Give-way vessel's measures

Course change for single target in open sea

When two vessels have the collision risk, the give-way vessel has the obligation to keep out of the stand-on vessel's track. The give-way vessel has to do it without confusing the stand-on vessel. In the open sea, the sea room is wide and both vessels are in full sea speed, the give-way vessel should alter course to starboard side in 4-6 miles range and swing the vessel to aim at the stand-on vessel's stern. After the stand-on vessel's RB is well on the port bow, the give-way vessel can swing back to original course step by step without been interference the stand-on vessel's intention. 

Course change for single target in confined water

In the confined water, the give-way vessel may have not enough sea room to carry out the full swing to the stand-on vessel's stern or this maneuvering may cause other vessel's confusion. The give-way vessel should alter course to starboard side at least 30 degree in 4-6 N.M. range to indicate the intention to give way. By continuous checking the stand-on vessel's bearing change, the give-way vessel can swing back to original course step by step. 

Course change for multi targets in open water

In the heavy traffic waterway, the give-way vessel's large heading change may lead to another collision risk. The give-way vessel's action should be very cautious. In this situation, the collision risk may not involve in only one vessel. The action taken by the give-way vessel should clear all the collision risk once for all. The useful technical will regard all the vessels involved in the collision risk as one big vessel. The one has the shortest TCPA should regard as the big ship's bow and the one has more RB as the big vessel's stern. When the avoidance action been taken, the action should clear all the vessels at one single move. 

In the illustration above, radar screen is setting in relative mode. Each circle is one N.M. range. Three different color vessels are plotting at regular time interval. If OS keep original course and speed, the relative motion line will be shown as plotted. The red ship is a crossing vessel which has collision risk with OS, the CPA is zero. The green vessel and purple vessel are two overtaking vessels. The green vessel CPA is about half N.M. The purple vessel CPA is about one N.M.

For avoiding the collision risk with red target, OS should alter course to starboard. The course alteration will create some transverse distance to starboard side and bring OS close to other two vessels. These three targets should regard as one big vessel which have one mile long. To avoid any confusion to other vessels, OS should alter course to clear all three vessels at the same time.

Reducing speed: avoid multi targets in confined water

When the course changing is further restricted by the sea room, another option can be taken to avoid the collision will be the timing lapse. The mean of creating the timing lapse to pass the POC separately is the speed reduction. In the drawing above is the method to reduce the speed or stop the vessel. No speed reduction is more effective than the full rudder turning when the ship is proceeding with full sea speed. When conducting the full rudder turning, the whole shipside can be regarded as a brake on the water. The ship's speed can be reduced to two third of her original speed after 90 degree turning and can achieve the reduction within 3 to 5 SL . The problem here is OS have to reduce speed because has not enough sea room to avoid the collision. Using full rudder turning to reduce speed is not applicable. Another drawback of using the full rudder is the uncertainty of the timing to ease the wheel and apply the counter rudder to steady on the new course we need. 

The rudder cycling is preferred in this respect which can achieve the speed reduction and heading control at the same time. The cycling amplitude should determine by the available sea room. The more course change to each side, the more speed can be reduced. Once again, the distance to the POC is the decisive factor to determine the necessary rudder or heading amplitude. By the study of turning characteristic, we know each rudder order used have two SL inactive distance. The first full rudder OS used will determine the final resting position of the rudder cycling. The second full counter rudder is used when the heading is 20-30 degrees before the intended amplitude. The third full rudder is used to bring OS back to its original course. The revolutions of main engine should be reduced when OS begin to response to each full rudder been used. With three reduced engine and hard over rudder, OS can reduce to her dead slow ahead speed in which OS can still have bare steerage to keep desired heading. 

From the drawing above, full rudder turning need almost 4 SL transverse distance to complete the turn. Rudder cycling can maneuver within 1 SL transverse space. The drawback of rudder cycling is more advance distance (6-7 SL) needed for reducing the speed. As these maneuverings are used to reduce the original speed of give-way vessel, give-way vessel always has some ample sea room available as long as OOW make up decision earlier.     

