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ARPA - Stabilization mode
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What is wrong with Ground Stabilisation?
Captain Peter Starkey
NORWEGIAN DREAM& EVER DECENT
REPORT
To all Bahamian Shipowners:
To determine risk of collision using ARPA vectors, only the relative vectors should be used.
True vectors should be used to determine aspect
NORWEGIAN DREAM& EVER DECENT
REPORTTo all Bahamian Shipowners:
speed input for an anti-collision plot on radar/ARPA should always be:
speed through the water
not speed over the ground
The Relative Plot&
Relative Vector
Independent of input error
“Instant” assessment of risk of collision
CPA
TCPA
The True Plot&
True Vector
“ASPECT”
THE TRUE PICTURE – THE SITUATION
TRIAL MANOEUVRE
ASPECT
The International Regulations for the Prevention of Collisions at Sea
THE TRUE PICTURETHE TRUE SITUATION
Situation Awareness
TRIAL MANOEUVRE
Knowledge of Target Data required to calculate trial manoeuvre
But………
All true functions are dependent on sensor input and sensor accuracy
and are related to the stabilisation
Sea or Ground Stabilisation
Does the choice of stabilisation matter?
ASPECT
Visual aspect - heading
Radar aspect
sea stabilised - approximate visual aspect
ground stabilised - may be very different
Does radar aspect matter?
Clear visibility - look out of the window!!
Restricted visibility - vessels not in sight
Rule 19
What is aspect in Rule 19?
Relative Vector
Own Ship
RELATIVE VECTORS SEA OR GROUND STABILISED
Heading
Target
Current
Heading – Visual AspectTrue Vector – Radar Aspect
Current
Own Ship
Heading - True Vector
Target
SEA STABILISEDTRUE VECTORS
True Vector – Radar Aspect
Current
Own Ship
GROUND STABILISEDTRUE VECTORS
Heading
Target
True Vector – Radar Aspect
Own Ship
GROUND STABILISEDTRUE VECTORS
Heading
Target
The Practical Effect
Current
Own Ship
Heading
CHANNEL
Slow speed target
GROUND STABILISEDTRUE VECTORS
Current
Own Ship
CHANNEL
Slow speed target
RELATIVE VECTORS SEA OR GROUND STABILISED
Heading m
arker
Current
Own Ship
Heading
CHANNELSlow speed target
SEA STABILISEDTRUE VECTORS
Current
Own Ship
CHANNEL
Slow speed target
GROUND STABILISEDTRUE VECTORS
Current
Own Ship
Heading
CHANNEL
Slow speed target
SEA STABILISEDTRUE VECTORS
COLLISION AVOIDANCE
SEA OR GROUND
RELATIVE OR TRUE
SEA STABILISEDTRUE VECTORS
CURRENT
TARGET
OWN SHIP
SEA STABILISEDTRUE VECTORS
CURRENT
TARGET
OWN SHIP
RELATIVE VECTORS
CURRENT
TARGET
OWN SHIP
Heading marker
GROUND STABILISEDTRUE VECTORS
CURRENT
TARGET
OWN SHIP
Own Ship
RELATIVE VECTORS
North Up
RM (TT)
Ground Stabilised (GPS)
Heading 350°
CMG (GPS) 355°
Channel 355°/175°
HL
Current 090° 2 kts
Own Ship
TRUE VECTORS
North Up
RM (TT)
Ground Stabilised (GPS)
Heading 350°
CMG (GPS) 355°
Channel 355°/175°
HL
Current 090° 2 kts