Chapter 7: Voyage Planning for Master

Location, location, location

This is golden rule for real estate. Not so many seamen understand this is also golden rule for voyage planning. In EDCIS training we know ” no go area“ and safety contour to avoid static danger like reef, shallow waters, ship’s wreck etc.…  For dynamic danger something movable like coastal vessel we just try our luck when we transit. The most prudent navigator will use extremely caution in these hot spots with the help of “ Call the Captain when arrive here” write in standing / night order book or on paper chart.   

Figure 7-01: Roundabout for collision avoidance in multiple targets

In figure 7-01, we can see the hot spots are those crossing point of two vessel’s course line. In radar lookout we will say it is the crossing point of two vessel’s speed vectors. One simple rule is to avoid all these hot spots like No.1 target go around to north which is far away from these hot spots. No.5 target did not go around. He tries his luck there and collide with No.7 target. Give way vessel is not only change her course when needed. She also changes her collision position with other vessel to a more favorable position like target’s stern where target vessel had passed already when ownship arrive there. No.5 target is a slow vessel compare to those vessels crossing from port side and starboard side. Nevertheless, if No.5 target can read her collision risk with No. 7 and No.8 target 6 minutes before collision she still has time to alter course to starboard. If No. 5 target alter course to starboard side to give way to No. 7 and 8 target those vessels in No.5 target’s port side may find their action to give way to No. 5 target a little trouble than no. 5 vessel keep her original course and speed. It is still manageable. But how?  With this new area of precaution every vessel approaching should alter course to starboard side to avoid the collision.

In COLREG, there are no rule for multiple vessels encounter situation. But it happened everyday around the world.  The solution is roundabout concept like land base, every vessel alter course to starboard side to avoid the collision if more than two vessels around. There is a VHF call from no. 7 vessel to No.5 vessel ask for his attention of collision risk 5 minutes before collision. After that VHF conversation, No. 7 target just maintain her course and speed until the collision happened. The COLREG had asked No.7 target to take best aide action to avoid the collision as long as No. 5 target had not taken action. The truth is after so many years at Dover Strait North Sea pilot are used to this practice and leave the obligation of give way to port side vessel only. In another words, they don’t worry what port side vessel will do and pay no attention to port side vessel movement. It is a wrong setting of the collision scene make the collision unavoidable when the one on port side need to give way had not act in any cause.  Never mind the rule now.  If No. 7 target alter course to starboard side 5 minutes before collision happen the collision position will move to his starboard side which can give stand on vessel more time to collision position. No. 7 target can evaluate the movement of no. 5 target after course change to starboard side. If No. 5 target had not change course to starboard side to give way No. 7 target will become overtaken vessel overtaking by No. 5 target.  The collision happened due to the action of “Full astern” and “hard starboard “rudder angle used too late.  If port side target had the obligation to alter course to starboard side it will give both vessels more time to avoid the collision.  After both vessels altered course to starboard side and the collision risk is resolved port side vessel should resume her original course and speed.           

Figure 7-02: Crossing situation: Stand on vessel A/C to Starboard

The collision position is a very precise location as we have discussed in chapters before 

• •       1852 x 1.8 sin10⁰ = 579 meters, for an 18 Knots vessel A/C 10 degrees 6 minutes before collision will have 579 meters distance different. 
• •       If No. 7 target who should stand on had altered course to starboard side 10 degrees the collision situation will be very different. 
• •       Even No. 5 target’s course had not changed, the collision position of no. 7 target will shift to starboards side about 579 meters as figure 7-02.  

This collision position shifting will give way vessel about one more minute to arrive new collision position if give way vessel had not alter course to starboard side as figure 7-03 blue speed vector from original course line.  

• •       Compared with range ring distance = 0.25 nm, new collision point is 0.25 nm further east of original collision position. 
• •       New collision position for stand on vessel is also shift about one-minute distance north. 

The collision situation seems no change after stand on vessel alter course 10 degrees to starboard side.

• •       Stand on vessel only gain one more minute before collision.  
• •       Or we can say give way vessel had not influenced by stand on vessel’s movement to starboard side. 
• •       Give way vessel only have one more minute extra time before collision.    

The collision situation changed dramatically after give way vessel alter course 3 degrees to starboard side as 7-03 right drawing. 

• •       Stand on vessel’s original course is green speed vector and red speed vector is 10 degrees to starboard side. 
• •       The distance of new collision position (give way vessel A/C 3 degrees to starboard side, moving along give way vessel’s range ring) to original collision position if stand on vessel don’t alter course in green speed vector is 1.54 Kts x 1852 x sin (3⁰) = 149.3 meters. (not enough for one ship’s length)
• •       The distance of new collision position to original collision position (moving along stand on vessel’s blue range ring) of stand on vessel had altered course 10⁰ degrees in red speed vector is 1.00 kts x 1852 x sin (10⁰) = 321.6 meters. ( about one ship’s length)
• •       If give way vessel want to keep 3216 meters safe distance without give way vessel A/C 10 degrees, she will need to alter course 1.54 Kts x 1852 x sin (ø⁰) = 321.6 meters. Ø = 6.47 degrees.

