1 Floors and Double Bottoms
Jan 11, 2016
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Floors and Double Bottoms
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Floors and Double Bottoms
• Bottom Structure– acts as lower flange – along with the keel acts to resist longitudinal
stresses produced by the uneven support of hull by crests and “hollows” of waves at sea
– must be strong enough to withstand concentrated pressures due to dry docking, grounding, and the wgt. of cargo
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Floors
• some of the additional strength and stiffness comes from the “deepening” of transverse frames (ribs) across the bottom of the hull.
• these structural members are called floors
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Floors
• not horizontal
• not like house floors
•Ship floors are not equal to house floors
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Floors
• ship floors are– vertical– transverse– extend across ship– from bilge to bilge– usually at every frame (rib)
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Formation of the “Strength Ring”
• floors along with deck beams, beam brackets, and frames (ribs) complete the “strength ring”– The entire vessel hull forms a structure
similar to a duct keel– This structure is referred to as the hull
girder
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Three Types of Floors
• closed floors
• solid floors
• open or bracket floors
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Closed Floors
• constructed from plates of steel
• tank end members– make tank boundaries
• watertight
• oil tight
• pierced only by piping, then seal welded
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Solid Floors
• like closed floors in that they are fabricated from steel plate
• biggest difference is ...
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Solid Floors
• biggest difference is that solid floors are not watertight or oil-tight
– solid floors have…• lightening holes
• air holes
• limber holes
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Solid Floors
• lightening holes– allow access• for maintenance
• for inspection
– reduce weight– cut along neutral axis
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Solid Floors
• air holes– located at top of floor– allows air, to escape or enter , via vent pipes
(goose neck vents) when loading or discharging or when ballasting or de-ballasting
– air holes allow equalization of pressure • atmosphere escapes through goose neck vents
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Solid Floors
• limber holes– drainage holes
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Open Floors
• constructed mainly from plain angle
• 25% lighter then solid floors
• not allowed under machinery spaces
• not recommended under areas subjected to heavy pounding (from loading or discharging)
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Double Bottom
• compartment at the bottom of the ship between the inner bottom (tank top) and the outer bottom
• cellular (with many “bays”)– think...• ice cube tray
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Double Bottoms
Double bottoms may be Transversely or Longitudinally framed
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Double Bottom
• advantages over single-bottom construction– results in stronger bottom
– tanks can be used to carry fuel oil and ballast
– results in a structure which can withstand bottom damage from grounding, without flooding the holds or machinery spaces, so long as the inner bottom remains intact
– better resists pollution
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