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Sep 113 min read

Ship's Sea Chests: What is their function?

Did you know that blockages in ships' internal seawater systems have led to engine room flooding, power loss, and even ship sinking? These systems are critical and depend on a key component: the ship's sea chest. As a vital part of marine engineering, sea chests are the entry point for seawater. This seawater is essential for various shipboard equipment to work correctly. It's crucial to grasp the role and significance of these systems for the smooth operation and safety of ships.


A sea chest grating, as seen during underwater cleaning (diver's perspective)
A sea chest grating, as seen during underwater cleaning (diver's perspective)

Sea chests are built into the ship's hull, usually below the waterline. They function as an intake and filter for seawater. This water is used for cooling systems, lubricating oil, and other systems. The capacity of sea chests varies by ship type, with larger vessels needing more space.


Key Takeaways

  • Sea chests are vital for a ship's seawater intake, acting as a gateway for seawater.

  • Blockages in these systems can cause engine room flooding, power loss, and even ship sinking.

  • Sea chests filter and store seawater for cooling and freshwater generation on board.

  • The capacity of sea chests depends on the ship's size, with larger vessels needing more space.

  • Knowing how sea chests work is key for marine engineers and those in ship operations to ensure safety and efficiency.


Introduction to Ship's Sea Chests

Sea chests are crucial for a ship's hull, enabling the intake of seawater for cooling systems and ballast tanks. They are essential for the vessel's operation and upkeep. Knowing the sea chest definition and their position is key for marine engineers and ship operators.


Definition of sea chests

A sea chest is a recess in the ship's hull, mostly found in the engine room. It's protected by gratings to keep out debris and marine life. Sea chests are vital for drawing seawater into the ship for cooling and other uses.


Location of sea chests on a ship

Sea chests are placed on the lowest levels of a ship, to ensure effective seawater intake. They sit between the ship's side and the engine room, serving the cooling systems and ballast tanks. Their exact location depends on the ship's size and the seawater's intended use.


The size, number, and dimensions of sea chests vary considerably with vessel size and type. Larger vessels have a greater demand for ballast water, resulting in larger and a greater number of sea chests.

The effectiveness of sea chests relies on their placement. They must be at a depth that guarantees a steady seawater supply, even in shallow waters & in light-ballast condition. Their location should also protect them from damage and reduce biofouling and corrosion risks.


Vessel Type

Number of Sea Chests

Typical Location

Bulk Carriers

2-4

Engine room, forward and aft

Container Ships

4-6

Engine room, forward and aft

Oil Tankers

2-4

Engine room, midship

Cruise Ships

6-8

Engine room, forward, midship, and aft


The strategic placement of sea chests is vital for a reliable seawater supply. Understanding their definition and location helps marine professionals maintain and optimize these crucial components. This ensures the safe and effective operation of the vessel.


Primary Purpose of Sea Chests

Sea chests are crucial for ship operations, enabling the intake of seawater for vital systems. They act as the primary entry point for seawater, distributing it through the ship's piping systems. This supports essential operations.


Drawing seawater into the vessel

Sea chests are designed to draw seawater into the vessel efficiently. They provide a controlled entry point, ensuring a steady supply for shipboard systems. Their strategic placement ensures optimal seawater intake, even in challenging conditions or shallow waters.


Acting as a gateway for seawater intake

Sea chests serve as the primary gateway for seawater, distributing it to various vessel parts. Their design, with protective gratings and baffle plates, minimizes debris and marine life entry. This supports critical systems, such as:

  • Cooling systems for engines and machinery

  • Ballast water management

  • Firefighting systems

  • Desalination plants for freshwater production


The number and size of sea chests vary by ship size, type, and operational needs. Larger vessels, like bulk carriers and tankers, may have multiple sea chests. They are strategically placed, usually in the engine room, for efficient distribution to critical components.


Sea chests are the unsung heroes of a ship's operations, quietly performing their crucial role in ensuring the vessel's smooth functioning and the safety of its crew and cargo.


Design and Structure of Sea Chests

Sea chests are crucial for a ship's seawater intake system. They draw in seawater efficiently, keeping debris and marine life out. The sea chest design includes rectangular or cylindrical recesses in the hull. These provide a secure spot for seawater intake.


Rectangular or Cylindrical Recesses in the Hull

Sea chests come in various shapes based on the vessel's needs and hull design. Rectangular sea chests are often used in large ships like cargo vessels and tankers. They offer a larger intake area and fit well into the flat hull bottom. Cylindrical sea chests suit smaller ships or those with curved hulls, blending seamlessly into the hull's shape.


