ship structure final – Flashcards
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| equation for stress |
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| load/area (tensile, compressive, shearing) |
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| ultimate tension for steel (tension & shear) |
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| tension: 30 sq in shear: 22 sq in |
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| equation for bending moment (fixed beam) |
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| distance x length |
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| equation for bending moment (concentrated load, unsupported ends) |
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| mass x length / 4 |
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| equation for bending moment (uniform load, unsupported ends) |
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| mass x length / 8 |
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| A _____ end beam will support _____ times the amount of load vs a _____ end beam |
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| fixed; 2; free |
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| The deflection of a _____ ended rectangular beam is only _____ the deflection of a ____ ended beam |
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| fixed; 1/4; free |
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| beam of equivalent size but made up of individual layers free to slip will only carry ____ the load of a solid beam |
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| 1/5 |
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| Relative strength equation (beams) |
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| (D_larger/D_smaller)squared x original |
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| comparing deflection equation |
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| (S_long/S_short)cubed, result x original deflection |
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| relative strength of beams |
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| original length/new length x original load |
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| torque equation |
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| HP x 5252 / RPM |
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| LOA |
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| Length Overall; Linear distance from bow to stern, measured parallel to baseline |
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| Sheer |
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| Longitudinal curvature of vessel's deck greater fwd than aft increases buoyancy w/ air space |
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| Beam |
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| Width of a Ship |
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| Extreme Beam |
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| Width + projections (bridgewing, gangway, etc) |
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| Tumble Home |
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| inward slope of the ships side measured widest beam less narrowest beam |
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| Flare |
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| opposite of tumblehome outward slope of ships side "dryer decks," throws waves from bow creates space/lessens impact force of water |
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| Draft |
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| vert distance from lowest part of hull to waterline indicated fwd aft amidships |
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| air draft |
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| distance from highest point to waterline important re: bridge clearances changes due to ballast |
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| Camber |
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| Transverse slope of deck directs water to drains at sides not specifically for added strength |
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| Dead Rise |
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| Rise or slant up athwartship from bottom keel to bilge aka rise of the bottom / rise of the floor |
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| Depth |
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| vertical distance from the lowest point of the hull to the side of the deck to which it is referred depth = draft + freeboard |
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| Molded Dims |
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| Dimensions taken from inside plating of a ship important for cargo stowage |
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| Freeboard |
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| distance measured vertically downard, at the side of vessel amidships, from upper edge of deckline to waterline |
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| Divisions of Hull |
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| Middle Body Entrance Run |
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| Middle Body |
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| mid-ship part of vessel where constant cross-sectional shape is maintained thru length. most merchant ships = parallel middle bodies, sides are vertical |
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| Entrance |
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| immersed part of the hull fwd of middle body expensive to build cuz it's curvy |
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| Run |
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| immersed part of hull aft of middle body where thrust is applied from prop where torque is applied from rudder |
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| parallel mid bodies |
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| cheapest to build, hold most cargo |
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| LC overlaid (symbol) |
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| symbol for centerline plane |
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| Reference Planes |
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| Used as an aid in locating points for design & building |
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| Baseline Plane |
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| established near base of ship runs thru upper edge of flat plate keel vert dims measured from this ref point |
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| Centerline Plane |
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| fore-aft (longitudinal) at right angles to BL hull shape essentially symmetrical on either side of CL |
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| Transverse Vertical Planes |
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| at equal intervals along length of vessel aka frame stations may NOT be equal to actual frame locations |
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| Forward Perpendicular (FP) |
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| line perpendicular to BL, intersecting the fwd edge of the stem at the design waterline |
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| After Perpendicular |
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| perpendicular to the baseline, intersecting the after end of the rudder post at the design waterline |
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| Mid-Ship Perpendicular |
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| center of ship (longitudinally), located at the midpoint between FP and AP |
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| LBP |
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| Length Between Perpendiculars measured parallel to BL |
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| Mean Draft |
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| Average between fwd and aft drafts |
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| Determination of Hog/Sag |
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| mean draft compared to midship draft |
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| Hogging |
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| mean draft is > mid ship draft (which is actual draft of vsl) |
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| Sagging |
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| mean draft < midship draft (which is actual draft of vsl) |
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| Static Hog/Sag |
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| Hog/Sag caused by cargo load |
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| Dynamic Hog/Sag |
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| Hog/Sag caused by crest & trough of wave under hull |
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| Reading Draft Marks |
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| Bottom of number is even top is + 6 inches middway is + 3 inches |
