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Pt E, Ch 14, Sec 2 SECTION 2 1 HULL AND STABILITY General 1.1 Application θC : Heeling angle of equilibrium, corresponding to the first intersection between heeling and righting arms θD : Heeling angle, to be taken as the lowest of: 1.1.1 The requirements of this Section apply to ships with one of the following service notations: ã the angle θM, corresponding to the position of GZMAX (see Fig 1), ã tug, mainly intended for towing services, which are to comply with the requirements i
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  Pt E, Ch 14, Sec 2 58 RINA Rules 2004 SECTION 2H ULL   AND  S TABILITY 1General 1.1Application 1.1.1  The requirements of this Section apply to ships withone of the following service notations: tug , mainly intended for towing services, which are tocomply with the requirements in [2]ã salvage tug , having specific equipment for salvage serv-ices, which are to comply with the requirements in [2]and [3]ã escort tug , mainly intended for escort services such asfor steering, braking and otherwise controlling escortedships, which are to comply with the requirements in [2]and [4].Ships with the additional service feature barge combined are to comply with the applicable requirements in Sec3. 2Tugs, salvage tugs and escort tugs 2.1General 2.1.1 In general, tugs are completely decked ships pro-vided with an ample drift surface and, where intended forservice outside sheltered areas, with a forecastle or half forecastle, or at least with a large sheer forward. Tugs of unusual design are to be considered by the Societyon a case-by-case basis. 2.2Stability 2.2.1 Intact stability  The stability of the ship for the loading conditions in PtB,Ch3, App2, [1.2.11] is to be in compliance with therequirements in PtB, Ch3, Sec2. 2.2.2 Additional intact stability criteria All the loading conditions reported in the trim and stabilitybooklet, with the exception of lightship, are also to bechecked in order to investigate the ship’s capability to sup-port the effect of the towing force in the beam direction.A tug may be considered as having sufficient stability,according to the effect of the towing force in the beamdirection, if the following condition is complied with:A ≥ 0,011 where:A:Area, in m . rad, contained between the rightinglever and the heeling arm curves, measuredfrom the heeling angle θ C  to the heeling angle θ D θ C :Heeling angle of equilibrium, corresponding tothe first intersection between heeling and right-ing arms θ D :Heeling angle, to be taken as the lowest of:ãthe angle θ M , corresponding to the positionof GZ MAX  (see Fig1),ãthe angle of downflooding,ã40°. The heeling arm curve is to be calculated as follows:where:b H :Heeling arm, in m T:Maximum towing pull, in kNWhere this force is unknown, it can be assumedequal to:ãT = 0,179 P for propellers not fitted withnozzlesãT = 0,228 P for propellers fitted with noz-zlesP:Maximum continuous power, in kW, of the pro-pulsion engineH:Vertical distance, in m, between the towinghook, or equivalent fitting, and half draught cor-responding to ∆∆ :Loading condition displacement, in t. Figure 1 : Heeling and righting arms curves b H  TH981 , ∆ ---------------- θ cos = heeling angles                  heeling and righting arm  Pt E, Ch 14, Sec 2 RINA Rules 2004  59 2.2.3 Exemption  Tugs of any length with the navigation notation shelteredarea  may be exempted from complying with the require-ment specified in [2.2.2], provided that the initial metacen-tric height GM, in m, corrected according to PtB, Ch3,Sec2, [4.7], in the most severe condition is not less than thevalue obtained from the following formula:where:B:Ship’s maximum breadth, in mf:Ship’s freeboard, in mm, to be assumed notgreater than 650 mm T, H, ∆ :Defined in [2.2.2]. 2.2.4 Damage stability  Tugs with a length equal to or greater than 80 m are to com-ply with the requirements in PtB, Ch3, App3. 2.3Structure design principles 2.3.1 Bollards For tugs equipped for side towing, the relevant bollards areto be effectively fixed on the deck in way of side transversesand deck beams or bulkheads. 2.3.2 Fenders A strong fender for the protection of the tug’s sides is to befitted at deck level.Alternatively, loose side fenders may be fitted, provided thatthey are supported by vertical ordinary stiffeners extendingfrom the lightship waterline to the fenders themselves. 