Floors and Double Bottoms

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

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

Ship floors are not equal to house floors not horizontal not like house floors Ship floors are not equal to house floors

Floors ship floors are vertical transverse extend across ship from bilge to bilge usually at every frame (rib)

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

Three Types of Floors closed floors solid floors open or bracket floors

Closed Floors constructed from plates of steel tank end members make tank boundaries watertight oil tight pierced only by piping, then seal welded

Solid Floors like closed floors in that they are fabricated from steel plate biggest difference is ...

Solid Floors biggest difference is that solid floors are not watertight or oil-tight solid floors have… lightening holes air holes limber holes

Solid Floors lightening holes allow access reduce weight for maintenance for inspection reduce weight cut along neutral axis

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

Solid Floors limber holes drainage holes

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)

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

Double Bottoms Double bottoms may be Transversely or Longitudinally framed

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