Terms Used In Ship Construction

 The hull form of a ship may be defined by a number of dimensions and terms which are often referred to during and after building the vessel. An explanation of the principal terms is given below.
After Perpendicular (A.P.): A perpendicular drawn to the waterline at the point where the aft side of the rudder post meets the summer load line. Where no rudder pot is fitted it is taken as the centre line of the rudder stock:
Forward Perpendicular (F.P.): A perpendicular drawn to the waterline at the point where the foreside of the stem meets the summer load line.
Length Between Perpendicular (L.B.P.): the length between the forward and aft perpendiculars measured along the summer load line.
Amidships: A point midway between the after and forward perpendiculars.
Length Overall (L.O.A.): Length of vessel taken over all extremities.

Freeboard: The vertical distance measured at the ship’s side between the summer load line (or service draft) and the freeboard deck. The freeboard deck is normally the uppermost complete deck exposed to weather and sea which has permanent means of closing all openings, and below which all openings in the ship’s side have watertight closings.
Moulded Beam: Measured at the midship section is the maximum moulded breadth of the ship.
Scantlings – the sectional dimensions of various parts of a vessel.
Strake – A line of vertical plating, extending forward and aft.
Sheet. Curvature of decks in the longitudinal direction. Measured as the height of deck at side at any point above the height of the deck at side amidships.
Stringer – A line of horizontal plating, extending forward and aft.
Floor – Transverse vertical stiffeners which strengthen the ship’s bottom plating and which may be enclosed to form double bottoms.
Pounding – When a ship meets heavy weather and commences hearing and pitching, the rise of the fore end of the ship may synchronise with the trough of a wave. The fore end then emerges from the water and re enters with a tremendous slamming effect, known as pounding. This may cause damage to the fore end. The shell plating must be stiffened to prevent buckling.
Panting – As waves pass along the ship they course fluctuations in water pressure which tend to create an in and out movement of the shell plating. The effect of this is greatest at the fore end where the shell is relatively flat. This is know as panting and can lead to metal fatigue; the structure at the ends of the ship is therefore stiffened to prevent excessive movement of the shell.