Ship Construction, Stresses, Plans & Basic Stability

Question-and-Answer flashcards covering ship construction terminology, vessel stresses, structural arrangements, statutory plans, corrosion, material comparison, and basic buoyancy and stability definitions.

Where is the Forward Perpendicular (FP) located on a ship?

At the point where the forward side of the stem meets the summer load line.

Where is the After Perpendicular (AP) located on a ship?

At the point where the aft side of the rudder post meets the summer load line.

What does the term "depth" mean in ship construction?

The distance between the keel and the top of the deck plating at the ship’s side.

How is the position "midships" defined?

The midpoint between FP and AP; the centre of the load-line circle should mark it.

Give two reasons sheer is built into the hull.

1) Adds volume and buoyancy at bow and stern. 2) Improves stability by reducing pitching and keeps decks drier.

What is Gross Tonnage (GT)?

The total volume of all enclosed spaces within the vessel.

What is Net Tonnage (NT)?

The volume of all enclosed spaces available for cargo or passengers.

Which static longitudinal stress causes the hull to bend upward at midships when loaded in port?

Hogging.

Which static longitudinal stress causes the hull to bend downward at midships when loaded in port?

Sagging.

What is dynamic hogging?

When a wave crest is amidships while bow and stern are in troughs, bending the ship upward at midships.

What is dynamic sagging?

When wave crests are under bow and stern and the midships is in a trough, bending the ship downward at midships.

Name two sources of transverse static stress.

Water pressure and dry-dock support.

What is racking stress?

A dynamic transverse stress that distorts a rectangular cross-section into a parallelogram under rolling or slamming.

What is pounding?

Local stress when the bow lifts clear of the water and slams into the next wave.

What is panting?

Alternating in-and-out movement of bow plating due to pressure changes when the bow rises and falls in waves.

What is localised loading?

Heavy weights concentrated on small deck areas, e.g., cranes or tenders.

What is vibration stress and its common causes on ships?

Oscillatory stress caused by main engines, propeller shafts or other machinery.

List three structural members used to reduce longitudinal stress.

Centre girder, deck stringers, and heavier deck/keel plating.

List three structural features that resist transverse stresses.

Double-bottom structure, knee beams, and tank-side brackets.

How is pounding resistance improved in the bow?

By fitting additional (thicker) bottom plating.

How is panting resistance provided?

By installing panting beams and panting stringers in the bow region.

Which plan shows the position of every compartment, decks, rigging, and means of access?

The General Arrangement (GA) drawing.

State four details normally found on a General Arrangement drawing.

Ship’s particulars, full-length profile, transverse sections, and plan views of each deck/tank (plus many more such as watertight bulkheads, frame numbers, access points).

Which plan shows the location, maintenance and testing requirements for all lifesaving appliances?

The Lifesaving Appliances Plan (LSAP).

Give five examples of items shown on an LSAP.

Lifeboats, life rafts, lifejackets, EPIRB/SART, and muster stations (others include EEBD, immersion suits, flares, etc.).

Which SOLAS-mandated plan depicts fire stations, "A/B" class bulkheads, detection and fixed systems?

The Fire Control Plan (Fire Plan).

List three pieces of information found on a ship’s Fire Plan.

Locations of fire extinguishers, hydrants/hoses, and fixed firefighting installations (also shows fire pumps, hazards, BA lockers, etc.).

What is chemical corrosion of steel?

Oxidation of iron with atmospheric oxygen forming iron oxide (rust).

Explain galvanic corrosion.

Corrosion caused by electrolytic action when two dissimilar metals electrically connected are immersed in an electrolyte.

How does a paint system help prevent corrosion?

By sealing the metal surface from water and oxygen.

Describe sacrificial anode cathodic protection.

Attaching a more reactive metal (e.g., zinc) that corrodes preferentially, protecting the ship’s steel structure.

State two advantages of aluminium compared with steel for shipbuilding.

Light weight and does not rust (also easy to work and low maintenance).

State two disadvantages of aluminium in ship construction.

High cost and poor fire resistance (also galvanic issues, specialist welding, lower melting point).

State two advantages of steel over aluminium.

Cheaper material and good fire resistance (also easy to build, repair and not easily damaged).

What is Archimedes' Principle as applied to ships?

A body immersed in a fluid experiences an upward force equal to the weight of fluid displaced.

State the Law of Flotation.

A floating object displaces its own weight of the liquid in which it floats.

Which instrument measures the relative density of water?

A hydrometer.

Define density and give typical values for fresh and salt water.

Mass per unit volume; fresh water ≈ 1000 kg/m³, salt water ≈ 1025 kg/m³.

What is Light Displacement?

The weight of the vessel completely empty of cargo, fuel, stores, passengers, etc.

What is Load Displacement?

The total weight of the ship when fully loaded down to its maximum draught.

Define Deadweight.

Weight of cargo, fuel, passengers, stores, etc.; calculated as load displacement minus light displacement.

What is the Water-Plane Area (WPA)?

The area of the hull enclosed by the waterline.

Define Reserve Buoyancy.

Volume of enclosed watertight space above the waterline.

What is a Load Line mark?

A mark on the ship’s side indicating the deepest permissible draught under various conditions.

What is Assigned Freeboard?

Vertical distance from the deck line to the top of the summer load line.

State the standard Fresh Water Allowance formula.

Assumed to be 1/48 of the summer draught.