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| 2 primary types of tonnage |
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| volume weight |
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| volumetric tonnage |
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| used to determine vsl earning capacity from 13 cen "tun" - wine cask equal to 100 cubic feet |
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| Volumetric tonnage determines... |
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| port fees, dock fees, dry dock chgs idea is to base fees on ability to earn |
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| Gross Tonnage |
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| entire volume of the inside of the hull from main deck down to keel |
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| Net Tonnage |
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| Remaining tonnage after non-earning spaces are removed from Gross ex tanks, foc'sle, psgr above main deck |
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| Tonnage Openings |
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| Nominally water tight; no gasket secured via bolt hooks (old wood battens) allows for space deduction from gross |
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| Non earning spaces |
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| doublebottoms fore/aft peak if water ballast only poopdeck, bridge, foc'sle w/ tonnage openings |
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| tonnage % rule |
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| design machinery space btwn 13 & 20% of total gross tonnage and 32% may be deducted |
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| cubic ft required per crewman |
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| 120 cu ft 16 sq ft |
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| weight tonnages |
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| displacement tons deadweight tons lightship tonos |
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| Displacement tons |
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| weight of water displaced by hull exactly equal to ships weight |
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| deadweight tons |
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| amount of water cargo fuel and stores a vessel can carry fully loaded |
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| lightship tons |
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| weight of empty ship displacement of vessel w/ no cargo crew stores fuel water or ballast |
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| Lightship tons + deadweight tons = ? |
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| Displacement tons |
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| volumetric tonnage: 1 ton = ? |
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| 100 cubic feet |
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| weight tonnage: long ton short ton metric ton |
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| long = 2240 pounds short = 2000 pounds metric = 2204.6 pounds (1,000 kg) |
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| 4 general categories of steel items used in shipbuilding |
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| beams plates columns shafts |
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| hull girder |
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| coordinated functions of all 4 groups of steel used in shipbuilding |
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| trochoidal wave |
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| length from crest to crest = length of vsl height = 1/20 length of vessel use of wave this size determines max load on hull girdle & scantling requirements |
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| Load |
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| total force acting on structure, usually expressed in pounds or tons |
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| Stress |
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| force per unit area, usually expressed in pounds/tons per square inch |
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| strain |
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| distortion resulting from stress |
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| tensile stress |
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| occurs between 2 parts of a body when each draws the other end toward itself |
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| equation for tensile stress |
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| Tensile Stress = Pull / Area Ts = P/A |
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| compressive stress |
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| opposite of tensile stress Cs = push/area |
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| shearing stress |
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| tendency of one body to slide over another body magnitude of this tendency at any point is termed shearing stress |
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| shear stresss equation |
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| pull/area of rivet |
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| Mild steel: ultimate tensile strength ultimate shearing strength |
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| ult ts = 28-32 tons per sq inch ult ss = 22 tons per sq inch |
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| steel flattens when... |
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| compressed at about 18 tons per sq inch |
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| limit of elasticity |
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| point at which metal will no longer return to its original shape |
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| yield overcome |
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| metal hardens, slight additional weight stretches it out of proportion until reaches ultimate strength, then fails |
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| standard factor of safety |
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| 4 |
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| local strength |
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| strength of individual parts of the ship |
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| hull girder strength |
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| strength of ship as a whole |
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| Bending moment |
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| A moment of a force about any line is the product of the force times the perpendicular distance to that line |
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| Bending moment: 100 lbs located 4' from end of board imbedded in a wall = |
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| weight x distance 100 lbs x 4' = 400 ft-lbs |
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| Bending moment: 100 lbs located 8' from end of board imbedded in wall |
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| BM = weight x distance BM = 100 lbs x 8' BM = 800 ft lbs |
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| Beams |
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| Horizontal strength members loaded vertically |
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| Load applied to center of beam causes... upper surface must be under... lower surface must be under... |
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| ...deflection ...compression ...tension |
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| zero point |
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| layer in deflected beam where compression & tension are neutral located along center of gravity (centroid) |
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| beam made up of 5 individual layers (versus solid beam) |
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| will only carry 1/5 load vs solid top 2 will NOT be under compression bottom 2 will NOT be tension middle will NOT be nuetral |
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| depth of solid beam... |
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| ...determines resistance/strength. AKA larger distance from neutral axis to edges = stronger beam |
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| 5 factors determine size of beam |
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| 1 type & amount of load on beam 2 distance btwn supports 3 type and efficiency of end connects 4 number of supports 5 material beam is made of |
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| type & efficiency of end connections |
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| A) fixed-ended rectangular beam supports twice as much concentrated load as free ended B) deflection of fixed ended rect beam is 1/4th that of free ended |
