1.1 Ship Hull Stiffeners
In addition to the shell plating, the internal structure of a ship's hull relies on a network of stiffeners to maintain its strength and resist the forces encountered at sea.
These stiffeners can be categorized as primary or secondary members based on their size and function.
Primary Members:
Frames : Symmetrical, curved frames span the width of the hull, giving support and strength as well as the curved form of the hull. Frames act like ribs, providing transverse strength against lateral (sideways) pressure from the water.
Bottom girders : also known as longitudinals, horizontal beams running along the bottom of the hull from bow to stern. They work in conjunction with floors to provide longitudinal strength against bending forces caused by waves.
Secondary Stiffeners:
Side Stringers : horizontal stiffeners that run along the sides of the hull, typically spaced between the main decks. They add longitudinal strength to the shell plating (outer skin of the hull) and help distribute loads from the decks.
Web frames : lighter vertical stiffeners spaced between the main floors. They further stiffen the side shell plating and prevent buckling under pressure.
Deck Transverses vertical stiffeners that run perpendicular to the deck beams. They provide additional support to the deck plating and prevent it from sagging under cargo weight.
Deck girders : similar to bottom girders, longitudinal beams running along the length of the deck. They add longitudinal strength to the deck structure and help distribute weight more evenly.
Bulkheads: Bulkheads are watertight partitions that divide the hull into compartments.
Vertical webs : the main structural elements of a bulkhead, running vertically from the bottom of the hull to the deckhead (ceiling) of a compartment. They provide transverse strength and prevent the bulkhead from bulging inwards under water pressure.
Horizontal stringers : similar to side stringers, welded across the vertical webs, adding stiffness and helping distribute loads across the bulkheads.
Key Point:
The primary members (frames, bottom girders) are larger and stronger than the secondary stiffeners (stringers, web frames, deck transverses, deck girders, vertical webs).
They form the main framework of the hull, and the secondary stiffeners act in between them, providing additional support and distributing loads more evenly throughout the structure.