Rule 7 tells us how to ascertain if a risk of collision exists. Rule 8 tells us what the action we take to avoid that collision should look like. This is a long article so make sure you have the time and energy to devote to it before you get started.
Relevant documents and M-notices: MSN 1781, MGN 369
Rule 8(a)
Any action taken to avoid collision shall be taken in accordance with the Rules of this Part and shall, if the circumstances of the case admit, be positive, made in ample time and with due regard to the observance of good seamanship.
Any action to avoid collision
In the COLREGS standing-on (keeping one’s course and speed) is considered an action. We’ll go into this more in Rule 17, but for now know that if the other vessel is directed to keep out of your way, you are directed to stand-on (keep your course and speed). This is your action.
‘shall’ (x2)
Wherever you see a ‘shall’ in the COLREGS, know that this is not an option. It seems obvious but it’s worth stating this point. Some later rules have ‘may’ statements as well, so it’s worth getting it into your head now that ‘shalls’ are obligatory.
in accordance with the Rules of this Part
This means the Rules that make up Part B (Rules 4-19)
if the circumstances of the case admit
There may be things going on that are difficult to account for in the rules. Remember Rule 2 (b) and how we have to have due regard to ‘all dangers of navigation and collision and to any special circumstances…’
be positive, made in ample time and with due regard to the observance of good seamanship
Now we start to come to the meat of this rule. ‘Positive, made in ample time’ means that, once you’ve identified that action is required to avoid a collision, you should take appropriate action as soon as possible to pass at a safe distance. If that is standing-on (keeping your course and speed) then do so. If it’s an alteration of course and speed, make sure it is readily apparent to the other vessel what you have done - that is, make sure the alteration is large enough to be immediately obvious. This will make more sense when we get to Rule 8(b).
the observance of good seamanship means not creating issues for any ship in the vicinity.
Rule 8(b)
Any alteration of course and/or speed to avoid collision shall, if the circumstances of the case admit, be large enough to be readily apparent to another vessel observing visually or by radar; a succession of small alterations of course and/or speed should be avoided.
any alteration of course and/or speed
We’re no longer talking about ‘action to avoid collision’ (which includes standing-on), now we are talking about alterations of course and/or speed. So you can alter course, alter speed or alter both.
shall
You already know this one, so I’ll stop mentioning it in future.
if the circumstances of the case admit
That phrase again. See above.
be large enough to be readily apparent to another vessel observing visually or by radar
So, how large enough is large enough? Alterations of course are a lot more obvious than alterations of speed, so let’s talk about those first. Visually, you want to change the aspect of your vessel as it appears to the other. In your answer go for alterations of at least 45 degrees in good visibility and 90 degrees in restricted visibility. As for alterations of speed, halving your speed is a good place to start; if already at a slow speed consider taking all way off by reversing your engines.
This rule is about preventing officers from gently altering course and'/or speed by a few knots or a few degrees at a time. This might increase a CPA but it does not quickly and easily convey an intention, which is what you want to do in order to prevent the OOW on the other vessel from doubting that you are complying with the rules.
A phrase you will remember from COLREGS 1 - Wording is ‘Bold and substantial’. Well, Rule 8(b) is being expressing when we use that phrase.
What about the sound and light signals?
When we alter course or use our engines astern (other than if altering as per Rule 19) we make sound (and possibly also light) signals. So should these not be enough to tell the other vessel what we’re doing? Possibly…but perhaps there are other vessels making sound signals in the vicinity, or they can’t see the light because of the sun.