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| effect of number of supports |
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| greater # of supports in given distance equals shorter span. shorter span equals smaller bending moment. |
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| beam materials |
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| most ship construction is mild grade steel other materials: stainless steel high tensile steel aluminum |
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| columns |
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| strut placed such that it is loaded vertically (also referred to as stanchion or pillar) usually symmetrical (round) |
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| shafts subjected to twisting motion... |
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| ...said to be in torsion twisting moment = torque |
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| Torque equation |
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| horsepower x 5252 / RPM |
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| continuity of strength |
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| vessels must be constructed so that stresses may be graduallly and continuously dissipated no part over/undersized discontinuity or change in shape = stresses = failure |
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| most common welding... |
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| ...fusion welding 6,000 degrees F usually electric arc, gas less common |
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| In the 1930's welding... |
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| ...starts to replace other joining methods. By WWII it has replaced them almost completely. |
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| discontinuity |
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| main cause of cracks aboard ships. ex hatches, port openings, faulty welds |
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| secondary causes of fractures |
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| low temp, unusually high bending moments, heavy seas |
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| keel |
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| backbone. ties together transverse bottom members. absorbs large portions of stresses from hull girder action. |
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| 4 types of keels |
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| bar keel. flat plate keel. box keel. bilge keel. |
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| bar keel (hanging keel) |
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| olderships. protects when grounded. 1st pt contact. reduced rolling. disadvantages: increased draft no xtra cargo space. |
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| flat plate keel |
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| utilizes increased shell plate thickness allowing it and components to better withstand dry docking /grounding loads. resembles i beam |
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| transverse bulkheads assist... |
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| ...in supporting keel and bottom by transforming long flexible girder into shorter length |
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| box (duct) keel |
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| act as conduit for wires/cables. allows access into other areas of double bottom. |
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| bilge keels |
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| fin like pieces of steel plate fitted to hull at turn of bilge along midship length . reduce rolling in heavy seas. NOT for stability. |
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| 2 types of drydock |
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| floating & graving |
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| Bottom structure acts as ________ |
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| lower flange |
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| ______ along with ________ acts to resist longitudinal stresses from passing over highs and lows of waves. |
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| Bottom structure; keel |
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| Bottom structure must be strong enough to withstand concentrated pressures due to _____, ____, and _____ |
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| dry docking, grounding, weight of cargo |
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| Floors |
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| transverse vertical frames across bottom of hull; not equal to house floors |
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| 5 features of ship floors |
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| vertical transverse extend across ship from bilge to bilge usually at every frame (rib) |
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| strength ring |
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| floors, deck beams, beam brackets, frames |
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| hull girder |
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| structure formed by entire vessel (similar to duct keel) |
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| 3 types of floors |
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| closed, solid, open (bracket) |
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| 4 features of closed floors |
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| steel plating tank end members water/oil tight pierced by piping then seal welded |
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| 3 features of solid floors |
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| lightening holes air holes limber holes |
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| 3 features of lightening holes |
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| allow access (maitnc/inspection) reduce weight cut across neutral access |
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| 3 features of air holes |
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| located at top of floor allow air to escape/enter during filling/emptying allow equalization of pressure |
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| limber holes purpose is... |
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| drainage holes |
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| open floors (3 things) |
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| constructed from plain angle 25% lighter vs solid floors not allowed under mach spaces or areas subjected to heavy pounding loading/discharging |
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| Double bottom |
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| compartment at bottom of ship between inner bottom (tank top) and outer bottom; cellular like an ice cube tray |
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| advantages of double bottom vs single |
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| stronger tanks can be used to carry fuel & ballast structure can withstand grounding and not flood holds/mach spaces as long as inner bottom remains intact better resists pollution |
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| Frame |
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| One of the ribs forming the skeleton of the ship |
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| intercostal |
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| longitudinal version of floors (which are horizontal) |
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| Two primary types of framing |
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| Transverse Longitudinal |
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| Large vessels (greater than 120 m) may be framed... |
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| longitudinally framed on the bottom shell and transversely framed on the side shell. |
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| 2 features of transverse framing |
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| Act as stiffeners holding the side shell plating against external water pressure Furnish vertical support to the outboard ends of the beams supporting the decks |
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| Transverse framing leads to greater or lesser number of frames within the hull? Frame spacing? |
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| greater; spaced 2-3 feet apart (less at bow and stern for strength) |
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| Transverse framing maximizes ____ ____ capacity. |
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| bale cubic |
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| Advantages of Longitudinal Framing? |
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| greater longitudinal strength, reduced vibration, weight savings, cost savings |
