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PRC Naval Architecture & Marine Engineering study materials
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PRC Naval Architecture & Marine Engineering practice questions

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Question 1Naval Architecture

In the PRC ship classification framework, the minimum freeboard assigned to a ship is primarily determined by which parameter?

  1. The assigned load line and the applicable freeboard deck Correct answer.
  2. The installed shaft horsepower of the main propulsion plant
  3. The maximum trial speed measured on the measured mile
  4. The number of watertight transverse bulkheads fitted

Explanation

Freeboard is the vertical distance from the freeboard deck to the assigned load line, and the load line rules set that minimum so that reserve buoyancy and strength are adequate. Speed, bulkhead count and installed power influence design, but they do not define the assigned minimum freeboard directly.

Question 2Naval Architecture

Which quantity is defined as the volume of the immersed hull, expressed in cubic metres, used with seawater density to obtain buoyancy?

  1. Block coefficient
  2. Displacement
  3. Volume of displacement Correct answer.
  4. Moulded volume

Explanation

The volume of displacement is the immersed volume of the hull and, multiplied by the density of the surrounding water, gives the buoyant force equal to weight in equilibrium. Block coefficient is a dimensionless ratio, while displacement is a force or mass quantity rather than a volume.

Question 3Naval Architecture

A box-shaped pontoon 40 m long, 10 m wide floats at a draught of 2.5 m in fresh water of density 1000 kg/m3. What is its displacement mass?

  1. 1500 t
  2. 2500 t
  3. 1000 t Correct answer.
  4. 1250 t

Explanation

Displaced volume equals 40 x 10 x 2.5 = 1000 m3, and in fresh water of 1000 kg/m3 this corresponds to 1000 t. The calculation uses the box volume directly because the pontoon has vertical sides.

Question 4Naval Architecture

The metacentric height GM of a floating body is defined as which relationship?

  1. KG minus KM
  2. KB minus KG
  3. KM minus KG Correct answer.
  4. BM minus KM

Explanation

GM is the distance from the centre of gravity to the metacentre, so it equals KM minus KG, where KM is the height of the metacentre above the keel. A positive GM indicates initial stability in the upright condition.

Question 5Naval Architecture

In resistance theory, which component arises from the generation of waves at the free surface and is strongly dependent on Froude number?

  1. Viscous pressure resistance
  2. Air resistance
  3. Wave-making resistance Correct answer.
  4. Appendage drag

Explanation

Wave-making resistance comes from the energy carried away by the ship-generated wave system and scales with Froude number. Viscous and appendage components are governed mainly by Reynolds number and wetted area.

Question 6Naval Architecture

Which structural member runs longitudinally along the bottom of a double-bottom ship and provides the central girder?

  1. Deck transverse
  2. Transverse floor
  3. Side stringer
  4. Centre girder Correct answer.

Explanation

The centre girder is the continuous longitudinal plate on the centreline of the double bottom, working with the tank top and bottom shell. Floors are transverse, and stringers and deck transverses serve other locations.

Question 7Naval Architecture

In a ship's lines plan, which view shows the hull form projected onto a vertical longitudinal plane?

  1. Buttock plan
  2. Sheer plan Correct answer.
  3. Body plan
  4. Half-breadth plan

Explanation

The sheer plan is the profile projection onto the longitudinal vertical plane, showing buttock lines and the profile of the hull. The body plan shows transverse sections and the half-breadth plan shows waterline shapes in plan view.

Question 8Naval Architecture

Which condition must hold for a floating body to be in static equilibrium?

  1. The metacentric height is negative
  2. The centre of gravity is always below the keel
  3. The centre of buoyancy lies above the metacentre
  4. The weight equals the buoyant force and their lines of action are collinear Correct answer.

Explanation

Static equilibrium requires force balance, so weight equals buoyancy, and moment balance, so the two forces act along the same vertical line. The relative positions of B, G and M govern stability, not equilibrium itself.

Question 9Naval Architecture

A ship of 8000 t displacement has KG = 7.0 m and KM = 7.6 m. What is the initial metacentric height?

  1. 14.6 m
  2. 0.6 m Correct answer.
  3. 1.4 m
  4. 0.9 m

Explanation

GM equals KM minus KG, so 7.6 minus 7.0 gives 0.6 m. The positive value indicates the ship is initially stable in the upright condition.

Question 10Naval Architecture

Adding a weight at the level of the existing centre of gravity of a ship will have which effect on KG and GM?

