ASSEMBLY OF SHELL PLATING

By:- JOPHIN JOSEPH NOUFAL P.NAJEEB SACHIN KUMAR SUBHENDU KUMAR SINGH

SHELL PLATING ASSEMBLY Identify the individual shell plates by

lettering of strake(starting from keel plate) around the girth to the shear strake.

Individual plating have coding related to eraction unit of which they are a part.

Particular shell plates may in some cases referred by name as example outer plate.

A plate having double curvature immediately below the transom floor and running into the fore side of the sternpost.

Shaping is mandatory after furnace heating Coffin and stealer plate used at ends.

PLATE AND SECTION PREPARATION

PANEL LINE ASSEMBLY Plate fitting:-Plates are moved by rollers and chain conveyors

to the fitting station, where they are fitted together manually and tack welded.

Standard size runoff tabs are added at the seams.Plate Welding: The panel is then conveyed to the seam

butt-welding station where adjustable copper backup bars are positioned according to the width of the plates. A line of magnets on each side of the backing bar holds the plate down on the conveyor bed. The backing bar is forced against the seam by air pressure. Flux is automatically supplied by the welding machine and removed manually after the welding is completed. The machines can weld up to three seams simultaneously, in plates up to one inch (2.5 cm) thick, with one pass.

One side SMW by flux copper back process used

Marking and Cutting: Plate is marked and cut to size at station. Marking of panels is done after welding to allow for neat cutting (i.e., to exact dimensions) of the panel.

After a panel has been welded, stiffener locations are marked. Cutting of deck openings, etc., is also carried out at this stage using semiautomatic and manual flame cutting equipment. The panels are then moved to the next station along the assembly area by crane.

SHELL PLATING 1.Deck plating2.Bottom plating3.Side shell plating

SIDE SHELL – EXTENDS FROM TURN OF THE BILGE TO TOP OF SHEER STRAKE

Side shell mainly consist of : 1.plates 2.stiffeners

FRAMING ARRANGEMENTS OF SIDE SHELL There are three type of framing

arrangement: 1.Longitudinal framing system 2.Transverse framing system 3.Combined framing system

The side shell along with bottom shell plating

provide the water tight skin and contribute to the longitudinal strength of the ship structure.

Because of the huge area the shell plating is composed of many strakes or plates arranged in fore and aft direction and welded together .

The several strakes are joined together as a part of unit by horizontal welds(seam) and vertical weld(butt)

The final structure must be capable of withstanding the many dynamic and static loads up to the hull

Internal strengthening of the shell plating both in longitudinal and transverse direction is designed to prevent collapse of the plating under various loads to which it is subjected.

LONGITUDINAL FRAMING SYSTEM - SHELL

TRANSVERSE FRAMING SYSTEM - SHELL

COMBINED FRAMING SYSTEM - SHELL

JOINING TECHNIQUES IN SIDE SHELL PANELING Welding is predominantly used joining

techniques in ship building Types of welding used in side shell paneling

are 1.Butt 2.Fillet 3.Lap In welding the shell platings forms a flush

skin with lesser resistance to motion through the water and also greater strength joining is possible using welding.

In modern ship construction methods adopted in shipyards are the possibility of shell butts to run in continuous lines across the strakes of plating.

FEATURES OF THE ASSEMBLY AND WELDING OF THE SHELL PLATING Special attention should be paid for fitting up

and welding of the side shell plating so maximum amount of welding is done with automatic machines .

The principles followed is that subdividing the panel of entire sections into separate parts .

Automatic welding is possible only in those areas where the inclination of weld does not exceed 15 degree or where the bed can be tilted so that automatic welding can be done.

Sometimes special reversable beds on composite moulds have to be used as opposed to the normal type of bed those reproduce the internal lines of the structure being assembled.

After they have been welded the sub sections are all laid on the same bed and fitted up for welding the butt joints and strake joints between them. In cases in which it is not possible not to use automatic welding they are fitted up for manual welding.

SIDE SHELL PLATE WITH 3D CURVATURE

PART OF SIDE SHELL ERECTED

TOWER TYPE SCAFFOLDING FOR SIDE SHELL ASSEMBLY

ASSEMBLY CONTINUED The outer plating of sections with complex

contours is fitted up for manual welding observing the correct gaps

The edges are bevelled according to thickness of the plates and the position in which the weld will be made

When each plate laid on the bed has been accurately positioned they are pressed by means of buckles against the supporting edges of the moulding bed and then tack welded to the plates which have already been placed in position.

