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1 INTRODUCTION
COLREGS which regulates the action of the ships’
collisionavoidanceintheencountersituation,action
rules, the distribution of rights and obligations of
avoidance and so on, is the guarantee of safe and
orderly navigation, prevention and reduction of
collisionof ships, and the maritime traffic rulesthat
shipdriversshouldabideby.Inrecentyears,withthe
further application of automation technology in the
field of navigation and with the gradually
development of intelligent ships represented by
unmanned boats, research on intelligent decision‐
making for vessel collision avoidance is also
developingrapidly.However,whethertheintelligent
decision‐
makingforvesselcollisionavoidancecanbe
appliedintherealships and acceptedbythesailors
dependsonwhetherthedecision‐makingfollowsthe
COLREGSandhastheabilitytosimulatetheordinary
practices of outstanding crews and reflect their
excellent seamanship. COLREGS is the essential
criteriontodecision‐making,
intheprocessofrefining
avoidance strategies under different encounter
situations; it is found that the effect of avoidance
accordingtotherulesisgreatlyaffectedbythehigh
ship speed ratio. Through the analysis on the
geometricchangelawoftwovessels’relativemotion
inOpenwaters,theeffects
oftheresponsibilityforthe
ship collision avoidance under the COLREGS and
special case for high‐speed ratio is discussed.
Accordingto thecollisionavoidancemeasurestaken
fortwovessels encounter situation,somereasonable
suggestions are put forward and the simulation
experiments thatbased on shipʹsintelligent collision
avoidance simulation
platform are given to support
theidea.
The Effect of High Ship Speed Ratio on Collision
Avoidance Behavior of COLREGS
X.H.Wang,L.Li&G.Chen
J
imeiUniversity,Xiamen,China
ABSTRACT: The speed ratio is an important factor that must be considered when two vessels will course
changetoavoidcollision.IntheprocessoftheresearchonPersonifyingIntelligentDecision‐makingforVessel
CollisionAvoidance(shortforPIDVCA),itisfoundthattheeffectofcollision
avoidancebasedontheexisting
“InternationalRegulationsforPreventionCollisionatsea”(shortforCOLREGS)isgreatlyaffectedbythehigh
speedratio(k=Vt/V0≥1.5).Throughtheanalysisonthegeometricchangelawoftwovessels’relativemotionin
Openwaters,theeffectsoftheresponsibilityfortheshipcollisionavoidance
undertheCOLREGSandspecial
case for high‐speed ratio is discussed. According to the collision avoidance measures taken for two vessels
encountersituation,somereasonablesuggestionsareputforwardandthesimulationexperimentsthatbased
onshipʹsintelligentcollisionavoidancesimulationplatformaregiventosupporttheidea.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 13
Number 2
June 2019
DOI:10.12716/1001.13.02.07
320
2 PIDVCAINSTRUCTIONS
2.1 GoalandPrincipleofPIDVCA
The aim of PIDVCA algorithm is to provide crews
safe, scientific and economic decision‐making for
vessel collision avoidance by a machine (computer),
whichcanfollowstheCOLREGSandhas theability
tosimulatetheordinarypracticesofcrewsandreflect
theirseamanship.Itssecurityisreflectedintheoutput
of the avoidance decision that is premised on the
maximized DCPA, and its scientific is embodied in
the organic integration of quantitative analysis of
vessels ’ relative motion geometric graphic and
qualitativeanalysisofCOLREGSandexpertempirical
knowledge, and its economy
is reflected in its
minimizedtrackoffset,whilesatisfytheprecondition
ofthesafety.
In the co‐existence stage of manned and
unmannedships,forthePIDVCAcanbeacceptedby
the sailors to achieve concerted avoidance between
manned ship and unmanned ship, algorithm’s
principles
areasfollows.
First,followthespiritofCOLREGS.
Second, simulate the ordinary practices of crews
andreflecttheirexcellentseamanship.
Thirdly, reflect the concretization, clearness and
reasonable extension about important concepts and
provisionsoftheCOLREGSinpractice.
COLREGSisveryclearabouttherulesofconduct
oftwovessels
inanyconditionofvisibility,andthere
is no specific advice or specific method for collision
avoidance of multiple vessels, only the wordsʺ
ordinary practice of seamen, excellent seamanshipʺ
are used. According to crew training and expert
consultation,ʺordinarypracticeofseamen” means
the making‐decisions for collision avoidance of
multiplevesselsthatcanbewidelyacceptedbycrews,
for example, adopt relevant requirements of
COLREGS about two vessels to avoid key vessel of
the multiple vessels ’ encounter situation.