  1. KG is unchanged and GM is unchanged Correct answer.
  2. KG rises and GM increases
  3. KG rises and GM decreases
  4. KG falls and GM increases

Explanation

A weight added at the existing centre of gravity produces no first moment about G, so the combined centre of gravity does not move. Consequently KG and GM remain unchanged while displacement increases.

Question 11Naval Architecture

The free surface effect of liquid in a partly filled tank acts to do which of the following?

  1. Lower the virtual centre of gravity and increase effective GM
  2. Increase righting moment at all heel angles
  3. Raise the virtual centre of gravity and reduce effective GM Correct answer.
  4. Leave GM unchanged but reduce displacement

Explanation

Slack liquid shifts its centre of gravity as the ship heels, producing a virtual rise of G equal to the free surface moment divided by displacement. This reduces the effective metacentric height and therefore the initial stability.

Question 12Naval Architecture

Which dimensionless number is used to scale ship resistance model tests so that wave-making resistance is correctly represented?

  1. Mach number
  2. Reynolds number
  3. Froude number Correct answer.
  4. Weber number

Explanation

Froude number equality ensures geometric similarity of the wave system, so wave-making resistance scales correctly between model and ship. Reynolds number equality would be needed for viscous similarity but cannot be satisfied simultaneously at model scale.

Question 13Naval Architecture

A propeller is said to have a high slip ratio when which condition applies?

  1. The advance per revolution is small compared with the pitch Correct answer.
  2. The propeller diameter exceeds the draught
  3. The advance per revolution approaches the theoretical pitch
  4. The propeller operates at zero thrust

Explanation

Slip is the difference between the theoretical advance at zero thrust and the actual advance per revolution, expressed as a fraction of pitch. A small actual advance relative to pitch means a high slip ratio, typical of heavily loaded or bollard conditions.

Question 14Naval Architecture

In IMO probabilistic damage stability for passenger ships, the attained subdivision index A must satisfy which requirement?

  1. A is independent of the ship's service length
  2. A is at least equal to the required index R Correct answer.
  3. A equals the deterministic one-compartment standard
  4. A is at most half of the required index R

Explanation

The probabilistic approach requires the attained index A, computed from the sum of damage case contributions, to be not less than the required index R. The required index is a function of ship length and reflects the accepted risk level.

Question 15Naval Architecture

Which factor most directly determines the required scantlings of a primary hull girder member under classification society rules?

  1. The number of crew berths provided on board
  2. The design still-water and wave bending moments together with the section modulus Correct answer.
  3. The type of anchor windlass installed
  4. The colour scheme of the external hull coating

Explanation

Rule scantlings for the hull girder are derived from the design vertical bending moments, including still-water and wave components, and the required section modulus. Accommodation, coating and deck machinery do not govern primary girder strength.

Question 16Naval Architecture

A ship has a righting lever curve that becomes negative at 40 degrees heel. What does this indicate about the vessel?

  1. The range of positive stability ends at 40 degrees Correct answer.
  2. The vessel is stable at all angles beyond 40 degrees
  3. The angle of vanishing stability is zero
  4. The metacentric height is unusually large

Explanation

The angle at which the righting lever becomes zero and then negative marks the end of positive stability, beyond which the ship would continue to heel. This is the angle of vanishing stability for the given loading condition.

Question 17Naval Architecture

Which phenomenon explains why a ship in following seas may lose stability when the wave crest is near midships?

  1. Reduced propeller slip in the wave trough
  2. Increased displacement from wave water on deck
  3. Parametric rolling caused by periodic variation of metacentric height Correct answer.
  4. Increased block coefficient in shallow water

Explanation

As a wave passes, the immersed hull geometry changes periodically, so the metacentric height varies and can excite parametric rolling at certain encounter frequencies. This is a dynamic stability problem rather than a simple static one.

Question 18Naval Architecture

In a transverse stability calculation, a weight of 200 t is shifted 3 m transversely. For a displacement of 10000 t, what is the resulting angle of list in radians (small angle approximation)?

  1. 0.6 rad
  2. 0.006 rad Correct answer.
  3. 0.06 rad
  4. 6.0 rad

Explanation

The heeling moment is 200 x 3 = 600 t-m, and dividing by displacement gives a shift of G of 0.06 m. Dividing this transverse shift by GM, taken here as 10 m for the small-angle estimate, gives about 0.006 rad.

Question 19Naval Architecture

Which statement correctly distinguishes the moulded breadth from the breadth extreme of a ship?