Whether new collision position compared with old collision position the distance gained (326.1 Vs 149.3 ) or alter course angle needed (6.47 Vs 3. 00), stand on vessel to A/C is preferable than stand on alone.   

Figure 7-03: Collision position shift after Stand on vessel A/C 10⁰ to Starboard

For fast stand on vessel the collision situation changed dramatically after stand on vessel alter course 10 degrees to starboard side as 7-04 figure. 

• •       Stand on vessel’s original course is red dotted speed vector and red speed vector is 3 degrees to starboard side. 
• •       The distance of new collision position (give way vessel A/C 3 degrees to starboard side, moving along give way vessel’s range ring) to original collision position if stand on vessel don’t alter course in red dotted speed vector is 1.0 Kts x 1852 x sin (3⁰) = 96.9 meters. 
• •       The distance of new collision position to original collision position (moving along stand on vessel’s blue range ring) of stand on vessel had altered course 10⁰ degrees in red speed vector is 1.5 kts x 1852 x sin (10⁰) = 482.4 meters. ( about one and half ship’s length for VLCS or VLCC)
• •       If give way vessel want to keep 482.4 meters safe distance without give way vessel A/C 10 degrees, she will need to alter course 1.0 Kts x 1852 x sin (ø⁰) = 482.4 meters. Ø = 15.1 degrees.

Figure 7-04: Collision position shift of Fast Stand on vessel A/C 10⁰ to Starboard

Whether new collision position compared with old collision position the distance gained (96.9 Vs 482.4 ) or alter course angle needed (15.1 Vs 10.0), Stand on vessel A/C to Starboard is preferable than stand on alone. It is no secret that fast speed vessel needs more room to maneuver and more option to avoid the collision especially in high speed craft. Even if the speed difference is two third (one vessel 15 Knots, another vessel 10.0 Knots), the course change needed for collision avoidance is 3 degrees Vs 10 degrees in figure 7-03.  Take a further look at the figure 7-04, fast vessel give way to slow give way vessel. About 10 degrees more to starboard side NE bound vessel will reach the point where give way will not have any collision point with him unless east bound vessel increase speed. This is what we said in Figure 4-15 Safety relative Bearing for High Speed Craft. The relative bearing of the East bound vessel is 55 degrees as the drawing which have 5 degrees difference as we estimated in chapter 4 due to this sketch is not so precise. For a multi-target situation in figure 7-05, the black vessel North bound’s situation is much more complicated if she stand on original course 000 degrees and speed 15.0 Knots when she met red vessel alter course to starboard side 20 degrees at last mile range in blue color. As we discussed at 7-02, Black vessel alter course 10 degrees to starboard side will shift his collision point with these two vessels further to her starboard side which may have more time to evaluate the meeting situation with other vessel rather than stand on and wait until it too late. The effect is like give way vessel to reduce speed or stop engine to gain more time for ownship. But Colreg had not stipulated this in its rules only leave a window to best aide to avoid the collision if collision cannot be avoided by give way vessel’s action along. If we look into figure 7-05 and 7-01 we can see stand on vessel alter course to starboard side enlarged the collision zone and make more room for ever vessel to maneuver to avoid the collsion.       

 Figure 7-05: Collision position shift after Stand on vessel A/C 20⁰ to Starboard

In any way, stand on vessel alter course to starboard side has more advantage than disadvantage. These effects should be considered to apply to New amendment of COLREG 1975, especially for multi ship situation as figure 7-01.

Wise men sail only fool rushed in

After these chapters discussed, Captain may notice that small course alternation is the core skill in coastal navigation safety when sea room is not enough for every vessel. All our maneuvering around the precaution area or hot spot of collision is to create one or two ship’s length distance to navigate through safely. Why not to save these precious spaces when we are making the voyage planning rather than we maneuver with all sweat at collision scene? “Wise men sail only fool rush in”. The bravery is not based on courage but our knowledge to avoid the danger.    

Figure 7-06: Collision position vessel east bound of Singapore Strait

In figure 7-06, one vessel eastbound to Far East in deep water route: she has three situations, overtaking and crossing from both sides. Captain stand by the engine and reduce speed in time proceed with extreme caution constantly check crossing vessel’s movement with visual and radar. Unfortunately, the passing shower heavily hinder the lookout by visual and radar. Captain properly adjust the radar gain and rain clutter to keep large vessel identified on radar screen but small targets are nowhere to be seen at radar after rain clutter adjustment. Safety relative bearing may be determined by small target’s speed and apply to avoid any accident. Sounding the fog signal may be a good idea now.      

Figure 7-06: Safe Side of precautionary area for Eastbound Vessel

Well, it seems the precautionary area had changed name to traffic crossing now with the recommended course line arrangement.  This is a basic arrangement of roundabout for vessel crossing each other. These roundabout areas should be enlarged by captain’s own decision if the traffic is heavy inside the area.  We know these crossing traffics are not major problem if both vessels are at constant speed to cross. These crossing traffics are near pilot boarding area which need inbound vessels to reduce speed to pick up the pilot. This is the major problem for transit vessel who want to keep original speed and not to impede by their maneuvering. We can see the precautionary or roundabout area has its safe side in starboard side as figure 7-06 where the green side has only one crossing traffic from south to deal with compared with the westbound overtaken vessel in its tricky way to cross traffic lane.