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Rule 06 - Safe Speed Part_C
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Transcript of Rule 06 - Safe Speed Part_C
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Squat
How can squat be evidenced ?
" Vessels experiencing squat will be difficult to steer.
" Waves formed by the ships movement will increase inamplitude and the wave making can cause seriousdamage to the side of the channel and moored vessels.
" Big rolling waves may follow the vessel and sometimesbeak on the after deck of the vessel
" The wake left by the vessel will probably be mixed withmud.
" The vessel may vibrate with a decrease in speed and areduced rpm.
The first and main thing to do is: REDUCE SPEED.
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Vessels in narrow waters such as rivers or canals
! When the vessel doesnt keep to the middle of the fairway,on the side closest to the shore, a reduction of the water
level will occur and the velocity of the water flow willincrease and its pressure decrease.
! Due to the difference in water level and consequently the
difference in pressure, the vessel will be pushed towardsthe closest shore
!
In the Figure above, the dotted line shows the vessel in a
floating position when at rest (not moving).! As the vessel approaches the side of the fairway, the
suction becomes greater.
Reducing the speed will, here too, avoid the vessel
from running into the shore. 40
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Vessel in close proximity to land or a shoal
! A vessel navigating close to the
shore or a sandbank or a shoal, willalso be influenced by a difference inwater pressure on the side closest tothe shallow.
! On this side, the vessel will alsoundergo a suction.
! As the turning point of a vesselmoving ahead lays about 1/3 fromthe bow, the sternof the vessel willbe attracted to the shore. If nothingis done to counter this suction, thevessel will sheer and there is a greatchance that she will run aground onthe other side of the channel, unlessthe necessary measures are taken intime:
" reduce the speed:" put the rudder on the opposite
side from the sheer
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Vessels meeting end-on passing too close
Two vessels meeting end-on and passing veryclose, will, in positions A and A both have thewater flow running faster on their starboard sidewith a reduced water pressure. They will both havea reduction of the water level on their starboardside, with a tendency to be pushed towards theshore.
As the distance between both vessels getsnarrower, the currents between them will increasein speed and their pressure will decrease. But, bothcurrents, which run in an opposite directionbetween them, will compensate each other.In that position (both vessels aboard) both vesselswill normally be pushed away from each other.
Conclusion
Two vessels meeting end-on may pass each otherquite close with no risk to collide; furthermore theywill run clear from each other in a very short time.
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Rule 6 - Safe speedBy all vessels
Vessels meeting end-on passing very close
Vessels will normally run clear of each other
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Vessels overtaking one another too close (i)
! As both vessels comeaboard of one another,strong currents will
develop between them,which will make overtakinga real hazard.
! In position (i) both
vessels tend to have theirbows to deflect inward asa result of both vesselsbeing attracted to theshore.Position i
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Vessels overtaking one another too close (ii)
! In position (ii), when both vesselsare aboard of each other, a strongcurrent will develop betweenthem and both vessels willexperience a serious decrease ofthe water level between them.The currents between the twovessels run in the same direction(and sense) with an importantincrease in speed and a decreasein pressure.
! Both vessels will be attracted to
each other. The smaller vesselwill be more influenced then thelarger one with a real chance ofrunning into her starboard shore.Position ii
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Vessels overtaking one another too close (iii)
! In position III, vessel B is sufficiently clearfrom vessel A. Vessel A being rather close toher starboard shore will still experience anattraction from her stern which she shouldcorrect by the proper helm action. Vessel Bwill also experience a slight increase inspeed.
! The paramount rule here is to engage in aclear conversation by VHF with the vesselbeing overtaken and to agree on the bestprocedure the overtaking should benegotiated. The overtaking vessel must alsomake the proper sound signals as prescribedin Rule 34 (c) of the Colregs or as prescribedin the local Regulations.
