Post on 24-Dec-2014
description
Grunt Productions 2007
Characteristics of WavesCharacteristics of Waves
HEAVY WEATHERHEAVY WEATHER
Grunt Productions 2007
WAVE WAVE DEVELOPMENTDEVELOPMENT
WIND 10 KTSWIND 10 KTS
WIND 15 KTSWIND 15 KTS
WIND 20 KTSWIND 20 KTS
WIND 30 KTSWIND 30 KTS
Generating Wave MotionGenerating Wave Motion
Surface FrictionSurface Friction
Particle MovementParticle MovementWell DevelopedWell Developed
Large Steep Seas DevelopLarge Steep Seas Develop
Grunt Productions 2007
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
Grunt Productions 2007
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
Grunt Productions 2007
HEAVY WEATHERHEAVY WEATHER
• CharacteristicsCharacteristics of Waves of Waves
• AvoidanceAvoidance ofof Damage Damage– Knowledge of ship handling Knowledge of ship handling
characteristics.characteristics.
Grunt Productions 2007
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
Grunt Productions 2007
HEAVY WEATHERHEAVY WEATHER
• CharacteristicsCharacteristics of Waves of Waves
• 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
Grunt Productions 2007
HEAVY WEATHERHEAVY WEATHER
• CharacteristicsCharacteristics of Waves of Waves
• 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.
Grunt Productions 2007
HEAVY WEATHERHEAVY WEATHER
• CharacteristicsCharacteristics of Waves of Waves
• 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..
Grunt Productions 2007
EFFECTSEFFECTS
• Broaching. Broaching.
• Pooping.Pooping.
• Hogging.Hogging.
• Sagging.Sagging.
• Turning. Turning.
• Heaving to.Heaving to.
Grunt Productions 2007
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
Grunt Productions 2007
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
Grunt Productions 2007
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
Grunt Productions 2007
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:
Grunt Productions 2007
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
Grunt Productions 2007
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.