Sailed4seas的部落格

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.     

https://www.youtube.com/watch?v=19suVDp8GnM

Collision Avoidance Nav Rules