# ship structure final – Flashcards

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 equation for stress
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 ultimate tension for steel (tension & shear)
 tension: 30 sq in shear: 22 sq in
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 equation for bending moment (fixed beam)
 distance x length
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 equation for bending moment (concentrated load, unsupported ends)
 mass x length / 4
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 equation for bending moment (uniform load, unsupported ends)
 mass x length / 8
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 A _____ end beam will support _____ times the amount of load vs a _____ end beam
 fixed; 2; free
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 The deflection of a _____ ended rectangular beam is only _____ the deflection of a ____ ended beam
 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
 1/5
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 Relative strength equation (beams)
 (D_larger/D_smaller)squared x original
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 comparing deflection equation
 (S_long/S_short)cubed, result x original deflection
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 relative strength of beams
 original length/new length x original load
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 torque equation
 HP x 5252 / RPM
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 LOA
 Length Overall; Linear distance from bow to stern, measured parallel to baseline
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 Sheer
 Longitudinal curvature of vessel's deckgreater fwd than aftincreases buoyancy w/ air space
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 Beam
 Width of a Ship
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 Extreme Beam
 Width + projections (bridgewing, gangway, etc)
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 Tumble Home
 inward slope of the ships sidemeasured widest beam less narrowest beam
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 Flare
 opposite of tumblehomeoutward slope of ships side"dryer decks," throws waves from bowcreates space/lessens impact force of water
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 Draft
 vert distance from lowest part of hull to waterlineindicated fwd aft amidships
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 air draft
 distance from highest point to waterlineimportant re: bridge clearanceschanges due to ballast
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 Camber
 Transverse slope of deckdirects water to drains at sidesnot specifically for added strength
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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
 vertical distance from the lowest point of the hull to the side of the deck to which it is referreddepth = draft + freeboard
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 Molded Dims
 Dimensions taken from inside plating of a shipimportant for cargo stowage
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 Freeboard
 distance measured vertically downard, at the side of vessel amidships, from upper edge of deckline to waterline
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 Divisions of Hull
 Middle BodyEntranceRun
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 Middle Body
 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
 immersed part of the hull fwd of middle bodyexpensive to build cuz it's curvy
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 Run
 immersed part of hull aft of middle bodywhere thrust is applied from propwhere torque is applied from rudder
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 parallel mid bodies
 cheapest to build, hold most cargo
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 LC overlaid (symbol)
 symbol for centerline plane
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 Reference Planes
 Used as an aid in locating points for design & building
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 Baseline Plane
 established near base of shipruns thru upper edge of flat plate keelvert dims measured from this ref point
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 Centerline Plane
 fore-aft (longitudinal)at right angles to BLhull shape essentially symmetrical on either side of CL
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 Transverse Vertical Planes
 at equal intervals along length of vesselaka frame stationsmay NOT be equal to actual frame locations
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 Forward Perpendicular (FP)
 line perpendicular to BL, intersecting the fwd edge of the stem at the design waterline
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 After Perpendicular
 perpendicular to the baseline, intersecting the after end of the rudder post at the design waterline
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 Mid-Ship Perpendicular
 center of ship (longitudinally), located at the midpoint between FP and AP
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 LBP
 Length Between Perpendicularsmeasured parallel to BL
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 Mean Draft
 Average between fwd and aft drafts
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 Determination of Hog/Sag
 mean draft compared to midship draft
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 Hogging
 mean draft is > mid ship draft (which is actual draft of vsl)
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 Sagging
 mean draft < midship draft (which is actual draft of vsl)
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 Static Hog/Sag
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 Dynamic Hog/Sag
 Hog/Sag caused by crest & trough of wave under hull
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 Bottom of number is eventop is + 6 inchesmiddway is + 3 inches
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 2 primary types of tonnage
 volumeweight
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 volumetric tonnage
 used to determine vsl earning capacityfrom 13 cen "tun" - wine caskequal to 100 cubic feet
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 Volumetric tonnage determines...
 port fees, dock fees, dry dock chgsidea is to base fees on ability to earn
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 Gross Tonnage
 entire volume of the inside of the hull from main deck down to keel
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 Net Tonnage
 Remaining tonnage after non-earning spaces are removed from Grossex tanks, foc'sle, psgr above main deck
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 Tonnage Openings
 Nominally water tight; no gasketsecured via bolt hooks (old wood battens)allows for space deduction from gross
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 Non earning spaces
 doublebottomsfore/aft peak if water ballast onlypoopdeck, bridge, foc'sle w/ tonnage openings
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 tonnage % rule
 design machinery space btwn 13 & 20% of total gross tonnage and 32% may be deducted
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 cubic ft required per crewman
 120 cu ft16 sq ft
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 weight tonnages
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 Displacement tons
 weight of water displaced by hullexactly equal to ships weight
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 amount of water cargo fuel and stores a vessel can carry fully loaded
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 lightship tons
 weight of empty ship displacement of vessel w/ no cargo crew stores fuel water or ballast
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 Lightship tons + deadweight tons = ?
