Timber Deck Cargo Stowage, Securing, and Stability

Vocabulary flashcards covering timber deck cargo lashing requirements, stowage, hazards, stability criteria, rolling period test, and load line markings based on the lecture transcript.

Lashing Breaking Strength Requirement

All lashings and components used for securing timber deck cargo must have a breaking strength of not less than $13.6\,\text{T}$ (or $133\,\text{kN}$).

Lashing Threaded Screw Requirement

Upon completion of lashing, the tightening device or system should be left with not less than half the threaded length of the screw remaining.

Maximum Lashing Spacing

The maximum spacing of lashings as per cargo height is $3\,\text{m}$ for heights of $4\,\text{m}$ or below, and $1.5\,\text{m}$ for heights above $4\,\text{m}$.

Hog Lashing

A lashing method used over immediate tiers of timber deck cargo to secure lower and intermediate layers using uprights.

Wiggle Wire Lashing

A lashing arrangement passed continuously through a series of snatch blocks held by a foot wire in the manner of a shoelace, kept tight using turnbuckles.

Lashing Elongation and Deformation Limits

Securing lashings must show an elongation of not more than $5\%$ at $80\%$ of their breaking strength and no permanent deformation under a proof load of not less than $40\%$ of their original breaking strength.

Windage Effect

The increase in wind resistance caused by high-profile timber deck cargo, which can induce excessive heeling moments and reduce ship maneuverability.

Free Surface Effect from Water Trapped Under Cargo

An adverse stability effect caused by water accumulating on deck when cargo drainage, scuppers, or freeing ports are blocked.

Rolling Period Test

An empirical test conducted at anchor or in calm seas to estimate a ship's metacentric height ($GM$) by measuring the duration of complete transverse oscillations.

Rolling Period Formula for Metacentric Height

The empirical equation $GM_0 = \left(\frac{f \cdot B}{T_r}\right)^2$, where $f$ is a constant based on ship dimensions, $B$ is ship breadth, and $T_r$ is the time for a full rolling period in seconds.

Stiff Ship vs. Tender Ship (Rolling Period Indicator)

A shorter rolling period indicates a higher metacentric height ($GM$) representing a stiff ship, whereas a longer rolling period indicates a lower $GM$ representing a tender ship.

Rolling Period Test Limitations

An approximate estimation test that requires calm seas, assumes symmetrical loading, and cannot detect longitudinal stability, dynamic stability, wind heeling moments, or free surface effects.

Minimum Metacentric Height ($GM(0)$)

The requirement that metacentric height $GM(0)$ shall not be less than $0.1\,\text{m}$ at all times during a voyage, taking into account water absorption and ice accretion.

Righting Lever ($GZ$) Requirements

The minimum required maximum value of the righting lever $GZ$ is $0.25\,\text{m}$, with an area under the $GZ$ curve of not less than $0.08\,\text{m}$.

Superstructure Requirements for Assigned Timber Freeboards

Ships shall have a forecastle of at least standard height with a length of at least $0.07\,L$, and for ships under $100\,\text{m}$, a poop or raised quarter-deck fitted aft.

Bulwark Requirement for Timber Cargo Ships

Ships assigned timber freeboards must be fitted with permanent bulwarks at least $1\,\text{m}$ ($39\frac{1}{2}\,\text{inches}$) in height or efficient rails of equivalent strength.

Timber Load Line Markings Position

A second set of load lines marked like standard load lines, positioned $540\,\text{mm}$ above the centre loading disc.

LS (Lumber Summer)

The timber load line mark whose upper edge marks summer saltwater timber loading, situated at a specified level above the Plimsoll line.

LW (Lumber Winter)

The timber load line mark situated at a distance of $\frac{1}{36}$ of the lumber summer draft below the LS line.

LT (Lumber Tropical)

The timber load line mark situated at a distance of $\frac{1}{48}$ of the lumber summer draft above the LS line.

LWNA (Lumber Winter North Atlantic)

The timber load line mark positioned at the exact same level as the standard WNA (Winter North Atlantic) load line.

LF and LTF Timber Load Lines

LF (Lumber Freshwater) is situated above LS by Fresh Water Allowance (FWA), and LTF (Lumber Tropical Fresh Water) is situated above LT by FWA.

Under Deck Log Stowage Requirements

Logs stowed in lower holds or tween decks must be trimmed compactly fore, aft, athwartships, and top to bottom with minimal voids, using a consistent log diameter per layer.

Under Deck Log Securing Gear

Arrangements such as side shoring, timber battens, wedges, vertical stanchions, steel wire lashings, chains, and cross-lashings used to restrict log movement.

Pre-loading Hatch and Vent Security

Before loading timber deck cargo, hatch covers below the loading area must be securely closed and battened down, and air pipes and ventilators efficiently protected.