Reducing speed only

For a stand-on vessel within 4 miles distance away, your rudder cycling is a mystique and may cause unnecessary panic to him. Take the multi targets situation above as example. If the starboard side does not have enough sea room to avoid the purple vessel, OS has three options. The first one is to reduce the speed along without any heading change to let the red vessel to pass ahead. By doing so, the red target will cross OS bow for the delay timing to pass the POC. However, the green target slower than OS may cross OS bow as well. For green target’s original course is crossing our course line, this is shown on the relative motion line getting closer as each plotting made. The bow crossing range of the green target may or may not safe for OS to clear. As the engine speed reduced, OS has to take another action to give way to green target. The illustration below show how the situation will deteriorate when the avoidance action didn’t take on time. 

Reducing speed together with some course altering 

The second option for OS is alter course to port side and reduce the ship speed. The speed reduction is to create some timing lapse to let the red target to pass our bow. This is the main action OS taken to avoid the primary collision risk with red target. For the secondary collision risk with green target, altering the course to port side is to create some safe transverse distance to avoid the green target (New course may choose the same course as green target which we discuss at last chapter). Speed reduction together with course altering ( use full rudder to turn) may combine as the Rudder cycling maneuvering to further reduce the give-way vessel speed. 

A complete 360 degree turn to portside

The third option to the OOW is a complete 360 degree turn to the port side if enough sea room is available. The turning can bring the vessel back to almost the same position as started. The time needed to complete 360 degree is the timing lapse for avoid the red target. The turning does not need to be a full rudder turning. OOW can adjust the turning rate as appropriate to the circumstance and the ship’s stability condition. The rudder angle used will determine the necessary advance we needed to complete the turn, usually within one N.M. This maneuvering needs longer time and wider sea room to complete. In this example, OS may need to attend the collision risk with green target after completing 360 degree turn.

Safe speed

In the multi targets situation, the only applicable rule in COLREG is safe speed. All ships must proceed at all times at safe speed. If the traffic situation is not clear to OS, the only option is to slow down the vessel. This will give us some extra time to ascertain the situation. 

Stop the engine alone and keep the original course may be an option to avoid the collision, if the distance to POC is still adequate. Once we stop the engine, it is clearly that in our mind we want to use the timing lapse technique. Timing lapse for what? For other vessel to pass ahead of us, in a crossing situation, this means its relative bearing should be decrease to zero. After the engine stop, if the relative bearing decrease is not apparent. This means the distance between two vessels is shorten and the collision risk is still present. The speed reduction is a slow process over the water. For more effective reducing the speed, rudder cycling should be used. 

Reducing speed more effectively

The rudder cycling does not necessary to swing the vessel to both sides with 30 degrees amplitude or cause other target’s confusion. It can be used even the heading have no apparent change to the stand-on vessel ,i.e. The turning tendency and the side-kick in the first 2 SL of turning characteristics will also help to reduce the ship's speed. The maneuvering can be accomplished by give the quarter master order to use hard port/starboard rudder and steady on + 5 or 10 degree off the original course. Before the master give the rudder order and heading to steer should check other vessel's movement first and decide to which way off the original course OS should go to gain a better position during the maneuvering.  This is an important concept when the maneuvering space is narrow in the waterway. We can still do something to reduce the speed rather than just stop the engine and go crash astern. 

Effectiveness of give-way vessel’s action

The effectiveness of give-way vessel’s action is reducing the RB of stand-on vessel to zero. Altering the course to stand-on vessel’s stern is the most effective means to meet the purpose. If the sea room is not available, alter course to starboard side at least 30 degree is the conclusion of marine court. Does this 30 degree course change have the desired effect we need to clear the stand-on vessel? After the course changed, the stand-on vessel’s RB have to observe closely. As the calculation of last chapter, 

The target's RB have to change over 5 degree before 4 N.M. Range.  
The target's RB have to change over 7 degree before 3 N.M.. Range. 
The target's RB have to change over 10 degree before 2 N.M.. Range. 
The target's RB have to change over 20 degree before 1 N.M.. Range.

to clear the necessary POC( 2 SL distance).

