Lesson 4

Shell Plating and Framing

ContentsContents

Bottom Shell Bottom Shell

Side ShellSide Shell

FramingFraming

Transverse

longitudinal

Structural members

Structural members

Language Points

• butt weld

• fiilet weld

• strake

• keel

• pounding region

• panting region

Plug welding, T-welding, lap welding, fillet welding , butt-welding

butt weld• Butt weld

welds where two pieces of metal are joined at surfaces that are at 90 degree angles to the surface of at least one of the other pieces

• There are many types of butt welds, but all fall within one of these categories: single welded butt joints, double welded butt joint, and open or closed butt joints. A single welded butt joint is the name for a joint that has only been welded from one side. A double welded butt joint is created when the weld has been welded from both sides. With double welding, the depths of each weld can vary slightly.

fillet weld

• A weld of approximately triangular cross section joining two surfaces, approximately at right angles to each other, as in a lap joint.

strake• a longitudinal strip along the side of a boat, usually constructed by

laying panels end to end. Strakes are important structural components of boats of all sizes and can be made from wood, metal, and other building materials. When a ship is designed, the layout of strakes is considered ahead of time to make sure panels of the right size and shape are cut, with the goal of minimal wastage and an even, aesthetically pleasing appearance.

Some strakes have special names, depending on their position along the hull. The very top strip is known as the sheer strake, while the panel next to the keel is the garboard strake. Boating companies may also use the term “strake” to refer to a strip added to increase control and speed. This is not an integral part of the hull, but an added component that will jut out from the finished boat. These are usually found on the bottom of the boat and can cut down on spray, a concern for some recreational boaters.

• 1 . Plate Keel2. Center girder3. Center (line) strake4. Side girder5. Horizontal margin plate6. Inner bottom plating7. Bottom plating8. Floor9. Manhole10 . Reverse frame11 . Main frame12 . Bilge strake13 . Sheer strake14. Side plating

• 15 . Upper deck16 . Bilge keel17. Bulwark plating18 . Frame19. Tank side bracket20. Beam bracket21 . Deck beam22. Shelter deck23. Horizontal stiffener24. Gunwale angle25. Bulwark stay26. Hand rail27. Hatch side coaming

keel

• The principal structural member of a ship, running lengthwise along the center line from bow to stern, to which the frames are attached.

pounding &panting

– Panting stresses is an in and out motion of the plating in the bows of a ship and is caused by unequal water pressure as the bow passes through successive waves.

– Pounding stresses exist when ships is pitching. Ship’s bows lift clear of the water and come down heavily. It causes damage to the bottom and girder at the bow.

• Panting is the in-and-out movement of the shell plating that results from variations in water pressure as the vessel pitches in a seaway. Special structural arrangements are provided in the bow region to strengthen the shell plating against this action. These arrangements include:

1. horizontal plates welded to the sides of the vessel (known as panting stringers)

2.transverse beams extending from side to side (known as panting beams)

3. partial bulkheads On some vessels, panting beams are replaced by

perforated flats. Perforated flats are flat plates, similar to decks, with round holes cut in them.

• Pounding results from the heaving or pitching of the vessel, which causes the forward region to ‘slam’ down on the water. To resist pounding, the shell plating is increased in thickness, frame spacing is reduced, and additional side girders and solid plate floors are fitted in the forward region.

Bottom shell plating

– Throughout the length of the ship the width and thickness of the keel plate remain constant where a flat plate keel is fitted. Its thickness is never less than that of the adjoining bottom plating.

– Strakes of bottom plating to the bilges have their greatest thickness over 40 percent of the ship’s length amidships, where the bending stresses are highest. The bottom plating then tapers to the lesser thickness at the ends of the ship, apart from increased thickness requirements in way of the pounding region.

Side shell plating

• The upper strakes of plating adjacent to the strength deck is referred to as the ‘sheer-strake’.

• The connection between the sheer strake and strength deck can present a problem, and a rounded gunwale may be adopted to solve this problem where the plating is heavy. This is often the case over the midship portion of large tankers and bulk carriers. Butt welds are then employed to make connections rather than the less satisfactory fillet weld at the perpendicular connection of the vertical sheer-strake and horizontal strength deck stringer plate. The radius of the rounded gunwale must be adequate (not less than 15 times the thickness) and any welded guardrails and fairleads are kept off the radiused plate if possible

• 1 . Center girder2. Floor3. Shaft tunnel4. Tank top plate5. Tank side frame6. Hold frame7. Shell plating8. Upper deck9. Transverse beam10 . Deck girder11 . Deck long .12 . Water tight bulkhead13 . Bulkhead stiffener14 . Second deck

• 15 . Manhole16 . Inner bottom plate17 . Tank side bracket18 . Bottom long .19 . Vertical stiffener20 . Beam bracket21 . Deck beam22 . Tween deck frame23 . Stringer plate24 . Bulwark plate25 . Bulwark stay26 . Derrick post27 . Screw shaft

Components of Framing• frame: On side plating, running vertically (up and down)

• beam: Under decks, runs transversely • transverse: Under decks (deck transverse) and on bottom

plating (bottom transverse) but not in Double Bottoms. Runs transversely but much heavier in construction than a beam.

• floors: Found only in double bottoms, running transversely.

• stringer: On side plating and longitudinal bulkheads, runs horizontally, forward and aft.

• longitudinal:Found in longitudinally framed ships, under decks, on side plating, on longitudinal bulkheads, on bottom plating and under the tank too. These members run fore and aft.

• girder: Found under decks and on the bottom plating. Girders run forward and aft and are deep and heavy in construction. These are important longitudinal strength members. Also increase the breadth of the forecastle and provides space for the mooring.

• scantlings: A ship construction term used generally to define dimensions of various parts of the structure. Used to mean breadth, length, diameter, thickness, height etc.

Transverse Framing

1. This is system of framing is used in vessels of relatively less length, where longitudinal bending moments are not excessive. The framing system consists essentially of rings of strengthening around the shell plating.

2. Under the deck, deck beams are fitted at every frame space. A frame space is the distance between one frame on the side plating to the next frame.

3. On the side plating, frames are fitted to stiffen the 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 bean directly to the frame.

Longitudinal Framing

1. This is a common method of framing found in long ships usually those exceeding 100 m in length. The system is designed to withstand longitudinal bending moments, which are pronounced in long vessels.

2. The main feature of strengthening in this system is the longitudinal , an L shaped stiffener, which is fitted under the decks, on the side plating, on the bottom plating under the tank top and on the longitudinal bulkheads as well. The longitudinals run the full length of the vessel, from forward to aft, providing longitudinal strength ..

Fig.I

Transverse Framing of single deck hull

Fig.II

Longitudinal Framing of hull

1. deck plating2. sheer strake3. side plating4. bilge strake5. bottom plating6. centerline vertical keel7. flat keel8. side keel9. beam bracket10. deck longitudinal11. frame12. web frame13. side longitudinal bracket14. bracket15. beam 16. transverse bulkhead plate

1. upper deck2. deck girder3. deck longitudinal4. top side plating5. web beam6. horizontal stiffener7. web beam8. bracket9. side longitudinal10. longitudinal bulkhead11.web frame12.strut

Assignment

• Memorize the language points

• Review the drawings with structure terms