  1. Breadth extreme includes any permanent projections beyond the moulded lines Correct answer.
  2. Moulded breadth is measured between the inside surfaces of the shell plating
  3. Breadth extreme is measured at the waterline only
  4. Moulded breadth is always larger than breadth extreme

Explanation

Moulded breadth is measured to the moulded line, usually the inside of shell plating, while breadth extreme includes permanent projections such as fenders or bulwarks. The extreme value is therefore normally larger than the moulded value.

Question 20Naval Architecture

A ship's GM is small and positive. Which combination of behaviour is expected in a beam sea?

  1. Long roll period and gentle righting moments Correct answer.
  2. Zero roll period and immediate capsize
  3. No relationship between GM and roll period
  4. Short roll period and large righting moments

Explanation

Roll period increases as GM decreases, so a small positive GM produces a long, gentle roll with modest righting moments. This is comfortable for crew but leaves little margin against heeling moments.

Question 21Naval Architecture

In the context of the PRC maritime regulatory system, which body administers ship survey and certification for seagoing vessels?

  1. China Classification Society acting as a recognised organisation Correct answer.
  2. The Ministry of Transport directly issuing all statutory certificates
  3. The port authority of the home port only
  4. The local fisheries bureau for all merchant ships

Explanation

Statutory survey and certification are typically delegated to a recognised organisation such as China Classification Society, which acts on behalf of the flag administration. The administration retains overall responsibility for the regulatory framework.

Question 22Naval Architecture

A hull girder is idealised as a beam. Which stress component dominates at the deck and keel under vertical bending?

  1. Direct axial stress in the longitudinal direction Correct answer.
  2. Transverse shear stress across the breadth
  3. Local plate bending stress only
  4. Torsional shear stress about the longitudinal axis

Explanation

Vertical bending of the hull girder produces longitudinal direct stress that is maximum at the deck and bottom, decreasing toward the neutral axis. Transverse and torsional stresses are secondary for this bending mode.

Question 23Naval Architecture

Which parameter is used to characterise the fullness of the underwater hull form in the longitudinal direction?

  1. Prismatic coefficient Correct answer.
  2. Deadrise angle
  3. Waterplane coefficient
  4. Midship section coefficient

Explanation

The prismatic coefficient is the ratio of the volume of displacement to the product of midship section area and length, describing longitudinal distribution of volume. Midship and waterplane coefficients describe transverse and plan-form fullness respectively.

Question 24Naval Architecture

During an inclining experiment, which precaution is essential for valid results?

  1. Mooring lines should be slack and all loose weights secured and accounted for Correct answer.
  2. The experiment should be conducted in rough weather
  3. Tanks should be partly filled to maximise free surface
  4. The ship should be moored tightly to the quay

Explanation

Valid inclining experiments require the vessel to be free to heel, so mooring lines must be slack, and all loose or unaccounted weights must be secured or recorded. Free surfaces and weather disturbances introduce errors in the derived KG.

Question 25Naval Architecture

Which of the following best describes the purpose of a ship's stability booklet?

  1. To specify the engine room maintenance schedule
  2. To list the crew's qualifications
  3. To provide approved loading conditions and stability criteria for the master Correct answer.
  4. To record the ship's cargo manifests for customs

Explanation

The stability booklet contains approved loading conditions, hydrostatic data and stability criteria so the master can verify that the ship remains within safe limits. It is a statutory document tied to the ship's approved trim and stability.

Question 26Naval Architecture

In a ship's hydrostatic curves, what does the block coefficient (Cb) represent?

  1. The ratio of the waterplane area to the product of length and breadth
  2. The ratio of the midship section area to the product of breadth and draught
  3. The ratio of the immersed volume to the product of length, breadth, and draught Correct answer.
  4. The ratio of the displacement to the volume of a prism with the same length and breadth

Explanation

The block coefficient Cb is defined as the immersed volume divided by the product of length between perpendiculars, breadth, and draught. It indicates the fullness of the underwater hull form, with values approaching 1.0 for full forms such as tankers. The other ratios describe different coefficients: midship section coefficient (Cm) and waterplane coefficient (Cw).

Question 27Naval Architecture

Which of the following is the primary purpose of a ship's load line mark (Plimsoll mark)?

  1. To mark the location of the ship's longitudinal centre of buoyancy
  2. To show the position of the centre of gravity for stability calculations
  3. To indicate the maximum permissible draught under various seasonal and density conditions Correct answer.
  4. To define the minimum freeboard required for structural strength in waves

Explanation

The load line mark, assigned under the International Convention on Load Lines, sets the maximum draught to which a ship may be loaded in different seasons and water densities. It ensures adequate freeboard and reserve buoyancy. It is not related to the centre of gravity or centre of buoyancy positions.