! If no proper action is taken both vessels will
be sucked to each other and the overtakenvessel (usually the smallest and the slowestof the two) will, as we already saw, besucked by the stern and run aground in deshoulder on her starboard side.Position iii
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Rule 6 - Safe speedBy all vessels
Vessels overtaking one another too closeBoth vessels must agree on how to pass one another and reduce speed
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Vessel negotiating a bend in a narrow channel
Bank cushion effect
! A vessel can negotiate a bend in anarrow channel, maintaining her rudderin a midship position, when she is closeenough to the inner side of the channel.This can be materialized thanks to thebank cushion effect.
! If the position of the helm is maintainedin the correct position, the ship willsheer away from the bank, just enoughto allow the vessel to negotiate the bendby herself
! The person responsible for thismanoeuvre must keep the shipsmovement well under control andascertain himself that the vessel doesntsheer away too much, with the risk torun into the opposite shore or to collide
with an oncoming vessel. 48
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
Nowadays, nearly all ships arefitted with a proper radar
All ships of over 10.000 grt
must be fitted with an ARPA
terma.com
Rule 6, (b)
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
For details see alsoMarine Guidance Note
MGN 63 (M + F) : TheUse of Electronic Aids to
Navigation.
See also : InternationalRegulations for
Preventing Collisions at
Seaby Capt. Pierre
Deseck, page 75
www.austin-insulators.com
Rule 6, (b)
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
"
Range performance" Minimum range" Diameter of PPI" Scale of display"
Plotting facilities"
Range accuracy"
Heading indicator" Bearing accuracy" Azimuth stabilisation
"
Etc.
The characteristics, efficiency and limitations of the radarequipment Rule 6, (b) (i)
Efficiency of radar
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
Types of radars Rule 6, (b) (ii)
" 3 cm radars
"
10 cm radars
Rain and sea
clutter are less on10 cm wavelength
radars
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
Image presentations Rule 6, (b) (ii)
Relative motion radars
The center of the screen is the own ship
a)
Unstabilized ships head-up or course-upb)
Stabilized north-up or azimuth stabilization
c)
Stabilized ships head-up or course-up
True motion radars
Own vessel moves over the screena)
North-up
b)
Ships head-up or course-up
c)
Anti-collision or collision avoidance system (C.A.S.)
d)
Automatic plotting system (ARPA), photo plot, situation display
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Rule 6 - Safe speed
Relative Motion versus True Motion
Additionally, by vessels with operational radar
Relative Motion
All tracked targets display motion vectors includingstationary objects (e.g. buoys and the like). Own ship is
stationary in the center of the screen
True Motion
Ships and other vessels display their true motion vector.Buoys and other tracked stationary objects show no
motion vectors. Own vessel moves over the screen.
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Rule 6 - Safe speed
Ships head-up versus North-up
Additionally, by vessels with operational radar
Ships Head-up
Similitude between the outside view and the presentationon the radar screen
North-upEasy to compare chart with radar screen
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
Relative motion radar, north-up
hansbuch.dk 56
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
Relative motion radar, head-up
hansbuch.dk 57
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
True motion radar, head-up, off-center
norinco.co.in
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
True motion radar, head-up
rstmarine.com 59
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
Relative motion radar, north-up
rosepointnav.com
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
Any constraints imposed by the radar range
scale in use Rule 6, (b) (ii)
The choice of range scale depends upon several factorssuch as:
" Traffic density" Speed of own ship
"
Presence of coastlines" Weather conditions
" Frequency of observations
" Etc.
mecys.com
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
Any constraints imposed by the radar range scalein use Rule 6, (b) (ii)
Range Scale
A good rule of thumb todetermine the range scale to be
used, is the speed of own vessel
1.
Speed between 5 and 10 knots: 5mile range
2. Speed between 10 and 20 knots: 12
mile range
3.
