Heavy weather lrg

Grunt Productions 2007
Characteristics of WavesCharacteristics of Waves
HEAVY WEATHERHEAVY WEATHER

WAVEWAVE
DEVELOPMENTDEVELOPMENTWIND 10 KTSWIND 10 KTS
WIND 15 KTSWIND 15 KTS
Generating Wave MotionGenerating Wave Motion
Surface FrictionSurface Friction
Particle MovementParticle Movement
Well DevelopedWell Developed
Large Steep Seas DevelopLarge Steep Seas Develop

1. Wave Height1. Wave Height
2. Wave Length2. Wave Length
3. Period3. Period - The time interval between passage of successive crests
relative to a stationary observer.
DEFINITIONDEFINITION
SS
Height
Crest Still Water
Level
CrestCrest
Wave Length
Trough
Trough

SWELL
Waves that continue through their own inertia after the wind
has stopped generating them.
FETCH
The straight distance a wave has travelled over the surface.
PERIOD OF ENCOUNTER
The time interval between passage of successive waves
relative to a moving observer.
Direction of WavesDirection of Waves

• CharacteristicsCharacteristics of Wavesof Waves
• AvoidanceAvoidance ofof DamageDamage
– Knowledge of ship handlingKnowledge of ship handling
characteristics.characteristics.

PERIOD OF ROLL ANDPERIOD OF ROLL AND
PITCHPITCH
WL
WL
ROLL
PITCH
PIVOT OF BUOYANCY
The Time Required From
Upright to Right to Left
To Upright
The Time Required From
Level to Down to Up to Level

– Knowledge of ship handling characteristics.Knowledge of ship handling characteristics.
– Careful use of powerCareful use of power
– Assessment of speed v possibleAssessment of speed v possible
damagedamage

• PrecautionsPrecautions
– Secure for Sea.Secure for Sea.
– Stability adjustment:Stability adjustment:
• Bilge KeelBilge Keel
• Slack TanksSlack Tanks
• Cargo ShiftCargo Shift
• Anti-rolling tanks - Comp tanks.Anti-rolling tanks - Comp tanks.

• PrecautionsPrecautions
• Consideration for CrewConsideration for Crew
– Violent motion reduces efficiency.Violent motion reduces efficiency.
– Safety of men on exposed decks.Safety of men on exposed decks.
– Keep Ship’s Company informed.Keep Ship’s Company informed.
– Consider change in daily routineConsider change in daily routine..

EFFECTSEFFECTS
• Broaching.Broaching.
• Pooping.Pooping.
• Hogging.Hogging.
• Sagging.Sagging.
• Turning.Turning.
• Heaving to.Heaving to.

STAGES IN BROACHINGSTAGES IN BROACHING
WIND AND SEA
Ship may run on crestShip may run on crest
Stern too high - rudder loses effectStern too high - rudder loses effect
Bow pitches into trough and buriesBow pitches into trough and buries
Stern swings round bringing ship abeam to elementsStern swings round bringing ship abeam to elements
Next wave will possibly break over ship and cause severe damageNext wave will possibly break over ship and cause severe damage
SOLUTION - reduce to 40% of wave speedSOLUTION - reduce to 40% of wave speed

STAGES IN A VESSEL BEING POOPEDSTAGES IN A VESSEL BEING POOPED
WIND AND SEA
FACTORSFACTORS
1. Stern lifts at wave speed1. Stern lifts at wave speed
2. Breaking crest travels faster forces down2. Breaking crest travels faster forces down
ACTIONACTION
Crest sweeps over ship from aftCrest sweeps over ship from aft
TO AVOIDTO AVOID
Either select a speed equal to 40% below wave speedEither select a speed equal to 40% below wave speed
oror heave-toheave-to

HOGGING AND SAGGINGHOGGING AND SAGGING
PROLONGED SAGPROLONGED SAG
DIRECTION OF SEADIRECTION OF SEA
Particle Movement IsParticle Movement Is
Reduced Past RudderReduced Past Rudder
Hence Less ControlHence Less Control
Better Control AndBetter Control And
Even Strain at WaveEven Strain at Wave
Speed ± 3 KnotsSpeed ± 3 Knots
PARTICLE
MOVEMENT
PARTICLE
MOVEMENT

A.A. Head to sea:Head to sea:
a.a. Short bursts of power, wheel hard over, noShort bursts of power, wheel hard over, no
headway consider reversing innerheadway consider reversing inner screw to start the turn.screw to start the turn.
b.b. ½ way, full power to complete.½ way, full power to complete.
B.B. Following sea:Following sea:
a.a. Reduce speed, no sternway.Reduce speed, no sternway.
b.b. ½ way, plenty of power and wheel then reduce½ way, plenty of power and wheel then reduce
when ship answers the helm.when ship answers the helm.
TURNING IN HEAVYTURNING IN HEAVY
SEA:SEA:

1.1. Sea on the bowSea on the bow
a.a. Necessary if there is a lack of sea room to leeward.Necessary if there is a lack of sea room to leeward.
b.b. May need 3-5 knots.May need 3-5 knots.
c.c. Possible damage:Possible damage:
1.1. Engines driving ship against the sea.Engines driving ship against the sea.
2.2. Greater risk of structural damage with a flared bow.Greater risk of structural damage with a flared bow.
d.d. Heavy pitching/pounding likely.Heavy pitching/pounding likely.
e.e. Single screw ships keep wind fine on port bow (sidewaysSingle screw ships keep wind fine on port bow (sideways
force of propeller).force of propeller).
2.2. Stop engines and driftStop engines and drift
a.a. Plenty of searoom to leeward required (surface drift may reach 3kts in forcePlenty of searoom to leeward required (surface drift may reach 3kts in force
8).8).
b.b. Best option in a confused sea.Best option in a confused sea.
3. Running before the sea3. Running before the sea
a.a. Less satisfactory.Less satisfactory.
b.b. Danger of pooping.Danger of pooping.
HEAVING TOHEAVING TO

HEAVINGHEAVING
TOTO
4.4. Steaming directly into seaSteaming directly into sea
Minimum speedMinimum speed
5.5. DoDo
a.a. Watch the weather.Watch the weather.
b.b. Know ship stability.Know ship stability.
c.c. Secure loose gear.Secure loose gear.
d.d. Recognise tropical storms.Recognise tropical storms.
e.e. Alter course in a beam sea if possible.Alter course in a beam sea if possible.
6.6. Don’tDon’t
a.a. Drive too fast into head sea.Drive too fast into head sea.
b.b. Be afraid to reduce speed.Be afraid to reduce speed.
c.c. Run too fast before a following sea.Run too fast before a following sea.

Heavy weather lrg

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