What Is The Lower Deck Of A Ship?

What Is The Lower Deck Of A Ship?

As we all know, decks are the horizontal boundaries of a ship. They mainly define the height of the hull and mark the upper and lower boundaries of any space.

The main deck is the most common deck on a ship. It defines the upper limit of the main hull, has a high load-bearing capacity, and contributes to the overall strength. Therefore, it is also called the strength deck.

Since it is exposed to the outside environment in practical applications, it is also called the bare deck. In addition, in almost all conventional ships, since the bulkheads mainly extend to their height, the main deck is also called the bulkhead deck.

All other decks within the main hull are intermediate decks of varying lengths and unique numbers. While most cargo ships, such as oil tankers and bulk carriers, do not have multiple decks containing cargo holds or spaces, other types of ships, such as passenger ships, have multiple overlapping decks. The lower deck is an essential element of the ship's structure.

As the name suggests, the deck below the lower hull of a ship is called the lower deck. The definition of the lower deck varies depending on the type of ship.

Lower deck

If the ship is a double hull or double bottom structure , the inner bottom is the lower deck. If the ship is a single bottom structure with one or more intermediate decks below the main deck, the lower deck is the deck located directly above the lower hull.

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If the ship is simpler in structure and has no intermediate decks, the lower deck is usually a partial deck, especially in the engine room that must withstand high loads without directly affecting the hull, or a specific space with vertical separation. See the figure below.

Even on small fishing boats or small, simple inland passenger ships, the concept of a lower deck does not exist. The machinery/engine is simply mounted on the lower support of the superstructure and deck.

Some elevated structures, such as small platforms or grooved plates for placing machinery or equipment, are directly connected to the bottom of the plate and other less solid members and should not be confused with the lower deck.

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Lower deck of a ship

The lower deck is mainly composed of a flat reinforced concrete slab, similar to other decks. However, it can be stepped or corrugated.

If the lower deck is intermediate, it is reinforced both horizontally and vertically, like other decks. The bottom support as well as the supports are lower than those of the main deck or lower hull.

However, when they have to bear heavy loads (e.g,. machinery), the lower decks are significantly reinforced and have higher supports.

The inner bottom covers or tanks have a lower protective layer than the lower decks, but they are susceptible to corrosion if located in the area of tanks containing liquids.

However, all surfaces that are subject to heavy loads, such as machinery or equipment, have a thicker protective layer and higher rigidity. The lower deck mainly supports the interior of the bottom.

Depending on the stability of the ship's structure against damage, the lower deck plays a vital role in preventing water intrusion. However, manholes and drains are provided when necessary, especially in the engine room and compartments for sanitary and other services.

Like other decks, the lower decks are also additionally reinforced at the openings. In general, the lower decks are mostly horizontal.

On most ships, these decks are crucial for storing cables, pipes, ducts, hydraulic systems, and other essential components. On warships, the lower deck is used as a storage deck for weapons and ammunition Although it is not common today, the lower deck was also formerly known as the "orlop deck".