The minimum course change to clear the POC is same the table above. If OS only change course as the minimum requirement, the stand-on vessel will only pass OS bow at very close range and at very prolong time.    

In close range

For a fixed object at remote distance away, our ship's heading change 30 degree will change the object relative bearing more or less 30 degree. For a fixed target inside our turning circle, the relative bearing change of the target is lesser than our heading change. The relative bearing changed of a fixed target outside of our turning circle at close range will be more than our ship's heading change. The inconsistent is because the ship turning is turning along a curve line which has 4-6 SL diameter. 

Whether the give-way vessel can or cannot turn away from stand-on vessel's stern is depend on the distance between two vessels. Once the target is inside the 4-6 SL turning circle diameter, the course altering is useless to avoid the collision. So, the distance judgment is important in avoidance actions to take. As long as the give-way vessel's bow is clear of the stand-on vessel's stern, the give-way vessel should steady the vessel and come back to original course keeping the stand-on vessel's RB still fine on the port bow. It is this steady action that is very important to the collision avoidance actions, especially in the heavy traffic area. No matter how desperate our avoidance action is, never the less we should manage to avoid the second collision with another vessel.

The way to treat the coastal vessel close to a stand-on vessel

The common scenario as the drawing above: own vessel found the collision risk with a coastal vessel in a close range and other stand- on vessels also at the scene. The passing distance (CPA) is the first factor to decide the proper action. The maneuverable sea room left for OS is half mile transverse distance to the starboard side.

Generally speaking, stopping the engine is the safest way to avoid any danger. But, the vessel won't stop immediately after engine stop. Some rudder cycling is necessary to stop the vessel more quickly. The maneuvering can be accomplished by give the quarter master order to use port/starboard rudder and steady on + 5 or 10 degree off the original course. If the full rudder turning is used, the ship's heading should closely monitor even in the emergency case. Check the swing with counter rudder before the vessel clear the danger to steady the vessel in time. 

If master make sure that the red target is a coaster vessel and her length over all (LOA) is only 50-60 meters. The LOA of target compare with the available sea room 960 meters is still maneuverable. Master then decide not to stop the engine but only steer clear of target by rudder only. As always, own ship should keep well clear the path of stand-on vessel. The problem here is the coastal vessel come out of blue and our avoidance action should not too much that reduced the proper sea room saved for the stand-on vessel. So, the way to sail clear both vessels is keep the sea room to the coastal vessel as minimum as possible. OS then will have enough space to maneuver clear of the stand-on vessel. The skill to keep minimum distance to the coastal vessel is based on the through understanding of the vessel's characteristics of turning circle and serpent swing techniques mentioned before. 

 POC of 1 mile away

The discussion above is the give-way vessel's action to avoid collision and through all the stage the target is always in sight of each other. If, for any reason unexpected, the target comes within about one mile range, the consideration for a large vessel will be the angle of blow. This means we have to aware of own and other ship's bow and stern position during the avoidance maneuvering. In this close range, we can only have two effective rudder orders. (a full rudder turning take 3-4 times SL advance to have necessary heading change and two full rudder have to have 6-8 times SL advance.) That is a hard starboard followed by hard port or hard port followed by hard starboard

By the experience of Williamson turn, ship's heading will continue turning 10-20 degree after the counter full rudder had been used. This over-swing should bear in mind when take emergency action. Together with the over-swing is the ship's bow position will be 20-30 meters away from its original course line when the counter rudder been used. For a small target, this distance is its ship length. For a large target, this is it's ship's width. For an overtaking case, this is will be enough for the overtaking vessel to swing clear the overtaken vessel.

By the simulation track of turning, the PP will travel out a distance perpendicular to original course line at different rudder angle been used. This transverse distance will reach a ship's length after 6 times SL advance with 10 degree rudder been used. The IMO resolution is every vessel should complete a 90 degree turn with full rudder been used under 4.5 SL. For a right-handed single screw vessel, a 90 degree turn will have at least 2 SL transverse distance to the original course line. This 2 SL distance is measured by the position of PP. After the ships body deviate from its original course line, the rudder should reduce to midship in time. The turning rate should control by the counter rudder to avoid lost control of the turning and bring the ship back to original heading.  