“seamanship of crews” is short for excellent
seamanship is expressed in excellent crews making
reasonableandeffectiveavoidancedecisions,concrete
embodiment
in the correctly evaluation of risk of
collision, safety distance approaching (SDA),
avoidancetime,avoidancemeasureandresumetime,
as well as inthe flexible reactioncapacity to handle
complicatedsituation.
2.2 PIDVCAalgorithmcomposition
Tothe problemthat the collisionsituationisendless
andunrepeatableinthenavigationdue
tothevessels’
differenttypes,scales,speeds,sailingwatersandthe
angles of the two vessels’ rendezvous, PIDVCA
adoptsthepersonalizedmachinelearningmethodto
realize the purpose of automatic target perception,
cognitive target, generation, verification and
optimizationdecision.
Accordingtotheprinciple,PIDVCAconsistsofthe
initial PIDVCA generation algorithm
and the
PIDVCAverificationandoptimizationalgorithm.The
initialPIDVCAgenerationalgorithmiscomposed of
the target intercrossing characteristics recognition
algorithm, target potential danger judgment
algorithm,encounter attributerecognitionalgorithm,
the shipʹs avoidance attribute recognition algorithm
for dangerous targets, encounter situation analysis
and classification algorithm, dynamic hazard
assessment algorithm
and PIDVCA plan generation
algorithm. PIDVCA verification and optimization
algorithm is made up of predicting target potential
risk analysis algorithm, ordinary algorithm of
simulation of ordinary practice and seamanship
algorithm of excellent seamanship, space searching
optimization algorithm, algorithm of space‐time
searching optimization, algorithm of coordination
collisionavoidanceoptimization,PIDVCA plan
local
dynamicoptimizationalgorithm,PIDVCAgeneration
algorithm and emergency decision algorithm of
dangeroussituation.
PIDVCAalgorithmisdividedintotwo‐vesseland
multi‐vessel PIDVCA generation and optimization
algorithm considering two‐vessel and multi‐vessel
encounter situation. For the two‐vessel PIDVCA
generation and optimization algorithm, the initial
PIDVCA generation
algorithm can basically achieve
satisfactory avoidance effect, When necessary, it is
supplemented by coordinated collision avoidance
decision optimization algorithm, spatial searching
optimization algorithm and PIDVCA plan dynamic
optimization algorithm under the guidance of
dynamic optimization objective function. For
example, in Condition of restricted Visibility, when
the own‐ship avoids the target
ship near the left
beam, it needs to be supplemented by the local
PIDVCA plan dynamic optimization algorithm to
avoidproducingalargetrackoffset.ForthePIDVCA
generation and optimization algorithm of multi‐
vessel,itisnecessarytoperformthepredictiontarget
ship potential risk analysis algorithm of PIDVCA
verification and optimization algorithm, and
supplementedbyotheralgorithmswhennecessary.
3 ANALYZEOFTHERELATIVEMOTION
GEOMETRICCHANGERULESOFCROSSING
INCONDITIONOFNVISIBILITY
3.1 Encountersituationdescription
TakingthecrossingsituationandintheOpenwaters
asanexample,itisassumedthatthetwovesselshave
the
samescaleanddifferentspeeds,andtheaffecting
of vessels’ maneuvering are ignored, and the SDA
betweenthetwovesselsisthesame,setas1seamile,
and the DCPA is zero. In order to facilitate the
comparativeanalysis,thetwovesselsareeachotherʹs
target‐vesselsand
altercoursetorightforavessel.
FIG. 1 and 2 are geometric diagrams of relative
motionoftwo vesselsin thesamecrossing situation
astheirleftcrossingandrightcrossing.Thatis,when
the portside vessel as the own‐ship,the other vessel
on her right, and when the
starboard vessel is the
own‐ship, the other vessel on her left. For ease of
comparison, two independent relative motion
geometriesarepresentedintheonegeometry.Inthe
figures,C0andV0respectivelyrepresenttheheading
andvelocityoftheown‐ship,VtandVrrespectively
representthetrue
andrelativevelocityofthetarget‐
ship,andACistheturningangle.
321
Figure1. Geometric diagram of relative motion of a faster
give‐wayvessel andalower stand‐onvessel’s alter course
asown‐shiprespectivelytoaltercourse
Figure2. Geometric diagram of relativemotion ofa lower
give‐way vessel and a faster stand‐on vessel as own‐ship
respectivelytoaltercourse
3.2 Analysisfigures
Asshowninfigure1,iftheown‐shipistheonevessel
that faster and Give‐way, and alters course to
starboardforanothervessel.
1 Iftheown‐shipalterscourseatanequaldistance
and the target‐ship’s angle remains unchanged,
thegreatertheturning
angleACisandthelarger
DCPAvaluewillbe,andwiththedecreaseofthe
ship speed ratio k=Vt/V0 value, the smaller the
steeringAngleACisrequired,ifyouwanttoget
thesameDCPAvalue.
