Basic Ship Construction and Naval Architecture Terms

 Port and Starboard Sides: Viewing the ship from the aft, the left side of the ship is called the Port side, and the right, is called the Starboard side.


Length overall :The distance from the extreme fore part of the ship to a similar point aft and is the greatest length of the ship. This length is important when docking.

Stem: Front-most part of the boat or ship's bow is termed as stem of the ship

Length between perpendiculars :The fore perpendicular is the point at which the Summer Load Waterline crosses the stem.

    The after perpendicular is the after side of the rudder post or the center of the rudder stock if there is no rudder post.

    The distance between these two points is known as the length between perpendiculars, and is used for ship calculations.

Breadth extreme :The greatest breadth of the ship, measured to the outside of the shell plating.

Breadth moulded :The greatest breadth of the ship, measured to the inside of the inside strakes of shell plating.

Depth extreme :The depth of the ship measured from the underside of the keel to the top of the deck beam at the side of the uppermost continuous deck amidships.

Depth moulded : The depth measured from the top of the keel.

Draught extreme : The distance from the bottom of the keel to the waterline. The load draught is the maximum draught to which a vessel may be loaded.

Draught' moulded : The draught measured from the top of the keel to the waterline.

Freeboard: The distance from the waterline to the top of the deck plating at the side of the deck amidships.Freeboard represents the safety margin showing to what depths a ship may be loaded under various service conditions—e.g., the type of cargo, the waters to be navigated, and the season of the year.

Camber or round of beam: The transverse curvature of the deck from the centreline down to the sides. This camber is used on exposed decks to drive water to the sides of the ship. Other decks are often cambered. Most modern ships have decks which are flat transversely over the width of the hatch or centre tanks and slope down towards the side of the ship.

Sheer: The curvature of the deck in a fore and aft direction, rising from midships to a maximum at the ends. The sheer forward is usually twice that aft. Sheer on exposed decks makes a ship more seaworthy by raising the deck at the fore and after ends further from the water and by reducing the volume of water coming on the deck.

Rise of floor: The bottom shell of a ship is sometimes sloped up from the keel to the bilge to facilitate drainage. This rise of floor is small, 150 mm being usual.

Bilge radius: The radius of the arc connecting the side of the ship to the bottom at the midship portion of the ship.

Tumble home: In some ships the midship side shell in the region of the upper deck is curved slightly towards the centreline, thus reducing the width of the upper deck and decks above. Such a tumble home improves the appearance of the ship.

Strake: external hull of a ship consists of bottom shell, side shell and deck which are formed by longitudinal strips plating called strake. Or continue the range of plate forming the side of the vessel, or metal plate extending the ship's hull from stem to stern.

Bilge strake: strake at the turn of the bilge called.

Stealer strake: No.of adjacent strakes fitted at the end of ship called.

Garboard strake: strake adjacent to the keel on each side of the ship called.

Sheer strake and its importance: it is the largest continuous strake at the top of the side of the vessel on the main deck. Or uppermost strakes of side plating which meet the upper deck. It is 10-20% thicker than other side plating.

IMPORTANCE: when vessel is bending to forces from tension to compression and sheer strake is subjected to maximum compressive and tensile stress. Which contributes to the strength of the hull.

Stringer: the stiffners used to strengthen the sides surface of the ship are called, without stringer the hull shape does not form.

Coffin plate: used to connect the stern frame to the flat plate keel.

Shoe plate: used to connect stem to the flat plate keel.

Margin plate: at bilges, the tank top may be either continued straight out to the shell by means of a tank margin plate. Which is water tight and sets an angle of about 450 to the tank top and meets the shell almost at right angle.

Bulwark: It is a solid wall that extends above the weather deck or any other deck to be exposed to weather and fitted for the safety of the crew. At Least 1 m in height spacing of stays and is not exceed 1.2 m on the forecastle.

Transom space: situated in S.G. room there you can find a manhole door near Rudder Trunk, purpose is to inspect Rudder Trunk condition, Lubrication etc.. you can enter inside this place for carried out inspection in Port only and in calm weather or sea.

Buttock line:It is an equidistant transverse section line from the midship to fwd of the ship, such that they give you the cross section at various stations at all possible drafts and trim.

They are mainly used for knowing the light weight displacement at the time of the end of the construction phase of a ship.

Gunwale: the upper edge of a ship’ s side where the sheer strake meets the deck plating called.

Margin line: is a line drawn at least 76 mm below the upper surface of the bulkhead deck at side.

It is the imaginary line, which is drawn 76mm below the uppermost continuous deck. It denotes the limit, up to which ship can be flooded/ loaded without sinking.

For a ship which has a continuous bulkhead deck, the margin line is to be taken as a line drawn not less than 76 mm below the upper surface of the bulkhead deck at side, except that where there is a variation in the thickness of the bulkhead deck at side the upper surface of the deck should be taken at the least thickness of deck at side above the beam.

If desired however, the upper surface of the deck may be taken at the mean thickness of the deck at side above the beam as calculated for the whole length of the deck, provided that the thickness is no greater than the least thickness plus 50 mm.


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