From 1942 to 1945, inclusive, in excess of one hundred combatant vessels of the United States Fleet were damaged or sunk due to collision. For the same period, War Shipping Administration records show the number of merchant vessels involved in collision exceeded two thousand. These figures would appear to indicate the need for a new approach to collision prevention.
The material presented here was compiled by the writer and assistants from 1944 to the present at the parent Emergency Shiphandling school, Pearl Harbor, T. H. These data represent an attempt to reduce the hazards attendant to safe navigation at sea by scientific analysis of tactical data and its relationship to the various collision situations. Before the various collision situations could be studied, it was first found desirable to determine some means of classifying these situations.
Collision Angle
The term “collision angle” has been found to be the best means available to classify the various collision situations. It may be defined as follows: Collision angle is the angle between the intersection of the projected courses of two crossing, meeting, or overtaking vessels where risk of collision exists, measured clockwise from the projected course of the vessel to starboard to the projected course of the vessel to port.
Where two vessels are meeting exactly end on, the collision angle of 180° may be measured clockwise from the projected course of either vessel to the projected course of the other vessel. To obtain collision angle in an overtaking case, measure the angle from the projected course of the vessel to starboard, clockwise to the projected course of the vessel to port.
By definition, collision angle cannot exceed 180°. This limit was set in order to simplify the classification of collision situations into Case One and Case Two types. For convenience, collision angles have been grouped into two cases: Case One, From 0° to 90°; Case Two, From greater than 90° to 180°.
Collision Angle vs. Range and Relative Speed
It has been noted from analyses of collision cases that one of the more common errors in shiphandling, when risk of collision was present, has been the tendency of the conning officer of the burdened vessel to fail to take avoiding action at a sufficiently ample range, particularly where the collision angle exceeded 90°.
Figure 8 and Figure 9 are included to demonstrate the relationship between relative speed, collision angle, range, and time available to avoid collision. Figure 8 shows a situation in which relative speed, collision angle, and range are relatively small. Note the time available to avoid collision is 120 seconds from a range of 730 yards. Figure 9 shows a situation in which relative speed, collision angle, and range are relatively large. The point this comparison brings out is this: although the range has increased from 730 yards to 1850 yards, the time available to avoid collision is still 120 seconds.
Prior to these studies conducted at Pearl Harbor, it was a common conception that range alone was the only criterion upon which imminence of collision need be based. It should be apparent from a study of Figure 8 and Figure 9 that other factors enter into the collision problem. From a study of factors involved, the following generalizations concerning collision angle may be drawn:
1. The greater the collision angle, the greater the relative speed.
2. The greater the collision angle, the greater the range at which action normally should be taken by the burdened vessel in order to avoid embarrassing the other vessel.
Legal Maneuvers Available to Conning Officer of Burdened Vessel While Still a Safe Distance from Other Vessel
A thorough knowledge of all Rules of the Road is an essential requirement for successful shiphandling at sea. But it should also be understood that the International and Inland Rules of the Road contain certain Articles which are of particular importance in the study of collision prevention. For example, Articles 18 to 24 inclusive should be studied and thoroughly grasped before attempting to analyze the legal maneuvers available to the conning officer of the burdened vessel while still a safe distance from the other vessel.
Once Articles 18 to 24 have been thoroughly mastered and proper attention is given to the basic factors entering into collision recognition and avoidance—i.e., steady bearing, collision angle, range, relative speed and time available to avoid collision—it is believed that situations which might otherwise result in collision can be recognized and proper evasive action taken by the conning officer of the burdened vessel in ample time to prevent serious risk of collision from developing.
Figures 10 to 16 represent an attempt to summarize and illustrate the legal maneuvers available to the conning officer of the burdened vessel (or vessels) shown.
It should be noted no attempt is made to set down any maneuver or maneuvers which must be carried out, other than those actually stipulated in the Rules of the Road. The Rules must be read carefully, since wide latitude may be read into them due to the inclusion of such phrases as “when it is safe and practicable,” and “if the circumstances of the case admit.” However, when the word “shall” is used in an Article, it may be construed as meaning “must,” and should therefore be obeyed.