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| Disadvantages longitudinal framing? |
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| loss of bale cubic due to depth of web frames |
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| longitudinals made from either _____ or ____ brackets welded to shell plating |
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| bulb; L |
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| Panting Frame |
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| Additional framing in bow area to distribute the panting stresses encountered in seaway |
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| Boss Frame |
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| Curved frame designed to accomodate the prop shaft and housing |
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| Shell plating purpose |
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| keep water out tie together ship framework resist longitudinal bending stresses |
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| strake |
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| shell plating arranged longitudinally, one plate after another in a row |
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| 3 types of shell plating |
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| flat plate rolled plate furnaced plate |
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| rolled plates |
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| curvature in only one direction most often @ turn of bilge |
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| furnaced plates |
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| curvature in two directions must be heated and shaped over form most expensive; avoided as much as possible |
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| shell plates girth greater or lesser at mid ship than at ends? results in? |
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| greater; results in excess plating at ends |
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| drop strake |
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| when 2 rows of shell come together,top strake is dropped (called dropped strake), lower row remains (called through strake) |
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| stealer plate |
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| "new" single plate that butts up against drop strake and through strake |
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| Butt |
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| transverse joint between plates |
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| seam |
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| longitudinal joint between plates |
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| sheer strake |
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| top strake that joins with deck plating |
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| garboard strake |
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| first strake after keel plate |
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| thickened plates (where)? |
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| sheer strake, keel plates, bottom forward plates, bottom & bilge plates, margin plates, deck stringer |
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| deck stringer |
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| outboard most strake on deck |
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| on shell expansion plan, lettering runs from _____ and up, and numbering runs from _____ ______ |
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| keel strake; from aft forward |
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| Deck beams are... |
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| athwart ship members located under deck plating |
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| Deck beams usually fitted.... |
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| ...on every frame |
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| frames act as ______ |
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| pillars |
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| frames carry load _____ , where it is distributed over the bottom by the ______. |
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| downward; floors |
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| 3 primary functions of beams |
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| act as beam to support vertical deck loads acts as a tie to keep the sides of a shp in place acts to keep the deck plating from wrinkling due to racking |
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| racking |
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| twisting action on vessel as the ship sails at an angle to a heavy sea |
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| weather deck beams are of _____ scantling then would be used elsewhere |
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| heavier |
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| beam size depends on these other structural members of the vessel... |
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| pillars girders thickness of plating height between deck |
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| Camber is measured... |
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| ...at the centerline |
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| standard camber? |
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| 1/50th of beam |
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| bow sheer |
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| .2(length of ship)+20 |
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| stern sheer |
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| 1/2 of bow sheer |
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| What are the purpose of cant frames in steel vessels? |
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| provide strength to shell plating at stern |
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| what is a stanchion? |
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| a vertical strength member |
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| what are the synonyms for pillar? |
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| post stanchion column |
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| why should pillars always be fitted in a vertical line? |
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| To transmit load directly down to the keel, and not onto beams and deck plates. |
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| why is a pillar fitted under the windlass? |
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| to absorb the stress, vibration, and weight of the windlass |
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| what is a partial bulkhead |
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| bulkhead that does not extend across a compartment; used to strengthen the structure |
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| what three things does the size of a pillar depend on? |
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| load, location, and length |
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| How does acceleration affect the size of the pillar? |
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| dynamic load can be double the static load |
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| what is the purpose of deck girders? |
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| support deck beams by reducing span |
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| why should pillars be well protected when cargo is loaded/unloaded? |
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| to prevent damage, bent pillars provide little to no vertical support |
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| what is the purpose of wood sheathing |
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| insulates - wood has low heat transmission absorbs damage and protects deck keeps outer decks cool for passengers prevents sweating due to rapid temp change under deck add aesthetic value to appearance of ship |
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| what is the purpose of the stringer plate? |
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| thicker outboard plating to prevent racking and provide support for cargo hatchess |
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| why should corners of all hulls cut into the strength deck be rounded, doubled, or both? |
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| to prevent cracks and notches from forming due to stress |
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| differentiate between side stringer, girder, and longitudinal |
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| side stringer: longitudinal strength member inside deck plating longitudinal: fore and aft strength members in bottom structure girder: fore and aft longitudinal strength members supporting decks |