 Displacement tons
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 volumetric tonnage: 1 ton = ?
 100 cubic feet
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 weight tonnage: long tonshort tonmetric ton
 long = 2240 poundsshort = 2000 poundsmetric = 2204.6 pounds (1,000 kg)
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 4 general categories of steel items used in shipbuilding
 beams platescolumns shafts
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 hull girder
 coordinated functions of all 4 groups of steel used in shipbuilding
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 trochoidal wave
 length from crest to crest = length of vslheight = 1/20 length of vesseluse of wave this size determines max load on hull girdle & scantling requirements
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 total force acting on structure, usually expressed in pounds or tons
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 Stress
 force per unit area, usually expressed in pounds/tons per square inch
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 strain
 distortion resulting from stress
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 tensile stress
 occurs between 2 parts of a body when each draws the other end toward itself
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 equation for tensile stress
 Tensile Stress = Pull / AreaTs = P/A
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 compressive stress
 opposite of tensile stressCs = push/area
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 shearing stress
 tendency of one body to slide over another bodymagnitude of this tendency at any point is termed shearing stress
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 shear stresss equation
 pull/area of rivet
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 Mild steel:ultimate tensile strengthultimate shearing strength
 ult ts = 28-32 tons per sq inchult ss = 22 tons per sq inch
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 steel flattens when...
 compressed at about 18 tons per sq inch
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 limit of elasticity
 point at which metal will no longer return to its original shape
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 yield overcome
 metal hardens, slight additional weight stretches it out of proportion until reaches ultimate strength, then fails
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 standard factor of safety
 4
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 local strength
 strength of individual parts of the ship
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 hull girder strength
 strength of ship as a whole
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 Bending moment
 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 =
 weight x distance100 lbs x 4' = 400 ft-lbs
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 Bending moment: 100 lbs located 8' from end of board imbedded in wall
 BM = weight x distanceBM = 100 lbs x 8'BM = 800 ft lbs
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 Beams
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 Load applied to center of beam causes...upper surface must be under...lower surface must be under...
 ...deflection...compression...tension
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 zero point
 layer in deflected beam where compression & tension are neutrallocated along center of gravity (centroid)
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 beam made up of 5 individual layers (versus solid beam)
 will only carry 1/5 load vs solidtop 2 will NOT be under compressionbottom 2 will NOT be tensionmiddle will NOT be nuetral
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 depth of solid beam...
 ...determines resistance/strength. AKA larger distance from neutral axis to edges = stronger beam
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 5 factors determine size of beam
 1 type & amount of load on beam2 distance btwn supports3 type and efficiency of end connects4 number of supports5 material beam is made of
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 type & efficiency of end connections
 A) fixed-ended rectangular beam supports twice as much concentrated load as free endedB) deflection of fixed ended rect beam is 1/4th that of free ended
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 effect of number of supports
 greater # of supports in given distance equals shorter span. shorter span equals smaller bending moment.
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 beam materials
 most ship construction is mild grade steelother materials: stainless steelhigh tensile steelaluminum
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 columns
 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...
 ...said to be in torsiontwisting moment = torque
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 Torque equation
 horsepower x 5252 / RPM
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 continuity of strength
 vessels must be constructed so that stresses may be graduallly and continuously dissipatedno part over/undersizeddiscontinuity or change in shape = stresses = failure
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 most common welding...
 ...fusion welding6,000 degrees Fusually electric arc, gas less common
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 In the 1930's welding...
 ...starts to replace other joining methods. By WWII it has replaced them almost completely.
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 discontinuity
 main cause of cracks aboard ships. ex hatches, port openings, faulty welds
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 secondary causes of fractures
 low temp, unusually high bending moments, heavy seas
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 keel
 backbone. ties together transverse bottom members. absorbs large portions of stresses from hull girder action.
