rule 06 - safe speed part_c

7/24/2019 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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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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"

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

www.raytheon-anschuetz.com51


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Types of radars Rule 6, (b) (ii)

" 3 cm radars

"

10 cm radars

Rain and sea

clutter are less on10 cm wavelength

radars

www.globalsecurity.org 52


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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


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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Relative motion radar, north-up

hansbuch.dk 56


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Relative motion radar, head-up

hansbuch.dk 57


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True motion radar, head-up, off-center

norinco.co.in

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True motion radar, head-up

rstmarine.com 59


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Relative motion radar, north-up

rosepointnav.com

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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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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, (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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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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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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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

misimulators.co.uk66


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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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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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khaolak.net

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Rule 6 - Safe speed



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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Small ice patches like growlers are difficult to detect by radar

smh.com.au

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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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The number, location andmovement of vessels

detected by radarRule 6, (b) (v)

media-cdn.tripadvisor.com 73


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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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rule 06 - safe speed part_c

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