RULES FOR PLANNING AND EXECUTION OF MARINE OPERATIONS PART 2 : OPERATION SPECIFIC REQUIREMENTS PART 2 CHAPTER 2 TOWING JANUARY 1996 SECTIONS 1. INTRODUCTION. «js sesssesse 2, PLANNING AND PREPARATI 3. TOWING EQUIPMENT... 4, TOWING OPERATIONS..... DeT NORSKE VERITAS Veritasveien 1, N-1322 Hovik, Norway Tel.: +47 67 57 99 00, Fax.: +47 675799 11bi DNV DNV - RULES FOR PLANNING AND EXECUTION OF MARINE OPERATIONS - 1996 REVISION CORRECTION SHEET NO, 2 JANUARY 2000 Please note the following corrections to the DNV Rules for Planning and Execution of Marine Operations: Pr.2 Cu.2 Towine - [rem 3.1.2 Replace old 3.1.2 with new: 3.1.2 Main Towing Line 3.1.2.1 For unrestricted towing, the minimum breaking load (MBL), in tonnes, of the main and spate towing lines shall be taken according to Eg. 3-1. - 30BP BP .<40 G.64- 0.8 BP/SO) BP 40< BP< 90 - 22BP BP290 eq. 3-4 where BP: continuous static bollard pull ofthe vessel in tonnes Guidance Note BP loss than the carted board pul of the vessel may be ‘accepted in £q, 3-1 for calulation of minimum towing Srongth, provided a corresponding resrtion on the board pull (.2. owine tension] to be exeresed by the tug is specified inthe marval forthe actual towing operation. Continuous monitoring of towne tension from the tug's wheetnouse as Spectieg n 2.3.42 should thon be possible. 3.1.2.2. The main towing line should for unrestricted. towing have a length not less than; Liowtue = 2000 BPIMBLooyie Eg. 3-2 where Leontne: tninimum tow line length (m) BP continuous static bollard pull of che vessel in tonnes MB Loonies: towline MBL in tonnes 3.1.2.3. Towline MBL and minimum length less than required by 3,1.2.1 and 3.1.2.2 may be accepted after evaluation of: + geographical area and tow route, = season and possible weather restrictions, = number of tugs and tow spread arrangement, = characteristics of the towed object, = winch design, and = available back-up/contingency. However, the towline MBL. shall nover be less than 2BP. Rev. OF ‘Sign. Ran Page 1 of 2Pr2 Cu.2 Towne - Irem 3. Replace old 3.3.2.6 with new: 33.2.6 Required tug bollard pul shall be estimated based on calculated required towing force and tug resistance, se0 3.3.2.3, 33.2.4 and 3.3.2.5, and tg efficiency in waves. Unless more accurate calculations or model tests of towing efficiency of the tug in waves are made, the continuous bollard pall stated in the bollard pall certificate shall be multiplied with an efficiency factor according to Eq. 3-4 ‘ye = 0.751 1) Eg. 3-4 where Ym: tugefficiency factor vu: tug length factor, 4, = (1 -L/45) L: tug length (m), not to be taken more than 45 m Guidance Note For tugs performing weather routed towing of towing in protected aroashharbours, a tug ofcioncy factor according to Eq, 3.5 below may be used instead of £9.34. ‘Yow = (0875 -Yo/8)(1 = 1) 4, 35 whore L lengta of tug (m), not tobe taken snore than 48 m. Yer tug length factor, 7. (1 - 45) yw: wave factor, Ywe= Hel Hs: limiting signicant wave height () for tho woathor ‘outed toning operation, othe probable sigicant ‘ave heigh! in the protected aroafharbour. Hs not tobe taken less than { meter and nat more than § ‘meter in this equation, Pr2 Cu.2 Towing - [rem 3.3.2. Eq. 3-4 to be renumbered Bq, 3-6. Rev. OF Sign. RHan Page 2 of 2Rules for Marine Operations. P.2Ch.2’ rt 12 Qt 22 23 EBT 32 ‘Towing L.1.1 Application DEFINITIONS... 1.2.1 Terminology. 1.2.2 Symbols. PLANNING AND PREPARATIONS «.....0005 PLANNING Datel General reserve 2.1.2 Weather routed towing. 2.1.3 Unrestricted towing 2.1.4 Documentation. DESIGN...... 2.2.1 Environmental conditions 2.2.2 Motions «.. 2.2.3 Simplified motion criteria. 2.2.4 Stability afloat... 2.2.5 Loads and lond effects. 2.2.6 Lond cases STRUCTURAL DESIGN CALCULATIONS 2.3.1 General 2.3.2 Grillage and seafwstening. 2.3.3 Barge global strength ... 3.4 Barge local strength 6 6 ners 7 7 ‘TOWING EQUIPMENT. ‘TOWING ARRANGEMENT. 3.1.1 General 0 3.1.2 Main towing line ..... 3.1.3 Towing bridle 3.1.4 Towline attachments . BARGES ... 3.2.1 Genera . 3.2.2 Bmergency towing arrangement... 3.2.3 Anchoring and mooring equipment... 3.2.4 Ballast and drainage systems. 3.2.5 Access 3.2.6 Inspection and testing . 4d 42 January 1996 Page 3 of 14 ‘TOWING VESSELS 10 3.3.1 General. 10 3.3.2 Criteria for selection of owing vessels .. 