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WACE Marine Maritime Studies ATAR study materials
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WACE Marine Maritime Studies ATAR practice questions

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Question 1Marine and maritime environments, ecosystems and sustainability

Which term describes the zone where a river's fresh water mixes with seawater?

  1. Abyssal plain
  2. Estuary Correct answer.
  3. Continental shelf
  4. Pelagic zone

Explanation

An estuary is a semi-enclosed coastal body of water where freshwater from rivers meets and mixes with seawater, producing brackish conditions. These zones are highly productive because nutrients arrive from both land and sea. The other terms refer to open-ocean or deep-sea features, not mixing zones.

Question 2Marine and maritime environments, ecosystems and sustainability

In a rocky shore food web, a mollusc grazing on algae is best described as which of the following?

  1. A primary consumer Correct answer.
  2. A tertiary consumer
  3. A primary producer
  4. A decomposer

Explanation

A primary consumer feeds directly on primary producers such as algae, occupying the second trophic level. Grazing molluscs therefore act as herbivores in the food web. Producers make their own food, higher consumers eat other animals, and decomposers break down dead matter.

Question 3Marine and maritime environments, ecosystems and sustainability

Which human activity is the main cause of excess nutrient enrichment, or eutrophication, in coastal waters?

  1. Underwater volcanic activity
  2. Migration of pelagic fish
  3. Natural tidal movement
  4. Runoff carrying fertiliser from farmland Correct answer.

Explanation

Eutrophication occurs when runoff delivers excess nitrogen and phosphorus from fertilisers and sewage into coastal waters, triggering algal blooms and oxygen depletion. Tides, volcanism and fish migration are natural processes that do not add these nutrients in the same way. Human nutrient loading is the recognised driver of coastal eutrophication.

Question 4Marine and maritime environments, ecosystems and sustainability

What is the main ecological role of mangrove forests along tropical coastlines?

  1. They prevent all coastal erosion permanently
  2. They provide nursery habitat and stabilise shorelines Correct answer.
  3. They replace seagrass meadows entirely
  4. They raise deep-ocean salinity levels

Explanation

Mangroves trap sediment with their roots, buffer wave energy and provide sheltered nursery habitat for fish and crustaceans. These functions support coastal biodiversity and shoreline stability. They do not raise ocean salinity, stop erosion completely, or displace seagrass meadows.

Question 5Marine and maritime environments, ecosystems and sustainability

Which property of seawater most directly determines the depth to which sunlight penetrates for photosynthesis?

  1. Dissolved oxygen
  2. Salinity
  3. Surface tension
  4. Turbidity Correct answer.

Explanation

Turbidity measures how much suspended sediment and plankton scatter and absorb light, so it directly controls light penetration and the depth of the photic zone. Photosynthesis depends on available light rather than on salinity, surface tension or dissolved oxygen. High turbidity therefore reduces the depth at which algae and seagrasses can grow.

Question 6Marine and maritime environments, ecosystems and sustainability

Which of the following best describes a keystone species in a marine ecosystem?

  1. A species found only in one small geographic area
  2. A species that is the most numerous in the community
  3. A species whose influence on community structure is disproportionately large Correct answer.
  4. A species that produces most of the ecosystem's oxygen

Explanation

A keystone species has an effect on community structure that is large relative to its abundance, so its removal triggers major changes. Examples include predators that control prey populations. Abundance, restricted range and oxygen production are different concepts and do not define keystones.

Question 7Marine and maritime environments, ecosystems and sustainability

What is the primary source of energy that drives the marine food web?

  1. Wind-driven waves
  2. Tidal friction
  3. Heat from deep-sea vents
  4. Sunlight captured by phytoplankton Correct answer.

Explanation

Most marine food webs are powered by photosynthesis, in which phytoplankton capture sunlight and convert it into organic matter. These producers are then eaten by zooplankton and higher consumers. Vent heat supports only localised chemosynthetic communities, while tides and waves are physical forces rather than energy sources for the food web.

Question 8Marine and maritime environments, ecosystems and sustainability

A marine protected area is established primarily to achieve which outcome?