Speed over 20 knots: 20 mile range www.photolib.noaa.gov 62
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
Rule 6, (b) (ii)
Long Range Scale
Use of long range scale allows:
Early observation of targets
Observation of land and sea marks
Observation of coast line
Observation of close-quarters
situations
Negative points are:
Definition and discrimination are
reduced
Small targets are less visible
12 miles range dspnor.no
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
Short Range Scale
Use of a short range scale allows:
Better definition and accuracy
(especially by risk of collision)
Small target can be better observed
Negative points are:
Entire radar picture is reduced
More difficult to assess close-
quarter-situations
It is good practice to regularly switch
from long range to short range scales
dspnor.no3 miles range
Rule 6, (b) (ii)
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
The effect on radar detection of the sea state, weather
and other sources of interference Rule 6, (b) (iii)
Anti-clutter
The anti-clutter must beproperly regulated
Too much clutter:real
echoes become invisible
Too little clutter:sea waves
or rain are not properly
detected or
Sea waves or rain can be
mistaken for real echoes 65
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
The effect on radar detection of the sea state,weather and other sources of interference Rule 6, (b) (iii)
InterferencesInterferences on the radar can be caused
by rain and sea waves but also by
atmospheric phenomena like thunder
Proper use of sea clutter allows normal
echoes to be distinguished sea and rain
Rain and sea waves are less visible on
a 10 cm wavelength radar (compared to
3 cm)
Echoes of small vessels are often
undetected with interference
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
Small vessels, ice and other floating objectsRule 6, (b) (iv)
taniwani.de
A dhow is a traditional Arab sailing vessel with one or more lateen sails.
They are primarily used along the coasts of the Arabian Peninsula, Pakistan,
India, and East Africa. Larger dhows have crews of approximately thirty, while
smaller dhows typically have crews of around twelve.
At night, dhows often do not carry navigation lights and can
be a real hazard, not always visible on the radar
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
Small vessels, ice and other floating objectsRule 6, (b) (iv)
Fiberglass boats and other small boats give usually very poor echoes
They may not be detected in time to take effective collision avoiding action68
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
Small vessels, ice and other floating objectsRule 6, (b) (iv)
khaolak.net
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Rule 6 - Safe speed
Additionally, by vessels with operational radar
Small vessels, ice and other floating objectsRule 6, (b) (iv)
Navigational hazards, like drifting logs or even containers,
may not be detected on the radar and may require thevessel to maintain a safe speed
kristiina.kaapeli.fi
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
Small vessels, ice and other floating objectsRule 6, (b) (iv)
Small ice patches like growlers are difficult to detect by radar
smh.com.au
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
Small vessels, ice and other floating objectsRule 6, (b) (iv)
Radar Reflectors
Vessels under 150 GT are
required to carry a radar reflector
store.crowleys.com sailingproshop.com
It may double the detection range
of small vessels
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
The number, location andmovement of vessels
detected by radarRule 6, (b) (v)
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Rule 6 - Safe speedAdditionally, by vessels with operational radar
The number, location and movement of vessels detected byradar Rule 6, (b) (v)
The more vessels that are
detected, the more difficult it
becomes to observe themindividually or to plot them
The risk of close quarters-
situation becomes greater andthe speed must be altered
accordingly
admin.royalnavy.mod.uk 74
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Rule 6 - Safe speed
Assessment of visibility Rule 6, (b) (vi)
At sea, visibility can be
assessed by radar when
ships or objects appear or
disappear. It is however
limited to the direction of the
objects and the conditions of
visibility may alter rapidly
after they have been
observed
The fixed or variable range
rings are used for that
purpose
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Rule 6 - Safe speed
SOME CONCLUSIONS
! Even the most efficient equipment may not be substituted for
human observation
! Electronic equipment may fail unexpectedly and some time may
elapse before it has been assessed
! Radar may fail to detect small vessels or small objects
!
Small course alterations made by other vessels are usuallyless apparent
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Rule 6 - Safe speed
SOME CONCLUSIONS
! The efficiency of electronic and other equipment depends, to
some extend, to the experience and competence of those
using it
!Some electronic equipment such as AIS and ECDIS have notyet been integrated in the Colregs. Every OOW should
however use them to their best ability to prevent collisions at
sea
!Never rely blindly on your equipment. Each piece of equipment
should be regularly checked, eventually by comparing it with
another piece of equipment
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