10 3.3.3 Towing lines n 3.3.4 Towing winches . etl 3.3.5 Equipment for personnel transfer wn. LL 3.3.6 Vessel documentation ...racaeeeeeeee Hd 3.3.7 Inspections and testing..rsesorveseese Hl ‘TOWING OPERATIONS TOW OUT..... 4.1.1 Tow out criteri 4.1.2 Weather forecast. 4.1.3 Internal seafastening,. 4.1.4 Towing manual TOWING .. 4.2.1 Routing.. 4.2.2 Towing clearances.. 4.2.3 Towing procedures Det NORSKE VERITASJanuary 1996 Page 4 of 14 Rules for Marine Operations Pt.2 Ch.2 Towing 1, INTRODUCTION 1.1 GENERAL 1.1.1 Application ALLL P12 Ch.2, Towing, give specific requirements ‘and recommendations for single vessel and barge towing, operations. Guidance Note Requirements and recommendations for transportation onbeard ship, towing of mul hull vessass, self eating and self prepeled ‘ater anspor are given in PL2 Ch.3. Requiterents and recommenations for transit and postioning of Mable Offshore Uns are given in PL2 Ch, 7. 1.1.1.2 General requirements and guidelines in Pr. of these Rules applies for towing operations. ‘This chapter is complementary to Pt. 1.1.1.3 Conditions for using these Rules are stafed in PLO Ch. I See.1.2, 1.2. DEFINITIONS 1.2.1 Terminology 1.2.1.1. Definitions of terms are included in P.O Ch. 1. ‘Terms considered to be of special importance for this, chapter are repeated below. Bollard pull - Continuous stato t tug, i.e. continuos tow Tine force foroe applied by Coastal towing : Towing in waters less than 12 nautical miles of the coust line. Object: The object handled during the marine operation, typically @ module, deck structure, jacket, sub-sca structure, pipes, other equipment Grillage : Structural load distributing elements installed to avoid excessive local loads. Seafastening : Structural elements providing horizontal and uplift support of object during towing operations Certified item : Ttem with a capacity or property certified by a recognised body. Inshore towing : Towing in sheltered waters. Internal seafastening : Securing of loose items within the handled object. Offshore towing : Towing in waters more then 12 nautical miles of the coastline. 1.2.2. Symbols ‘The list below define symbols used in this chapters ‘Aug: Exposed cross sectional area in mi. a: Accelerations in vessel longitudinal direction. 4: Accelerations in vessel transverse direction. a: Accelerations in vessel vertical direction, B Breadth. BP: Static tug bollard pull in tonnes, Raa: Wave drift forces, 8 ‘Acceleration of gravity. H,: Significant wave height. L Length. Leow + Length of towline, MBL: Certified minimum breaking load. MBLiuis : Towline MBL SWL? Certified safe working load. rat Current velocity. + Mean wind velocity, v Towing speed. Oe: ‘Interaction efficiency factor. 1 Shape factor. DET NoRske VERITASRules for Marine Operations January 1996 Pt.2 Ch.2 Towing Page 5 of 14 2. PLANNING AND PREPARATIONS 2.1 PLANNING 2.1.4 Documentation ALA General 2.1.4.1 The planned towing operation shall be 2.11.1 Towing operations shall be planned and prepared according to philosophies and requirements in Pu Ch2. 2.1.1.2 Towing operations may be categorised as; = weather routed, or = unrestricted. Guidance Note For transportation operation the termination point may be assumed, lnless otherwise agreed, when mearlng in recelving pot Is complete. 2.1.2 Weather routed towing 2.1.2.1 Weather routed towing operetions may be designed for specified environmental criteria, see Pe Ch.2 Sec.3.1 2.1.2.2 Weather routed tows shall seek shelter if weather situations exceeding the operation criteria are forecasted or experienced. 2.1.2.3. Ports and/or area of shelter shall be defined in towing procedures. Entrance, geography and size of shelter shall be considered, Guidance Note For weather resticted towing operations crossing open waters, wih anestinated operation reference period (Ta) exceeding 72 hous, and were a Marine Opataion Declaration Is requested, a ONY representative wil normally be requlec ondoard te tug during lowing, £08 aso PLT Ch2 So0.24.1 and See.3.12. 2.1.3 Unrestricted towing 2.1.31 Unrestricted towing operations are designed for unrestricted environmental conditions, see Pr. Ch.2 Sec, 3.1, Note also requirements for tow out given in 411. deseribed by procedures and drawings. Documentation ‘quality shall comply with requirements in Pt. Ch.2 Sec. ‘A manual covering the relevant aspects of the towing operation shall be prepared, see also 4.1.4 and Pt.1 Ch.2 Sec.3.5. 