2.3.3 Floors Floors are to be arranged with a welded face plate in themachinery space; elsewhere, floor flanging may beaccepted as an alternative to the fitting of welded faceplates. 2.3.4 Shaft tunnels For tugs having small depth, the shaft tunnel may be omit-ted. In this case, access to the shaft line is to be giventhrough the floor of the space above. 2.4Hull scantlings 2.4.1 General  The net scantlings of plating, ordinary stiffeners and primarysupporting members are to be in accordance with PartB,Chapter7 or PartB, Chapter8, as applicable, where the hull girder loads and the local loads are defined in PartB,Chapter5 or PtB, Ch8, Sec1, as applicable, to be calcu- lated for T not less than 0,85 D. 2.4.2 Side plating thickness for tugs with L < 65 m For tugs with L < 65 m, the net thickness of the side platingis to be increased by 1 mm with respect to that calculatedaccording to PartB, Chapter8, without being greater than that of the adjacent bottom plating calculated for the samepanel dimensions. 2.5Other structures 2.5.1 Machinery casings Exposed machinery casings are to be not less than 900 mmin height, measured from the upper surface of the deck, andprovided with weathertight means of closure.In general, the longitudinal sides of the machinery casingsare to be extended downwards by a deck girder to whichthe deck beams are to be connected.Side ordinary stiffeners are to be connected to the deck. Their spacing is to be not greater than 0,75 m. 2.5.2 Emergency exits from machinery space Emergency exits from the machinery space to the upperdeck are to be located as high as possible above the water-line and in way of the ship’s centreline, so that they may beused even at extreme angles of heel.Escape hatch coaming heights are to be not less than 600mm above the upper surface of the deck.Escape hatch covers are to have hinges arranged athwart-ship and are to be capable of being opened and closedwatertight from either side. 2.5.3 Height of hatchway coamings  The height of the hatchway coamings is to be not less than300 mm. Hatch covers are to be fitted with efficient secur-ing devices. 2.6Rudder and bulwarks 2.6.1 Rudder For tugs, the rudder stock diameter is to be increased by 5%with respect to that calculated according to PtB, Ch10,Sec1, [4]. 2.6.2 Bulwarks  The bulwarks are to be sloped inboard to avoid distortionslikely to occur during contact. Their height may be reducedwhere required by operational necessities. 2.7Equipment 2.7.1 Equipment number for tugs with the navigation notation “unrestricted navigation” For tugs with the navigation notation unrestricted naviga-tion , the equipment number EN is to be obtained from thefollowing formula:EN = ∆ 2/3  + 2 (a B + Σ h n b n ) + 0,1 Awhere: ∆ :Moulded displacement of the tug, in t, to thesummer load waterlinea:Freeboard amidships from the summer loadwaterline to the upper deck, in mh n :Height, in m, at the centreline of tier “n” of superstructure or deckhouse having a breadthgreater then B/4. Where a house having abreadth greater than B/4 is above a house with abreadth of B/4 or less, the upper house is to beincluded and the lower ignored.GM66THB ⋅⋅⋅ f  ∆⋅ ------------------------------- =  Pt E, Ch 14, Sec 2 60 RINA Rules 2004 Figure 2 : Effective area of bulwarks or fixed screens to be included in the Equipment Number b n :Breadth, in m, of the widest superstructure ordeckhouse of each tier having a breadth greaterthan B/4A:Area, in m 2 , in profile view, of the parts of thehull, superstructures and houses above the sum-mer load waterline which are within the lengthL E  and also have a breadth greater than B/4L E :Equipment length, in m, equal to L withoutbeing taken less than 96% or greater than 97%of the total length of the summer load waterline.Fixed screens or bulwarks 1,5 m or more in height are to beregarded as parts of houses when determining h and A. Inparticular, the hatched area shown in Fig2 is to beincluded. The height of hatch coamings and that of any deck cargomay be disregarded when determining h and A.For tugs where the vertical extent of the superstructure ismuch greater than usual, the Society may require anincreased equipment number EN. 2.7.2 Equipment number for tugs with the navigation notation coastal area or sheltered area For tugs with the navigation notation coastal area  or shel-tered area , the equipment number EN is to be obtainedfrom the following formula:EN = 2,51 (L B D) 2/3  For tugs where the vertical extent of the superstructure ismuch greater