Deck General

Key points (G, M, B):

- G (Center of Gravity): the point through which all the weight of the vessel acts. G rises when weight is added high; G lowers when weight is added low or when weight is removed from above G. - B (Center of Buoyancy): the centroid of the underwater volume of the hull. B shifts outward as the vessel heels. - M (Metacenter): the imaginary point at which the buoyancy force acts when the vessel is slightly inclined. At small angles, M is fixed. - GM (Metacentric Height): the vertical distance between G and M. GM is the single most important stability measure.

GM and stability:

- Positive GM (M above G): vessel has positive initial stability — it will right itself when heeled. Desired condition. - Negative GM (G above M): vessel has negative initial stability — it will loll (rest at an angle) and may capsize. - Large GM ("stiff" vessel): returns quickly to upright. Short, sharp rolling period. Uncomfortable. - Small GM ("tender" vessel): slow, gentle roll. Acceptable if still positive, but small reserve.

Righting lever (GZ):

At larger angles of heel, stability is measured by the righting lever GZ — the horizontal distance between the lines of action of gravity and buoyancy. The GZ curve (static stability curve or GZ curve) shows righting lever vs. angle of heel.

Free surface effect:

A tank that is partially filled with liquid has a free surface. When the vessel heels, the liquid shifts to the low side, raising the effective G and reducing GM. Free surface effect reduces stability. Two tanks partially filled are worse than one full and one empty.

Loading effects:

- Adding weight above the current G: raises G, reduces GM. - Adding weight below the current G: lowers G, improves GM. - Adding weight at G: no change to GM. - Removing weight above G: lowers G, improves GM. - Removing weight below G: raises G, reduces GM.

Angle of loll:

When GM is negative, the vessel heels until it finds equilibrium at a positive GZ value — the angle of loll. The vessel is unstable near 0° but may be quasi-stable at the loll angle. NEVER ballast both sides simultaneously — this raises G further and may cause capsize. Ballast the LOW side first to bring the vessel upright.

Wire rope construction:

Wire rope is described as 6×19 or 6×37 (strands × wires per strand). More wires per strand = more flexible. Wire rope is measured by its circumference in older usage, but by diameter in modern usage. Safe Working Load (SWL) is typically listed by the manufacturer.

Safe Working Load (SWL) and Breaking Strength:

- SWL = Breaking Strength ÷ Safety Factor. The safety factor for standing rigging is typically 5:1; for running rigging and lifting gear, often 6:1 or higher. - Never exceed SWL. Shock loading greatly increases effective load.

Knots, bends, and hitches:

- A knot reduces the breaking strength of a line — a bowline reduces it by approximately 40%. - Bends join two lines: sheet bend (joining lines of different sizes), carrick bend (heavy cordage). - Hitches secure a line to an object: cleat hitch, clove hitch, round turn and two half hitches. - Splices are stronger than knots and are preferred for permanent connections.

Ground tackle:

- Anchor holding power comes from the anchor digging into the bottom — not from the weight of the anchor. - Scope: the ratio of the length of cable let out to the depth of water. Minimum: 5:1 for chain. For rope/chain combination: 7:1 minimum. Heavy weather: 10:1 or more. - Chain catenary: the curve formed by hanging chain provides a shock-absorbing cushion and helps keep the pull on the anchor horizontal. - Dragging anchor warning signs: bow falls off, current/wind vector doesn't explain movement, depth sounder showing change.

Block and tackle:

- Mechanical advantage = number of parts (rope runs) at the moving block. - A gun tackle (two single blocks): 2 parts at the moving block = 2:1 mechanical advantage. - A luff tackle (1 double + 1 single block): 3 parts = 3:1 mechanical advantage. - Dead end of the fall does not count in mechanical advantage.

The fire triangle:

Fire requires three elements simultaneously: fuel, oxygen, and heat (ignition). Remove any one element and the fire goes out. Modern training adds a fourth element — chain reaction — making it the "fire tetrahedron."

Classes of fire:

- Class A: ordinary combustibles (wood, paper, fabric). Extinguish with water. - Class B: flammable liquids and gases. Extinguish with foam, CO₂, dry chemical, Halon. - Class C: energized electrical equipment. Use non-conductive extinguishants (CO₂, dry chemical). NEVER water on live electrical. - Class D: combustible metals (rare on vessels). Use specialized dry powder. - Class K: cooking oils. Use wet chemical.

Fixed fire fighting systems:

- CO₂ systems: effective for engine room and cargo hold fires. Displaces oxygen. Crew must evacuate compartment before activation — CO₂ is lethal at fire-fighting concentrations. - Halon systems: effective, non-toxic at low concentrations. Phased out under Montreal Protocol; existing systems may be maintained but no new Halon. - Foam systems: for fuel and cargo fires on tank vessels. - Sprinkler systems: required in accommodations spaces on SOLAS vessels.

Fire patrols:

SOLAS vessels must maintain a continuous fire patrol and fire detection system. On uninspected vessels, the master is responsible for implementing fire prevention measures.

