On A Ship Or Boat, What Is A Sea Chest? (Explained In Detail)

Fact Checked By James A Rockey | Post Updated On: December 1, 2022
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A sea chest is a cavity or bay made in a special way to house pipes in the boat or ship that take in seawater. The water in the sea chest is used to cool the vessel’s engines, wash the decks, and as ballast to maintain the vessel’s stability.

Key Takeaways

  • A sea chest is one of the areas that play a crucial role in sustaining both flexibility and stability of any vessel on the water
  • The design of a sea chest depends on the era it was produced; therefore not all sea chests are alike
  • The sea chest comes with its strainer, named the Sea chest strainer

What is a sea chest used for?

What is a sea chest used for

As earlier stated, a sea chest is an area set aside to house a vessel’s pipes tasked with the taking in of seawater. In short, they are just cavities or holes made inside a vessel to support sustainability. In what ways, you ask? The cooling of the engines requires water, and ballasting and firefighting also require water. Carrying enough water for all these purposes will add extra and unnecessary weight to the boat; that’s why seawater is used. Seawater is used instead by letting it in and out at convenient intervals; the sea chest’s pipework system plays this role. 

Other than the part of a boat that houses pipes, the sea chest sometimes refers to where the sailors store their precious items as they sailed. These chests are lockable, and they came in handy for storing precious items. 

A brief history of the sea chest

This section looks at the sea chest used for storing precious elements, their history, and their significance. In many families that had previously had ancestors who sailed the sea, it is often found that the families have preserved and retained the chests. The chests have also been stored as coveted antiques in various communities. With technological advancement, many replicas have also been made to house items, just as the initials chests did.

The design of a sea chest depends on the era it was produced in. You may have noticed that not all sea chests are alike. The most used design, which is also familiar to many, is the one with a large bottom, slanting slides leading to a smaller defined top. You get the picture. However, the chests with flat lefts for more accessible storage were also common. Either several drawers or shelves also characterized them for storage purposes of items and specifically important ones. The materials were then stored under lock and key as the chests were equipped with a lock and handle for easy movement. 

The big difference between then and now is that the sailors would use the chests as sacred possession, holding areas back then. It was also safer as no sailor would touch another’s chest without permission. All these materials were kept in the sea chests, from utensils to clothing to important documentation. Space for storage was also minimal in the vessels, so all the personal possessions of the sailors were supposed to fit in their chests. Some were elegant, while others were simple and plain as long as they served their purpose. We are in the modern era now; the sea chests act as house decorators. It is normal to find homes with chests acting as either tables or seating areas.

Modern chests are still made historically with very skilled artisans to work on designing, carvings, and edging. This leads to the expensive cost of the chests, whether modern or old, and it is essential to inspect any chest before acquisition or paying for it carefully.

What is a sea box on a ship?

A sea box is commonly referred to as a shipping container. They are generally large but standardized containers that hold materials from one place to another by transportation, the road to air. They come in handy as they do not require loading and unloading during transportation.

How a sea chest is fitted for shipping

How a sea chest is fitted for shipping

Before stating how a sea chest is to be fitted for shipping, it is essential to know that the proper maintenance of these chests is essential. Maintenance comes with its cleaning and also handling.

The purpose of suction filters in the maintenance of sea chests

The sea chest comes with its strainer, named the Sea chest strainer. It is fitted in line with the central section of the seawater system of the vessel. The filter is also fitted with a marine growth preventive system casing to prevent the growth. Before it is cleaned, the suctions level of water is determined.

The cleaning of the sea chest filter

The filter is first opened and cleaned in periods to get rid of any debris or sediments collected inside it. This is to allow a more effortless flow of water during cleansing. If the filter is clogged, a drop in the water pressure will be the outcome which may later lead to instability due to damage or corrosion of the pipelines.

Fitting the sea chest Procedure

  1. Open the inlet isolated valves, then put them in the unused sea chest 
  2. Keep the vent open to drive the air out of the sea chest
  3. Immediately air has been purged out; water will come out via the vent. Close the vale vent and quickly open the outlet valve, bringing the sea chest into use.
  4. It is then time to isolate the other sea chest by closing either of the valve openings where the maintenance is carried out.
  5. Open the vent, which will lead to the draining of water into the sea’s chest
  6. Make sure to ease up the sea chest screw covers from the chest body. The jointing may be stuck due to access to water and debris.
  7. Take the cover out by using tackles and blocks of the chain
  8. Be keen to withdraw the filter element, which will assist in removing all the debris and other elements which may have been collected. These may include seaweeds, shells, and seaweeds.
  9. Place the filter in its original position and close its top with a new joint. This will tighten the cover nuts progressively and in sequence.
  10. Shut the draining valves while keeping the vent open to bring the chest under work by ensuring that the operating valves pump out the air from the sea chest.
  11. After all the air has been withdrawn, make sure to shut the vent and close the isolating valves under the chest by maintaining their cleanliness as the chest stands by.

The difference between the high and low chest

The difference between the high and low chest

It is usual for vessels to have both chests. The high chest is usually used in shallow waters mainly to reduce the intake of sediments and materials that may cause difficulties when sailing. The low chest is mainly used in ice-covered waters to control the intake of ice and slush, which may also cause sailing problems. Apart from the ice-covered waters, the low chest can also come in handy when the vessel is rolling to avoid losing stability and losing its suction.

Sludge, the clean drain tank, the bilge water holding tank, and the cargo tank

Sludge is the waste made or generated as a vessel operates under normal conditions. It is mainly formed from oil purification—oily bilge results from leaking and work maintenance and is mainly contaminated by other solvents.

The clean drain tank is a tank that is set aside for the retaining of the clean drains only, while the oil bilge water holding tank is kept for the retention of the dirty oiled and bilged water. The cargo tank, on the hand, is designed for carrying either liquids or gases, and it includes fittings and closures. The arrangement of all the tanks in the vessel is systemized and independent to prevent mixing of the contents either being stored or transported. This mainly helps in preventing contamination of fluids and dirt. 

Final word

Just as all the body parts are considered essential for the efficient functioning of man, all parts of water vessels, either a ship or a boat, are also important. As mentioned, stability will be hard to manage without the sea chest. Cooling of engines will also be a challenge. Therefore, it is essential to understand the functions carefully and not only identify and name the various parts of a water vessel to be on the safer side.


  • https://en.wikipedia.org/wiki/Sea_chest_(nautical)
  • https://teara.govt.nz/en/photograph/8663/trawler-sea-chest

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