Question 28Naval Architecture

In ship construction, what is the function of a transverse watertight bulkhead?

  1. To support the propeller shafting along its length
  2. To provide longitudinal strength to the hull girder
  3. To divide the hull into watertight compartments and limit flooding Correct answer.
  4. To separate the cargo holds from the engine room in the transverse direction

Explanation

Transverse watertight bulkheads subdivide the hull into watertight compartments, restricting the spread of flooding and thereby improving survivability after damage. They also contribute to transverse strength and may serve as tank boundaries. Longitudinal strength is primarily provided by longitudinal members such as the keel, girders, and shell plating.

Question 29Naval Architecture

Which of the following statements correctly describes the relationship between metacentric height (GM) and the period of roll for a ship?

  1. The roll period is directly proportional to GM.
  2. A larger GM generally results in a shorter roll period. Correct answer.
  3. A larger GM generally results in a longer roll period.
  4. The roll period is independent of GM.

Explanation

The natural roll period T is approximately proportional to the transverse radius of gyration divided by the square root of GM. Therefore, increasing GM reduces the roll period, making the ship stiffer. A small GM gives a longer, gentler roll period.

Question 30Naval Architecture

A ship of 12000 t displacement has KG = 8.0 m and KM = 8.6 m. A weight of 200 t is loaded at a vertical position of 12.0 m above the keel. What is the new KG?

  1. 8.07 m Correct answer.
  2. 8.13 m
  3. 8.27 m
  4. 8.20 m

Explanation

The new KG is calculated by taking moments about the keel: new KG = (Δ × KG + w × kg) / (Δ + w). Here, (12000 × 8.0 + 200 × 12.0) / (12000 + 200) = (96000 + 2400) / 12200 = 98400 / 12200 ≈ 8.066 m, which rounds to 8.07 m.

Question 31Naval Architecture

In a ship's lines plan, what does the body plan show?

  1. The intersection of the hull surface with horizontal planes
  2. The profile of the hull in a vertical longitudinal plane
  3. The intersection of the hull surface with transverse vertical planes Correct answer.
  4. The intersection of the hull surface with longitudinal vertical planes

Explanation

The body plan (or end elevation) displays transverse sections of the hull, i.e., the intersections of the hull surface with vertical planes perpendicular to the ship's longitudinal axis. It is used to define the shape of the hull at various stations. The other views are the half-breadth plan (waterlines) and the sheer/profile plan (buttocks).

Question 32Naval Architecture

A ship has a displacement of 15000 t and a transverse metacentric height GM = 1.2 m. A weight of 100 t is shifted transversely by 6 m. What is the resulting angle of heel (in degrees), assuming small angles?

  1. 3.1 degrees
  2. 1.9 degrees Correct answer.
  3. 4.0 degrees
  4. 2.3 degrees

Explanation

The heeling moment is w × d = 100 × 6 = 600 t·m. The righting moment per degree is Δ × GM × sin(θ) ≈ Δ × GM × θ (rad). For small angles, tan(θ) = heeling moment / (Δ × GM) = 600 / (15000 × 1.2) = 600 / 18000 = 0.0333, so θ ≈ 1.91 degrees.

Question 33Naval Architecture

Which of the following best explains why a ship with a large metacentric height (GM) may experience high accelerations in a seaway?

  1. Large GM causes a short roll period, leading to rapid roll motions that can be uncomfortable and stress cargo. Correct answer.
  2. Large GM decreases the waterplane area, making the ship more sensitive to wave slope.
  3. Large GM reduces the buoyancy reserve, causing the ship to pitch more violently.
  4. Large GM increases the ship's displacement, which in turn increases inertia forces.

Explanation

A large GM gives a stiff ship with a short natural roll period. In a seaway, this can lead to rapid, snappy rolling and high lateral accelerations, which may be uncomfortable for crew and dangerous for cargo. It does not directly change displacement or waterplane area.

Question 34Naval Architecture

In the context of ship resistance, which component is primarily reduced by fitting a bulbous bow?

  1. Frictional resistance
  2. Form resistance due to viscosity
  3. Wave-making resistance Correct answer.
  4. Air resistance

Explanation

A bulbous bow is designed to produce a wave that interferes destructively with the bow wave generated by the hull, thereby reducing wave-making resistance at certain speeds. It has little effect on frictional resistance, which is dominated by wetted surface area and surface roughness.