Fire extinguisher types and applications:

- Water: Class A only. - AFFF foam: Class A and B. - CO₂: Class B and C. - Dry chemical: Class A, B, and C (multipurpose ABC). - Purple K (potassium bicarbonate dry chemical): Class B and C — highly effective on flammable liquid fires.

Lifeboat types:

- Open lifeboat: traditional open craft, required on older vessels. - Enclosed (fiberglass) lifeboat: protects crew from weather, fire, and flooding. - Free-fall lifeboat: launched by gravity from a high stern ramp; used on tank vessels. - Rescue boat: designed for search and rescue, must be capable of recovering a man overboard.

Davit types:

- Gravity davit: uses vessel heel and gravity to swing out lifeboat. Most common on modern vessels. - Radial davit (quadrant): older type, uses mechanical arm. - Sliding gravity davit: boat slides inboard/outboard on rails.

Life raft requirements:

- Inflatable life rafts: stowed in canister. Must be SOLAS-approved (SOLAS A pack or SOLAS B pack). The A pack contains more survival equipment. - Hydrostatic release unit (HRU): releases the life raft when the vessel sinks to 1.5–4 meters, inflating the raft automatically. - Weak link: connects the raft painter to the vessel. Breaks at depth, allowing raft to float free.

EPIRBs:

- Category I EPIRB: automatically activates when submerged (1–4 meters). Registered to vessel. - Category II EPIRB: manual activation only. - Emergency Position Indicating Radio Beacon: transmits on 406 MHz to COSPAS-SARSAT satellite system. - Must be registered with NOAA (U.S. vessels) — unregistered EPIRBs cause false alerts.

SART (Search and Rescue Transponder):

Activates on receipt of a 9 GHz radar pulse and returns a series of blips on the search vessel's radar screen, forming a pattern of 12 dots indicating the survivor's position.

Immersion suits:

Required for vessels operating in cold waters. Must be donned within 2 minutes in practice. Provides thermal protection and keeps wearer afloat.

Effects of wind and current:

Wind acts on the exposed freeboard and superstructure. Current acts on the submerged hull. In restricted maneuvering situations (entering a slip, anchoring), the combined effect must be anticipated.

Pivot point:

The pivot point is the point about which a vessel rotates when turning. On a vessel making headway, the pivot point is about 1/4 of the vessel's length from the bow. When a vessel is making sternway, the pivot point shifts toward the stern.

Twin-screw maneuvering:

Two propellers rotating inboard (toward each other at the top — starboard shaft turns clockwise, port shaft counterclockwise when viewed from astern) allow tight maneuvers with differential thrust. Kick the bow to port: ahead on starboard, astern on port.

Squat:

As a vessel increases speed in shallow water, the reduced pressure under the hull causes the vessel to sink deeper into the water. Squat is proportional to the square of the speed. In shallow water, reduce speed to minimize squat and increase underkeel clearance (UKC).

Bank effect (canal effect):

- Cushion: as a vessel passes close to a bank, water is compressed between vessel and bank, pushing the bow away. - Suction: at the stern, water is drawn from between vessel and bank, pulling the stern toward the bank. The net effect is a bow-out, stern-in tendency when passing a bank. - Passing vessels: two vessels passing in a narrow channel experience interaction forces — the bows push apart, the sterns are drawn together.

Anchoring:

Select a position with good holding ground, adequate scope, clear of traffic, and with sufficient swinging room. Let go when vessel has minimal headway or sternway — letting go at speed causes the cable to pile on top of itself.

Man overboard (MOB):

- Williamson Turn: used in restricted visibility. Put the helm over to the side of the MOB, turn 60° past the original course, reverse helm, come around to reciprocal bearing. Returns vessel to its original track line. - Anderson Turn (single turn): immediate hard rudder to the MOB side. - Racetrack (Scharnow) Turn: used when some time has elapsed since MOB.

Stowage factors:

The stowage factor is the volume (in cubic feet or cubic meters) occupied by one long ton of a particular cargo. Low stowage factor = dense cargo. High stowage factor = bulky cargo.

Broken stowage:

The percentage of cargo hold volume that cannot be used due to the shape of the cargo, the shape of the hold, or dunnage. Typical broken stowage: 10–20%.

Dunnage:

Materials placed under, around, and between cargo to prevent movement and protect from moisture. Also used to improve air circulation.

Dangerous goods:

IMO categorizes dangerous goods by class under the IMDG Code (International Maritime Dangerous Goods Code). The nine classes: (1) Explosives, (2) Gases, (3) Flammable liquids, (4) Flammable solids, (5) Oxidizing substances/Organic peroxides, (6) Toxic/Infectious, (7) Radioactive, (8) Corrosives, (9) Miscellaneous.

Draft survey:

A method of determining the weight of cargo loaded or discharged by reading the vessel's draft before and after the operation and applying hydrostatic data from the vessel's stability booklet.

Lashing and securing:

Cargo must be secured against all motions — pitching, rolling, surging, and swaying. The required lashing strength is calculated from the anticipated acceleration forces, which increase with distance from the vessel's center of gravity.