  1. Removing all predators from the area
  2. Protecting habitats and species from extractive pressures Correct answer.
  3. Increasing the maximum catch allowed
  4. Encouraging unrestricted anchoring

Explanation

Marine protected areas are set aside to conserve habitats and species by limiting extractive and damaging activities. Well-designed reserves can allow populations to recover and can support nearby fisheries through spillover. They do not raise catch limits, promote unrestricted anchoring, or aim to remove predators.

Question 9Marine and maritime environments, ecosystems and sustainability

A survey finds that a seagrass bed has declined by half after a nearby marina was built. Which explanation best links the two events?

  1. Seagrass migrated inland to escape the boats
  2. Boats added oxygen that harmed the seagrass
  3. Increased turbidity from dredging reduced light reaching the seagrass Correct answer.
  4. The marina raised seawater salinity to toxic levels

Explanation

Dredging and construction stir up sediment, raising turbidity and reducing the light available for seagrass photosynthesis. Seagrass is rooted and cannot migrate inland, and marina construction does not raise ocean salinity to toxic levels. Added oxygen would not harm the plants, so the light-reduction pathway is the most plausible link.

Question 10Marine and maritime environments, ecosystems and sustainability

A fishing authority wants to reduce bycatch of turtles in a trawl fishery. Which measure most directly addresses the problem?

  1. Reducing the mesh size of nets
  2. Increasing engine power of vessels
  3. Fitting turtle excluder devices to nets Correct answer.
  4. Extending fishing hours into the night

Explanation

Turtle excluder devices are grids fitted in trawl nets that allow turtles to escape while retaining the target catch. This directly reduces incidental capture. Engine power, night fishing and smaller mesh do not target turtle escape and may increase bycatch.

Question 11Marine and maritime environments, ecosystems and sustainability

A coral reef experiences a prolonged period of unusually warm water. Which sequence of events is most likely?

  1. Rapid calcification, then bleaching, then cooling
  2. Increased algae, then coral expansion, then cooling
  3. Loss of symbiotic algae, bleaching, then reduced growth Correct answer.
  4. Increased growth, then coral spawning, then recovery

Explanation

Warm water stresses corals so they expel their symbiotic zooxanthellae, losing colour and much of their energy supply, which is bleaching. Prolonged bleaching reduces growth, reproduction and survival. The other sequences reverse or misorder these cause-and-effect steps.

Question 12Marine and maritime environments, ecosystems and sustainability

Why is upwelling important for marine productivity?

  1. It warms surface water and reduces density
  2. It removes oxygen from surface waters
  3. It brings nutrient-rich deep water to the surface Correct answer.
  4. It increases the salinity of coastal waters

Explanation

Upwelling lifts cold, nutrient-rich water from depth to the surface, where sunlight allows phytoplankton to use those nutrients. This supports productive food webs and major fisheries. Upwelling does not primarily warm surface water, strip oxygen, or raise coastal salinity.

Question 13Marine and maritime environments, ecosystems and sustainability

A coastal community wants to restore a degraded saltmarsh. Which action is most consistent with ecological restoration principles?

  1. Draining the marsh to create dry land
  2. Introducing fast-growing exotic grasses for quick cover
  3. Reinstating natural tidal flows and replanting native species Correct answer.
  4. Building a hard seawall over the marsh

Explanation

Restoration aims to reinstate natural processes such as tidal flow and to re-establish native vegetation, allowing the marsh to recover its functions. Exotic species can become invasive, and hard structures or drainage destroy the marsh habitat rather than restore it.

Question 14Marine and maritime environments, ecosystems and sustainability

Which factor most strongly limits phytoplankton growth in large areas of the open ocean?

  1. Excessive sunlight at the surface
  2. Low nutrient concentrations in surface water Correct answer.
  3. High numbers of phytoplankton
  4. Rapid water evaporation

Explanation

In much of the open ocean, nutrients such as nitrate and phosphate are scarce in the sunlit surface layer, limiting phytoplankton growth. Light is usually adequate near the surface and phytoplankton do not limit themselves by abundance. Evaporation is not the principal control on this growth.

Question 15Marine and maritime environments, ecosystems and sustainability

In a marine ecosystem, a large shark population declines sharply. Which outcome best illustrates a trophic cascade?