A sea chest, as seen from the drydock. The sea chest is being blanked, prior to commencement of painting operations
A sea chest, as seen from the drydock. The sea chest is being blanked, prior to commencement of painting operations


Protective Gratings and Baffle Plates

Sea chests use protective gratings to keep out large debris and marine life. These gratings filter out big objects while letting seawater through. They're made from materials like stainless steel or copper-nickel alloys to resist corrosion.


Baffle plates are also used in sea chests. They help distribute water flow evenly, reducing turbulence. This ensures a steady supply of seawater to the ship's systems, even in rough seas.


Varying Intake Sizes

The number and size of sea chests vary with the ship's size, type, and needs. Large ships like bulk carriers and container vessels need more seawater for cooling and ballast. They have multiple sea chests of different sizes along the hull for a reliable seawater supply.


Vessel Type

Typical Number of Sea Chests

Common Intake Sizes

Bulk Carriers

2-4

400-800 mm

Container Ships

3-6

500-1000 mm

Tankers

2-5

600-1200 mm

Cruise Ships

4-8

800-1500 mm


Optimizing sea chest design, using protective gratings and baffle plates, and choosing the right intake sizes helps ships draw seawater efficiently. This approach minimizes damage to internal systems and ensures optimal performance in various conditions.


Sea Chests as a Reservoir and Filter

Sea chests are vital for a ship's seawater intake, serving as an intake reservoir and filter. They help stabilize water flow and shield the vessel from debris and marine growth. This dual function is crucial for maintaining the ship's internal systems.


Intake reservoir for piping systems

Sea chests serve as a buffer between the ocean and the ship's piping. They maintain a steady seawater volume, ensuring a consistent supply for various shipboard functions. This is essential for cooling systems, which need a constant flow to regulate temperatures effectively.


Removable gratings for protection

Removable gratings at the intake prevent large debris from entering the sea chest. These gratings, crafted from durable materials, shield the ship's systems from driftwood, seaweed, and marine life. They can be easily cleaned, keeping the sea chest clear and functional.


Sea chest covers made of metal are susceptible to bio-fouling, including the growth of algae and barnacles. Corrosion is also a concern for metal sea chest covers, especially due to the high concentration of salt in seawater.


Baffle plates to dampen effects of vessel speed or sea state

Baffle plates inside the sea chest help stabilize water flow and reduce turbulence. They break up the water flow, ensuring a consistent supply to the ship's systems. This helps maintain the sea chest's efficiency and reliability as a reservoir and filter.


After the seawater passes through the sea chest, it undergoes further filtration to remove smaller particles. This multi-stage process, starting with the sea chest's gratings and baffle plates, is crucial. It protects the vessel's critical components and ensures optimal performance throughout its life.


Uses of Seawater Drawn from Sea Chests

Seawater from a ship's sea chests is crucial for various onboard systems. It cools machinery and provides essential services, ensuring the vessel operates efficiently and crew comfort. Let's delve into the diverse applications of seawater from sea chests.


Cooling for Fresh Water in Central Coolers

Seawater is a key component in the ship's cooling systems. In central freshwater cooling systems, it cools the fresh water circulating through machinery. This process keeps engines and equipment at optimal temperatures.


This seawater cooling system is vital for the reliable operation of the ship's propulsion and auxiliary machinery.


Cooling of Condensate in Auxiliary/Atmospheric Condensers

Seawater also cools condensate in auxiliary and atmospheric condensers. It acts as a heat sink, absorbing heat from the condensate. This process is crucial for maintaining the efficiency of the ship's steam systems and preventing overheating.


Cooling of Exhaust/Gland/Condensate Steam from Turbines

Seawater cools exhaust steam, gland steam, and condensate steam from turbines, like those in cargo pumps. This helps dissipate heat, preventing excessive temperatures. It ensures the safe and efficient operation of the turbines.


Cooling of Air Conditioning/Refrigeration Condensers

Seawater cools air conditioning and refrigeration condensers on ships. These systems are vital for crew comfort and preserving perishable goods. By absorbing heat from the refrigerant, seawater keeps these systems functioning effectively.


Cooling of Lubricating Oil/Stern Tube Oil/Intermediate Shaft Bearing Oil

Seawater cools various oils used in shipboard machinery, including lubricating oil, stern tube oil, and intermediate shaft bearing oil. Through heat exchangers, it removes excess heat, maintaining optimal temperature and viscosity. This is crucial for preventing overheating and ensuring mechanical components operate smoothly.


