NAUT Drafts, Load Lines, and Basic Deck Seamanship

Vocabulary practice flashcards covering vessel drafts, Plimsoll and load line marks, tonnages, deck seamanship equipment, mooring configurations, and anchoring terminology.

Draft

The vertical distance measured from the bottom of the keel to the waterline.

Draft Marks

Hull markings that are $6\,\text{inches}$ high with $6\,\text{inches}$ of space between them, used to read vessel draft and best approximated in $3\,\text{inch}$ increments.

Freeboard

The vertical distance measured amidships from the waterline to the top of the maindeck (freeboard deck).

Air Draft

The vertical distance from the waterline to the highest point on the vessel (usually the radar mast), used to calculate overhead bridge clearance.

Reserve Buoyancy

An air mass deliberately trapped inside the vessel hull above the waterline to ensure stability and seaworthiness.

Trim

The longitudinal balance or condition caused by the difference between the bow draft and the stern draft.

Down by the Head

The trim condition where a vessel's bow is immersed deeper in the water than its stern.

Sag

The hull condition where the center of the ship slumps or dips below the calculated midships draft.

Rise

A naval architecture term describing a hull design where the bow sweeps upward relative to a parallel weather deck.

Load Line

A line painted amidships on a ship hull that limits the maximum allowable draft to ensure safe operation.

Plimsoll Mark

A symbol painted amidships consisting of a disk with a horizontal line through its center indicating the summer load line, accompanied by letters designating the certifying Class Society.

Class Society

An independent organization, such as the American Bureau of Shipping (ABS) or Det Norske Veritas (DNV), that certifies vessel load lines and structural integrity.

Lightship

The weight of the empty ship structure and gear out of the shipyard, excluding cargo, fuel, water, stores, crew, and passengers.

Deadweight

The total weight capacity a ship can carry, calculated as loaded (heavy) ship weight minus lightship weight.

Long Ton

A unit of mass equal to $2240\,\text{lbs}$, corresponding to $35\,\text{cu ft}$ of salt water per ton.

Metric Tonne

A unit of mass equal to $2204.616\,\text{lbs}$ or $1000\,\text{kg}$.

Length Overall (LOA)

The extreme total length of a vessel measured from the foremost part of the bow to the aftermost part of the stern.

Length Between Perpendiculars (LBP)

The distance measured between the forward perpendicular and the after perpendicular of a ship.

Breadth Molded

The maximum width of the hull measured between the outer surfaces of the structural frames.

Load Line Symbol 'WNA'

Load line marking indicating the maximum draft allowed for navigation in the North Atlantic during Winter.

Load Line Symbol 'S'

Load line marking indicating the maximum draft allowed in Summer in waters other than the Indian Ocean.

Load Line Symbol 'T'

Load line marking indicating the maximum draft allowed in Tropical Waters.

Load Line Symbol 'TF'

Load line marking indicating the maximum draft allowed in Tropical Freshwaters.

Load Line Symbol 'IS'

Load line marking indicating the maximum draft allowed in the Indian Ocean in Summer.

Load Line Symbol 'FW'

Load line marking indicating the maximum draft allowed in Fresh Water.

P&I Clubs

Protection and Indemnity clubs; mutual underwriting associations of shipowners (such as The Standard) that provide marine insurance and perform initial damage assessments.

Preformed Wire

Steel wire rope manufactured with low internal stress so that it maintains its shaped position without unlaying, kinking, or uncoiling when cut.

Mooring Pendant

A flexible synthetic shock-absorbing line attached to the eye of a mooring line that absorbs dynamic strain and increases line breaking strength by $25\%$ to $37\%$.

Snap Back Zone

The hazardous area on deck where a mooring line under strain will violently recoil if it parts.

Chock

A heavy cast-steel deck fitting (open, closed, or roller type) used to provide a smooth, sturdy lead for mooring lines passing off the vessel.

Fairlead

A deck fitting equipped with rollers used to redirect the path and direction of a mooring line on deck.

Bitts

A pair of heavy vertical cast-steel posts mounted on deck used to secure mooring lines.

Stopper

A temporary line or chain knot applied to a mooring line to hold tension while transferring the line from a winch drum or capstan to the bitts.

Capstan

A motorized vertical rotating drum used on deck to heave in line or take up slack during mooring operations.

Chafing Gear

Protective material (such as old fire hose) fitted around mooring lines at hull contact points to prevent friction and abrasion damage.

Ground Tackle

The collective term for all equipment involved in anchoring and securing a ship to the seabed, including the anchor, chain, windlass, and shackles.

Shot

A standard unit of measure for anchor chain length equal to $15\,\text{fathoms}$ ($90\,\text{feet}$).

Wildcat

A sprocketed wheel on an anchor windlass shaped specifically to engage the links of the anchor chain.

Fetching Up

The state when the dropped anchor chain has fully stretched out and the ship rides back forward on the catenary, indicating the anchor is set.

Anchor Aweigh

The state when the anchor has broken free of the seabed floor, officially making the vessel underway.

Mooring Line Layout

The standard numbered arrangement of mooring lines from bow to stern: (1) Bow line, (2) after bow spring, (3) forward bow spring, (4) waist breast, (5) after quarter spring, (6) forward quarter spring, and (7) stern line.