding to the flexibility D-shackle Bow shackle of sisal and polypropylene some of the strength of steel. It is most frequently supplied in coils of 10mm diameter. The breaking strain of composite ropes should be considered as about 0.8 tonnes for sisal based and 1.8 tonnes for polypropylene based ropes. Nylon fibre absorbs between 8% and 9% of water: the Bottle-screw (solid body) overall effect when under load is to reduce its effective strength by about 15%. Premature failure of nylon rope occurs under limited cyclic loading up to 70% of its effective strength. Therefore nylon rope is not recommended for deck cargo securing purposes. Stretching-screw (open body) The figures for breaking strain, which are quoted above, refer to new material and not to rope which has been in use for any length of time. Turnbuckles The same precautions apply to the use of turnbuckles. Shackles The word ‘turnbuckle’ is used collectively to include solid-cased bottle-screws and open-sided rigging Shackles are supplied in several shapes, sizes and screws or straining screws. These are most commonly strengths of material. The two shapes most commonly used for general cargo lashing and are supplied in a range of sizes and strengths with a closed eye at each Fig 13. Tightening rope lashings end. Open-sided rigging-screws and straining-screws tend to have noticeably lower strengths than solid Tightening rope lashings Tightening rope lashings by means of bottle-screws of the same size. The suppliers or by means of frapping bowsing manufacturers should be asked to provide the relevant test data before those responsible for lashing cargoes assume a MSL or SWL which may be erroneous. Solid bottle-screws are typically sold by size of screw- pin diameter. Those of 24mm diameter have a proof-load of 4 tonnes and those of 38mm have a proof- load of 10 tonnes. Special purpose turnbuckles are available with much greater strengths than those given above. These may have particular fittings and modifications such as those used in the container trade.
- 15. Again it is important that the manufacturers’ literature should be consulted before such equipment is brought into use. Turnbuckles should always be used with the pulling forces acting in one straight line. They should never be allowed to become the fulcrum of angled forces no matter how slight. Care should always be taken to see that the screws are at adequate extension when the cargo is finally secured. In this way scope is provided for further tightening if this should prove necessary during the voyage as the cargo and lashing arrangements settle. Where high torque upon a main lashing is involved the eyes of the turnbuckle should be seized or stopped against its own body in order to prevent the screws working back under load during the voyage. UK P&I CLUB For further information please contact: IS MANAGED Loss Prevention Department, Thomas Miller P&I Ltd BY THOMAS Tel: +44 20 7204 2307. Fax +44 20 7283 6517 MILLER Email: lossprevention.ukclub@thomasmiller.com