Shipbuilding Materials: Testing and Selection

• Materials commonly used for ship construction include steel, aluminum alloys, Fiber Reinforced Plastic (FRP), and wood

Tensile Testing

• It is a mechanical test measuring a material's strength and elasticity
• It involves applying a stretching force to a material sample until it breaks
• The test determines ultimate tensile strength, yield strength, and elongation

Materials Used In Shipbuilding

• Ferrous and non-ferrous metals, plastics, Glass Reinforced Plastic (GRP), fiber glass (FRP), and wood are all used
• The most widely used material is steel, especially mild steel, accounting for approximately 90%

Material Considerations For Ship Construction

• Strength is a primary consideration
• Ductility is a factor
• Toughness is important
• Weldability needs to be considered
• The potential for Marine Corrosion needs to be taken into account
• Formability is a factor
• Cost is crucial

Material Strength

• It is a measure of the stress a material can withstand, such as ultimate and yield stress

Material Ductility

• It measures a material's ability to deform plastically before fracture

Material Toughness

• It is a measure of a material's ability to absorb energy up to fracture

Ship Building Materials

• Metallic materials include Ferrous and Non-Ferrous metals
• Examples of Ferrous metals include Special Steel Alloy, High Tensile Steel, and Mild Steel
• Examples of Non-Ferrous materials include Aluminum, Copper, and Nickel
• Non-Metallic materials include Wood, Rubber, Reinforced Plastic, Fiber Glass, and Cement

Mild Steel vs High Tensile Steel

• Steel is a versatile ship construction material used extensively for its integral structure
• It has been used in shipbuilding for over 150 years due to its mechanical properties and low cost
• Mild steel is the most common steel used for hull construction
• Mild steel contains 0.15% to 0.23% carbon and a reasonable amount of manganese
• High Tensile Steels include a higher carbon content of around 0.3% to 0.6%
• High Tensile Steels may also contain alloying elements like manganese, chromium, and nickel to enhance strength and durability

Mild Steel vs High Tensile Steel Considerations

• High tensile steel is stronger than mild steel, withstanding more force without breaking
• Mild steel is more ductile than high tensile steel
• Mild steel is easier to weld, while high tensile steel requires specialized techniques and equipment
• Mild steel is generally less expensive than high tensile steel
• Mild steel is commonly used in construction and automotive industries
• High tensile steel is often used in aerospace, defense, and heavy equipment industries

Aluminum Alloys vs Steel

• Aluminum is a lightweight, corrosion-resistant material used in high-speed vessels and smaller boats
• Aluminum requires less maintenance than steel

Advantages of Aluminum

• Aluminum is lighter than mild steel; using Al alloys can save up to 60% of a steel structure's weight, which increases cargo capacity
• Aluminum is highly resistant to corrosion
• Non-magnetic properties and low-cost maintenance

Disadvantages of Aluminum

• High initial cost, estimated to be 8 to 10 times the price of steel per tonnage
• Fatigue stress is a consideration

Fiber/Glass Reinforced Plastic (FRP)

• FRP ships have composite hulls made of fibers like fiberglass, carbon, or Kevlar in a resin matrix
• FRP is lightweight, strong, and corrosion-resistant

FRP vs Steel Hulls

• FRP is lighter than steel, improving fuel efficiency and top speed
• FRP is not susceptible to corrosion like steel, which provides longer service life
• FRP can be molded into complex shapes, allowing design flexibility and aesthetic appeal
• FRP provides better thermal insulation than steel for regulating temperature

Disadvantages of FRP Hulls

• FRP is more brittle than steel and has low impact resistance
• FRP may degrade over time with UV exposure
• FRP is more expensive than steel
• FRP has low fire resistance

Shell Plating Definition

• Shell plating forms the watertight skin of the ship
• In merchant ship construction, it contributes to longitudinal strength and resists vertical shear forces
• Bottom and side shell plating consists of flat and curved steel plates, butt welded together

Shell Expansion Plan

• A shell expansion plan is a two-dimensional drawing of a three-dimensional surface representing the ship's hull form
• Strakes are marked with letters (A, B, C, etc.) vertically, starting from the keel strake (A) and ending with the sheer strake
• Strake numbers start from 1 at the stern and end at the forward bow
• Each strake is indicated by a letter (level) and a number (position)

Uses for Shell Expansion Plan

• The Plan marks the location of hull damage by identifying the strake number, letter, and frame number
• The Plan finds areas of painting surfaces by applying Simpsons rules
• The Plan provides information on the thickness of the original strake, indicated by a number in a circle