Relevant documents and M-notices:
MGN 315, MGN 369, MGN 379
Rule 6 is extremely important for safe navigation. There’s a reason we’re devoting a whole article to it. From MGN 369:
approximately 60% of all collisions are said to involve excessive speed
and an example from MGN 315:
In the well known case of THE LADY GWENDOLEN, the Court of Appeal stated that “excessive speed in fog is a grave breach of duty and vessel owners should use their influence to prevent it.” Because of their failure to do so, it was held in that case that the owners could not limit their liability.
Rule 6 questions are often asked during oral exams without the candidates initially realising that they are answering a Rule 6 question. An examiner will describe conditions of worsening visibility and will ask you about your actions. Candidates normally start with the ‘Bridge Procedures Guide’ checklist on entering restricted visibility, which is the right answer to give. Once you’ve stated that you’d reduce to maintain a safe speed (more on this later) they will start asking you what a safe speed would be and what factors you’d take into account; you’re now answering a Rule 6 question. Depending on your level (OOW, Mate or Master candidate) they will drill down into your underlying knowledge, checking that you really understand what is meant by phrases from the rule.
Before we start quoting Rule 6, breaking it down into its parts and seeing what they mean in practical terms, let’s think about safe speed in a very different setting; when you’re driving your car.
When driving a car, we continuously make decisions about safe speed. Whether consciously or not, we’re thinking about:
The characteristics of our car. Is it a ground-hugging, sporty number or a high-sided load carrier?
The road. Is it wet, covered in leaves, icy?
Visibility. Is it foggy, or snowing? Is there a blind bend coming up?
Other traffic. Is the road busy, or is it deserted?
Understanding this continuous process of appraisal, along with two mnemonics that you’ll learn below, is key to remembering how we go about maintaining a safe speed on ship.
A quick historical note; the 1960 version of the collision regulations used the phrase ‘moderate speed’. This was changed to ‘safe speed’ in the 1972 amendments. Why? Consider the car analogy above. Move people would agree that 30mph is a moderate speed for a car. But, if you’re travelling downhill, on a snowy road, with a school crossing at the bottom, is it a safe speed?
If you are asked what Rule 6 deals with, there could be no better answer than to quote from MGN 369:
Rule 6 states that, every vessel shall at all times proceed at a safe speed so that she can take proper and effective action to avoid collision and be stopped within a distance appropriate to the prevailing circumstances and conditions. Rule 6a lists the factors for safe speed that apply to all vessels, and Rule 6b lists factors that apply to ships fitted with radar.
We’ll come to those lists of factors later on in this article.
What does Rule 6 say?
Every vessel shall at all times proceed at a safe speed so that she can take proper and effective action to avoid collision and be stopped within a distance appropriate to the prevailing circumstances and conditions.
‘At all times’
In your orals, you may well be asked for actions on entering restricted visibility. Along with putting a helmsman on the wheel, posting additional lookouts and calling the master, your answer should include the phrase ‘I would reduce to maintain a safe speed’.
If you said ‘I would reduce to a safe speed’ the examiner will likely push you, asking if you had previously been going at an unsafe speed. This is another circumstance where phrasing matters and can save you from a long, painful (for you) explanation. Using the phrase above shows the examiner that you know what you’re talking about.
‘so that she can take proper and effective action to avoid collision’
This will depend on your vessel. A 45m survey vessel equipped with twin Becker rudders will be able to take proper and effective action a lot more easily than a 250m long VLCC. Proper and effective action is action that allows you to avoid a collision.
‘and be stopped within a distance appropriate to the prevailing circumstances and conditions’
If asked what an acceptable safe speed would be with a visibility of one mile, an excellent answer is:
‘A speed that allows the vessel to come to a dead stop within half a mile.’
This answer should be adapted, of course, for half of any given state of visibility.
‘…the prevailing circumstances and conditions’
This brings us to Rule 6 (a) and (b), and how to remember them.
In determining a safe speed the following factors shall be among those taken into account:
(a) By all vessels:
(i) the state of visibility;
(ii) the traffic density including concentrations of fishing vessels or any other vessels;
(iii) the manoeuvrability of the vessel with special reference to stopping 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;
(v) the state of wind, sea and current, and the proximity of navigational hazards;
(vi) the draught in relation to the available depth of water.