  1. Nutrient input from rivers doubles
  2. Phytoplankton immediately become extinct
  3. Mid-level predators increase and grazers decline Correct answer.
  4. Seawater salinity rises rapidly

Explanation

A trophic cascade occurs when removing a top predator releases mid-level predators from control, so they increase and suppress the next level down. Extinction of all phytoplankton, salinity change and river nutrient input are not direct cascade effects of losing sharks.

Question 16Marine and maritime environments, ecosystems and sustainability

Which statement best explains why estuaries are highly productive despite stressful conditions?

  1. Freshwater kills most competing organisms
  2. Nutrients are trapped and recycled within the sheltered system Correct answer.
  3. Tidal flow removes all nutrients
  4. Salinity is constant throughout the estuary

Explanation

Estuaries trap nutrients delivered by rivers and recycle them within sheltered waters, supporting high primary production. Freshwater does not kill competitors, tidal flushing does not remove all nutrients, and salinity varies considerably across an estuary.

Question 17Marine and maritime environments, ecosystems and sustainability

A manager wants to reduce the risk of introduced marine pests spreading between ports. Which measure is most effective?

  1. Painting hulls in brighter colours
  2. Increasing vessel speed in port
  3. Anchoring vessels in deeper water
  4. Treating and managing ballast water before discharge Correct answer.

Explanation

Ballast water carries plankton and larvae between ports, so treating or exchanging it before discharge reduces the transfer of introduced species. Hull colour, port speed and anchoring depth do not address the main transport pathway. Biofouling management is also important, but ballast treatment is the direct measure listed.

Question 18Marine and maritime environments, ecosystems and sustainability

Which characteristic best distinguishes a marine mammal from a fish?

  1. Marine mammals are always larger than fish
  2. Marine mammals live only in shallow water
  3. Marine mammals have scales and gills
  4. Marine mammals breathe air and nurse their young Correct answer.

Explanation

Marine mammals are air-breathing vertebrates that nurse their young with milk, whereas fish typically use gills and do not nurse. Size and depth range vary widely in both groups and do not reliably distinguish them. These reproductive and respiratory traits are the defining differences.

Question 19Marine and maritime environments, ecosystems and sustainability

A reef survey records a fall in herbivorous fish alongside a rise in fleshy macroalgae. Which interpretation is most reasonable?

  1. The algae caused the fish to become carnivorous
  2. Corals grew faster because algae increased
  3. Salinity fell and killed the herbivores
  4. Reduced grazing allowed algae to outcompete corals Correct answer.

Explanation

Herbivorous fish graze algae that would otherwise compete with corals for space and light. When grazing pressure falls, fleshy macroalgae can expand and suppress coral recruitment and growth. The other options misstate the relationship between grazing, algae and corals.

Question 20Marine and maritime environments, ecosystems and sustainability

Which practice best supports sustainable management of a wild-capture fishery?

  1. Removing all competing predator species
  2. Targeting breeding adults exclusively
  3. Allowing unlimited catch during peak season
  4. Setting catch limits based on stock assessment data Correct answer.

Explanation

Sustainable management uses stock assessments to set catch limits that allow populations to reproduce and replenish. Unlimited catch, targeting breeding adults and removing predators all increase pressure on the stock or disrupt the ecosystem. Science-based limits are the core tool of sustainable harvest.

Question 21Marine and maritime environments, ecosystems and sustainability

A scientist samples water at increasing depth and finds dissolved oxygen falls sharply below a certain layer. Which explanation is most likely?

  1. Sunlight destroys oxygen molecules at depth
  2. Salinity at depth converts oxygen to hydrogen
  3. Cold deep water cannot hold any oxygen
  4. Bacterial decomposition of sinking organic matter consumes oxygen at depth Correct answer.

Explanation

Organic matter sinking from the surface is broken down by bacteria, and this decomposition consumes dissolved oxygen in deeper water, sometimes creating oxygen-minimum zones. Light does not destroy oxygen molecules, cold water holds more oxygen rather than none, and salinity does not convert oxygen to hydrogen.

Question 22Marine and maritime environments, ecosystems and sustainability

Two estuaries receive similar nutrient loads, but only one develops severe algal blooms. Which difference most plausibly explains this?

