Suez-Max Tanker Optimization

Design Analysis of a New Generation of Suezmax Tankers Igor Belamarić,1 Predrag Čudina,2 Kalman Žiha3 A thoroughly investigated design of a new generation of Suezmax tankers incorporating the builder's consideration in the form of a condensed mathematical model is presented. The design model is provided for practical application and for a fast assessment of the conceptual design. The design model is subjected to different methods of design analysis in order determine an adequate design and the appropriate procedure applicable in the design office. In addition, the computational, building and operational uncertainties involved in the design and mathematical model are considered. The uncertainty analysis based on tolerances indicates a wider choice of designs within acceptable limits. INTRODUCTION The enlarged profile of the Suez Canal, along with The design concept of the Suezmax tanker is intensive development of double-hull structures described by a mathematical/numerical model during the past number of years, has had a great following design principles [Watson & Gilfillan impetus on the design of a new generation of 1977, Taggart 1980]; this concept is subjected to an Suezmax tankers. analysis giving a solid basis for design selection and Basic dilemmas in the design of tankers concern the decision-making, [Žanić, Grubišić & Trincas 1992]. longitudinal bulkheads, shape of the midship section, Due to the large number of uncertainties involved cargo loading/unloading equipment, capacity and in the design model, a certain skepticism may arise design of segregated ballast tanks, as well as the among practicing engineers concerning highly arrangement of engine room, and have been sophisticated and accurate numerical procedures. substantially influenced by the relevant IMO and US- In practice there exists a wide range of solutions OPA requirements. The deepening of the Suez Canal within acceptable limits which cannot be mutually had a considerable effect upon maximal ship distinguished due to objective, subjective, numerical, dimensions [Suez Canal Authority 1986, 1995]. operational and other uncertainties or inaccuracies involved in the design model. Some design variables Two reasons which motivated the present work: and problem parameters applied in mathematical • Suezmax size itself suiting physical passage models, or even all of them, can be uncertain, either through the Canal. with known tolerance limits or with given statistical • Expectation that the Suezmax tanker will show properties. other advantages and become a convenient and The idea underlined in the paper is to investigate preferable size for future oil carriers. the effect of tolerances of variables and parameters, [e.g. Creveling 1996] in post-optimal non linear Furthermore, the fact that Split Shipyard has analysis [e.g. Žiha 1997] of a design of a Suezmax already built a series of eight segregated ballast tankers. tankers of 144 000 dwt as well as several double-hull Aframax tankers, all in accordance with TSPP DESIGN CONCEPT OF A SUEZMAX TANKER Protocol'78, represents a reliable and encouraging basis. The basic concept assumes following features: • The adopted present design assumes double bottom and double sides in way of cargo space in accordance with the respective IMO rules and with the US Oil Pollution Act 1990. The mid- deck tanker concept was considered too, but it _________________________ was rejected due to lack of experience and some 1 Retired chief designer, Split Shipbuilding Industry 2 Chief designer, Split Shipbuilding Industry open problems regarding the relevant regulations 3 Assistent professor, University of Zagreb and requirements. NOMENCLATURE B =Breadth, molded, m CF =cost of fuel, $/t CB =Block coefficient CS =cost of steel, $/t Ci =distance to ith goal in distance in L1 metrics TCS=total cost of steel, $ standardized and L = (w C )2 t =tolerance in general 2 ∑ i i 3 normalized space i Vct =cargo tanks capacity, m distance in L metrics d =draft, m 2 Vt =speed on sea trials ds =maximal draft, m Lw∞ = min max iiCi at draft ds, knots D =depth, m Wi =weight if i-th goal distance in L∞ metrics DW=deadweight, t Wm =weight of machinery, t Mp =power margin hts =influence of built-in high WO =outfit weight including MW =weight margin tensile steel upon total N =propeller speed, rpm equipment for cargo, t steel, % NCR =Normal Continuous WS =hull and superstructure Lpp =length between Rating, kW weight, t perpendiculars, m Pb =engine brake power, kW LCF=lifetime fuel cost, $ SMCR=selected maximum Greek symbols LCT=total lifetime costs, $ continuous rating, kW ∆ =displacement, t LT=ship's lifetime, years SFOC =specific fuel η =service margin consumption, t/kW h κ = Vct/L×B×D ST =sailing time, days/year specific volume capacity ρsea =density of sea