1. Floors and Double Bottoms

2. 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

3. 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

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

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

10. 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

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

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

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

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

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

21. 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

22. Solid Floors
limber holes
drainage holes

23. 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)

30. 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

31. Double Bottoms
Double bottoms may be Transversely or Longitudinally framed

36. 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