2.1.4.2 Costficates, test reports, and classification documents for equipment and vessels involved shall, xs applicable, be presented before start of towing, oporations. 2.2, DESIGN 2.2.1. Environmental conditions 2.2.1.1 Characteristic environmental conditions for towing operations shall comply with Pt. Ch.3 Sec.2. 2.2.2 Motions 2.2.2.1 Determination of motions shall comply with Pt.t Ch.3 Sec.3. 2.2.2.2 For single barge towing simplified criteria according to 2.2.2 may be used for preliminary design evaluations. 2.2.2.3. These criteria should be confirmed by more accurate methods. 2.2.3. Simplified motion criteria 2.2.3.1 ‘The simplified criteria given below may be used for preliminary design evaluations of objects, seafastening and grillage. The conditions for using the simplified erteria are; = towing in open sea on a flat top barge with length greater than 80m, = barge natural poriod in roll equal to oF less than 7 = object positioned close to midship and with no part overhanging tho barge sides, and = object weight less than 500 tonnes Der NORSKE VERITASJanuary 1996 Page 6 of 14 ‘The simplified criteria (including the component for self weight) may be taken as; + ay (transverse acceleration due to roll and sway): 0.65 g at waterline, increasing 0.015 g cach meter above the bottom of the object, = ax (longitudinal acceleration duc to pitch and surge): 0.45 g at waterline, increasing 0.01 g each meter above the bottom of the object, ~ an (vertical acceleration due to gravity and hheave), maximum 1.35 g, mininum 0.55 g (both conditions to be checked) and = wind pressure: 1000N/m’. 2.2.4.1 General requirements to stability are given in Ptd Ch.2 Sec.d, 2.2.5 Londs and load effects 2.2.5.1 Characteristic loads and load effects should be taken according to Pt.d Ch.3 See. 3. 2.2.5.2. Additional loads due to barge deflections should be considered. ‘This is particularly important for cargo supported by more than two vertical supports over the length of the barge and for cargo secured horizontally with a indetermined seafastoning system, see also Pt.1 Ch.3 See.3.7. 2.2.6 Load cases 2.2.6.1 Load cases for the towing operations shall be according to Pt. Ch.4 Sec.2, 6. 2.2.6.2 ‘The towing operation should be represented by ‘sequence of load cases determined by environmental loads, wave headings, self weight, relevant accidental loads, and combinations of these. 2.2.6.3. The most critical load casos for the each specific member of the object shall be ideotified. 2.2.6.4 Critical Ioad eases may be analyse as 4 static load cases, adding loads du to dynamic motions ‘of the barge with cargo to the static loads eaused by the self weight of the object. Rules for Marine Operations PL2 Ch.2 Towing 2.3 STRUCTURAL DESIGN CALCULATIONS: 2.3.1 General 2.3.1.1 Structural strength verifications shall comply. with Pet Ch.4, 2.3.1.2 All load carrying elements without a cottfied ‘capacity shall be verified by calculations, Typical elements requiring separate verification aro; local barge capacity, - —grillage elements, + seafastning elements and + internal seafastening for items exceeding 5 tonnes. 2.3.1.3, Global and local conditions with respect to corrosion shall considered in the design calculations, see also Pt] CheA See. 2.1.4, 2.3.1.4 Blement properties (e.g. strength, capacities, dimensions, weight otc.) may be verified by having centfied propertios. The conditions for the cectfieation shall be stated, see also Pt. Ch.2 Sec.2.2. lements that may be subject for this verification procedure are: + barge global strength, + towing brackets, + towing equipment, = mooring equipment, and ~ winches and foundations. 2.3.1.5 Modifications to, or use of certified equipment outside specified limitations require an acceptance from the certifying body. ‘Typical examples are; = exoeedanee of allowable global bending moments in restricted waters, snd ballasting below load line. 2.3.2. Grillage and seafastening 2.3.21 ‘The transported object are normally supported and seoured tothe barge by seafastening and grillage elements, 2.3.2.2 ‘The grillage elements shall be used to distribute concentrated deck load to a sufficient number of barge load carrying elements. 