water, 3 appendages included, t/m Lw= C 1 ∑ ii i breadth [Suez Canal Authority 1986], had resulted in designs with optimal breadth of • The tanker is conceived with 12 cargo and 2 slop 44.5 m for 15.6 m of draft, by which the tanks; the latter may be used for cargo too, when stipulated deadweight could not be reached. The carrying oils of lower density. Such a recent increase of draft to 17.07 m and breadth of compartmentation allows three cargo 48.16 m [Suez Canal Authority 1995], see Fig. segregations, as usual, and further complies with 1(a), influenced design particulars for the better. IMO requirements for segregated ballast tanks However, the adopted maximal draft for the protectively located (SBT-PL) as well as with design model is d=ds=17.10 m, assuming that criteria for damaged stability. The double-skin until arrival at the Canal, some stores will be Suezmax tanker could rather easily cope with consumed, and the draft at the start of the classification societie’s rules, omitting centerline passage will be about the allowed of 17.07 m. longitudinal bulkhead. Nevertheless, other The maximal design beam is set to B=49 m, just maritime authorities favor design with centerline exceeding the minimal breadth of 48.16 m when longitudinal bulkhead, in view of higher stability the beam-to-draft product B×ds is maximal; see standards during loading/unloading operations. Fig.1(b). Therefore, the adopted concept assumes one • The block coefficient of 0.828 as the upper centerline longitudinal plane bulkhead with bound is assumed empirically, for which a horizontal stiffeners and vertical webs, which is satisfactory hull form can be selected. also more efficient with respect to longitudinal • Approximately 60% of high tensile steel is used strength than the analogous corrugated bulkhead. in the hull construction. It decreases the steel • The assumed deadweight equals weight of the hull by about 7%. DW=150 000 t. The volume of cargo tanks is • The maximal length of the ship is limited to 3 Vct=170 000 m . The assumed range of Lpp=265 m in view of length restriction of navigation of 20 000 nm. Fuel stores, based on building berths in Split Shipyard. average loaded/ballast service speed of 14 knots • One low speed two-stroke direct coupled diesel and sailing time of about 60 days, amounts to engine is assumed. The speed on sea trials at the 2 700 t of heavy oil. By adding other stores, i.e. maximal draft is Vt=14.7 knots. The diesel oil, lub oil and fresh water, then crew, corresponding speed at slightly lower design provision and extra spares, amounting to about draft is approximate 15 knots. 1 300 t, results a payload • Addi tional design constraints, the minimal PL=150 000-4 000=146 000 t. This length/beam ratio of Lpp/B=5.6 and the gives, against the presupposed cubic capacity, a minimum length-to-depth ratio of Lpp/D=10.5 are 3 typical cargo density of about 0.86 t/m . introduced following the empirical assessments in order to avoid potential structural, propulsion and maneouvrebility problems. • The draft and the beam are defined by Suez Canal limitations. Earlier constraints in draft and • IMO requirements for ballast conditions, OUTLINE DESCRIPTION OF DESIGN MODEL concerning the minimum draft and propeller immersion, trim and displacement, are fully met. The design model is defined by the basic design • Minimum freeboard requirements are in concept outlined in previous section. A suitable accordance with ILLC66. mathematical model is set out for the purpose, based on the widely introduced expressions from the literature, [Watson & Gilfillan 1977, Taggart 1980] (a) Limitations on drafts as well as those tested and practised by the Split Shipyard. The model depends upon four design 20 variables: Lpp, B, ds and CB. The depth of the ship can be obtained from the following relation: 17.07 m V D = ct (1) 1995 LBpp ⋅⋅κ 15 where the value of the specific cubic capacity κ is draft [m] 1986 assumed empirically as 0.620, in order to satisfy the required cargo and water ballast capacity. The expression for brake power Pb, being equal to the service continuous rating SCR, in kW, has been obtained through regression analysis from as many as 360 ships, and it reads: 10 0.04917 1.03279 0.64437 40 45 50 55 60 Pb = 0.0072886⋅ Lpp ⋅ B ⋅ds ⋅ (2) Beam [m] 2.1262 3.2722 ⋅CB ⋅Vtrial ⋅(1−0.002966⋅ Lpp / ds ) The regression formula (2) is applicable within the (b) Limitation on section limits ∆=171 000-173 000 t, Lpp=250-260 m, B=45-48 m, d=16.8-17.4 m, C =0.80-0.83, 850 B 1995 Vt=14.4-15.0 knots at draft ds and N=98 rpm propeller speed and for moderate extrapolations. 800 Following engineering practice, the selected maximum continuous rating (SMCR) can be obtained 750 by adopting a power margin of Mp=0.10, as follows: Pb

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