SS NOBSKA  Bringing her home

Nautical Terms

Some nautical and shipbuilding terms and concepts explained.

- A -

ABS

Common abbreviation for American Bureau of Shipping, a classification organization that issues guidelines (scantlings) and reviews vessels' design and construction for seaworthiness. Similar international societies are: Lloyds Register (LR), and Bureau Veritas (BV). The letters next to a vessel's loadline indicate which bureau approved her. Note that Coast Guard rules concentrate on safety equipment not construction.

- B -

Bilge

The lower part of a ship's hull, extending outward from the keel to port and starboard to where the sides rise vertically. Any water in a vessel will collect there, thus ships always "pump their bilges".

Boiler

Two types of marine boilers existed. In the older Scottish boiler, water surrounds an internal fire-box and flame-tubes (similar to the arrangement on a steam locomotive). The flame-tubes, through which the fire's hot gasses escape, much increase the area for heat exchange. Conversely, the more modern water-tube boiler heats its water inside many tubes that are surrounded by the fire's burning gasses. Water-tubes' heat exchange area is larger than that of flame-tubes and the newer boiler contains less water.

Breasthook

Triangular plate fitted inside and across the stem to tie the frames.

Bulkhead

The interior 'walls' in a ship. In dry-cargo vessels watertight bulkheads normally run athwartship from side to side and extend from keel to weatherdeck. Seamen call the cabin partitions, that show in the picture, bulkheads as well.

- C -

Cladding

Protective sacrificial overlay. Cladding can wear away without affecting a structure's strength.

- F -

Floor

Plate running athwartships low down in the bilges, connecting a pair of port and starboard frames. Normally a ship has as many floors as frames.

- G -

Guard

Heavy potruding timber running the length of the hull at decklevel, to protect the hull plating during docking. Guards are a typical feature of coastal and inland shipping, ocean liners do not have permanent 'fenders'.

- K -

Knot

A metric for speed, i.e. nautical miles per hour. Distance is not measured in knots. The name derives from an archaic practice. To measure his speed the ancient mariner would float a small wooden marker attached to a long logline from the stern. The logline is marked with knots at regular intervals and is allowed to run out freely, keeping the marker, with its large submerged area, stationary in the water. The number of knots that run out in a given time period, as the stationary marker falls astern, indicates the vessel's speed through the water. Even so, modern airliners' speed is expressed in knots.

- L -

Lofting

The process of converting scale plans or offsets into full-size construction drawings.

- M -

Margin plate

Longitudinal plate that connects the bilge plating to the tanktop.

Mate

Short for Captain's mate; the person in charge of the deck when the Captain is below. On ocean going ships this is a licensed function called Deck Officer.

Mile

The nautical mile is defined as the length of one minute of arc on a perfect sphere whose surface equals the earth's. In practical terms, because our globe is spheroidal, this corresponds to one minute of latitude at 48 degrees, or 6080 feet. The statue mile of our highways is shorter at 5280 feet.

- O -

Offsets

Full size numerical measurements, lifted from the lines drawing, from which vessels' members are shaped. Frequently referred to as: 'Table of Offsets'.

- P -

Pilot

A seaman with extensive knowledge of local conditions. Traditionally often a native fisherman.

Propwalk

While moving ahead a propeller driven ship follows a straight line, but with the engine going astern a vessel's stern decidedly 'walks' to port or starboard depending on the direction of the prop's rotation. A vessel with the usual right-handed propeller can more easily be turned starboard round, conversely a left-handed (counter-clockwise) prop facilitates turning over port, and docking 'starboard to'.
The explanation is somewhat complex; in simple terms: with the engine going astern the revolving prop-wash is thrown forward against the vessel's sides causing different hydrostatic pressure between port and starboard. This pressure difference pushes the stern sideways.

- Q -

Quartermaster

An experienced hand, trusted at the wheel.

- R -

Rider plate

The inboard cap of the keelson.

- S -

Scantlings

Dimensions of structural parts, e.g. frames, beams and plates. Classification societies, such as ABS, specify minimum scantlings for various types of service.

Shaft alley

A.k.a shaft tunnel, a narrow low tunnel from the engine room to the sterntube that houses and gives access to the propeller shaft. This passage also provides an emergency exit from the engine room.

Sterntube

A long tube with bearings, situated in the stern, that supports the final section of propellor shaft.

Strake

A row of hull or deck plates. Their position is indicated by a capital letter, starting with A for the strake alongside the keel. Several strakes have very nautical sounding names as well, e.g.: garboard strake also sand strake (next to the keel), bilge strake also closing strake (at the turn of the bilge), sheer strake (at the upper edge of the hull along the maindeck).

Stringer

A longgitudinal girder that connects and supports the frames or deckbeams. The major ones are named: bilge-, side-, and deckstringer.

Stuffing box

A watertight fitting round a propellor shaft or rudderstock, that allows a shaft to rotate while preventing water from entering a ship.