Showing the Right Day Shape

Study of the International Navigation Rules is a rewarding pastime, practical and captivating. They constitute a remarkable document with an immense assigned task—the prevention of collisions between a vast array of vessels in a vast array of circumstances: vessels barely visible at 100 yards to vessels the size of horizontal skyscrapers; drifting without power or traveling at 30 knots or more; following unmarked lanes or crisscrossing open waters offering nothing more than an educated guess as to their intended course; in all conditions of weather, clear or fog, calm or storm; and often with no common language between their drivers.

But despite this enormous assignment, they do the job. Collisions can always be traced to at least one violation of the Rules by both vessels involved in the collision. Thus we teach that from a statistical point of view alone, you will not be in a collision if you obey the Rules yourself. The key to avoiding further proof of this is a thorough understanding of the Rules, and how to apply them, including the rules on what to do if an approaching vessel does not obey the rules.

Part of the Rules includes a specification of day shapes that vessels should show when for some reason they are  "unable to maneuver as required by these Rules."  After the collision, the USS John S McCain was able to make it back to port under her own power (according to reports), but was clearly restricted in maneuverability, which calls for showing one of these day shapes on the vessel. And they did show a day shape, which appears to be ball-diamond-ball.

Here is the pertinent Rule:

Rule 27 - Vessels Not Under Command or Restricted in Their Ability to Maneuver

(a) A vessel not under command shall exhibit:
(i) two all-round red lights in a vertical line where they can best be seen;
(ii) two balls or similar shapes in a vertical line where they can best be seen;
(iii) when making way through the water, in addition to the lights prescribed in this paragraph, sidelights and a sternlight.

(b) A vessel restricted in her ability to maneuver, except a vessel engaged in mineclearance operations, shall exhibit:
(i) three all-round lights in a vertical line where they can best be seen. The highest and lowest of these lights shall be red and the middle light shall be white;
(ii) three shapes in a vertical line where they can best be seen. The highest and lowest of these shapes shall be balls and the middle one a diamond.
(iii) when making way through the water, a masthead light(s), sidelights and a sternlight in addition to the lights prescribed in Rule 27(b)(i);
(iv) when at anchor, in addition to the lights or shapes prescribed in Rule 27(b)(i) and (ii), the light, lights, or shapes prescribed in Rule 30.

At this point we need to refer to the definitions, which are in Rule 3.

Rule 3 - General Definitions 

For the purpose of these Rules [ and 33 CFR §83-90 ], except where the context otherwise requires:


(f) The term "vessel not under command" means a vessel which through some exceptional circumstance is unable to maneuver as required by these Rules and is therefore unable to keep out of the way of another vessel.

(g) The term "vessel restricted in her ability to maneuver" means a vessel which from the nature of her work is restricted in her ability to maneuver as required by these Rules and is therefore unable to keep out of the way of another vessel. The term "vessels restricted in their ability to maneuver" shall include but not be limited to:

(i) A vessel engaged in laying, servicing, or picking up a navigational mark, submarine cable or pipeline;
(ii) A vessel engaged in dredging, surveying or underwater operations;
(iii) A vessel engaged in replenishment or transferring persons, provisions or cargo while underway;
(iv) A vessel engaged in the launching or recovery of aircraft;
(v) A vessel engaged in mine clearance operations;
(vi) A vessel engaged in a towing operation such as severely restricts the towing vessel and her tow in their ability to deviate from their course.

So, admittedly not knowing precisely what "not be limited to" might encompass in this definition, we see two choices for the day shape:  limited maneuverability because of "the nature of her work," which would be ball diamond ball, or limited maneuverability because of "some exceptional circumstance," which would call for two balls in a vertical line.

The question we are left with is this: is a collision of a war ship with a tanker in peace time considered "the nature of her work" or is it "some exceptional circumstance?

Or more broadly, we have the question: does the vessel's choice of day shape matter at all, or is it trying to tell us something?

This is a maritime tragedy involving possibly the loss of life and certainly injuries. That is the main concern, not day shapes, but anything we might learn that could help prevent this in the future is worth pursuing.

We do have an unfortunate terminology to deal with. Essentially every vessel that is according to the Rules "not under command," is indeed under command at all times, even if they cannot, say, turn the vessel to the right or left. (The macabre nemonic we hear in the classroom "red over red, the captain is dead" is never the controlling factor, and only buffers the poor terminology.) It is a technical term, in the sense of being defined in the Rules, though not completely logical. It would seem unlikely that such reasoning could take place, but it could be difficult for the Commander of a war ship to put up a sign that says I am not under command, in which case "restricted maneuverability" could be a compromise for obtaining the needed extra right of way that is granted once either of the day shapes is shown.

It seems this collision and the return to port took place in daylight, which somewhat reduces the impact of the day shape choice. At night, this distinction would have greater bearing in the event of a subsequent collision. The extra lights corresponding to these two shapes are different (red over red, vs. red over white over red) and the potential of these being confused amongst other navigation lights becomes a possibility that has been addressed in collision court cases.  Illegal lights almost guarantees some share of liability, regardless of the primary cause of a collision.

With all that said, if you are a small craft captain and get stuck without power in the middle of the shipping lanes without a radio, you might want to have two of these on hand that you can raise in the rigging, regardless of how you are feeling otherwise.

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Just found this picture. Not sure if it was earlier or later than the one above. Not sure what it means, but looks like two balls in this one.  They did show up later in the transit and in port with ball diamond ball

Here is another pic from long before the collision, showing ball diamond ball during some type of maneuver that does not appear to be restricted, so it is some exercise that needs clearance or will need it shortly.

In response to Carl's comment below: I agree. The single flag showing is likely Romeo, meaning they are preparing to take on provisions or fuel.

This is a perfectly normal use of ball diamond ball. A collision is another question.