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| functions of bulkheads? |
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| provide additional vertical support & act as structural diaphragms to resist racking create fire & flooding boundaries |
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| what is a 2 compartment ship? |
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| A ship that can be flooded in 2 compartments and stay afloat |
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| max number of passengers a merchant ship can carry without being considered a passenger vessel? |
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| 12 |
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| what is the maximum distance the collision bulkhead can be from the stem? |
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| 1/20th the vessel length at summer load line |
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| what are the functions of the stem? |
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| vertical extension of the keel gives strength and rigidity to hull along center-line ties shell plating gives rigidity to entire bow |
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| advantages of a clipper bow? |
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| additional space and buoyancy flare throws water away from bow when headed into heavy seas |
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| what is the function of the stern frame? |
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| vertical extension of the keel provides strength for rudder and single prop ties shell plating together at stern |
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| pillars give vertical support to... |
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| girders deck beams decks heavy concentrated loads: ground tackle, anchor windlass, line handling winches, capstains |
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| why place pillar under deck beam or girder? |
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| redices deflection by reducing span relieves stress on beam brackets & transverse frames |
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| top/bottom of pillar (names)? |
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| top: head bottom: heel |
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| purpose of doubling plate at bottom of pillars? |
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| to spread the load over larger portion of deck plating |
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| ideal depth of beam brackets |
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| 2.5 times depth of beam |
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| purpose of upper deck? |
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| increases seaworthiness by forming watertight top of hull and contributes strength by acting as upper flange of hull girder |
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| purpose of lower deck? |
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| working platforms for operation of machinery and loading of cargo living spaces for passengers and crew |
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| Additional purpose of all decks |
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| serve as horizontal diaphram, keeping the ship in shape longitudinally |
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| Girder stress concentration? |
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| amidships and outboard |
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| 2 methods of insulation on ships? |
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| insulation bats fixed to underside of deck via wire studs spray on insulation applied directly to steel deck |
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| purpose of insulation? |
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| insulate space prevent sweating noise barrier in engine room decks and bulkheads on passenger vessels |
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| deck coverings |
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| paint cement composite that flexes with deck carpet, tile or linoleum over top of cement composite |
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| bulkhead construction |
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| flat plate steel or corrugated (adds strength, reduces need for additional framing) |
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| collision bulkhead |
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| acts as auxiliary watertight bow in event actual bow is punctured in collision |
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| afterpeak bulkhead |
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| encloses shaft in watertight compartment required on all screw type vessels prevents broken prop shaft from flooding aft section of vessel |
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| machinery space bulkheads |
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| enclose machinery spaces - watertight regulatory requirement due to large through-hulls in engine rooms |
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| 3 bulkheads required by regulation |
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| collision bulkhead afterpeak bulkhead machinery space bulkhead |
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| Bulkheads are usually plated... |
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| horizontally |
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| plate thickness thicker towards the bottom of the ship.. |
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| due to increased water pressure |
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| Why are longitudinal bulkheads avoided |
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| danger of capsizing due to collision and flooding of one side of the ship but they are seen in tankers |
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| longitudinal bulkheads in tankers |
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| single hull: port and starboard longitudinal bulkheads form boundaries between port, center, and stbd tanks double hull: usually only centerline longitudinal bulkhead |
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| 3 major types of bows? |
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| plumb clipper spoon |
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| plumb bow |
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| straight up and down classic passenger ship, aided with riveted construction |
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| clipper bow |
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| flared bow, extra space and buoyancy, throws water when headed into seas |
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| spoon bow |
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| ice breaker, allows bow to ride up on ice and break it with the weight of the vessel |
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| forefoot |
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| curved connection between stem and keel sometimes cast |
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| solid stem bar |
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| lower stem section joining forefoot to upper stem |
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| rolled plate |
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| plate heated and rolled to form plating around upper stem |
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| breasthook |
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| triangular plate that joins plating and reinforces the solid stem bar |
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| peak tank/forepeak tank |
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| located forward of collision bulkhead serves as forwardmost ballast tank exerts greatest moment for trim changes, good for lessening sag |
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| components of forepeak tank |
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| valves and piping reach rods to open and close valves swash bulkheads reduce wave motion, can be longitudinally or transverse (generally longitudinal) |
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| Bulbous bow - what vessel speed? |
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| higher vessel speed - improves vessel flow through water, overcomes wave making resistance acts to fill in trough of bow wave = less power needed to reach medium/high speed |
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| two primary types of sterns |
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| cruiser: rounded, requires cant frames and beams to make curve. older construction transom: flat, modern construction cuz its cheaper, and waterline is carried further aft |