2.3.2.3, Seafastening, including shimming plates, shall bbe used to secure the transported object from translations in all directions. Dt Norske VERITASRules for Marine Operations : 1.2 Ch.2 Towing 2.3.2.4. Grillage and seafastening strength shall be vorified according to Pt. Ch. 4 for characteriatic loads according to Pr. Ch.3. Guidance Note Furtner guidance fr design of saafastening and grilage systems ae given in VMIO 1.2 Guideline for Grilage and Seafastening systems, : 2,3.2.8. Scafastoning for all items excees shall normally be verified with calculations. 5 tonnes 2.3.2.6. Seafastening design for offshore or inshore installation operations should allow for easy release and provide adequate support and horizontal restraints unti the object can be lifted cleer of the barge, or launched as applicable, 2.3.2.7. Elements providing horizontal and/or verti ‘support after cutting/removal of seafastening shall be verified for characteristic environmental conditions applicable for the installation operation. 2.3.2.8 For seafastoning and grillage for harbour moves ‘see Pt.2 Ch,1 See.2.7.4. 2.3.3 Barge global strength 2.3.3.4 The global barge capacity shall be confirmed. For barges or vessels classed with a recognised classification society itis recommended to base the global strength verification on stated allowable shear and bending capacities. 2.3.3.2 For barges without class the global strength shall be verified according to Pt. Ch.4, and with loads according to Pt.1 Ch.3. The verification shall considered all relevant loads and load combinations, i.e, hydrostatic loads, hydrodynamic loads, motion and weights shall be evaluated 2.3.4 Barge local strength 2.3.4.1 The barge loval strength shall be verified. Local strength verifications shall considered actual barge condition, i. effects of corrosion, local damages, ‘modifications and structural details shall be taken into account. January 1996 Page 7 of 14 2.3.4.2, If allowable deck load is based on “oad chacts”, theso shall clearly stste limitations and/or conditions with respect to number of loads, spacing between londs and number of simultaneous acting loads. Ie shall also be clasified if stated capacities include or exclude dynamic loads and if any design/load factors are included or not. Applied load and material factors shall be specified. Guidance Note ‘Approved “oad chart shal be use wih care, specially fr heavy object ( 500 tonnes). For highly leaded barges separate ‘natslaicalculations are recommended or verioan of local deck strength Det NORSKE VERITASJanuary 1996 Page 8 of 14 Rules for Marine Operations Pt.2 Ch.2 Towing 3, TOWING EQUIPMENT 3.1 TOWING ARRANGEMENT 3.4.1 General 3.1.1.1 Towing equipment shall be arranged so that proper control over towed object is ensured, 3.1.1.2. ‘The following items should be considered w.t.t to structural strength and operational practicalities, = towing brackets on towed object, ~ fairleads on towed object, ~ arrangement of towing line, ~ possible fibre rope towing pennant, + wire rope towing pennant, ~ ebin bridle/wire rope bridle/single leg chain, = flounder plate, = shackles, ings, - — thimbles, and ~ recovering arrangement. 3.1.2. Main towing line 3.1.2.1. ‘The minimum breaking load, in tonnes, of the towing line should be taken according to Eq. 3-1. - 4EP BP < 25 = O8BP+16VBP 25 < BP < 130 - 2.2BP BP > 130 Eq. 31 where EP: static bollard pull of the vessel in tonnes. Guidance Note “The nar lit of 2.2 BP corresponds toa load factor of 1.3, a matoral factor of 1.5 and a DAF of 1 3.1.2.2. The required towline MBL may also be influenced by = length of towing line to be used, = tow route, number of tugs and tow fleet arrangement, = nature of the towed object, = winch design, and = available back-up/contingency. 3.1.2.3. Tho main towing line should for offshore towing have a length not less than; Leentin = 2000 BP/MBL yay Eq. 32 where Lectin + tminimum tow Line longth (rn) BP: static bollard pull of the vessel in tonnes. MBLiguag : (oWline MBL in tonnes 3.1.3 Towing bridle 3.1.3.1. A bridle should be used for connection of the tow line to the towed object. Chains should be used in the way of chafing areas such as fairleads, 3.1.3.2 Bach single leg, components and connections (shackles, rings etc.) in the bridle shall have « MBL not less than the MBL of the main tow line. Reductions of equipment MBL due to bending in way of fairleads, end connections ete, shall be considered. Pairleads shall have a shape preventing excessive bending stress in the chain links/wise. Guidance Note ‘Shackles, rings eo, ere normally aoceptabie if sated safe working lead (SWAL) is minimum 179 of the main towne MBL. 3.1.3.3 A towing bridle should normally be attached to towing brackets. 