Seawater Feed for Freshwater Generators

Seawater is also used as a feed source for freshwater generators on ships. These systems produce potable water for crew and passengers by distilling or desalinating seawater. This ensures a reliable supply for drinking, cooking, and other needs.


Scrubber Towers and Deck Seals in Oil Tankers

In oil tankers, seawater is used in scrubber towers and deck seals. Scrubber towers clean exhaust gases, reducing emissions and meeting environmental standards. Seawater in deck seals prevents oil vapors from escaping, ensuring a safe deck environment. These oil tanker systems depend on seawater for their effectiveness.


The GH by Carver Pump is a high-capacity centrifugal pump for marine seawater cooling with flows up to 2,500 GPM and heads up to 520 feet.

In conclusion, seawater from sea chests is essential for various onboard systems. It cools machinery, produces fresh water, and supports scrubbing and sealing operations. These functions are vital for the safe, efficient, and environmentally responsible operation of modern ships.


Importance of Sea Chests for Ship Operations

Sea chests are essential for a ship's seawater supply system, crucial for the smooth operation of vital functions. These structures, strategically placed, serve as the primary source of seawater. This seawater is readily available and cost-effective, making sea chests vital for the ship's engines, cooling systems, and machinery.


A basic schematic of the location of sea chests onboard a ship
A basic schematic of the location of sea chests onboard a ship

The consistent supply of seawater through sea chests is critical for ship operations. Inadequate or imbalanced water intake can lead to overheating, causing severe damage to the ship's systems. This can result in power loss, engine room flooding, running aground, or even sinking.


A sea chest on commercial ships can typically hold around 1-3 cubic meters of sea water, with larger ships having larger and more numerous sea chests to meet their increased demand.

Seawater from sea chests serves multiple purposes, including:

  • Cooling fresh water in central coolers

  • Cooling condensate in auxiliary and atmospheric condensers

  • Cooling exhaust, gland, and condensate steam from turbines

  • Cooling air conditioning and refrigeration condensers

  • Cooling lubricating oil, stern tube oil, and intermediate shaft bearing oil

  • Providing seawater feed for freshwater generators

  • Supplying water to scrubber towers and deck seals in oil tankers


The efficient functioning of sea chests directly impacts the ship's engines and machinery performance and longevity. Proper engine cooling is crucial to prevent overheating, ensure optimal performance, and reduce wear and tear. Seawater from sea chests acts as a heat sink, absorbing excess heat from the engines and equipment, maintaining optimal operating temperatures.


In summary, sea chests are critical for a ship's seawater supply system, ensuring the smooth operation of essential functions. Their importance in ship operations is immense, affecting the vessel's performance, safety, and reliability.


Common Issues with Sea Chests

Sea chests are crucial for a ship's operation but face various problems that affect its performance and system efficiency. These issues, if ignored, can lead to reduced water intake, increased fuel consumption, and engine damage. Such problems can severely impact the vessel's operations.


Clogging and Blockages by Marine Debris and Organisms

Sea chests often face clogging and blockages from marine debris and organisms. Seawater entering the vessel through these chests carries debris and marine life. Over time, this accumulation can restrict water flow, affecting the ship's cooling systems and other vital components.


Biofouling of Internal Surfaces

Biofouling, the growth of marine organisms on sea chest surfaces, is a major concern. These organisms, such as barnacles and algae, thrive in the warm, nutrient-rich environment of sea chests. This growth can obstruct water flow and reduce sea chest efficiency, potentially causing blockages.


Vessel Type

Biofouling Impact

Lower activity vessels (leisure and passenger)

Heavily impacted due to travel speed and idling/downtime

Global shipping fleet

Niche areas account for 10% of total underwater hull surface

249-ship sample (2015-2019)

44% had unacceptable levels of hard fouling coverage (>10%)

249-ship sample (2015-2019)

Animal fouling present in 95% of niche area observations


Potential for Engine Damage due to Inadequate Water Intake

Sea chest clogging and biofouling can lead to restricted seawater flow. This can cause engines to overheat, potentially leading to damage. Such damage can result in costly repairs, downtime, and reduced efficiency. In severe cases, engine failure can threaten crew safety and vessel integrity.


The International Maritime Organisation (IMO) suggests that vessel biofouling has been comparable to, if not more significant than, untreated ballast water for introducing invasive aquatic species (IAS), with evidence indicating that 70-80% of IAS introductions occur through biofouling.