2 Ifaltercourseoftheown‐shipremainsunchanged,
thelarger
thetarget‐ship’sangleis,thegreaterthe
DCPA value will be. With the decrease of ship
speedratiok value,the smallerthe DCPA value,
andthelesseffectivetheavoidanceis.
Iftheown‐shipistheonevesselthatisslowerand
should Stand‐on, and alters course
to starboard for
anothervessel.
1 If the own‐ship alter course at an equal distance
andthetarget‐ship’sangleremainsunchanged,the
greater the turning angle AC is and the larger
DCPAvaluewillbe,andwiththeincreaseofthe
ship speed ratio k value, the bigger
the steering
Angle AC is required to obtain the same DCPA
value.
2 Ifaltercourseoftheown‐shipremainsunchanged,
thelargerthetarget‐ship’sangleis,thegreaterthe
DCPA value will be. With the increase of ship
speedratiok value,the smallertheDCPA value,
and
thelesseffectivetheavoidanceis.
Asshowninfigure2,thelowerStand‐onVesselas
the own‐ship and alter course to right for another
vessel. The give‐way vessel is a lower ship and the
stand‐on vessel is faster ship. If the faster Stand‐on
Vessel
astheown‐shipandaltercourseto starboard
foranothervessel.
1 Iftheown‐shipalterscourseatanequaldistance
andthetarget‐ship’sangleremainsunchanged,the
greater the turning angle AC is and the larger
DCPAvaluewillbe,andwiththeincreaseofthe
ship
speedratio k value, thesmaller the steering
Angle AC is required to obtain the same DCPA
value.
2 Ifaltercourseoftheown‐shipremainsunchanged,
thelargerthetarget‐ship’sangleis,thegreaterthe
DCPA value will be. With the decrease of ship
speedratiok
value, the smallerthe DCPAvalue,
andthebettereffectivetheavoidanceis.
IfthelowerGive‐wayVesselastheown‐shipand
altercoursetostarboardforanothervessel.
1 If the own‐ship alter course at an equal distance
andthetarget‐ship’sangleremainsunchanged,the
greater
the turning angle AC is and the larger
DCPAvaluewillbe,Andthelargertheshipspeed
ratiois,thelargertheAngleneededtochange;
2 Ifaltercourseoftheown‐shipremainsunchanged,
the greater the speed ratio is, and the worse
effectivetheavoidanceis.
3.3 Analysisresults
Althoughtheencounteroftwovesselsisjustatrivial
case, it can help us to anlysis whether the decision‐
makingisreasonableandhowtooptimize.
Inconclusion,COLREGSiscompletelyreasonable
forthe twovessels in sightof one anotherto divide
the Give‐way and
the Stand‐on vessel according to
regionsexceptthesituationofovertaking,butinthe
caseofcrossingabeamsituation,onlywhenthespeed
ofStand‐onVesselissmallerorthespeedratioofthe
twovesselsisnotmuchdifferent(k=Vt/V0)<1.5),the
effective of the avoidance would
seem satisfactory.
When the speed ratio is (k=Vt/V0) >=1.5, if avoid
target‐ship according the COLREGS, there are
unreasonableeffectiveoftheavoidance.
4 SIMULATIONEXPERIMENTANDDECISION‐
MAKINGOPTIMIZATION
In order to make the decision‐making of collision
avoidancemoresafe,scientificandeconomic,alotof
simulation experiments of
PIDVCA algorithm were
done on the intelligent control simulation platform
that is approximate the real ships. It is found that
there is unreasonable decision‐making of avoidance
collision that strictly perform the COLREGS in the
condition of ship speed ratio (k=Vt/V0) >=1.5. As
shown in figure 3, in visibility, according
the
COLREGS, the encounter situation is the crossing,
and target‐ship 1 isthe give‐way own‐ship, and the
simulationresultsofavoidancecollisionisnotgood.
The bigger ship speed ratio k is, and the worse the
resultbecames.Thisis,thecollisionavoidanceaction
of the lower ship
will be farearlier than the faster
ship,andtheLeadsdependonthevalueofVt/V0,the
biggerkisandtheLeadsgetslarger.
322
Acrossingleftnearthebeamencounter situation
in restricted visibility is taken as an example to
illuminate the effect of high speed ratio on collision
avoidance behavior of COLREGS. According to the
COLREGS,therulesofconductofvesselsinrestricted
visibilityarethateveryvesselshallproceedat
asafe
speed adapted to the prevailing circumstances and
conditions of restricted visibility. A power‐driven
vessel shall have her engines ready for immediate
maneuver.Thisis,inrestrictedvisibility,everyvessel
have responsibility to undertake obligation of
avoidance. It is unreasonablefor the lowerstand‐on
own‐ship, from
whichthe target‐ship iscoming left,
especiallyforthecrossingleftnearthebeam(247.5°<
relativeorientationoftarget‐ship<292.5°).