than usual, the Society may require anincreased equipment number EN. 2.7.3 Equipment number for tugs with C B  less than 0,60 For tugs with total block coefficient C B  less than 0,60, at adraught T equal to 0,85 D, the equipment number EN is tobe obtained from the following formulae:EN = 1,76 (L B D) 2/3  For tugs where the vertical extent of the superstructure ismuch greater than usual, the Society may require anincreased equipment number EN. 2.7.4 Anchors, chain cables and ropes  Tugs are to be provided with equipment in stocklessanchors, chain cables and ropes to be obtained as a func-tion of the Equipment Number EN (see [2.7.1] to [2.7.3] ) from:ã PtB, Ch10, Sec4 for tugs with the navigation notation unrestricted navigation ã Tab1 and  Tab2 for tugs with the navigation notation coastal area  or sheltered area . 2.7.5 Additional equipment  Tugs are to be fitted with the additional equipment specifiedin  Tab3. 2.8Towing arrangements 2.8.1 General In general, towing hooks and winches are to be arranged inway of the ship’s centreline, in such a position as to mini-mise heeling moments in normal working conditions. 2.8.2 Hooks and winches  The hook and the winch materials are to comply with theapplicable requirements of Part D. The maximum towing force T, in kN, defined in [2.2.2], isto be specified in the structural arrangement plans of thehook and the winch. The hooks and the winches are to be subjected to a statictest, where the testing force C  T  is to be not less than thatobtained from  Tab4 as a function of T.Winches may be equipped with a device for automaticadjustment of the tow.  Pt E, Ch 14, Sec 2 RINA Rules 2004  61 Table 1 : Equipment for tugs with the navigation notation coastal area or sheltered area2.8.3 Hook quick-release device  The quick-release device is to be capable of being operatedfrom a remote control device on the bridge, or as near aspracticable, while the hook is under load. It is required that,in the case of a critical situation, the towline can be imme-diately released regardless of the angle of heel and thedirection of the towline. The quick-release device is to be tested both at maximumtowing pull T and testing force C  T , defined above. The forcenecessary to open the hook under load is to be not greaterthan 150 N.After installation on board, an unhooking trial under load isto be carried out by means of the above remote controldevice. This trial may be performed with a test load lessthan the maximum towing pull T. 2.8.4 Winch slip device Winches are to be equipped with a suitable slip device,operable by remote control, allowing the rope to unwindwhen necessary. 2.8.5 Winch quick-release device  The unhooking of the rope from the winch drum is to beenabled by means of a suitable device or by using a ropewhose terminal is not fixed to the drum. 2.8.6 Connection with the hull structures  The scantlings of the structures intended to connect thetowing arrangements to the hull are to be in accordancewith PartB, Chapter7 or PartB, Chapter8, as applicable, where the load to be considered is the maximum towingpull T defined in [2.2.2].Equipment number ENA<EN ≤  BStockless anchorsStud link chain cables for anchorsABN (1) Mass per anchor, in kg Total length, in m (2) Diameter, in mmmild steelhigh strength steel05565758595105115125140160180200220245265290 315335 365390 415445475505 535570556474849410411412413915917919921924426428931433436438941444447450453456960022222222222222222233333333314014816618019821022023024426028031434638442046650054057569077088510001130127014201540110,0110,0110,0110,0110,0110,0110,0110,0110,0137,5137,5165,0165,0192,5192,5220,0247,5275,0302,5302,5330,0330,0357,5357,5385,0385,0440,014,0 (3) 14,0 (3) 16,0 (3) 16,0 (3) 17,517,519,019,020,522,022,024,026,026,028,030,030,032,034,034,036,036,038,038,040,040,042,0----16,016,017,517,517,519,019,020,522,022,024,026,026,028,030,030,032,032,034,034,034,034,036,0 (1)  The third anchor is intended as a spare and is not required for the purpose of classification. (2) Where the total length required for chain cables is less than 220 m, one only of the two anchors may be linked with the chain cable and arranged in a hawse pipe. In this case, the second anchor is to be stowed such that it can be easily joined to the chain cable and dropped overboard in the event of loss of the first anchor. (3)  These diameters are applicable to studless chain cables.

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