The classic mnemonic for this list is:
V.D Makes Little Willies Drip
(V.D., for any non-native English speakers, stands for ‘Venereal Disease’, a disused term for what we now call Sexually Transmitted Infections.)
V - Visibility
D - Density
M - Manoeuvrability
L - Lights (background lights)
W - Weather (wind, seas, current and proximity of navigational hazards
D - Draught (in relation to available depth of water)
So, why consider these? Some are obvious, others less so.
Visibility, traffic Density and the Manoeuvrability of your vessel are obvious enough; think about our analogy of driving your car from the the start of this article. The presence of background light (such as from shore lights or from the backscatter of our own lights) will affect night vision, and may disguise lights belonging to other vessels. Weather conditions can make it harder to stop or turn a vessel, and the presence of navigational hazards may limit your options with regards action to take.
Draught is a bit different than the others, in that there is a bit more to think about. Firstly, the obvious; if you’re navigating in a narrow channel and due to your draught in relation to the depth of the surrounding water you can’t leave it without running aground, that will limit your options with regards to collision avoidance. Secondly, draught that results in lack of under keel clearance may result in squat, which will affect the handling of your vessel and reduce her ability to take avoiding action.
Rule 6 (b)
(b) Additionally, by vessels with operational radar:
(i) the characteristics, efficiency and limitations of the radar equipment;
(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 other objects in the vicinity.
We’ll go through these one by one. Let’s focus on Rule 6 for now, but if you need a refresher about radar then have a read of our series on the subject once you’re finished this article (links at the bottom).
How to remember i-vi?
The mnemonic most commonly used is ‘Chinese Charle Exports Pencils No More’; remember, we don’t use china marker pencils any more when doing radar plots!
C - Characteristics, efficiency and limitations of the radar set
C - Constraints imposed by the radar range scale
E - Effect of the sea state, weather and other sources of interference
P - Possibility that small targets may not be detected at an adequate range
N - Number, location and movement of other vessels
M - More exact assessment of visibility
‘Characteristics, efficiency and limitations of the radar equipment’
S-band, X-band
All ships of 300GT and up (and all passenger vessels) must have an X-band radar (9GHz); all ships of 3000GT and up must have a S-band radar (3GH).
These radars differ in their characteristics; we won’t go into those now (see the radar articles linked above for details) but know that:
X-band radar is heavily affected by rain and has less range than S-band
S-band suffers from promulgation errors, needs high sea clutter settings and gives large target ‘spread’, making it harder to take accurate bearings.
Performance monitor
An OOW should be aware of how well their radar units are performing. As scanners age, their efficiency decreases. One way of testing this is by carrying out a ‘performance monitor’ (known as a PM) test. This is a feature that is built into the unit; generally selecting the ‘PM’ creates a flare on the display, which can be measured; this gives an indication of how the radar is performing. Another way to test a radars performance is to spend time tuning it on a day with excellent visibility and experimenting with the targets that you’re able to pick up, and at what range.
Blind sectors and shadow sectors
Unless you have a scanner mounted at the very highest point of your vessel, any radar will have blind sectors. From MGN 379:
The observer should be aware of the arcs of blind and shadow sectors on the display caused by masts and other on-board obstructions. It is recommended that these zones be plotted on a diagram and placed near the radar display. This diagram should be updated following any changes which affect the sectors.
Every effort will have been made to minimise these blind sectors, as per MSC SN.1/Circ.271 which deals with the installation of radar units:
‘…To make full benefit from the radar, it is vitally important for the OOW that horizontal and vertical blind sectors for the radar antennae are minimized. The objective is to see the horizon freely through 360° as nearly as possible, noting the requirement of 7.1 below. … (c) Blind sectors should be kept to a minimum, and should not occur in an arc of the horizon from right ahead to 22.5º abaft the beam to either side.
Constraints imposed by the radar range scale in use
The scale in use determines the information that is shown to the officer. Short range scanning (i.e. 3 miles) gives good resolution and makes it easier to detect small targets. Large scale (i.e. 12 miles) allows early detection. A prudent navigator keeps one set on a short range and another set on a long range, or switches between ranges on their one set. From MGN 379:
The choice of range scale is important on any radar set, and periodic scanning at a longer-range scale will allow advance warning of hazards. Acquiring targets on a short-range scale may not allow enough time to appreciate the risk of collision and take appropriate action as necessary. This applies particularly when approaching areas where high traffic density is likely or when an early appraisal obtained from the use of longer-range scales may be an important factor in determining safe speed. More generally, the choice of range scales for observation and plotting is dependent upon several factors such as traffic density, speed of own ship, prevailing weather conditions, proximity of navigational hazards, and the frequency of observation.
