As we already discussed, the bottom shell may be transversely or longitudinally framed, longitudinal framing being preferred particularly for vessels exceeding 120m in length.
The side shell is supported by frames which run vertically from the tank margin to the upper deck. These frames are in the form of bulb plates.
A ship is subjected to tremendous stresses while at sea. This requires special strengthening of the ship's plating. The shell plating of the ship is not strong enough to withstand all these stresses on its own and required to be framed throughout its length.
The main stiffening members used in ship framing are,
Beam: A beam is a structural element that increases load bearing capability and avoids bending of the structure. Under deck runs transversely
Frame: On side plating, running vertically up and down (see dia)
Floors: On the double bottom we already discussed
Stringers: On Side Plating and longitudinal bulkheads, runs horizontally, fore and aft
Longitudinals: Longitudinal is a short name for longitudinal stiffners. These are mainly L shaped frames found on under decks, on side plating, on longitudinal bulkheads, on bottom platting and under the tank top.
Transverse: Transverse is the short name for “transverse stiffeners”. Transverse found under the deck is called deck transverse and the bottom platform is called bottom transverse. Runs transversely but much heavier in construction than beams.
Remember similar stiffeners have different names for different planes, refer below table
There are three type of Hull framing system:
> Transverse Framing System
> Longitudinal Framing System
> Combined or Mixed Framing System (Hybrids framing system)
Transverse Framing System
> This system of framing is used in vessels of relatively less in length, where longitudinal bending moments are not excessive.
> The framing system consists essentially of a ring of strengthening around the shell plating. Underdecks, deck beams are fitted at every frame space.
> On side plating frames are fitted to stiffen the shell plating.
> The deck beams are connected to the frames on the side by means of beam knees. Beam knees are very efficient connections as compared to joining the beam directly to the frame.
Bottom structure is already discussed in previous section
Longitudinal Framing System
> This is the most popular framing method in long ship usually exceeding 100m in length
> It is designed to withstand longitudinal bending moments.
> The main stiffeners are longitudinals which run the full length of the vessel from forward to aft parallel to keel..
> An L- shaped stiffener, which fit under the decks, on the side plating on the bottom plating under the tank top and on the longitudinal bulkheads as well
> In addition to longitudinals deck are stiffened with deck girders and deck transverse
> Side plating is stiffened with vertical webs and stringers
Combined Framing
> As you know, a purely longitudinal framed ship is very strong in the longitudinal direction and a transversely framed ship has tremendous transverse strength. The combined framing ships have the advantage of both longitudinal and transverse framing systems.
> In this type of framing system, under the decks and on bottom plating, the vessel is longitudinally framed.
> Side plating is transversely framed
