Competence 13: Maintain a seaworthiness of the ship KUP 50 Have general knowledge of the principal structural members of a ship and the proper names for the various parts

KUP 50 Have general knowledge of the principal structural members of a ship and the proper names for the various parts

sahil 3 Courses

The specialized terminology used in ship construction fosters a shared understanding within the maritime industry, forming a common language for shipbuilding yards and onboard communication. This vocabulary is a key component of maritime English and essential knowledge for all seafarers. As an operational-level engineer officer, you’re expected to not only understand these terms but also recall and apply them effectively.

Learning Content

Nomenclature

Length overall(LOA): It is the horizontal distance measure lengthwise between the extreme forward end and the extreme aft of a ship.

Forward perpendicular: Forward perpendicular is the perpendicular drawn at a point where the ship’s summer load waterline intersects at the stem or forward part of the ship.

After perpendicular: It is a vertical distance drawn at a point where the aft end of the ship’s rudder post meets the summer load waterline. In case of no rudder post, the perpendicular is taken from the centre line of the rudder stock.

Length between perpendiculars (LPP): It is the distance between the forward and after perpendiculars measured along the ship’s summer load line.

Midships: It is a point in the centre or middle between the forward and aft perpendiculars.

Depth: Depth is measured at ship’s side in midships position. It is the height of the ship from base line to the moulded line of the deck.

Moulded depth: It is the vertical distance measured along the ship’s side from the top of the keel to the underside of the uppermost continuous deck.

Draft: It is the vertical distance measured at ship’s side from the waterline to the bottom of the keel.

Moulded draft. It is the vertical distance measured at ship’s side from the waterline to the top of the keel.

Freeboard: It is the vertical distance measured along the ship’s side from the upper edge of the deck line to the waterline.

Camber (Round of Beam): Camber is the transverse curvature of decks, measured as the height difference between the deck’s center and its sides. Some ships use straight-line camber to simplify building.

Sheer: Sheer is the upward curve or incline of a ship’s deck from the middle towards the bow and stern. It is measured as the difference in height between the deck at any point along its length and the deck at its lowest point amidships.

Rise of Floor (Deadrise): It is the upward angle of the bottom shell plating from the baseline, measured at the molded beam line. Large cargo ships often have no deadrise.

Half Siding of Keel: The flat width of the bottom shell on either side of the ship’s centerline. This measurement is important for drydocking.

Tumblehome: The inward curve of the side shell above the summer load line, rare in modern ships.

Flare: The outward curve of the side shell above the waterline, typically seen at the bow to keep the deck drier.

Stem Rake: The angle of the stem (frontmost part of the hull) from the vertical.

Keel Rake: The angle of the keel from the horizontal. Some vessels like trawlers have aft-raked keels for better propeller clearance.

Tween Deck Height: The vertical distance between two decks, measured from the top of the deck beams at the ship’s side.

Parallel Middle Body: The section of the ship where the midship cross-section remains uniform in shape and area.

Entrance: The submerged part of the ship’s hull forward of the parallel middle body.

Principal structural members

The principal structural members in a ship are essential for its strength, stability, and seaworthiness. These components work together to form a robust framework that can withstand the harsh marine environment and various operational loads. The key structural members include:

1. Keel: Keel is the backbone of the ship. It runs along the entire length at the bottom of the hull. It provides longitudinal strength and acts as the foundation for other structural members. The most prevalent keel type is the “flat plate” keel, commonly found in ocean-going vessels. Smaller vessels like trawlers, tugs, and ferries may have a “bar keel.” Bar keels are suited for potential grounding due to their robust construction, but they increase draft without boosting cargo capacity. Ships with double bottoms almost always utilize flat plate keels, while bar keels are often associated with single bottoms.

“Duct keels” are sometimes incorporated into double bottoms, extending from the forward engine room bulkhead to the collision bulkhead. They house piping for easier access during cargo loading, with an entrance at the engine room’s front. Aft of the engine room, no duct is needed as piping can be placed in the shaft tunnel.

2. Frames (or Ribs): Frames are transverse members that form the ship’s skeleton, providing shape and strength. They are spaced along the ship’s length. Frames support hull plating in resisting water pressure and other loads. The bottom shell of a ship can be framed either transversely or longitudinally, with longitudinal framing favored for larger vessels, usually mandatory for ships over 120 meters in length. Side shell framing also offers these options, but transverse framing is often used in traditional cargo ships to maximize bale capacity. However, deep transverse frames supporting longitudinal framing tend to reduce this capacity significantly. Longitudinal framing is employed within double-hull spaces and is typical in bulk carrier hopper and topside tanks. Smaller single-skin bulk carriers then have transverse frames placed between these tanks at the side shell.

3. Beams: Beams are horizontal members that run athwartships (across the ship’s width) and support the decks. They provide transverse strength and maintain the shape of the decks.

4. Stringers: Stringers are the longitudinal members located along the sides and bottom of the hull, providing additional longitudinal strength.

5. Bulkheads: Bulkheads are vertical partitions that divide the ship into compartments. They can be watertight or non-watertight, providing structural support, fire protection, and damage control. The hull bulkheads are constructed to be watertight, serving as barriers to contain flooding if a compartment is breached. Additionally, they contribute to the ship’s structural strength, supporting vertical loads and resisting transverse deformation. Typically, these bulkheads extend up to the strength deck, which might be higher than the freeboard deck. Lastly, they often act as effective firewalls, preventing the spread of flames in holds or machinery spaces.

6. Girders: They are large beams that provide additional support to decks and bulkheads. Girders are often used in areas with high loads, such as engine rooms or cargo holds. A ship’s hull can be compared to a box-shaped beam, bending under load. Its neutral axis and second moment of area can be determined, with the deck and bottom shell acting as the “flanges” of this beam, contributing far more to longitudinal strength than the sides, which function like the “web” and primarily handle shear forces.

7. Hull Plating: Hull plating is the outer skin of the ship, attached to the frames and forming the watertight enclosure. The platings protect the internal structure from the elements and provide the ship’s shape. The bottom and side shell plating of a ship is made up of flat and curved steel plates, usually longer than they are wide, joined together by butt welding. The vertical welded connections are called “butts,” while the horizontal ones are “seams.” Stiffening members, both lengthwise and across the ship, are typically fillet welded to the shell plating. The framing is notched where it meets the welded plate butts and seams.