rule 06 - safe speed_part a

7/24/2019 Rule 06 - Safe Speed_Part A

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Rule 6 - Safe speed

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Rule 6 - Safe speedEvery vessel shall at all times proceed at a safe speed so that shecan take proper and effective action to avoid collision and be

stopped within a distance appropriate to the prevailingcircumstances and conditions.

In determining a safe speed the following factors shall be amongthose taken into account:

(a) By all vessels:

i. the state of visibility.

ii. the traffic density including concentrations of fishing vessels orany other vessels;

iii.

the manoeuvrability of the vessel with special reference tostopping distance and turning ability in the prevailing conditions;

(iv) at night the presence of background light such as from shore

lights or from back scatter of her own lights;

iv. the state of wind, sea and current, and the proximity ofnavigational hazards;

v. the draught in relation to the available depth of water. 2


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Rule 6 - Safe speed(b) Additionally, by vessels with operational radar:

i. the characteristics, efficiency and limitations of the radarequipment;

ii. any constraints imposed by the radar range scale in use;

iii. the effect on radar detection of the sea state, weather and other

sources of interference;iv. the possibility that small vessels, ice and other floating objects

may not be detected by radar at an adequate range;

v. the number, location and movement of vessels detected by radar;

vi. the more exact assessment of the visibility that may be possible

when radar is used to determine the range of vessels or otherobjects in the vicinity.

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Rule 6 - Safe speed

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Rule 6 - Safe speed

! Safe speed

Difficult to define. In practice:

A speed whereby proper and effective

action can be taken to avoid collision A speed whereby the vessel can be

stopped within a distance appropriate tothe prevailing circumstances and

conditions

It applies to:

! All vessels and at all times

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Rule 6 - Safe speedAll vesselsPower-driven vessels, sailing vessels, large and small vessels, fast and slowvessels, etc.

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Rule 6 - Safe speedAt all times

By day as well as at night! In clear weather

! In restricted visibility

! In open seas

!In local waters

! Etc.

Thus: WHENEVER NECESSARY but ESPECIALLY

! In restricted visibility

!In areas of high traffic density

! Where frequent manoeuvres are required

In accordance with the local prevailing circumstances and conditions

If speed is not reduced, put at least engines on stand-by fimr.fi7


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Rule 6 - Safe speed

By all vessels Rule 6 (a)

The state of visibility

The traffic density

Manoeuvrability of the vessel! Stopping distance

! Turning ability

Background lights

The state of wind, sea and current

The proximity of navigational hazards

The draught in relation to the available depth ofwater!

Interaction

!

Squat

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Rule 6 - Safe speed! By all vessels

The State of Visibility Rule 6, (a) (i)

golfcoursehome.typepad.com

A rough rule for maintaining a safe speed could be thevisibility of the sidelights:

" Vessels of 50 m or more in length: 3 miles

" Vessels between 12 m and 50 m in length: 2 miles

" Vessels of less than 12 m in length: 1 mile

Safe speed will also be influenced by the density of the visibility and

the manoeuvrability of the vessel

The more the visibility is restricted, the more your speed should be restricted

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10/19

Rule 6 - Safe speedBy all vessels

The state of visibility Rule 6, (a) (i)

In certain circumstances the speed can be :

Too high: restricted visibility

heavy traffic areas

Too low: steering may be difficult or impossible

excessive drift, due to current and/or wind(especially in narrow channels)

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The Traffic Density Rule 6, (a) (ii)

Light or heavy traffic

Traffic separation schemes

Number of fishing vessels in the vicinity The proximity of a convoy of warships

Vessels at anchor

Concentration of pleasure crafts

Etc.

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The manoeuvrability of the vessel Rule 6, (a) (iii)

The type of engine: steam, diesel, turbine,!.

The power of the engine

Fast or slow vessel

Manoeuvrability of the vessel with regard to:

loading

draught

trim

etc.