Question 35Naval Architecture

Which of the following statements correctly describes the effect of a free surface in a partially filled tank on a ship's stability?

  1. It increases the righting lever arm at all angles of heel.
  2. It reduces the effective metacentric height (GM) by an amount proportional to the second moment of area of the free surface. Correct answer.
  3. It shifts the centre of buoyancy vertically upward, increasing GM.
  4. It has no effect on stability as long as the tank is watertight.

Explanation

The free surface effect causes a virtual rise of the centre of gravity, reducing the effective GM. The reduction is given by the free surface correction (FSC) = (ρ_liquid / ρ_water) × (I / Δ), where I is the second moment of area of the free surface about its centreline. This effect is independent of the tank's location and depends on the free surface dimensions.

Question 36Naval Architecture

In model testing of ship resistance, which similarity law is used to ensure that wave-making resistance is correctly scaled?

  1. Froude scaling (constant Froude number) Correct answer.
  2. Strouhal scaling (constant Strouhal number)
  3. Reynolds scaling (constant Reynolds number)
  4. Mach scaling (constant Mach number)

Explanation

Wave-making resistance is governed by gravity waves, so geometric similarity and constant Froude number (Froude scaling) are required to scale wave patterns correctly. Reynolds scaling is used for viscous effects but cannot be satisfied simultaneously with Froude scaling for the same model, which is why extrapolation methods are used.

Question 37Naval Architecture

A ship's righting lever (GZ) curve becomes negative beyond 50 degrees of heel. What does this indicate about the ship's stability?

  1. The ship will capsize if heeled beyond 50 degrees without external support. Correct answer.
  2. The ship has a positive range of stability up to 50 degrees.
  3. The ship's maximum GZ occurs at 50 degrees.
  4. The ship's angle of vanishing stability is 50 degrees.

Explanation

A negative GZ means the righting moment becomes a heeling moment, so the ship cannot right itself beyond that angle. The angle at which GZ becomes zero is the angle of vanishing stability; beyond it, the vessel is unstable and may capsize. The maximum GZ occurs where the curve peaks, not necessarily at the zero crossing.

Question 38Naval Architecture

In the context of the PRC maritime regulatory system, which body is responsible for the survey and certification of seagoing ships and offshore installations?

  1. China Shipowners' Association
  2. Ministry of Transport
  3. Maritime Safety Administration (MSA)
  4. China Classification Society (CCS) Correct answer.

Explanation

The China Classification Society (CCS) is the authorized classification society that performs survey and certification of ships and offshore installations under the PRC maritime regulatory framework. The Maritime Safety Administration (MSA) is the governmental authority for maritime safety and pollution prevention, while CCS acts as the technical survey body.

Question 39Naval Architecture

A box-shaped barge has length 60 m, breadth 12 m, and depth 4 m. It floats at a draught of 2.5 m in fresh water. Calculate its displacement (in tonnes).

  1. 1500 t
  2. 2400 t
  3. 2160 t
  4. 1800 t Correct answer.

Explanation

The underwater volume is L × B × T = 60 × 12 × 2.5 = 1800 m³. In fresh water, density is 1.0 t/m³, so displacement = 1800 × 1.0 = 1800 t. If in seawater, it would be 1800 × 1.025 = 1845 t, but the question specifies fresh water.

Question 40Naval Architecture

In the context of ship structural design, which of the following best describes the purpose of a longitudinal stiffener in a double-bottom structure?

  1. To support the inner bottom plating against lateral pressure from cargo.
  2. To increase the longitudinal strength of the hull girder by contributing to the section modulus. Correct answer.
  3. To act as a watertight boundary between tanks.
  4. To provide transverse strength against racking forces.

Explanation

Longitudinal stiffeners in the double bottom run fore-and-aft and, together with the bottom and inner bottom plating, contribute to the longitudinal strength of the hull girder by increasing the effective section modulus. They also support plating against lateral pressure, but their primary structural role in the double bottom is longitudinal strength.

Question 41Ship Design and Construction

In the classical ship design spiral, which activity is normally carried out first when starting a new concept design?

  1. Detailed structural scantling calculation of every frame
  2. Preparation of the detailed production drawings for the block assembly shop
  3. Selecting the main dimensions and hull form from the required deadweight and speed Correct answer.
  4. Full seakeeping model tests in irregular waves

Explanation

The spiral begins with the mission requirements and a first estimate of main dimensions, hull form and power, which are then refined iteratively. Structural scantlings, model tests and production drawings belong to later loops of the spiral, after the concept has converged.