Analyses of Emergency Shiphandling Procedures When Both Vessels are Considered to be “In Extremis”
Research has disclosed that collisions at sea might be considerably curtailed if it were possible to set down a hard-and-fast doctrine which would stipulate the exact maneuver for each conning officer to execute when the situation has become one of in extremis.
However, since the Rules of the Road set forth no preferred rudder or engine action when the situation is one of in extremis, no hard-and-fast emergency shiphandling doctrine can be advanced.
Thus, in no sense are the following emergency shiphandling procedures to be considered mandatory or binding. The Rules of the Road still permit a conning officer to “take such action as will best aid to avert collision.”
It is hoped that the analyses presented in Figures 17 to 20 will help each conning officer to analyze any collision situation and take such action as will best aid to avert collision promptly and decisively. Collision records show that time after time officers have found themselves in situations calling for emergency shiphandling—only to lose precious seconds in indecision while waiting for the other vessel’s maneuver to become clear.
Figures 17 to 20 were analyzed with the following premise in mind: Considering rudder action only, which direction of turn should enable the conning officers of both vessels to avoid each other by the greatest “miss distance” when the vessels are considered to be in an in extremis situation?
Summary of Emergency Shiphandling Procedures*
In Case One in extremis situations, it would appear that the conning officers of both vessels normally should have most to gain by turning away from each other (burdened turns left; privileged turns right), due to the following factors:
1. Greater “miss distance.”
2. Lower relative speed.
In Case Two in extremis situations, it would appear that the conning officers of both vessels normally should have most to gain by turning right, due to the following, factors:
1. Acts to curtail possibility of a high relative speed, bow-on type of collision.
2. Complies with the spirit of Article 22.
3. Helps privileged vessel get across burdened vessel’s bow.
4. When the collision angle appears to be on the borderline between a crossing and a meeting situation, a right turn by both vessels should normally aid in eliminating uncertainty.
Exceptions to Analyses of Emergency Shiphandling Procedures
The preceding analyses of emergency shiphandling procedures are normally regarded by the writer as proving most likely to be successful in the majority of situations encountered at sea. However, it must be repeated that these procedures are not intended for unreasoning adherence. Rather, they should be used as a basic guide upon which decisions may be made by each conning officer after all factors have been evaluated.
It should be noted that the emergency shiphandling procedure for the conning officer of the privileged vessel to follow, if practicable, is based on the use of right rudder whenever possible.
What is possibly the chief exception to this procedure is precipitated in crossing collision situations where the collision angle is greater than 90° and the conning officer of the burdened vessel considers the bearing apparently to be drawing aft with sufficient rapidity to permit him to attempt to cross the bow of the privileged vessel (a maneuver specifically prohibited by Article 22 of the Rules of the Road).
When confronted with such a situation, the conning officer of the privileged vessel has little recourse but to consider the possibility of using left rudder instead of right rudder.
The conning officer of the privileged vessel may consider the use of left rudder to be indicated when the following apply:
1. The burdened vessel shows no intent of altering speed or changing course to give way, but is apparently attempting to cross the bow of the privileged vessel in violation of Article 22 of the Rules of the Road.
2. The burdened vessel is so far up on the bow of the privileged vessel that the privileged vessel is inside the burdened vessel’s turning circle.
3. The burdened vessel is to be considered privileged under one or more applicable paragraphs contained in the General Maneuvering Instructions of FTP-183.
4. A meeting of the minds has been reached by radio, whistle signals, or other means of communication and both conning officers have agreed to the proposed departure from the Rules of the Road. (Burdened vessel holds on, and privileged alters course, or speed, or both, and passes under the burdened vessel’s stern.)
Collision Analyses Tables
The contents of the Collision Analysis Tables I and II, are the result of research conducted at the parent Emergency Shiphandling school, Pearl Harbor, T. H., in an attempt to present in tabular form the result of an attempt to determine in the laboratory, insofar as was possible, how successful the analyses of emergency shiphandling procedures should prove when executed by various vessels, with various advances, at various speeds and approaching at various collision angles.
Three types of collision angles were studied: Less than 90° (45°), approximately 90°, and greater than 90° (135°).