3.1.3.4 Bnd conneotions of wire ropes should preferably be spelter sockets. Pressed connections fited with thimbles may be used. Spliced connections should bo avoided. 3.1.3.5 Pennants with lower minimum breaking lords than the main towline may be atiached if a reduction of the dimensions of the towline attachments is desired, However the minimum requirements in 3.1.2 shall always be complied with 3.1.3.6 A recovery wire rope should be fitted to the flounder plate, or if single leg connections are used, to the end of the legs. “The recovery wire rope should be lead to a winch in an accessible position. ‘The recovery wire rope should have a minimum breaking {oad not less than 3 times the weight of the bridle or leg. ‘Det NORSKE VERITASRules for Marine Operations PL.2 Ch.2 Towing 3.1.3.7 Fibre rope pennants should normally nat be used where there is adequate depth and sea room to allow for sufficient shock absoxbing inthe tow line catinary If fibre rope pennants ere used the pennants shall new condition, Minimum breaking load of any fibre rope pennants shall not be less than; = 2.3 times the tow line MBL for tugs with bollard pull less than $0 tonnes, - 1.5 times the tow line MBL. for tugs with botlard pull greater than 100 tonnes, and + Tinearly interpolated between 1.5 and 2.3 times the tow line MBL. for tugs with bollard pull between 50 and 100 tonnes 3.1.4 Towline attachments 3.1.4.1 Towline attachments shall be designed to resist towline pull from any likely diteotion, withthe use of fairlonds if necessary. 3.1.4.2 ‘The ultimate capacity of any towline attachment (bracket, bollard and their foundations) shall not be less than 1.3 times the minimum breaking load of the towlipe, 3.2 BARGES 3.2.1 General 3.2.1.1 Goneral requirements to barges are given in Pt Ch.2 Sec.5.2, ‘Strength verification of barge structure and barge equipment shall be according to 2.3. 3.2.1.2. Towing equipment shall comply requitements in 3.1. 3.2.2 Emergency towing arrangement 3.2.2.1 An emergency towing wire rope of with sninimum length equal to barge length shall be connected {0.8 bridle or single log connection, and lashed to the barge side for easy release, A recovery trailing Fine with «pick-up buoy shall be fitted to the emergency towing wire rope. January 1996 Page 9 of 14 3.2.2.2 The trailing line shall be of floating material and shall bave « minimum breaking load not less than 30 tonnes. The distance from the aft extremity of the towed object to the buoy shall not be less than 50 metres. In ‘addition to the trailing line, a messenger line of length 100 metres may be considered necessary between the buoy and the trailing line, 3.2.3 Anchoring and mooring equipment 3.2.3.1 A barge should normally have at least one anchor available for emergency anchoring. A windlass oor similar arrangement should be and capable of paying ‘out and holding the anchor. ‘The anchor should be secured with a easy release arrangement. ‘The anchor line length and MBL shall comply with the Rules of the Classification Society. Guidance Note For barges classed by Det Norske Veritas reference le made to ues fr Classification of Shipe, La Ch.3 820.3, 3.2.3.2 Mooring ropes of adequate strength and length shall be available on board. Guidance Note itis recommended to have at least 4 mooring ropes of 110m each {or 2of 220m each) avaiable enboard, 3.2.4 Ballast and drainage systems 3.2.4.1 The drainage system and bilge pumps should comply with the Rules of the Classification Society, 3.2.4.2 If the barge bilge pumps are out of order or if bilge pumps are not fitted, bilge suction may be arranged by portable pumps placed on board the barge. 3.2.5 Access 3.2.5.1 The barge shall be equipped with adequate access means, allowing safe entering from both sides of the barge during towing. 