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 4 types of keels
 bar keel. flat plate keel. box keel. bilge keel.
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 bar keel (hanging keel)
 olderships. protects when grounded. 1st pt contact. reduced rolling. disadvantages: increased draft no xtra cargo space.
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 flat plate keel
 utilizes increased shell plate thickness allowing it and components to better withstand dry docking /grounding loads. resembles i beam
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 ...in supporting keel and bottom by transforming long flexible girder into shorter length
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 box (duct) keel
 act as conduit for wires/cables. allows access into other areas of double bottom.
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 bilge keels
 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
 floating & graving
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 Bottom structure acts as ________
 lower flange
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 ______ along with ________ acts to resist longitudinal stresses from passing over highs and lows of waves.
 Bottom structure; keel
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 Bottom structure must be strong enough to withstand concentrated pressures due to _____, ____, and _____
 dry docking, grounding, weight of cargo
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 Floors
 transverse vertical frames across bottom of hull; not equal to house floors
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 5 features of ship floors
 verticaltransverseextend across shipfrom bilge to bilgeusually at every frame (rib)
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 strength ring
 floors, deck beams, beam brackets, frames
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 hull girder
 structure formed by entire vessel (similar to duct keel)
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 3 types of floors
 closed, solid, open (bracket)
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 4 features of closed floors
 steel platingtank end memberswater/oil tightpierced by piping then seal welded
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 3 features of solid floors
 lightening holesair holeslimber holes
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 3 features of lightening holes
 allow access (maitnc/inspection)reduce weightcut across neutral access
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 3 features of air holes
 located at top of floorallow air to escape/enter during filling/emptyingallow equalization of pressure
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 limber holes purpose is...
 drainage holes
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 open floors (3 things)
 constructed from plain angle25% lighter vs solid floorsnot allowed under mach spacesor areas subjected to heavy pounding loading/discharging
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 Double bottom
 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
 strongertanks can be used to carry fuel & ballaststructure can withstand grounding and not flood holds/mach spaces as long as inner bottom remains intactbetter resists pollution
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 Frame
 One of the ribs forming the skeleton of the ship
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 intercostal
 longitudinal version of floors (which are horizontal)
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 Two primary types of framing
 TransverseLongitudinal
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 Large vessels (greater than 120 m) may be framed...
 longitudinally framed on the bottom shell and transversely framed on the side shell.
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 2 features of transverse framing
 Act as stiffeners holding the side shell plating against external water pressureFurnish 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?
 greater; spaced 2-3 feet apart (less at bow and stern for strength)
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 Transverse framing maximizes ____ ____ capacity.
 bale cubic
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 greater longitudinal strength, reduced vibration, weight savings, cost savings
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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
 bulb; L
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 Panting Frame
 Additional framing in bow area to distribute the panting stresses encountered in seaway
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 Boss Frame
 Curved frame designed to accomodate the prop shaft and housing
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 Shell plating purpose
 keep water outtie together ship frameworkresist longitudinal bending stresses
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 strake
 shell plating arranged longitudinally, one plate after another in a row
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 3 types of shell plating
 flat platerolled platefurnaced plate
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 rolled plates
 curvature in only one directionmost often @ turn of bilge
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 furnaced plates
 curvature in two directionsmust be heated and shaped over formmost expensive; avoided as much as possible
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 shell plates girth greater or lesser at mid ship than at ends? results in?
 greater; results in excess plating at ends
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 drop strake
 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
 "new" single plate that butts up against drop strake and through strake
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 Butt
 transverse joint between plates
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 seam
 longitudinal joint between plates
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 sheer strake
 top strake that joins with deck plating
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 garboard strake
 first strake after keel plate
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 thickened plates (where)?
 sheer strake, keel plates, bottom forward plates, bottom & bilge plates, margin plates, deck stringer
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 deck stringer
 outboard most strake on deck
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 on shell expansion plan, lettering runs from _____ and up, and numbering runs from _____ ______
 keel strake; from aft forward
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 Deck beams are...
 athwart ship members located under deck plating
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 Deck beams usually fitted....
 ...on every frame
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 frames act as ______
 pillars
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 frames carry load _____ , where it is distributed over the bottom by the ______.
 downward; floors
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 3 primary functions of beams
 act as beam to support vertical deck loadsacts as a tie to keep the sides of a shp in placeacts to keep the deck plating from wrinkling due to racking
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 racking
 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
 heavier
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 beam size depends on these other structural members of the vessel...
 pillarsgirdersthickness of platingheight between deck
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 Camber is measured...
