SOME IMPORTANT NAVAL ARCHITECTURAL TERMS

1 Page 1(6) 2009 Foreship IMPORTANT NAVAL ARCHITECTURAL TERMSF ebruary 2009 ITEMEXPLANATIONA-, B- and C-class divisionsSOLAS has tables for structural fire protection requirement ofbulkheads and decks. The requirements depend on the spaces inquestion, and are different for passenger ships and cargo , A-15, A-30, A-60:Shall be constructed of steel or equivalent material, shall beconstructed to prevent passage of smoke and flame for 1 h inStandard Fire Test, shall be insulated so that the average temperatureof the unexposed side does not rise more than 140 C (any point nomore than 180 C) above the original temperature within 0, 15, 30 or60 , B-15:Shall be constructed to prevent passage of flame for h in StandardFire Test, shall be insulated so that the average temperature of theunexposed side does not rise more than 140 C (any point no morethan 225 C) above the original temperature within 0 or 15 be constructed of approved non-combustible materials(However, combustible veneer may be used).

2 C:Shall be constructed of approved non-combustible materials(However, combustible veneer may be used).Alternative Design,Alternative ArrangementsRegulation allows for designs and arrangements which are notaccording to SOLAS requirements, providing an analysis is made thatshows the proposed alternative design or arrangement is, with regardsto safety, at the same or better level than the SOLAS of an alternative design are lifeboats with a higher than 150person Subdivision Index, A According to probabilistic damage stability rules the vessel sprobability to survive a flooding damage (collision, grounding) iscalculated with formula: = where:irepresents each compartment or group of compartments the probability that only the compartment or group ofcompartments under consideration may be the probability of survivability after flooding of thecompartment or group of compartments under A is calculated for three different drafts and summarized with aweighted formula.

3 If the A R (R=required subdivision index), thevessel fulfills the requirement. Typically the vessel s GM-limits fordamage stability are adjusted so that A = R .Ballast Water Convention, BallastWater Treatment, BWTNew regulation requiring ballast water treatment systems on all ships(new and old), in order to avoid harmful organisms spreading fromone location to another. Typically the treatment is by filtering and , Breadth divided by 5, B/5-lineImaginary line used in ship design and damage stability calculations:according to old rules, no damage extends inside the B/5-line ( ona vessel with breadth of m, maximum extent of any damage m from ship s shell). Due to this, bilge main lines, fuel tanks, normally located inside this B/5. New probabilistic rules havemade this rule obsolete on new Coefficient, CBImportant coefficient which describes the fullness of the hull: a lowercoefficient means typically lower resistance.

4 CB = DisplacementVolume / (L x B x T). A typical figure for a cruise vessel is often used coefficient is CM, Midship Section Coefficient, whichdescribes the fullness of Midship 2(6) 2009 Foreship of Gravity, Vertical Center ofGravity (VCG), Longitudinal Center ofGravity (LCG), KGCenter of Gravity is used especially in connection with lightweight,deadweight and displacement. VCG is the vertical distance betweencenter of gravity and keel, LCG is the longitudinal distance betweencenter of gravity and frame #0. Lower VCG means more stability andLCG affects vessel s trim. Typical VCG figures for a Panamax cruiseship are, for example:Item Weight VCGL ightweight 39,000t 8,000t 47,000t this example shows, deadweight has a lower VCG than lightweightand thus reduces the VCG of displacement (and improves stability).The situation is kept like this by replacing used fuel with ballast is the same than VCG.

5 See also , Computation Fluid DynamicsCalculation method or software which enables hydrodynamicoptimization of hull form. Has lately enabled fast development ofefficient hull forms. RANSE in connection with CFD denotes ReynoldsAveraged Navier Stokes Equation , and means simulation of theviscous flow. In future CFD calculations can likely replace model , Coefficient of PerformanceDescribes the efficiency of AC-cooling compressors (chillers). Forexample, COP of indicates that for a 4,000 kW cooling power, thechiller requires 1,000 kW of electric LengthThe length of damage used in damage stability calculations. Forpassenger ship the old (pre 2009) rules defined this length to be 3m+ 3% of Lpp or 11 m, whichever is less . In new probabilistic rules thecalculated damage lengths are based on probabilistic distribution, andthe calculation can include much longer damages than was required inold StabilityThe vessel s stability characteristics in damaged condition.