3.2.6 Inspection and testing, 3.2.6.1 ‘The barge, object, equipment, and acrangemeats shall be available for inspection before departure of the tow. 3.2.6.2 Functional testing of machinery that may be used during the voyage should be performed. ‘The imachinery should be tested in presents, or by the personnel who will operate the systems ‘Der NoRske VERITASJanuary 1996 Page 10 of 14 3.2.7 Barge documentation 3.2.7.1. General description of barge systoms shall be prevented, Ballast and towing equipmentsystems shall bbe deseribed in detail. 3.2.7.2 ‘The following main particulars should as & minimum be described; = object particulars, 7 jaime, signal leters, owners and port of registry of barge, = draught during towing, | stability properties for intact and damaged conditions, = specification of anchoring and mooring equipment, and =the class of the barge (if any), length, breath, dopth, and year of build, ele. 3.2.7.3. The following main drawings should normally be presented; = general arrangement, = Toad charts if applied, pls seotion, longitudinal section and other plans for evalustion of structural strength, if such evaluation is found necessary, = deawings showing arrangement and scantlings of towing brackets, bollards and faisleads, _ the main and emergency towing arrangement, and = recovering arrangement. 3.3. TOWING VESSELS 3.3.1 General 3.3.11. General requirements to towing vessels are given in Pt. Ch.2 Sec.5.2. 3.3.1.2 Towing equipment shall comply with 3.1. 4.3.2. Criteria for selection of towing vessels J.R.2A Towing vessels shall be selected to enable; = effective utilisation of bollard pull, = good manoeuvrability, Simple disconnecting operations, and = simple recovery: 3.3.2.2. The towing vessels shall be equipped with a towing winch, see 3.3.4. Towing with hooks should fly be used for assistance and in sheltered waters. 3.3.2.3 Nevessary towing force should be estimated ppased on the planned towing route. Rules for Marine Operations Pt.2-Ch.2 Towing 4.3.2.4 Towing foree for open sea towing shall be ‘rafficient to maintain zero speed under the following ‘eonditions. = ustained wind velocity Vw = heed current velocity Ve = significant wave height Hy 0 {m/s}, [avs], end [mk 3.3.2.3. Towing foree for coastal towing and towing in harrow or shallow waters representing a danger for grounding, shall bo sufficient to maintain a speed over ground, in safe direction, of minimum 2 knots under defined environmental design conditions. Guidance Note : ‘Above requirements are based on the necessty to control the ow @ ‘i aitchore, ond to eneure adequate manoeuvrabilly inshore ard in H rao waters. Guidance Note Siniiod weve crf free components for single “box shaped tparges may be caleulted accercing Eq. 2-3, provided: uas3e ( B60 v=o _ Fact Po £4.28 syhere Fea Wave dit rons rr Be signifeant wave height ‘mn 8 Breath tm L ena im} T Draft ( v “Tontng speed (hrough water) knots) 3.3.2.6 Required tug bollard pull shall be estimated dased on calculated required towing force, tus resistance, and tug efficiency in waves. Unless more accurate calculations of tug efficiency ato (7 nade, the continuous bollard pull stated in the bollard pill certificate sball be multiplied with an efficiency factors of; - 085 = 0.15 insure offshore ¢ 3.3.2.7 For towing with short towlines the interaction fects due to propeller race between tug and the towed Sbjoct shall be considered in estimates of required pull, Unless more accurats analysis azo performed an efficiency factor may be taken a8, 140.015Aeg soe] Loonteo 7 30m, Eq. 3-4 where tig: Interaction efficioney factor. ‘Ang Projected eros sections zea of toed objet in antiesTowline length in ractres. 1 for typical barge shapes. n= DET NORSKE VERITASRules for Marine Operations Pt.2.Ch.2 Towing 3.3.3 Towing lines 3.3.3.1. The requirements of 3.1.2 apply. Minimum required tow line MBL. shall consider bending of tow line over stora, of around other tow line guiding/steering ‘equipment. 