Lecture: Cont... Principal Structural Parts of a Ship a. Ship Dimension and Forms b. Structural Members c. Characteristics d. Various Types of Ships e. Functions of Different Bulkheads f. Bow and Stern g. Rudders, Thrusters, and Propellers-2
TA :
Facilitate learning thru Film Viewing and power point presentation. Interactive discussion about common steel used in shipbuilding, purpose and advantages of transverse and longitudinal framing systems and construction of hatch openings and superstructures in relation to the seaworthiness of the ship.
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LA :
Students shall
- identify common steel used in shipbuilding.
- Explain the purpose and advantages of transverse and longitudinal framing systems
Describe the construction of hatch openings and superstructures in relation to the seaworthiness of the ship.
Many materials are used in shipbuilding, including fiber-reinforced composites (FRP), non-ferrous metals, plastics, and more. Yet almost 90% of materials consumed by maritime engineering are comprised of marine steels. Common steels for shipbuilding include carbon and mild steel grades that combine exceptional tensile strengths with good workability, but there are several critical parameters for materials to meet the standards of master shipbuilders.
Steel for shipbuilding must first be classified according to one or more of the relevant classification societies: American Bureau of Shipping (ABS), Lloyd’s Register, or Det Norske Veritas (DNV). These have established globally-accepted standards and rules that steel for shipbuilding must follow, from chemical composition to downstream plate thickness.
Brief History of Steel for Shipbuilding
Although there was a moderate use of steel for shipbuilding in the latter part of the 19thCentury, timber and wrought iron remained the material of choice in maritime applications for decades. It was not until the outbreak of World War II that large vessels like cargo freighters and military ships were engineered almost exclusively from welded steel. This was largely a response to the ballistics capabilities of the time: steels were stronger and lighter than wrought iron, enabling the fabrication of faster and more durable vessels designed to operate in active theatres of war.
After the war, iron was completely supplanted by steel for shipbuilding due to the material’s inherent cost- and weight-savings. This catalysed a new era of ingenuity in shipbuilding characterised by block construction of prefabricated steel sections. Now, steel is used almost exclusively when it comes to construction of ship superstructures.
Key Properties of Steel for Shipbuilding
Plain carbon and mild steel are the most common grades of steel for shipbuilding, as they boast a raft of beneficial properties that make them uniquely suited for marine engineering. These include:
High yield strengths and typical tensile strengths on a range of 490 – 620 MPa
Easy joining and tight control of potential weld defects
Superior metallurgical properties to overcome brittle fracture/fatigue
Reasonable cost to ensure tangible ROIs
ASTM/ASME specification and can be classified according to any of the relevant societies. Our steels for shipbuilding include:
AH36: A common steel for shipbuilding that is typically formatted as heavy plates and fabricated surfaces for large, heavy-duty vessels like commercial ships and bulk carriers.
DH36: Another common shipbuilding steel used to construct and retrofit ship superstructures.
EH36: A desirable steel for shipbuilding that is available in prefabricated sections and heavy plates for hull construction and superstructure design.
Hatchways are a very important part of a ship’s structure, and on a cargo ship they extend over at least 1/3 of the ship’s beam. In container ships they are much wider and are only (approximately) 2 meters shorter in width as compared to the ship’s beam (Figure 97).
Figure 97.Openings of the hatchways.
The disadvantage of a ship’s hatchway lies in the fact that—in effect—it is a very large discontinuity as far as the ship’s deck is concerned. This reduces thestrengthof the deck so steps must be taken to reinforce the deck and overcome this negative effect.
This is achieved by arranging inserts (gusset plates) of greater thickness than the deck plating at the corners of the hatch opening. Figure 97 depicts the way these gusset plates (elliptical shape corners) extend in the hatch opening. These plates are of similar form in a tween-deck vessel. In bulk-carriers the protruding part of the gusset plate is covered by a shedder plate so that bulk cargo does not accumulate on these plates.
The hatch coaming extends in a fore and aft direction beyond the hatch opening, in the form of a bracket (see Figure 98“A”).
Figure 98.Hatchway elliptical corner-plates (gussets) at weather deck level. The diagram on the RHS shows the extended longitudinal hatch coamings.
To provide additional strength, beams and longitudinal girders are arranged i.w.o. the hatch opening. In tween deckers, pillars are arranged at the corners of the hatchway opening to support the intersections of the beam and girders (Figure 99).
Figure 99.Hatch-coaming extensions. The photo on the RHS shows hatch coaming and stays.
The height of thehatch coamingsdepends on whether they are located forward or aft on a ship’s deck. At the fore location they are most likely to become exposed to green seas, accordingly they are of a greater height than the hatches in after locations, where they are better protected from adverse weather effects.
Previous Module: WEEK 1 Laboratory: Cont... Principal Structural Parts of a Ship a. Ship Dimension and Forms b. Structural Members c. Characteristics d. Various Types of Ships e. Functions of Different Bulkheads f. Bow and Stern g. Rudders, Thrusters, and Propellers-2