  1. The other estuary has stronger tidal flushing that disperses nutrients Correct answer.
  2. The other estuary has higher salinity throughout
  3. The other estuary has no phytoplankton at all
  4. The other estuary is located closer to the equator

Explanation

Flushing rate controls how long nutrients remain in an estuary; strong tidal exchange disperses nutrients and limits the accumulation that fuels blooms. Phytoplankton are present in most estuaries, and latitude or salinity alone do not determine bloom severity. Residence time is the key difference.

Question 23Marine and maritime environments, ecosystems and sustainability

A marine reserve increases fish biomass inside its boundaries, but nearby fishers report little change. Which explanation is most consistent with reserve theory?

  1. Fish inside reserves cannot reproduce
  2. Fishers are not permitted near any reserve
  3. Reserves never benefit fisheries outside their boundaries
  4. Spillover depends on larval dispersal, adult movement and time since protection Correct answer.

Explanation

Benefits to adjacent fisheries depend on larval export, movement of adults across boundaries and how long protection has been in place; these processes can take years. Reserves can benefit outside fisheries, fish inside do reproduce, and fishers are often allowed right up to the boundary. The timing and dispersal factors best explain the observation.

Question 24Marine and maritime environments, ecosystems and sustainability

A coastal developer proposes removing a dune system to build a seawall. Which ecological consequence is most defensible?

  1. Improved sand supply to adjacent beaches
  2. Loss of buffering habitat that absorbs wave energy and supports shore species Correct answer.
  3. Elimination of all coastal erosion
  4. Permanent increase in beach width from the seawall

Explanation

Dunes absorb wave energy, store sand and provide habitat for specialised shore species, so removing them for a hard wall reduces buffering and biodiversity. Seawalls commonly narrow beaches and interrupt sand supply rather than widen them, and they cannot eliminate erosion. The ecological loss of the dune habitat is the most defensible consequence.

Question 25Marine and maritime environments, ecosystems and sustainability

An ecosystem shows high species richness but low evenness, with one species dominating. How should its diversity be described?

  1. Richness is high, but overall diversity is limited by low evenness Correct answer.
  2. Diversity is maximal because richness is high
  3. Diversity is zero because one species dominates
  4. Evenness is high and richness is low

Explanation

Diversity combines species richness with evenness of abundance. High richness with a single dominant species gives low evenness, so overall diversity is lower than the richness count alone suggests. Maximal diversity requires both high richness and high evenness, and diversity is not zero when many species are present.

Question 26Marine and maritime environments, ecosystems and sustainability

Which term describes the variety of species present in a marine community together with their relative abundances?

  1. Carrying capacity
  2. Species diversity Correct answer.
  3. Trophic level
  4. Primary productivity

Explanation

Species diversity combines two components: species richness, which is the number of species present, and evenness, which describes how similar the abundances of those species are. A community with many species but one dominant species is less diverse than one where abundances are balanced. Carrying capacity, trophic level and productivity describe other ecosystem properties.

Question 27Marine and maritime environments, ecosystems and sustainability

Which group of organisms forms the base of nearly all marine food webs?

  1. Large predatory fish
  2. Detritivorous worms
  3. Benthic filter feeders
  4. Phytoplankton Correct answer.

Explanation

Phytoplankton are photosynthetic microscopic organisms drifting in the sunlit surface layer, and they fix the carbon that supports almost all marine food webs. They are the dominant primary producers in open water, while other groups depend on the organic matter produced. Grazers, filter feeders and predators all ultimately draw energy from this production.

Question 28Marine and maritime environments, ecosystems and sustainability

Which zone of the ocean receives enough sunlight for photosynthesis to occur at a significant rate?

  1. Benthic zone
  2. Aphotic zone
  3. Abyssal zone
  4. Euphotic zone Correct answer.

Explanation

The euphotic zone is the upper, sunlit layer where light intensity is sufficient for net photosynthesis by phytoplankton and algae. Its depth varies with water clarity but is typically tens to around two hundred metres. Below it, light is too weak for photosynthesis, and the abyssal zone lies far deeper still.

Question 29Marine and maritime environments, ecosystems and sustainability

Which process returns nitrogen from the atmosphere into a form usable by marine primary producers?

  1. Denitrification
  2. Sedimentation
  3. Eutrophication
  4. Nitrogen fixation Correct answer.

Explanation

Nitrogen fixation is carried out by certain bacteria and cyanobacteria that convert atmospheric nitrogen gas into ammonia, which can then be used by producers. This process is a key input to the marine nitrogen cycle because most organisms cannot use nitrogen gas directly. Denitrification removes fixed nitrogen instead of adding it.