3.3.3.2. Tugs should bo equipped with suitable an chafing equipment, 3.3.3.3. Gog rope or alternative arrangement should be provided to prevent athwartship pull from the towing, Tine. 3.3.3.4. For offshore towing one spare towline, satisfying requirements in 3.1.2, shall be available ‘onboard, preferably on a second winch drum, Aaditionally the following spare equipment should be kept available on board the towing vessel and/or the towed object. +t pennant = 2fibre rope springs, ifused = Assuitable number of shackles, rings, and other connecting equipment for atleast one complete towing line configuration 3.3.4. Towing winches 3.3.4.1. ‘The towing winch shall be approved according, classification requirements. 3.3.4.2. Winches for open soa towing should be remote ‘operated from the wheel house and so designed and. instrumented that it will be possible to determine the: loads in the wire rope from the drum, As examples, this may be arranged either directly by use of a load cell or indirectly when the brake is actuated by hydraulic pressure. 3.3.5. Equipment for personnel transfer 3.3.8.1. At least one suitable workbost with propulsion should be carried onboard for transferring persoancl and equipment from the towing vessel to the towed barge. If the workboat is of the inflatable type, a flooring of | adequate strength should be fitted to allow the carriage of heavy objects. January 1996 Page Ii of 14 3.3.6 Vessel documentation 3.3.6.1 The following main particulars should normally bo described; = name, signal letters, owners and port of registry, = main engine(s): manufacturer and number, ‘maximum continuous output and corresponding pam = state continuous bollard pull, = propeller(s): number, type, whether nozzle is fitted or not, + side thrusters (if fited): postion and thrust, = fol capacity, = fuel consumption, tonnes per day, and = stability particulars for departure and arrival loading conditions. 3.3.6.2. Towing vessels shall have a bollard pull certificates not older than 10 years. The bollard pull test procedure shall be stated. Ifthe vessel has undergone significant structural or iachinery changes @ renewed bollard pull test may be required. 3.3.6.3. For the towing winch and towing lines the following should be available: = Certificate and particulars for the towing winch stating manufacturer, type, maximum holding and stalling power. = Certificates for main and spare towing wire ropes, stating manufacturer, diameter of rope, length, ‘construction, nominal tensile strength of wires, breaking strength, = Allog for the towing lines, giving the following information on each rope; ~ date taken in use, records of inspection, = date of renewal of end sockets or other end connections and = report on damage to the rope. - Certificates for shackles, rings and connecting equipment, 3.3.7 Inspections and testing 3.3.7.1. Before departure an inspection of the towing vessel and towed object including all parts of the towing arrangement shall be carried out to confirm compliance with above stated requirements, Functional testing of towing winch systems shall as a ‘minimum be carried out. 3.3.7.2 An inspeotion of the towing wire ropes shall be performed. At least the fist 50 metres of the towing ‘wire should be streamed for inspection. Der Norske VERITAS:January 1996 7 Rules for Marine Operations Page 12 of 14 Pt.2.Ch.2 Towing 3.3.7.3 The towing line shall not be used ify = the reduction of towline strength due to weer, ‘corrosion and broken wires exceeds 10 % and = there are severe kinking, crushing, of other damages resulting in distortion of the rope structure, End sockets or other end connections should normally not be older than 2 years, depending on the extent of use (wear and teat). Guidarce Note ‘The tow ine should be subject for spacial evaluations if number ot broken sires over a lenathof7 times th towne ameter exceeds ‘bo fll numberof wees nth rope I sgnificant wear of ater Se ear oeekas Eau) Sat € Guidance Note ‘Special attention should pas tothe connection of end sockets Det NORSKE VERITASRules for Marine Operations January 1996 Pt.2 Ch.2 Towing Page 13 of 14 4, TOWING OPERATIONS 4.1 TOW OUT 4.1.4 Towing manual 4.1.41 ‘Tow out eriteria 4.1.1.1 A tow out criteria shall be established for all towing operations. A tow out criteria of Beaufort force 5 or better for the coming 24 hours is normally acceptablo. Based upon evaluations of tow out route, type of tow ‘and tow arrangement other tow out criteria may be accepted, Guidance Note ‘The intention vith the tow out eri is to allow time for ‘arillacieation wih the tow, and to ensure adequate distance to hore in case of adverse weather conions. 