‘Effect on radar detection of the sea state, weather and other sources of interference’
The radar articles linked above deal with this in detail. However, for simplicities sake, this is summarised below.
Sea state
The greater the sea state, the more interference this will cause on the radar, particularly to windward where radar returns from the steep leading edges of waves will be strongest. This clutter can mask the returns from small vessels, chunks of ice etc.
Weather
Precipitation in general and rain in particular are problematic for radar, especially for x-band radar.
Other sources of interference
Dense flock of birds or swarms of insects, interference from other ships radars, interference from unauthorised broadcasts…this statement covers anything else that might affect a radars effectiveness.
‘The possibility that small vessels, ice and other floating objects may not be detected by radar at an adequate range’
The smaller a target is, and the material that it is made from, affect how large a radar return it gives. Small wooden or fiberglass boats (particularly those without radar reflectors), trees, growlers (small icebergs, largely submerged, of dense glacial ice) may not show up well on radar until they are quite close to your ship. There are ways to increase your chances of seeing these targets, such as using longer trails to catch items as they bob up and down (particularly effective for ice), and tuning the radar to give optimum performance. But, if operating in an area where these sorts of targets are prevalent, consider slowing down to allow more time to take action should they be detected only at a smaller range.
When it comes to knowing when and where to expect small vessels, ice etc. a degree of common sense can be used. See also Admiralty Sailing Directions.
‘The number, location and movement of vessels detected by radar’
Number
Back to our road analogy; you will drive more slowly on a busy road than on a clear one. Likewise, when in congested waters, with multiple targets on the radar display, it is easier for the OOW to become distracted or lose situational awareness. Slowing down allows more time to think, plan and take action.
Location
Ships that are close to you will cause more concern than ships that are far away, and will be more likely to merit a reduction in speed.
Movement
If other vessels are moving quickly, or erratically, this would indicate that reducing speed to allow more time to react to their behaviour is warranted.
‘The more exact assessment of the visibility that may be possible when radar is used to determine the range of vessels or other objects in the vicinity’
It’s a foggy day and you’re having trouble gauging the visibility. Is it two miles or one mile? You know your stopping distances and turning circles at different speeds, and want to be able to stop dead or take avoiding action within half the distance of visibility.
A vessel passes you at two miles; you know this from your radar. You check and yes, you can see them. If the visibility stays as it is, you are right to keep a speed that allows you to stop or take avoiding action within one mile.
And now for the MCA definition
MGN 369 gives the MCA’s interpretation of ‘safe speed’:
Safe speed cannot be explained in absolute numbers for all vessels
The factors that determine a safe speed are dealt with in detail by Rule 6
Strong winds and high seas may influence the manoeuvrability of the vessel
Determination of safe speed must be continuously re-assessed as circumstances change
The OOW should be aware of the effect that different load conditions (full or partly loaded or in ballast) will have on the vessel handling characteristics
Why does Rule 19 double-down on ‘safe speed’?
Rule 19 deals with the conduct of vessels not in sight of one another. We’ll deal with this rule in detail in another article. For now, understand that it does mention safe speed, but mostly to reinforce Rule 6:
From MGN 369:
Rule 19 reinforces Rule 6 by requiring all vessels to proceed at a safe speed in restricted visibility and by requiring power-driven vessels to ‘have their engines ready for immediate manoeuvre’. In order to maintain a safe speed at all times a continuous appraisal of changes in circumstances and conditions should be made.
MCAQs
When should you make an appraisal of the vessels speed?
What would your actions be on approaching an area of restricted visibility?
What factors should be taken into account by all ships when assessing safe speed?
What additional factors should be taken into account by vessels with functional radar?
Explain what is meant by taking the limitations of the range scale in use into account.?
Explain how you’d adjust speed in heavy rain in the middle of the Atlantic.
Explain how you’d adjust speed in heavy rain in the English Channel.
Explain why sea state might affect safe speed.
Explain why draught might affect safe speed.