Heavy weather lrg

Grunt Productions 2007

Characteristics of WavesCharacteristics of Waves

HEAVY WEATHERHEAVY WEATHER


WAVE WAVE DEVELOPMENTDEVELOPMENT

WIND 10 KTSWIND 10 KTS




Generating Wave MotionGenerating Wave Motion

Surface FrictionSurface Friction

Particle MovementParticle MovementWell 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.

DEFINITIONDEFINITIONSS

Height

Crest Still WaterLevel

CrestCrestWave Length

Trough

Trough


SWELLWaves that continue through their own inertia after the wind has stopped generating them.

FETCHThe straight distance a wave has travelled over the surface.

PERIOD OF ENCOUNTERThe time interval between passage of successive waves relative to a moving observer.

Direction of WavesDirection of Waves



• CharacteristicsCharacteristics of Waves of Waves

• AvoidanceAvoidance ofof Damage Damage– Knowledge of ship handling Knowledge of ship handling

characteristics.characteristics.


PERIOD OF ROLL AND PERIOD OF ROLL AND PITCHPITCH

WL

WL

ROLL

PITCH

PIVOT OF BUOYANCY

The Time Required FromUpright to Right to LeftTo Upright

The Time Required FromLevel to Down to Up to Level




• AvoidanceAvoidance ofof Damage Damage– Knowledge of ship handling characteristics.Knowledge of ship handling characteristics.

– Careful use of powerCareful use of power

– Assessment of speed v possible Assessment of speed v possible damagedamage




• AvoidanceAvoidance ofof Damage Damage

• 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.




• AvoidanceAvoidance ofof Damage Damage

• 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 BROACHINGWIND AND SEA

Ship may run on crestShip may run on crestStern too high - rudder loses effectStern too high - rudder loses effectBow pitches into trough and buriesBow pitches into trough and buriesStern swings round bringing ship abeam to elementsStern swings round bringing ship abeam to elementsNext 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 POOPEDWIND AND SEA

FACTORSFACTORS1. Stern lifts at wave speed1. Stern lifts at wave speed2. Breaking crest travels faster forces down2. Breaking crest travels faster forces down

ACTIONACTIONCrest sweeps over ship from aftCrest sweeps over ship from aft

TO AVOIDTO AVOIDEither select a speed equal to 40% below wave speedEither select a speed equal to 40% below wave speedoror heave-to heave-to


HOGGING AND HOGGING AND SAGGINGSAGGING

PROLONGED SAGPROLONGED SAG

DIRECTION OF SEADIRECTION OF SEAParticle Movement IsParticle Movement IsReduced Past RudderReduced Past RudderHence Less ControlHence Less Control

Better Control AndBetter Control AndEven Strain at WaveEven Strain at WaveSpeed ± 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, no Short bursts of power, wheel hard over, no

headway consider reversing inner headway 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 reduce ½ way, plenty of power and wheel then reduce

when ship answers the helm.when ship answers the helm.

TURNING IN HEAVY TURNING 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 (sideways Single 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 force Plenty 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 HEAVING TOTO


HEAVING HEAVING 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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