As a rule the plates are not tack welded to rigid moulding plates.

ASSEMBLY CONTINUED The upper hand plates are first laid in position

and the position of their butt joints checked; the positions of the strakes edges over the half-breadth are also checked.

The plates making up adjoining regions are laid in position and assembly continues on both sides.

The edges are at same time are prepared for welding.

To ensure that the gap is uniform very thin strips, their thickness equal to the prescribed manual welding gap(for instance 2 mm)are sometimes inserted into joints between plates the dimension of which have been adjusted.

ASSEMBLY CONTINUED In order to secure the strake edges of sections

to the bed during welding screw clamps are used;these prevents the edge from bending inside section when frame is welded.

When shell plating is being assembled turn buckles and assembly bars are used,also fishtails and various types of screw and wedge clamps for proper alignment of butt joint.

To improve weld quality all tack weld made during fitting up must be of high quality done by highly qualified welder.

ASSEMBLY CONTINUED The gaps are checked after proper edge

preparation by means of special templates. When framings has been welded in position

sections are removed from the bed and overturned and the weld roots are dressed and the backing runs deposited in the shell plating.

These operations are only performed in the overhead position.

The weld root can be dressed and the edges prepared for depositing the reverse side head with pneumatic hammers, by flame planing with special blowpipes or by air.

BOTTOM SHELL PLATING Thickness and width of flat keel plate is

constant throughout length. Greater thickness than adjacent bottom

strake Strakes of bottom plating to the bilges have

reatrct thickness over 40% of length amidships.

Bottom plating tapers towards end. Panting/pounding allowances provided Thickness of shell plating depends on length

& also on frame spacing

SIDE SHELL PLATING Greater thickness over 40% length

amidships. Tapering also provided towards end. Provide enough increase in thickness at the

stern frame connection at any shaft bracket and in way of hawse pipes where canidreace chefing occurs

Further increase the thickness in panting region and in increased probability of shear load reason.

Special consideration for ice class vessels.

SIDE SHELL PLATING(CONTD.) Shear strake is provided with greater thickness

because of it’s distance from neutral axis. Special attention is required for welding and

cutouts. In case of rounded gunwale arrangement the

welding is permitted on the shear strake because of the high stress exposure which may result in formation of cracks.

Butt welding is adopted to prevent crack propagation (in the case of fillet weld).

All openings in the shell plating must have rounded corners and some form of composition to avoid discontinuity of strength

In every case the lenological process for fabricating block sections are precisely analogues with the standard building birth process.

In shell plating installation we have to consider the structural component associated with the shell plating and for this the framing system adopted and requirements should be known.

FRAMING SYSTEM Bottom shell may be transversely or

longitudinally framed. Longitudinal framing being preferred for

vessel having length greater than120 m. The side shell framing may also be

transversally or longitudinally framed, transverse framing is adopted in many cases :GC(optimum bale capacity needed)

When deep transverses are fitted bale capacity is considerably reduced.

In transverse framing the spacing should not be more than 1000 mm

FRAMING SYSTEM Between collision bulkheads and over 20% of ship’s length aft of

the two perpendiculars where where the ship’s depth exceeds 8.9 m,it should not be greater than 700mm.

But if depth is less than 8.9 m the frame spacing in this forward region will be decresed.within the cruise stern the frame spacing doesn’t exced 610mm.

Scantlings of main frames are primarily dependent on their depth and to some extent the rigidity of end connections.

In case of oil tankers/cargo deep tanks the side framing size will be increased except where supporting side stringers are fitted within tank spaces

Frame supporting hatch end beams and those in the way of transversers where the deck is frmaed longitudinally also have increased scantalings.

Very deep web frames are usualy fitted in the machinary space.

Web frames consisting of plate web and faceflat where the web is considerable deeper than conventional transverse frame are fitted in cargo holdes where top side wing tanks are fitted.here where tha top side wing tanks are fitted the web frame in the hold is in the line with the plate webs supporting the longitudinal in the top side tank.

In the tween decks above the after peak tank,web frames are required at every fourth frame space abaft the peak bulkhead

If the side shell is longitudinally framed offset bulb sections will be employed with the girder section scantlings at the lower side shell.

Direct continuity of strenght is to be mentioned,the upper longitudianl have the reast scantling and a uniform increase in size occurs down

The side shell untill the bilge is reached.the bilge longitudinals approaches that of the bottom shell.transverse webs are fitted to support the longitudinals.these being spaced not more than 3.7 m apart and increased strength if top side tanks are fitted