There are 3 type of bottom structure,
> Transversely Framed, Single Bottom
> Transversely Framed, Double Bottom
> Longitudinally Framed, Double Bottom
Transversely Framed Single Bottom
> The frames run transversely to the hull structure
> The plate floors act as transverse stiffeners, and their spans are reduced by the use of intercostal side girders that run longitudinally.
> To increase the bending stress all the plate floors are flanged at their top
Transversely Framed, Double Bottom
> Same linke single framed bottom frames run transversely
> This is used in ships of length less than 120 meters
> Transverse solid plate floors and bracket floors with transverse frames, provide the principal support for the inner bottom and bottom shell plating in this type framing
> The bracket floors form the transverse stiffeners at every frame, and plate floors are used at every 3 to 4 frame spaces, or 1.8 meters intervals.
> Intercostal girders or side girders, and plate floors will have lightening holes at regular intervals to reduce the structural weight, and will have manholes (flanged) to provide access.
> One intercostal side girder provides port and starboard where the ship’s breadth exceeds 10 m but does not exceed 20 m and two are fitted port and starboard where the ship’s breadth is greater.
Longitudinally Framed, Double Bottom
> Frames run longitudinally parallel to the keel of the ship
> One intercostal side girder is fitted port and starboard if the ship’s breadth exceeds 14 m, and where the breadth exceeds 21 m two are fitted port and starboard. These side girders always extend as far forward and aft as possible.
> The stiffeners running longitudinally on the bottom plating are called outer bottom longitudinals, and those that stiffen the tank top plating are called tank top longitudinals.
> At each three or four frame, there would be a plate floor to support the longitudinal. A bracker floor is placed at almost every frame, but it does not support the longitudinals.
Note: Longitudinally Framed single bottom does not exist because long ship more than 120m required double bottom