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Portside and Starboard Side of Ships (Ship Terms and Definitions)

Port and Starboard Side of Ships

Port and starboard are nautical terms of orientation that deal with the structure of ships. When looking forward, the Starboard side is the right-hand side of a vessel, while the Portside is the left-hand side of a ship. Therefore, seamen and mariners use portside and starboard side terms instead of left and right.

 

The origin Portside and Starboard side terms

 

Port and Starboard Side

 

In the past, steering ships were done with a steering oar at the right-hand side of the ship’s stern and rudders on their centerlines. The steering oars were at the right-hand side; as back then, the majority of the people were right-handed. Therefore, the right side of the ship was called “stéorbord,” the term stéorbord is a combination of two words, stéor (meaning ‘steer’) and bord (meaning ‘the side of a ship’), therefore, the term denoting the side on which the ship is steered. Which later was known as ‘starboard.’

 

Since the steering oar was on the ship’s right side, the port quay was on the left side to not interfere with steering oar operation. Hence, the left side of the vessel was called a portside. Previously, sailors have often used “larboard” instead of port; larboard term was used as the ship’s left side was the loading side. Larboard sounds similar to starboard, and sailors were easily confused between the two words, especially during rough sea conditions that made it difficult to hear. 1844, the Royal Navy ordered that port be used instead, and from there, the left side of a ship is called portside till today. 

 

Interesting article: 13 Notable Ship Canals That You Should Know.

 

Ship dimensions principal — Terminology and definitions

 

ship dimensions principal

 

Breadth

The maximum beam of the vessel measured from the outside edge on either side of the vessel is the extreme breadth.

 

Moulded breadth

The beam of the vessel measured amidships between the inside edge on either side of the vessel.

 

Depth

The extreme distance of the ship is measured from the bottom side of the keel to the top of the deck beams.

 

Freeboard

The vertical distance, measured at the ship’s side, from the waterline to the top of the freeboard deck edge measured at the midships point.

 

Draught (Draft)

The vertical distance, measured at the ship’s side, from the waterline to the keel’s bottom side, measured at the midships point.

 

Draft (T fwd)

The vertical distance, measured at the ship’s side, from the waterline to the bottom side of the keel measured at the forward perpendicular (FP).

 

Draft (T aft)

The vertical distance, measured at the ship’s side, from the waterline to the bottom side of the keel measured at the AFT perpendicular (AP).

 

Perpendiculars

A perpendicular is an imaginary line drawn to the waterline from a point on the summer load line either forward (stem) of the ship’s Aft (rudder post or rudder stock).

 

Forward perpendicular (FP)

A perpendicular line drawn to the waterline at a point where the stem meets the summer waterline.

 

Aft perpendicular (AP)

A perpendicular line drawn to the waterline at a point where the after side of the rudder post or the centerline of the rudder stock (when rudder post is not fitted) meets the summer waterline.

 

Length between Perpendiculars (LBP)

The distance between the forward perpendicular (FP) and AFT perpendicular (AP).

 

Length Overall (LOA)

The maximum length of the vessel measured from the extreme forward point of the vessel to the extreme aft point.

 

Length on the waterline (LWL)

The distance between the stern and stem intersecting points with the waterline when the ship is on her summer load line.

 

Displacement

The displacement of a ship is the weight of water that the ship displaces; the weight is including the weight of the ship and all it contains. To calculate the ship’s displacement by multiplying the ship’s immersed volume in cubic meters to the density of the water, expressed in tones per cubic meter.

 

Tonnage

Ships constructed on or after 8 July 1982 are measured by their Tonnage Measurement according to the IMO 1969 International Conference. The tonnage of a vessel is divided into Gross Tonnage (GT) and Net Tonnage (NT).

 

Ship Tonnage

 

Gross Tonnage (GT) is the measurement of the ship’s internal volume in cubic meters for the spaces below the main deck and enclosed spaces above the main deck.

 

Net Tonnage (NT) is the measurement intended to indicate the earning capacity of the vessel. The Net Tonnage is calculated from GT by subtracting the volume of space occupied by the crew, navigation and propulsion equipment, and workshops.

 

Load line marks (Plimsoll mark)

 

The international load line or Plimsoll line is the line that indicates the draft of the ship and the legal limit to which a ship may be loaded for specific water types and temperatures to maintain buoyancy safely. The purpose of a load line is to ensure that a ship has sufficient freeboard and thus sufficient reserve buoyancy. Commercial ships have a load line symbol permanently marked amidship to make it easy for anyone to determine if a ship has been overloaded.

 

Initially, the load line mark was a circle with a horizontal line to indicate the maximum draft. Over the years, additional marks have been added for different sea conditions and water densities.

 

Load line Mark
(Image credit: Welkinridge)

 

The two letters appear to the sides of the mark, indicating the classification society that surveys the vessel’s load line. The two initials are reflecting the specific classification society as follow:

 

  • AB for the American Bureau of Shipping.
  • LR for Lloyd’s Register.
  • VL for DNV.
  • BV for Bureau Veritas.
  • NK for Nippon Kaiji Kyokai.
  • RI for the Registro Italiano Navale (RINA).
  • IR for the Indian Register of Shipping.

 

The letters on the load line marks have the following meanings:

  • TF for tropical freshwater.
  • F for freshwater.
  • T for tropical seawater.
  • S for summer temperate seawater.
  • W for winter temperate seawater.
  • WNA for winter North Atlantic.

 

The summer load line is the primary load line, and it is from this mark that all other marks are derived. The horizontal line through the circle of the Plimsoll mark is at the same level as the summer load line.

The winter load line is one forty-eighth of the summer load draft below the summer load line.

The tropical load line is one forty-eighth of the summer load draft above the summer load line.

The freshwater load line is at the same level as the tropical load line. The position of the tropical fresh load line relative to the tropical load line is found in the same way as the freshwater load line is to the summer load line.

Winter North Atlantic load line is used in some regions of the North Atlantic Ocean during the winter season.

 

 

References:

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Founded on the core mission of connecting mechanical engineers globally to share knowledge and experience. Our Authors are qualified Mechanical Engineers, Marine Engineers, Welding Engineers "CSWIP Certified", Coating Inspectors "NACE CIP LII" & NDT Experts "ASNT NDT LIII Certified".
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