Question 30Marine and maritime environments, ecosystems and sustainability

A coastal lagoon receives treated sewage with high nitrate concentrations. Which response is most likely in the following weeks?

  1. A rise in seagrass biomass across the lagoon floor
  2. A shift towards faster growth of algae and phytoplankton Correct answer.
  3. An immediate increase in dissolved oxygen at depth
  4. A decline in phytoplankton because nitrate inhibits photosynthesis

Explanation

Adding nitrate, a limiting nutrient, relieves the constraint on algal growth, so phytoplankton and opportunistic algae typically increase rapidly. Later, decomposition of this extra organic matter consumes oxygen, so deep oxygen levels usually fall rather than rise. Seagrasses, being rooted and light-demanding, are often shaded out rather than stimulated.

Question 31Marine and maritime environments, ecosystems and sustainability

Which feature most clearly identifies mangrove communities as adapted to their environment?

  1. Pneumatophores and salt-excluding tissues Correct answer.
  2. Dependence on freshwater flooding for seed dispersal
  3. Deciduous leaves that shed in winter
  4. Deep taproots reaching the water table

Explanation

Mangroves grow in saline, waterlogged mud where oxygen is scarce, so they possess aerial roots such as pneumatophores and physiological mechanisms that exclude or excrete salt. These adaptations allow them to tolerate regular tidal inundation. They are evergreen and disperse propagules by water rather than relying on deep taproots.

Question 32Marine and maritime environments, ecosystems and sustainability

A species is caught from a wild stock at a rate that consistently exceeds its natural rate of recruitment. What is the most likely long-term consequence?

  1. The stock will decline towards collapse Correct answer.
  2. Recruitment will rise to match the catch automatically
  3. The stock will stabilise at a higher biomass
  4. The species will rapidly evolve a larger body size

Explanation

When removals exceed recruitment, the spawning biomass falls and fewer young are produced, so the stock shrinks over time. This can lead to commercial collapse and ecological effects on predators and prey. Recruitment does not automatically rise to match catch; it depends on the number of surviving spawners.

Question 33Marine and maritime environments, ecosystems and sustainability

Which statement best explains why intertidal organisms on a rocky shore are often arranged in distinct bands?

  1. Predators are evenly distributed at all shore heights
  2. Larval supply is identical at every tidal height
  3. Species differ in tolerance to desiccation and competition across the tidal gradient Correct answer.
  4. Each species settles only where wave action is absent

Explanation

Zonation on rocky shores reflects differences among species in tolerance to the stresses of exposure at each tidal height, combined with competition and predation. The upper shore favours species resistant to drying out, while the lower shore supports those less tolerant of air exposure. Settlement and survival are not uniform across heights.

Question 34Marine and maritime environments, ecosystems and sustainability

What is the main ecological role of seagrass meadows in coastal waters?

  1. Stabilising sediments and providing nursery habitat Correct answer.
  2. Removing salt from the surrounding seawater
  3. Producing the oxygen needed by deep-sea communities
  4. Preventing all coastal erosion during storms

Explanation

Seagrass roots and rhizomes bind sediment, reducing erosion, while the leafy canopy shelters juvenile fish and invertebrates and supports high secondary production. Seagrasses are flowering plants that photosynthesise and provide food and habitat. Their influence is local and does not extend to supplying oxygen to deep-sea communities.

Question 35Marine and maritime environments, ecosystems and sustainability

A coral reef is heavily fished for parrotfish and surgeonfish, and divers begin to see bare rock expanding over the reef. Which explanation best accounts for this change?

  1. Removal of herbivores increases coral growth by reducing competition
  2. Fishing reduces water temperature and bleaches coral
  3. Removal of herbivores allows fast-growing algae to overgrow coral recruits Correct answer.
  4. The fish were the main producers of reef carbonate

Explanation

Parrotfish and surgeonfish graze algae that would otherwise colonise dead coral and rock surfaces. When these herbivores are removed, fleshy algae grow faster and can smother or outcompete slow-growing coral recruits, shifting the reef towards an algal state. Herbivores do not build the reef framework themselves.