Figure3. Simulation experiments trajectory of avoidance
collisionin crossing situation andin sight of one another
（Vt/V0=1.8,SDA=1.99）
From the above analysis results, in condition of
visibility, the avoidance moment of lower stand‐on
vesselisfarearlierthanthehighergive‐wayvessel.In
condition of restricted visibility, in order to avoid
dangerous, “the lower stand‐on vessel in visibility”
willchoose totake avoidanceaction first,and
when
theavoidancetimeof“thehighergive‐wayvesselin
visibility”arrives,itwill choosenot totake collision
avoidance action for disappearing of the risk of
collision,sothatandtwovesselshavelongstandoff,
because of the smaller relative speed, As shown in
figure 4 (a). Obviously,
this kind of collision
avoidance action does not conform to the safety,
scienceandeconomyofnavigationofships.
Inorderto solvethe aboveproblems, andsatisfy
thepremiseofscientific,safeandtheminimumtrack
offset, it’s integrated PIDVCA algorithmto dynamic
optimizedecision‐makingofcollisionavoidance,and
theoptimizationresultsisshowninfigure4(b)and
4(c).Optimizationapproachinfigure4(b)istomake
“the lower stand‐on vessel in visibility” perform
avoidance action in condition of restricted visibility
accordingtothelastopportunityofsteeringrudderof
“thelowerstand‐onvesselinvisibility”.
Infigure4(c),
Optimization approach is thatʺthe higher give‐way
vesselʺwilltaketheinitiativetofulfilltheirobligation
to give way in advance in condition of restricted
visibility, so that “the low‐speed stand‐on vessel in
visibility” will remain stand on for disappearing of
thecollisiondangerous.
(a)Decision‐makingoptimizationbefore
(b) Optimized decision‐making of “the lower stand‐on
vesselinvisibility”
(c) Optimized decision‐making of “the higher give‐way
vesselinvisibility”
Figure4.Simulation experiment resultsofbefore and after
optimizationofdecision‐makingfortheleftnearthebeam
encountersituationandinrestrictedvisibility
Theabove simulation examplesshow thatif “the
lower stand‐on vessel in visibility” take action to
avoid collision strictly according to COLREGS in
condition of restricted visibility, there is
inharmonious situation. If “the higher give‐way
vessel”cantakeonmoreresponsibilityforavoidance
collision,theavoidancedangerouswillbe
better.
5 CONCLUSIONSANDSUGGESTIONS
Whetheritistoprovideauxiliarydecision‐makingfor
manned ship or automatic decision‐making of
collisionavoidancefor intelligentship orunmanned
ship, intelligent decision‐making for vessel collision
avoidance must follow the spirit of COLREGS and
can simulate the ordinary practices of crews
and
reflect their seamanship. However, with the rapid
development of artificial intelligence and computer
technology, vessels are developing in the direction
large‐scale,high‐speedandintelligence,anditmakes
somerules ofCOLREGS unreasonable.For example,
theactionofavoidancecollisiononlyisbasedonthe
relativebearingofapproaching
vessels,thereisnothe
ship speed ratio to be taken into account, which is
reasonableintheyearsthattherewaslittledifference
323
of speed between power‐driven vessel. In the
moderns, the high‐speed vessel are ubiquitous, the
ship speed ratio should be taken into account. The
effectsaresummarizedbelow.
1 In visibilityand in rightcrossing situation, if the
stand‐onandgive‐onvesselhasahighspeedratio,
there is a less effective avoidance collision
according to COLREGS. Namely, avoidance
opportunities of the give‐way vessel will become
earlierwhichdependontheVt/V0.Thelargerkis,
andtheearlieravoidanceopportunitiesis.
2 Inrestrictedvisibilityandincrossingneartheleft
beam situation, the own‐
ship as the lower vessel
acttoavoidaccordingtoCOLREGS,thereisaless
effectiveavoidancealso,maybemoredangerous.
Inviewoftheseinfluences,itissuggestedthatthe
research of intelligent collision avoidance can
reasonably extend the COLREGS to solve the
unreasonablephenomenonofavoidanceeffectcaused
by
strictlyavoidcollisionaccordingtoCOLREGS.
ACKNOWLEDGMENT
ProjectsupportedbytheGeneralProgramfortheNational
NaturalScienceFoundationofChina(Grantno.51879119).
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