6 Big cruiseships can float with several flooded watertight compartments. Old (pre2009) rules required the ships to withstand a damage of any twoadjacent watertight compartments, but in new regulations thecalculation method and requirement is much more , DWTW eight (and center of gravity) of vessel s cargo, stores, fuel, freshwater, passengers, crew, liquids in tanks, etc. Deadweight of aPanamax cruise vessel is typically around 8,000 t. See also lightweightand Draught, TDESIGNThe draft the vessel (and her deadweight, stability, performance, etc.)is designed for. On a Panamax cruise ship design draft is typically m. Generally more draft means better seakeeping capabilities, butless draft often means more stability. See also Scantling , Displacement weightThe weight (and center of gravity) of the vessel herself and vessel scargo, stores, passengers, crew, etc. Displacement = Lightweight +Deadweight. Displacement of a Panamax (approximately 90,000 GT)cruise vessel is ca.

7 47,000 t. Displacement Force (symbol') isDisplacement Weight x g (g= m/s2), and is the same volume ( )The volume the vessel s hull displaces in water. In seawater withspecific gravity of kg/m3, the Displacement Volume for a vesselDisplacement of 47,000t is 45,854 m3. Thus the vessel needs moreDisplacement Volume (and draft) in fresh water than in sea water forthe same Displacement extension to ship s stern. On older ships the diminished stabilitycan be regained by adding a ducktail. Ducktail is also used onnewbuildings; there the primary purpose is often to reduce the powerconsumption for Number, FnFroude number describes the vessel s relative speed, which dependson vessel length: = [ ] [ ] [ ]where:vis vessel speed in [m/s] (1 knot| m/s)gis m/s2 Lis vessel s waterline lengthPage 3(6) 2009 Foreship a lower Fn means lower resistance (for fast, small vesselsthe situation can be opposite). Typical figure for a Panamax cruiseship is Fn= ConsumptionUsing a typical engine specific fuel oil consumption of 200 g/kWh(when tolerances, heat value corrections, etc.)

8 Are taken into account,the real heavy fuel oil consumption is seldom below this, and ofteneven above this), this corresponds to a fuel consumption of t/h per1 MW. Thus, a ship using 30 MW for propulsion and hotel load,consumes 6t heavy fuel oil (HFO) per surface correctionThe GM is corrected with free surface correction : tanks with freesurface reduce the stability of the vessel; this correction is The more free surfaces (slack tanks, pools, splash areas) thereis, the bigger the correction is, and thus more the GM , (transverse) Metacentric HeightDescribes the righting moment of the vessel: higher GM means betterstability (condition for positive stability is that GM>0.). Typical valuefor GM on a Panamax cruise vessel is ca. m. GM = KM KG,where KG is the VCG of the ship (lightweight + deadweight) and KM isthe distance from keel to the metacenter (see figure below). KM hasto be higher than KG for a ship stay upright (and GM to stay positive).

9 GM can also used for the longitudinal stability of the vessel: thensymbol GML is MarginAn additional margin added into vessel weight calculation to cover forlater weight increases. Practically all ships get heavier when they age;this is due to conversions, modifications, painting, etc. and withoutpreparing for this, the ship can later end up with stability problems,requiring a ducktail or a (Gross Tonnage), (formerly GRT)Gross Tonnage describes the volume and size of the vessel. GTincludes all the enclosed spaces (not balconies, sun decks or similarareas). GT is calculated with a formula: =( + ) where V = vessel s calculated volume in :xEarlier 1 GRT was 100 ft3, or m3; thus figures for Titanic cannot be directly compared with GT figures oftoday s example, if vessel s enclosed volume is 294 000 m3, theGT is ca. 91, is often the base for different port and other GT is logarithmic, it cannot be used for accuratecomparison between vessels of different size: for example, ona 10,000 GT ship one GT is m3, but on a 150,000 GTvessel one GT corresponds to , Heeling angleThe angle vessel is leaning away from upright LoadThe electric power needed for other ship functions than propulsion, AC, lighting, galleys, etc.

10 For a Panamax vessel a typical hotel loadis close to 10 StabilityThe vessel stability in intact (normal, non-damaged) condition. Inintact conditions the vessel has to withstand heeling, wind, etc. tofulfill the criteria stated in , (transverse) Metacentric HeightKM is the distance from Keel to Metacenter, which depends on thevessel draft, displacement and hull form. Typical KM for a Panamaxcruise vessel is 18 m. High KM means more stability, but often at theexpense of speed and sea keeping capabilities. See figure , LWTV essel s empty weight (and center of gravity), weight of thevessel without fuel, stores, water, cargo, passengers, crew, liquid in ship system piping and system tanks is included, butnot liquids in storage lightweight for a Panamax cruise ship is ca. 39,000 t. See alsodisplacement and Center of Buoyancy (LCB) Longitudinal Center is the longitudinal center of water the vessel shull displaces.