Question 36Marine and maritime environments, ecosystems and sustainability

Why do deep ocean waters generally contain higher concentrations of nutrients such as nitrate and phosphate than surface waters?

  1. Nutrients are produced only by deep-sea animals
  2. Surface waters are too cold to hold dissolved nutrients
  3. Sinking organic matter is decomposed and remineralised at depth Correct answer.
  4. Sunlight destroys nutrients in the surface layer

Explanation

Organic matter formed in the sunlit surface sinks and is broken down by bacteria at depth, releasing dissolved nutrients into deep water where they accumulate. Because there is little light at depth, these nutrients are not consumed by photosynthesis. Upwelling can later return them to the surface.

Question 37Marine and maritime environments, ecosystems and sustainability

An introduced seaweed is discovered on a rocky jetty in a new region. Which action would most directly reduce the risk of it spreading to other sites?

  1. Increasing the number of recreational boats allowed to moor
  2. Cleaning and drying vessels and gear before they move between sites Correct answer.
  3. Releasing a generalist herbivore to graze the seaweed
  4. Monitoring the jetty without changing any vessel practices

Explanation

Introduced marine species are commonly spread as hull fouling or in trapped water and gear, so cleaning and drying equipment before relocation breaks the transport pathway. This biosecurity measure targets the mechanism of spread rather than relying on later control. Monitoring alone does not prevent movement between sites.

Question 38Marine and maritime environments, ecosystems and sustainability

A scientist compares two bays and finds that one supports a far greater number of trophic links among its species. Which measure of ecosystem organisation is being described?

  1. Food web connectance Correct answer.
  2. Species evenness
  3. Primary productivity
  4. Population density

Explanation

Food web connectance describes how many of the possible feeding links among species are actually realised, so a bay with many trophic links has higher connectance. It is a property of the network structure rather than of abundance or production. Evenness and density concern abundances, not feeding relationships.

Question 39Marine and maritime environments, ecosystems and sustainability

In a marine system, nitrogen fixation by cyanobacteria is high, but measurements show low concentrations of dissolved nitrate in surface water. Which explanation is most consistent with these observations?

  1. Fixed nitrogen is rapidly taken up by producers and recycled within the surface community Correct answer.
  2. Nitrogen fixation produces nitrogen gas rather than usable compounds
  3. Cyanobacteria consume nitrate faster than it can be measured
  4. Nitrate is destroyed by the high light levels at the surface

Explanation

Nitrogen fixation supplies new usable nitrogen, but in an oligotrophic surface layer this nitrogen is taken up quickly by phytoplankton and recycled through grazing and microbial processes. As a result, standing concentrations of nitrate can remain low even when input rates are appreciable. Measurements of concentration therefore do not directly indicate input rate.

Question 40Marine and maritime environments, ecosystems and sustainability

A decision-maker must compare the ecological value of two coastal sites with limited funds. Which approach provides the most defensible comparison?

  1. Choosing the site closest to the city because access is easier
  2. Selecting the site with the larger area regardless of habitat type
  3. Relying on the number of species reported by local residents at each site
  4. Using consistent, measurable indicators of habitat condition and connectivity at both sites Correct answer.

Explanation

A defensible comparison applies the same measurable indicators, such as habitat condition, biodiversity and connectivity to other habitats, at both sites. This reduces bias and allows the results to be compared and reviewed. Convenience, anecdotal reports and area alone are weak proxies for ecological value.

Question 41Vessel design, construction, stability and buoyancy

Which term describes the upward force exerted by a fluid on an immersed or floating body?

  1. Deadweight
  2. Buoyancy Correct answer.
  3. Displacement
  4. Reserve buoyancy

Explanation

Buoyancy is the upward force a fluid exerts on a body, equal to the weight of fluid displaced by that body. It arises from the pressure difference between the deeper and shallower parts of the submerged hull. Displacement refers to the mass of water displaced, not the force itself.

Question 42Vessel design, construction, stability and buoyancy

A vessel floats in equilibrium when which condition is satisfied?

  1. Its reserve buoyancy equals zero
  2. Its centre of gravity lies below the keel
  3. Its weight equals the buoyant force Correct answer.
  4. Its weight exceeds the buoyant force

Explanation

A floating body is in vertical equilibrium when the downward weight equals the upward buoyant force. This is Archimedes' principle applied to a floating vessel. If the two forces are unequal the vessel either sinks further or rises until they balance.