So we still have the chance to clear the target with one mile to POC. In the drawing above, OS had midshiped the rudder at position 3 even when the RB of target is still not clear of OS bow. Master let the swing continue by the hard starboard rudder previous used. After OS bow had clear of target at position 4, master use the counter rudder to stop the swing and bring OS back to original heading. No matter the buoy presented or not, outside the course line there may have some shallow water.

In a canal or river

If vessel is steaming up in a canal or river, the ship's speed should not be too high. In the emergency case, the sudden speed reduction will create another potential hazard to the ship handling. The tailing wave following the vessel which creates by the high water pressure field around the vessel due to the excessive speed will surpass the vessel's stern. The surpass tailing wave will lift up the stern and push the ship's heading across the river which will block the passing vessel's way and may lead the vessel to go aground in the river bank. The excess speed may also lead the vessel's bow fall off to the open end in a canal junction area. The most common damage is breaking the mooring line of the vessel on berth. 

Many collision case in the river happened because the end-on vessel alter the course too early and feel the bank cushion at the bow. The ship's bow then push across the river and collide with the coming vessel. The correct distance to give way to coming vessel is 1.5 SL before meeting. The ship movement is different in canal than in the open sea.  

Read the distance from fore mast  

The blind area in ship's bow is regulated by IMO resolution which should not be more than 2 ship's length or 500 meters whichever is smaller. Any target within this range will not be visible from the navigational bridge. Two SL is the distance when the vessel conducting the turn will have no apparent movement of ship's heading.  From the blind area to the one N. M. range should estimated when the ship is still in berthing. This is a good practice should be taken when the ship is ready to sail at berth. At least the ship's bow position should be marked on some reference point by comparing the forward spring line's bitts and head line's bitts. By marking the ship's bow position will help the captain to know the distance from the bow to any obstacle ahead in the harbor maneuvering. Correctly estimated the distance from ship's bow to the pier or jetty or berth mark can also help the master to decide the safe approaching speed when docking the vessel.

In the canal convoy, the regulated distance between each vessel is important. By marked the distance of the vessel ahead on OS mast, OOW can check the safe distance by a single glance. 

The avoidance action of the vessel inside a canal is restricted by the river width. The most effective way is always reducing the speed. If the speed reduction is not enough by stop the engine along, the side kicking of the rudder can be used to further reduce the speed. For avoiding the slower vessel ahead, the side kicking effect of rudder should be correct applied. 

In the drawing above, OS give way to the red target ahead. OS should proceed with proper speed to avoid the interaction between two vessels. For green crossing target, OS had stopped the main engine already. Master decides to further reduce the ship by using the side kicking effect of the rudder. 

Second collision 

If the collision risks exist in more than one vessel or the avoidance actions may lead to another close quarter situation, all the vessels have or about to have the collision risk should treat as one big vessel. Give-way vessel should take the actions to avoid all vessels at the same time well before all the risks become imminent. This is a prudent navigator practice. 

Does it possible for a vessel to collide two vessels at the same time? We may like to say it is possible. But, we have to look it in the logic way. If both the vessel were in the POC with own ship, even without own ship's present, these two vessel will collide to each other. Then, in these two vessel must have one vessel shall give way to another vessel. So, when own vessel arrive the POC there must have only one vessel left in the POC area.  In the open sea, it is almost impossible for us to collide with two ocean going vessel in the same time. The ocean going vessel will leave some proper sea room for each other to pass safely. 

It is own ship's responsibility to access "does the sea room left by other give-way vessel is large enough for us to pass through?  If it is not enough, own ship will have to take more action to allow both vessels to pass clearly. But in the confined area or area been used by coastal vessel, the second collision is possible due to the sea room is not enough for every vessel to sail. The coastal vessel have no idea of the sea room needed by ocean going vessel is one N.M. and ocean going vessel won't spare their navigational safety to give more wide sea room to coastal vessel. In this case, these two vessels will sail very closely which will leave very small sea room between each vessel. 

The second collision did happen in the past. It is not the give-way vessel did not give enough sea room to both vessel, but encounter the coastal target in close range and lost control of the ship due to drastic avoidance actions been taken. 