 ...at the centerline
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 standard camber?
 1/50th of beam
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 bow sheer
 .2(length of ship)+20
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 stern sheer
 1/2 of bow sheer
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 What are the purpose of cant frames in steel vessels?
 provide strength to shell plating at stern
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 what is a stanchion?
 a vertical strength member
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 what are the synonyms for pillar?
 poststanchioncolumn
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 why should pillars always be fitted in a vertical line?
 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?
 to absorb the stress, vibration, and weight of the windlass
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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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 How does acceleration affect the size of the pillar?
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 what is the purpose of deck girders?
 support deck beams by reducing span
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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
 insulates - wood has low heat transmissionabsorbs damage and protects deckkeeps outer decks cool for passengersprevents sweating due to rapid temp change under deckadd aesthetic value to appearance of ship
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 what is the purpose of the stringer plate?
 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?
 to prevent cracks and notches from forming due to stress
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 differentiate between side stringer, girder, and longitudinal
 side stringer: longitudinal strength member inside deck platinglongitudinal: fore and aft strength members in bottom structuregirder: fore and aft longitudinal strength members supporting decks
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 provide additional vertical support & act as structural diaphragms to resist rackingcreate fire & flooding boundaries
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 what is a 2 compartment ship?
 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?
 12
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 what is the maximum distance the collision bulkhead can be from the stem?
 1/20th the vessel length at summer load line
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 what are the functions of the stem?
 vertical extension of the keelgives strength and rigidity to hull along center-lineties shell platinggives rigidity to entire bow
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 additional space and buoyancyflare throws water away from bow when headed into heavy seas
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 what is the function of the stern frame?
 vertical extension of the keelprovides strength for rudder and single propties shell plating together at stern
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 pillars give vertical support to...
 girdersdeck beamsdecksheavy concentrated loads: ground tackle, anchor windlass, line handling winches, capstains
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 why place pillar under deck beam or girder?
 redices deflection by reducing spanrelieves stress on beam brackets & transverse frames
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 top/bottom of pillar (names)?
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 purpose of doubling plate at bottom of pillars?
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 ideal depth of beam brackets
 2.5 times depth of beam
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 purpose of upper deck?
 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?
 working platforms for operation of machinery and loading of cargoliving spaces for passengers and crew
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 serve as horizontal diaphram, keeping the ship in shape longitudinally
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 Girder stress concentration?
 amidships and outboard
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 2 methods of insulation on ships?
 insulation bats fixed to underside of deck via wire studsspray on insulation applied directly to steel deck
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 purpose of insulation?
 insulate spaceprevent sweatingnoise barrier in engine room decks and bulkheads on passenger vessels
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 deck coverings
 paintcement composite that flexes with deckcarpet, tile or linoleum over top of cement composite
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 acts as auxiliary watertight bow in event actual bow is punctured in collision
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 encloses shaft in watertight compartmentrequired on all screw type vesselsprevents broken prop shaft from flooding aft section of vessel
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 enclose machinery spaces - watertightregulatory requirement due to large through-hulls in engine rooms
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 horizontally
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 plate thickness thicker towards the bottom of the ship..
 due to increased water pressure
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 danger of capsizing due to collision and flooding of one side of the shipbut they are seen in tankers
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 single hull: port and starboard longitudinal bulkheads form boundaries between port, center, and stbd tanksdouble hull: usually only centerline longitudinal bulkhead
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 3 major types of bows?
 plumbclipperspoon
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 plumb bow
 straight up and downclassic passenger ship, aided with riveted construction
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 clipper bow
 flared bow, extra space and buoyancy, throws water when headed into seas
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 spoon bow
 ice breaker, allows bow to ride up on ice and break it with the weight of the vessel
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 forefoot
 curved connection between stem and keelsometimes cast
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 solid stem bar
 lower stem section joining forefoot to upper stem
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 rolled plate
 plate heated and rolled to form plating around upper stem
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 breasthook
 triangular plate that joins plating and reinforces the solid stem bar
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 peak tank/forepeak tank
 located forward of collision bulkheadserves as forwardmost ballast tankexerts greatest moment for trim changes, good for lessening sag
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 components of forepeak tank