Question 43Vessel design, construction, stability and buoyancy

What does the term 'displacement' of a vessel mean?

  1. The total area of the waterplane
  2. The volume of cargo space available
  3. The mass of water displaced by the hull Correct answer.
  4. The distance from keel to main deck

Explanation

Displacement is the mass of water the hull pushes aside when floating, and by Archimedes' principle it equals the mass of the vessel. It is usually expressed in tonnes. Volume of displacement is the corresponding volume of water in cubic metres.

Question 44Vessel design, construction, stability and buoyancy

Which of the following best defines deadweight?

  1. The mass of the empty hull and machinery
  2. The mass of water displaced at the load line
  3. The volume of the hull below the waterline
  4. The total mass of cargo, fuel, stores and crew a vessel can carry Correct answer.

Explanation

Deadweight is the difference between the loaded displacement and the lightship displacement. It therefore represents everything the vessel can carry: cargo, bunkers, fresh water, ballast, stores and crew. It is expressed in tonnes.

Question 45Vessel design, construction, stability and buoyancy

Which point is the centre of buoyancy?

  1. The point where the rudder post meets the keel
  2. The centroid of the underwater volume of the hull Correct answer.
  3. The midpoint of the main deck
  4. The centre of gravity of the loaded vessel

Explanation

The centre of buoyancy is the geometric centroid of the displaced water volume, effectively where the total buoyant force acts. Its position changes as the vessel heels or changes draft. It is not the same point as the centre of gravity.

Question 46Vessel design, construction, stability and buoyancy

What is freeboard?

  1. The distance between two adjacent frames
  2. The depth of water from keel to seabed
  3. The total height of the superstructure
  4. The vertical distance from the waterline to the freeboard deck Correct answer.

Explanation

Freeboard is measured vertically from the summer load waterline to the freeboard deck at side. It represents the reserve buoyancy available before water can enter the deck. Greater freeboard generally improves seakeeping and reserve buoyancy.

Question 47Vessel design, construction, stability and buoyancy

Which statement correctly describes reserve buoyancy?

  1. It is the weight of ballast carried
  2. It is the water displaced by the rudder
  3. It is the buoyancy lost when the vessel heels
  4. It is the watertight volume above the waterline Correct answer.

Explanation

Reserve buoyancy is the volume of the watertight hull above the waterline that can be immersed before the vessel is overwhelmed. It provides the extra lift needed when additional weight is added or when waves wash over the hull. It is closely related to freeboard.

Question 48Vessel design, construction, stability and buoyancy

Which of the following is a property of the transverse metacentre (M)?

  1. It is the point where the vertical through the new centre of buoyancy meets the original centreline Correct answer.
  2. It is the point about which the vessel rotates in pitch
  3. It is the geometric centre of the cargo hold
  4. It is the point where the anchor chain is secured

Explanation

When a vessel heels through a small angle, the centre of buoyancy moves sideways. The vertical line through the new centre of buoyancy intersects the original centreline at the transverse metacentre. For small angles this point can be treated as fixed.

Question 49Vessel design, construction, stability and buoyancy

A box-shaped pontoon has a displacement of 400 tonnes and floats in seawater of density 1.025 t/m³. What is its volume of displacement?

  1. 390.2 m³ Correct answer.
  2. 400.0 m³
  3. 1.025 m³
  4. 410.0 m³

Explanation

Volume of displacement equals mass divided by water density, so 400 divided by 1.025 gives about 390.2 cubic metres. Density must be used in consistent units of tonnes per cubic metre. The displacement mass stays the same but the volume changes with water density.

Question 50Vessel design, construction, stability and buoyancy

A vessel of 2000 tonnes displacement moves from fresh water to seawater. What happens to its displacement and its draft?

  1. Displacement increases and draft increases
  2. Displacement stays the same and draft decreases Correct answer.
  3. Displacement stays the same and draft increases
  4. Displacement decreases and draft decreases

Explanation

Displacement is the vessel's mass, which does not change when it enters denser seawater. Because seawater supports more weight per cubic metre, less volume is needed and the vessel rises, so draft decreases. This is why load line marks differ between fresh and salt water.