As a starting point to determine what range might normally be used as the line of demarcation between what could be considered a “safe distance” and the point at which the situation could be considered as in extremis, twice the advance was used as the minimum distance for all three situations. Later, analysis of the results shown in Column 13 of the Collision Analysis Tables indicated that for the approximately 90° and the less than 90° Case One situations, this minimum distance of twice the advance might be cut in half.
Summary of Collision Analysis Tables*
It was found that when only one conning officer followed the emergency shiphandling procedures indicated in Figures 17 to 20, the maneuver proved successful in the majority of situations analyzed.
It was found that when both conning officers followed the emergency shiphandling procedures indicated in Figures 17 to 20, the maneuvers proved successful in every situation analyzed.
Collision Prevention Check-off List
In the parent Emergency Shiphandling school it was found that no standard procedure had been set up which could be used by conning officers—experienced as well as inexperienced—as a general guide or checkoff list to insure that all proper collision prevention steps had been taken in time to prevent an emergency from developing.
The following Collision Prevention Checkoff List is presented as a general guide which may be utilized wholly or in part, depending upon type of vessel and personal desires, by conning officers who may wish to standardize insofar as is possible and practicable, the procedure to be followed aboard each individual vessel when a contact is made with another surface craft by sight, by sound, or by radar.
Collision Prevention Check-Off List
On Contact:
1. Notify captain at once.
2. Check range and bearing by all means available.
3. If range is closing, and bearing is steady, report that risk of collision exists.
4. Alert wheel, engine room, lookouts and all departments concerned with safe navigation.
5. If circumstances permit, use radio or light to alert other ship; send own course, speed and intent, and request same.
6. If the circumstances indicate, make sure that proper sidelights (and other lights) are showing in accordance with Rules of the Road.
7. Use whistle as indicated by circumstances and Rules of the Road.
Day or Night Situations:
8. Obtain collision angle by visual or other means (radar), determine whether own vessel is burdened or privileged, and act accordingly:
WHEN PRIVILEGED, keep course and speed (Art. 21.) until a departure is indicated under the authority of Article 27, in order to avoid immediate danger.
WHEN BURDENED, if circumstances permit, avoid crossing ahead of privileged vessel (Art. 22.)—if necessary by slackening speed, by stopping, or by reversing engines (Art. 23.). In any event, take all possible precautions to keep clear of other vessel by as ample a range as is possible and practicable.
Fog Situations:
9. In fog, comply with Article 16: “Every vessel shall, in a fog, mist, falling snow, or heavy rainstorm, go at a moderate speed, having careful regard to the existing circumstances and conditions. A steam vessel hearing, apparently forward of her beam, the fog signal of a vessel the position of which is not ascertained shall, so far as the circumstances of the case admit, stop her engines, and then navigate with caution until danger of collision is over.”
“In Extremis: Situations:
10. When situation appears to be one of in extremis, use collision angle method of determining emergency shiphandling procedure considered most likely to prove successful, and execute (if practicable and desired).
Collision Situations:
11. In event of unavoidable collision, sound collision quarters: (a) general alarm; (b) one long blast on siren as signal to dog down water-tight openings; (c) start howlers; (d) sound “assembly”; (e) notify captain, executive officer, engine room and telephone control; (f) all hands to stations on the double; (g) break out collision mat, if available; (h) order boatswain’s mate to pass word.
On the four pages following will be found two tables of collision analyses which will be invaluable to every deck officer
Note: Illustrations contained in this article arc used by special permission of the copyright owner and are taken from a new text soon to be published by D. Van Nostrand Company, 250 Fourth Avenue, New York City, N. Y., entitled “Collision Prevention.”
*It must be emphasized that the actions which may appear to be indicated in the summary above are not to be construed as mandatory. The Rules of the Road prohibit establishment of any hard-and-fast emergency shiphandling doctrine.
*Collision Analysis Tables I and II are presented for study and information only. The maneuvers which may appear to be indicated in these tables or in the summary thereof are not to be construed as mandatory. The Rules of the Road prohibit the establishment of any hard-and-fast emergency shiphandling doctrine.