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Rule 6 - Safe speed

STOPPING DISTANCE

and

STOPPING TIME

By all vessels Rule 6 (a)

(Rule 6, (a) (iii))

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STOPPING DISTANCE - STOPPING TIME

! The stopping distanceis the distance that a vessel with her

rudder amidships and her engines full ahead, will run fromthe moment her engines are put to full astern until shecomes to a complete rest over the ground. The time takento accomplish this is called stopping time

!

Stopping distance and stopping time must:

Be expressed in Ships lengths (L) or m. and in min. andsecs

Be clearly exposed on the bridge

!

The water resistance, at a constant speed is equal to thepower of the engines and, as a rough estimate, that thewater resistance is proportional to the square of the speed(V2)

If the speed of a vessel, equal to 16 knots, is reduced to8 knots only !of the power is necessary to maintain

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!

Suppose a vessel with a speed of 16 knots with her enginesat the average power of 100%. The water resistance in that

case is also equal to 100%. The engines are stopped andthe vessel is continuing to move on her own inertia with herhelm at midships.

!

When the vessel has slowed down to 8 knots the waterresistance will be equal to 25% of the initial waterresistance. When she reaches a speed of 4 knots, the waterresistance will be equal to only 0,0625 % and at a speed of2 knots, 0,015625% of the initial water resistance.

!

In other words, since R = V2where R is the resistance ofthe water and V the speed in knots,

! 162 = 256

! 82 = 64! 42 = 16

! 22 = 4

! 12 = 1! 02 = 0

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! The Figure shows how

drastically the resistance ofthe water drops with adecrease in speed. At a speedless than 8 knots the waterresistance is so small that thevessel will continue to moveon her own inertia for quite a

long time.

! If the engines are put to fullastern instead of simply beingstopped, the speed patternwill be quite different.

! Suppose that a ship with anaverage speed of 14 knots istemporary moving at a speedof 7 knots (adverse weather,bad visibility, etc.), thus tohalf her speed. Her stoppingtime will, in that case, also be

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! GENERAL REMARKS

! The stopping distance depends for a great deal on the proportion between

the propeller power ahead and astern.!

The power of a turbine steam engine, working astern is about 70 % of itspower working ahead.

!

When applying astern propulsion to stop a ship, the ship may beconsidered as being stopped when the wake reaches the middle of theship. Another way to check when a vessel is stopped is to observe the

cooling water of the engines which must produce a stationary pool.!

When the stopping time and the speed of a vessel are known, it is quiteeasy to determine the stopping distance.

!

When considering the stopping distance, take into account the distanceran from the time the chadburn is put on full astern and that the propelleractually starts to turn astern. The engineer is not always close to themanoeuvring board and a whole minute can elapse before the propelleractually turns in reverse direction.

! Elements such as the wind, the state of the sea, the depth of water should

be taken into account when considering the stopping distance and thestopping time.

! Keep in mind that when astern power is applied, the vessel will not stay on

her original course but the bow will turn either to starboard or to portdepending on the type of propeller used. For instance, with a right handfixed propeller, the stern will move to port and the bow to starboard.When the vessel has come to a complete rest, the vessel may well haveturned over 90. 17


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Rule 6 - Safe speed

By all vessels

TURNING CIRCLE

Rule 6, (a) (iii)

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TURNING CIRCLE

!

The turning circleof a vessel is the circle the vessel willdescribe when her helm is put, hard over starboard or hard

over port, usually with her engines full ahead.

! The determination of the turning circle of a vessel isnormally carried out during the sea trials of the vessel priorto handover from the builders to the owners.

! The turning circle, together with the stopping distance, are

placed on board of the vessel in the trial papers, so thatthey can be consulted by the ships Master, the watchofficers and eventually the pilots.

!

With regard to the turning circle the following statementsare usually stated in the trial papers:" the advance of the vessel;" the transfer of the vessel;" the tactical diameter that the vessel scribes;" the final diameter that that the vessel has scribed.

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rule 06 - safe speed_part a

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