To address these risks, ship operators must prioritize sea chest maintenance. Effective antifouling measures, such as Marine Growth Prevention Systems (MGPS) and Impressed Current Cathodic Protection (ICCP), are crucial. Regular inspections and cleaning are also essential to keep sea chests clear of obstructions and biofouling.


Maintenance and Protection of Sea Chests

To ensure sea chests function properly, various maintenance and protection methods are used. Regular sea chest maintenance is vital, especially in regions like the UAE. Neglecting cleaning can lead to marine growth and debris buildup, causing blockages and impacting ship performance.


Marine Growth Prevention Systems (MGPS)

Marine Growth Prevention Systems (MGPS) like sacrificial anodic copper and chlorine-based dosing systems control marine organism growth in sea chests and internal pipework. Anodes in MGPS systems spread ions in seawater, creating an antifouling and anti-corrosive layer. There are three main types of alloys used for anodes:

  • Copper Alloyed

  • Aluminum Alloyed

  • Ferrous Alloyed


An MGPS system can be installed with anodes on sea chests, in strainers, or through a treatment tank with a spray nozzle. Its benefits include reduced marine organism growth, eliminating corrosion, and increasing system cleaning intervals. This leads to improved system efficiency and energy savings.


Impressed Current Cathodic Protection (ICCP)

ICCP systems, featuring copper, aluminum, or iron anodes and reference cells, fight corrosion of sea chests and internal pipes. A poorly set up MGPS/ICCP system can lead to severe corrosion incidents. Sacrificial anodes in sea chests are often underestimated. If damaged and combined with an improper MGPS/ICCP setup, they will consume faster than expected.


Conclusion

Ship's sea chests are crucial for a vessel's functionality and safety, showcasing their importance in marine engineering. They serve as the primary source of seawater, vital for various shipboard systems, including engine cooling and freshwater production. The International Maritime Organization advocates for marine growth protection systems and antifouling paints to combat biofouling. This issue can significantly increase vessel running costs by several million dollars annually.


Marine engineers and ship operators can maintain optimal performance and prevent costly damages by understanding sea chest design and common issues. Proper ship maintenance practices are essential. Issues with internal seawater systems can cause severe problems, such as complete power loss, engine room flooding, or even shipwrecks, as reported by international marine authorities. Regular inspections, cleaning, and the use of marine growth protection systems can extend sea chest life and ensure vessel efficiency. Effective ship maintenance of sea chests is vital for the safety, reliability, and cost-effectiveness of marine operations. This highlights the importance of marine engineering in the shipping industry.


FAQ

What is the primary function of ship's sea chests?

Ship's sea chests draw seawater into the vessel for essential engine room functions. They act as a controlled gateway for seawater to enter the ship through pipelines and valves.


Where are sea chests located on a ship?

Sea chests sit at the ship's hull bottom, in the engine room. They are situated between the ship's side and are shielded by sea chest gratings.


What is the purpose of sea chest gratings?

Sea chest gratings keep out large debris like trash, fish, and nets. They protect the seawater intake system from clogging.


How do sea chests function as a reservoir and filter?

Sea chests act as a reservoir and filter by allowing seawater to flow through removable gratings. Baffle plates stabilize the water flow and reduce the vessel's movement impact on intake.


What are some common uses of seawater drawn from sea chests?

Seawater from sea chests cools various ship systems. It cools fresh water in central coolers and condensate in auxiliary condensers. It also cools steam from turbines and air conditioning condensers. Additionally, it cools lubricating oil and supplies seawater for freshwater generators. It also feeds scrubber towers and deck seals in oil tankers.


Why are sea chests crucial for ship operations?

Sea chests are vital for ship operations by providing a steady seawater supply. This is crucial for the ship's engines, cooling systems, and machinery to function properly. Without adequate water intake, critical components may overheat, causing severe damage.


What are some common issues with sea chests?

Sea chests often face clogging from marine debris and organisms. This can lead to poor water intake. Biofouling on internal surfaces also restricts water flow, potentially damaging engines if not addressed quickly.


How are sea chests maintained and protected?

Sea chests are maintained with Marine Growth Prevention Systems (MGPS) and Impressed Current Cathodic Protection (ICCP) systems. Regular inspections and cleaning, by divers or during dry-docking, are also crucial.


What is the importance of understanding sea chests for marine engineers and ship operators?

Marine engineers and ship operators need to understand sea chests to ensure vessel safety and performance. Proper knowledge helps in maintaining systems, preventing damage, and optimizing operations.



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