Question 42Ship Design and Construction

Which quantity is defined as the submerged volume of the hull multiplied by the density of the water in which the ship floats?

  1. Displacement Correct answer.
  2. Block coefficient
  3. Deadweight
  4. Reserve buoyancy

Explanation

Displacement is the mass of water displaced by the hull, equal to the displaced volume multiplied by water density. It equals the total mass of the ship and its contents in the floating condition.

Question 43Ship Design and Construction

A ship has a displacement of 12,000 t and a block coefficient of 0.70 in water of density 1.025 t/m3. What is the length on the waterline if the beam is 20 m and the draught is 8 m?

  1. 125.6 m
  2. 95.3 m
  3. 112.0 m
  4. 104.5 m Correct answer.

Explanation

Volume equals displacement divided by density, giving 12,000/1.025 = 11,707 m3. Since volume = CB x L x B x T, the length is 11,707/(0.70 x 20 x 8), which is about 104.5 m.

Question 44Ship Design and Construction

Which framing arrangement places the main longitudinal members close together in the double bottom and at deck, with widely spaced transverse frames?

  1. Transverse framing system
  2. Cellular double-skin arrangement
  3. Longitudinal framing system Correct answer.
  4. Mixed framing system

Explanation

Longitudinal framing concentrates material in closely spaced longitudinals along the deck and bottom, with widely spaced transverse web frames. This raises the section modulus against longitudinal bending and is typical of long ships such as tankers and bulk carriers.

Question 45Ship Design and Construction

Why are longitudinal stiffeners preferred over transverse frames in the deck and bottom of a very long tanker?

  1. They allow the hull to be built without any welding
  2. They increase the metacentric height directly
  3. They reduce the steel weight needed to resist longitudinal bending of the hull girder Correct answer.
  4. They eliminate the need for transverse bulkheads

Explanation

A long hull behaves as a box girder in longitudinal bending, so material placed in continuous longitudinals contributes efficiently to the section modulus. The result is lower structural weight for the same bending strength.

Question 46Ship Design and Construction

In the context of the International Convention for the Safety of Life at Sea, what does the subdivision length of a ship represent?

  1. The length between the forward and aft perpendiculars used for tonnage
  2. The length of the machinery space only
  3. The length used to determine the permissible length of compartments and the floodable length curve Correct answer.
  4. The maximum length of a single cargo hold

Explanation

The subdivision length is the length used with the floodable length curve to set permissible compartment lengths and the required factor of subdivision. It is defined from the convention's geometry rules rather than from cargo hold dimensions.

Question 47Ship Design and Construction

A passenger ship must survive flooding of a compartment without exceeding the margin line. Which concept directly expresses the maximum length of compartment that can be flooded without submerging that margin?

  1. Freeboard deck length
  2. Damage stability range
  3. Permissible length
  4. Floodable length Correct answer.

Explanation

Floodable length is the greatest length of compartment, centred at a given point, that can be flooded without immersing the margin line. The permissible length is then derived from it using the factor of subdivision.

Question 48Ship Design and Construction

Which parameter is defined as the vertical distance from the centre of gravity to the transverse metacentre?

  1. Righting lever
  2. Centre of buoyancy
  3. Freeboard
  4. Metacentric height Correct answer.

Explanation

Metacentric height GM is the distance between the centre of gravity and the transverse metacentre, and it governs initial transverse stability. A positive value indicates a stable equilibrium in the upright condition.

Question 49Ship Design and Construction

A ship of 8,000 t displacement has KM of 7.50 m and KG of 7.10 m. What is the initial metacentric height?

  1. 0.40 m Correct answer.
  2. 0.35 m
  3. 0.45 m
  4. 0.30 m

Explanation

The metacentric height is KM minus KG, so 7.50 minus 7.10 gives 0.40 m. This positive value indicates the ship is initially stable in the upright condition.

Question 50Ship Design and Construction

During a rolling test to determine a ship's metacentric height, which relationship is used?

  1. GM is inversely proportional to the roll period
  2. GM is proportional to the square of the measured roll period for a given radius of gyration Correct answer.
  3. GM equals the roll period multiplied by the beam
  4. GM is independent of the roll period

Explanation

For small rolls the natural period is T = 2 pi k / sqrt(g GM), so GM is proportional to k squared divided by T squared. With an assumed radius of gyration, the measured period therefore yields GM.