Construction of ship is a complex work. It requires lot of efforts from planning to launching. Ships are built by Naval Architects in shipyards and certified by Classification societies.
Types of Ship
For constructing a ship, details of type of ship is quintessential. It’s necessary to know about which type of ship is required as type of ship decides the construction process. Different types of ships have different design. These are the basic types of ship are:
Dimension of ship is deciding factor for size and cost. According to dimension, sizes of different parts and machinery is required. Summer draft is an additional factor for ship’s size.
Dimensions are: Length, Breadth, Depth & Draft.
Length (L): It’s a measurement of distance between forward and aft of the ship. There are two popular length measurement i.e. Length Overall (LOA), Length Between Perpendicular (LBP) and Length on the Waterline (LWL).
Breadth (B): It’s also called Beam. There are two types of breadth (beam) measurement i.e. Beam Overall or simply Beam and Beam on centreline.
Depth (D): It’s a measurement of distance from the bottom of keel to the freeboard deck. It varies along the length of the ship. But as standard value, depth is measured at midship.
Draft (T): It’s a measurement of vertical distance from the bottom of keel to the waterline of the ship.
Materials used for ship’s construction depend on many factors:
Keeping in mind, following materials can be used: Steel, Ti alloy, Al alloy, Ceramics. But Steel is most suitable material for ships, because it has higher strength, higher toughness and low cost.
Material selection (Steel) – Cutting of steel into desired shape & size – Forming desired blocks and shapes by welding process – Starting construction with Keel (Keel-laying).
Shapes & Blocks for construction (Sections)
Basic shapes and blocks from which ship is constructed, called sections.
Plates: It is basic steel material of ship construction. It’s rectangular in shape and of different desired thickness.
Bar: It’s steel plate which has very less width of cross-section.
Beam: It is generally of two types i.e. transverse beam & longitudinal beam. Transverse beam tie the sides of the ship together and support the deck against water pressure and the weight of cargo. Longitudinal beams contribute to the ship’s longitudinal strength.
All construction parts are made with plates, bars or beams.
Basic Construction Parts
Keel: It’s a bottom-most structural member of ship. It acts like a base on which ship is constructed.
It’s the quintessential part of ship. And ship construction starts with this structural member only. It is also called as back-bone (spine) of ship. This structural member bisects the hull into two sections length-wise. It is also protected by keel-guard. It is placed longitudinally at the base of ship.
Shell Plating: It’s nothing but the steel plate used on the shell of ship. It is like outer hard steel cover and its main function is to provide watertight layer of ship and to increase the longitudinal strength of ship. There are two important categories of shell plating, i.e. Bottom shell plating & Side shell plating.
Bottom shell plating suggests shell plating on the bottom of ship in horizontal direction. Side shell plating suggests shell plating on the either sides of ship in vertical direction.
Deck Plating: As its name suggests that plating for main deck of ship is called deck plating. There may be deck plating for main deck as well as accommodation deck.
Strake: Ship’s side plating is made of various smaller sections of steel plates by welding or riveting in a certain pattern. These welded sections from forward to aft direction is called as Strake.
Types of strake: Shear strake, Keel strake & Garboard strake
Top most strake of ship’s side plating is called shear strake. It is connected with deck plating and usually of greater thickness and strength.
The bottom most plating of ship’s keel is called keel strake.
The first strake on each side of the keel strake is called garboard strake.
Stiffner: The flat bars used in fore or aft direction for strengthening the member, called stiffner. Stiffner means anything which provide strength for structure. It may be either longitudinal or transverse type.
Transverse (Transverse stiffner) is a stiffning member in transverse direction and having lesser strength and thickness than frames. It is further classified as inner bottom transverse etc. on the basis of location where it is used. Longitudinal (Longitudinal stiffner) is longitudinal stiffning member used along the length of ship.
Girder: It is special longitudinal form of stiffner. It is steel plate, generally large in size and used in forward & aft direction of ship. It is called with various names according to place of use like centre girder, side girder etc.
Frames: It may be either riveted or welded but welded frames are preferable. It decides the design of ship and its hull. It’s vertical members provide strength to the side shell and makes up the framing of vertical part of the hull.
Frames – used in transverse framing (spaced closely)
Web frames – used in longitudinal framing (spaced apart)
Stringer: It’s nothing but a stiffner welded in horizontal direction. It is mostly used in forward side of ship. There is simple difference of direction between stiffner and stringer, vertical stiffning member is called stiffner and horizontal stiffning member is called stringer.
System of Construction