4.1.1.2, ‘The tow out should take place with good. Visibility, Due care should be given to effects of snow, rain, fog, ete, ‘This is particularly relevant if tow master is unfamiliar with the area. Assistance from local pilots should be evaluated. 4.1.2, Weather forecast 4.1.2.1 Arrangements for receiving weather forecasts at regular intervals prior to and during towing shall be made 4.1.2.2 Weather forecast requirements shall comply with Pt. Ch.2 See.3.2. 4.1.3, Internal seafastening 4.1.31 All loose items shall be properly secured. and/or stowed. Items that may be damaged by water shall be adequately protected. 4.13.2. Scouring of internal items weighing more than 5 tonnes shall be verified by calculations according to 23. 4.1.3.3. Internal seafastening by means of steel wire ropes, clamping devices, etc., may be accepted for sccuring smaller items such as piping, valves, ete. 4.1.4.1 A towing manual shall be prepared and distributed to key personnel. The tow master shall familiarise himself with the towing procedure and briefed about essential information in the towing ‘manual (limitations, restrictions ete.), see also Pe. Ch.2 Sec.3.5. 4.1.4.2. The towing procedure shall normally contain detailed information regarding = tow out criteria, = oritesia for seeking shelter, = towing route, = ports/areas of shelter, = estimated towing time (BTD, ETA), = environmental limitations w.r.t, structural capacity of object, soafastening, grillage etc., = contingency actions, = deseription of the ballast condition, = reporting routines for progress of the tow, BTA, status, etc., contact persons and telephone numbers, = expeoted environmental conditions for the intended towing soute for the relevant scason, and = Procedures for departure and arrival as well as calls at intermediate ports. 4.2 TOWING 42.1 Routing 4.2.1.1 The routing shall be chosen so that adequate botiom clearance and sea room are available during the towing. Considerations should be given to navigational accuracy, environmental conditions and loads, motion characteristics ofthe unit, possible heel and trim effects, towing foree, ete 4.2.2. Towing clearances 4.2.2.1 The tow should normally be routed so that a minimum underkeel clearance of 5 metres for barge and tug is obtained. Clearances less than 5 metres shall be evaluated in each case. Det Noaske VenirasJanuary 1996 Page 14 of 14 4.2.2.2, The combination of bollard pull and towline length should be so that a clearance of at least 5 metres between towline bight and seabed is maintained, 4.2.2.3. The width of the towing route should ‘normally be at Ieast threo times the width of the tow. Narrow channels should be passed in with good 4.2.3 Towing procedures 4.2.3.1. The tow shall not commence under more adverse environmental conditions than specified by the operational or characteristic design criteria, 4.2.3.2 During normal operation, the length of the towing line should be adjusted at regular intervals to avoid chafing at the stern rail, 4.2.3.3. The crew of the towing vessol(s) and the boarding erew or permanent crew for the towed object ‘shall be familiar with the equipment and installations which may be used during the voyage. A demonstration of the operation of bilge and ballast systems, anchoring arrangement, etc. on the towed ‘object may be required before departure. 4.2.3.4 Slack tanks should be avoided. If used, it should be verified that the specified slack tanks will not jeopardise the stability or strength of the barge. 4.2.3.5. Inorder to avoid slamming and improve seakcoping it i recommended that the towed barge is trimmed minimum 0.005 times barge length by stern, and ballasted to a draft al bow of minimum 0.15 times barge dopth. 4.2.3.6 For large tows or towing close to shipping lanes the use of a guard ship to prevent other vessels ‘and objects from jeopardising the tow should be considered, 4.2.3.7. For towing in areas with high traffic density an escort tug should be available to assist in ease of & ‘break dovn of the main tg. “The presence of a riding crew on the barge may also be relevant in such waters fo pick up an towline, or release the anchor, in case of towline failure, Rules for Marine Operations Pt.2 Ch.2 Towing ‘Dar Norske VERITAS