Structure of a merchant ship

The concept of a merchant ship is often associated with a commercial vessel because of the word “merchandise”. However, it would be more appropriate to say that it is a ship that is not related to military aspects. In order to characterise them, the structure of a merchant ship will also be described, which, as will be seen, is not very different from other vessels.


What is a merchant ship?

By definition, a merchant ship is a vessel owned by private individuals and intended for the carriage of passengers or goods. In other words, it is not included in the navy, nor is it a pleasure vessel, but only pursues commercial purposes.

There are many types of merchant ships. Some of the best known are oil tankers, container ships, reefer ships, cruise ships, ferries and inland waterway vessels.



Parts of the merchant ship

The structure of large merchant ships is based on the same physical principles as those of other vessels, so there are many elements in common. Thus, we have:

  • Forecastle: the superstructure that rises above the bow. It runs from the bow to the middle of deck or the mainmast.
  • Amura: the part of the ship that narrows at the bow.
  • Side: is the hull side of the vessel.
  • Hold: space inside the hull, below the main deck, used to store goods or passengers, as the case may be.
  • Keel: the part that runs along the centre of the ship at the bottom, like the backbone of the ship.
  • Middle deck: the structure located amidships, between the mainmast and the foremast.
  • Bilge: this is the space located in the lowest part of the engine room, just above the double-bottoms. It is used to collect oily liquids from small leaks in pumps, pipes or seals.

Sterncastle: the superstructure that rises at the stern of the vessel, i.e. at the rear. The highest part of it is called the poop deck.


estructura de un barco mercante
Un buque mercante es un buque que pertenece a particulares y se destina al transporte de pasajeros o mercancía. Foto de Freepik.



There are different types of merchant ships, which will mark the distribution of the structure of a merchant ship. Dry cargo vessels can be general cargo, bulk cargo or containerised cargo; liquid cargo vessels can be liquid hydrocarbon, chemical or LPG (liquefied petroleum gas) and passenger vessels are grouped into cruise ships or ferries. Although in all of them we can distinguish the following structures.


Also known as exterior, it is made up of:

  • Bow: front part of the ship, with which it cuts through the water.
  • Stern: rear part of the vessel.
  • Port: left side of the vessel, facing the bow.
  • Starboard: right side of the vessel, facing the bow.

In addition, some structures on the outside of all vessels are:

  • Strake: these are the horizontal timbers that form the hull, parallel to the keel.
  • The rigging strake: this is the first timber next to the keel.
  • Stem: the part of the keel that protrudes.
  • Sternpost: this is the rear part of the keel, i.e. the part that faces aft. If the boat has only one propeller, a distinction is made between a fore and aft sternpost. The latter is that of the rudder shaft. If there are two propellers, both are simply called sternpost.
  • Amidships: the line between the port or starboard side and the stern.
  • Amidships: this is the middle part of the length. Thus, amidships is the middle part of the port side, and the same with the starboard amidships.

Outer skin: the wooden planks or steel plates that cover the hull, bulkheads and decks.


The ship is divided into frames, curved sections that cross the keel inside the inner skin. If you compare the keel to a backbone, it would be the ribs. They reach to the gunwale and can also extend out to the deck.

The inner covering is the inner planking of the hull, analogous to the outer skin.

The frame consists of all the pieces that make up the skeleton of the boat. The stringers is the thickest timber of the frame, located above the floor timbers, which is the lower longitudinal timber of the ship, placed on the inside of the keel to support the ship.

In turn, the interior can have one or two beams, which would be the “floors” of the ship’s interior. In any case, it always has one, the one that supports the deck.

The stringer is a thick timber nailed from bow to stern along the inner side of the side, on which the beams rest. On the other hand, the gunwale is the strong timber running fore and aft along both sides of the decks.

The ship’s rail is the part that protrudes over the sides of the deck, like the “rail” of the ship.

Bulkheads are the partitions or walls of the ship, which may be transverse or longitudinal.


Components of a merchant vessel
Discover the intricate details and vital parts that compose the framework of a merchant vessel, essential knowledge for maritime enthusiasts and industry professionals alike.


If you look at the ship crosswise, you can distinguish these parts:

  • Molded depth: maximum height of the ship, measured from the flat keel (i.e. amidships) to the deck.
  • Beam: width of a ship measured from the axis to the hull, along the main beam (the widest part of the ship).
  • Draft: the depth that the submerged part of a ship reaches in the water.

In addition, the parts of the internal structure are distinguished according to their usefulness:

  • Fresh water tanks: usually in the bow, at the bottom.
  • Storerooms: often in the bow, at the top.
  • Bow and stern lockers
  • The coolant charge: it is located in the centre of the ship.
  • Cargo itself: can be placed throughout the interior of the ship, depending on the nature of the cargo.

As you can see, the structure of a merchant vessel can be quite complex. But as a full service and supply provider, we at Suisca Group know this structure well, which is important when it comes to providing technical support.