The concept is controlling the OS movement all the time. Even if the collision did happen, master has to access the situation well before the collision. In the drawing above, OS used one hard starboard rudder try to avoid the crossing target. Before collision with the crossing target, OS stop the main engine due to the precedent of court ruling. The precedent is based on the assumption that OS should stop the engine to mitigate the collision impact to other vessel. The overtaking vessel in the starboard side didn’t aware of what happen in OS maneuvering. After collision with the crossing vessel, OS run into overtaking vessel’s course line. Collision after collision is the second collision. 

If the distance judgment is correct, OS should stop the engine at the first place. Master use the hard starboard rudder in the light of hoping the crossing vessel will stop the engine or alter course at the last stage. The option to use the hard port rudder may not prudent, for the port side course altering may jeopardize any intention of the crossing vessel. The meeting situation should consider as discussed before. 

If the collision spot is at fore part of OS, the hard port rudder is trying to bring the fore end of OS to meet the target. If the collision spot is at aft part of OS, the hard port rudder is used to reduce the angle of blow. In the situation above, this hard port rudder also help to reduce the turning rate to avoid the second collision. The purple overtaking vessel had also aware of the situation and used the correct maneuvering to avoid the collision danger.  

Aground after avoidance action 

Sometimes, the give-way vessels go aground after the avoidance action. As two vessel meet in close quarter situation, the POC is always on the safe water.  The reason is simple. The POC is on both vessel’s course line. One vessel may make wrong course line passing a shoal water or navigation hazards. But, it is almost impossible for two vessels to make the same mistake at the same place. The POC have two SL in diameter which is about 0.3 N.M.  In the voyage planning, any navigation hazards within one N. M. to the course line will need special precautions. Any avoidance actions should have precise control over the ship's movement, including the ship's bow and stern. Any side way (transverse distance) making for avoidance purpose should bear in mind the available sea room OS have. 

The reason why give-way vessels go aground is same as last paragraph. Take too much action to avoid the collision and lost control of her movement. If the OOW have no confidence to conduct the vessel well clear of the danger, captain should be called to the bridge to do the maneuvering. 

In the drawing above, all course line intersection point is the possible area of collision. These three course lines has only one intersection point. The blue vessel’s course altering point is to close to the center of fairway. Thus, leave very little sea room for red vessel to avoid the collision. This mistake will not only cost the red vessel extra danger to go aground, but will also make the blue vessel exposed to the danger of collision.      

Master's responsibility

The master's responsibility in ship's command is to preserve the life on board, the ship and her cargo. Any decision the master take will has his priority in mind. The first priority is always the safety. The safest way is always the slowest way. In the beginning of this chapter, we introduce the way to clear the stand-on vessel is altering the heading all the way to the stern of stand-on vessel. We had also learnt the minimum heading altering requirement: for the target over 4 N.M range, heading change should over 5 degree. As an OOW on the bridge, the duty officers will never known the effectiveness of his avoidance action until the stand-on vessel had clear OS bow. The prudent OOW will then check the bow crossing range of the stand-on vessel. Before OOW have confident of his decision, the avoidance action he takes should be as large as he can be sure of his avoidance action is safe. The master’s responsibility is to let the OOW to do the safest action to avoid the collision danger. If the situation permits, master should accompany the OOW during the maneuvering. Let the experiences of the avoidance action accumulated as OOW’s skill. Considering all the navigational hazards in the sea, these experiences should begin from the simplest situation: open sea. Master cannot be always on the bridge, the master order will be as simple as “Do as you can be sure of OS safety, if not, call me any time.”. 

All the possible scenarios at sea should bear in mind beforehand and put into our voyage planning for possible solution. All the collisions happened at OS course line, if OS can sail along the course line all the time. Every spot on the course line is a possible area of collision(POC). Before ship sailing to the spot, every danger ahead should have alternative way to prevent it. Try yourself to the worst situation and figure out what is the best way to solve it. Don't just trust yourself by the experience of yours or other's success and underestimate the danger. The master is like a general in the battle field, the only warrant of safety is well preparation of yourself.