Sailed4seas的部落格

1.  VISUAL TURNING

HOW TO TURN A VESSEL IN A WATERWAY? IF YOU ARE IN THE NAVY, THERE WILL A SET OF SOP NEEDS TO FOLLOW. FIRST YOU WILL AVE TO READ THE MANEUVERING BOARD VERY CAREFULLY TO IDENTIFY THE TACTICAL DIAMETER. IN THE MANEUVERING BOARD, THEY WILL INVARIABLE BE SHOWN IN METERS WHICH IS INPRATICAL FOR MARINE USAGE EVEN WE USE THE RADAR TO MEASURE THE DISTANCE AND THE RUDDER USED TO TURN THE VESSEL FOR MEASURING THE TACTICAL DIAMETER IS ALWAYS IN FIXED RATE.

THERE WERE A STUDY OF WHY A TURNING MANEUVERING WILL FAIL

1. THE VESSEL SPEED HAD NOT REDUCED BEFORE TURNING.
2. DIDN’T USE THE SLOW SPEED CONTROL WHEN APPROACH THE TURNING POINT.
3. WOP IS WRONG.
4. DIDN’T USE THE FULL RUDDER ANGLE TO TURN.
5. ENGINE SPEED IS NOT ENOUGH FOR TURNING.
6. DIDN’T STOP THE ENGINE BEFORE REDUCE THE RUDDER ANGLE.

• THE IMPORTANCE OF KEEP LOW INITIAL VESSEL SPEED.IS TO RESERVE THE NECESSARY MANEUVERING ABILILITY WHEN EXTRA RUDDER EFFECT IS NEEDED.
• SLOW SPEED CONTROL IS TAKEN ALL THE ENGINE SPEED OUT AND CONTROLLING THE VESSEL’S HEADING AND POSITION BY KICK AHEAD THE ENGINE.
• WHEEL OVER POSITION MAY BE INCORRECT BY APPLING THE RUDDER ANGLE TOO LATE OR THE VESSEL IS NOT IN THE MIDDLE OF THE FAIRWAY.
• TO USE THE FULL RUUDER IN THE FIRST RUDDER ORDER IS TO INITIALIZE THE TURNING. IF THE TURNING STARTED TOO LATE, THE ENGINE POWER MAY KICK IN.
• ENGINE SPEED NOT ENOUGH MEANS THE ENGINE POWER IS NOT RESERVED BEFORE THE TURNING OR DIDN’T USE AL THE ENGINE POWER AVALABLE.
• AFTER THE VESSEL HAVE INITIALIZED THE TURN AND IT’S SEEMS TURNING TOO FAST, THE ENGINE POWER SHOULD TAKE OFF FIRST TO SEE THE TURNING IS STILL GOING ON THE RIGHT TURNIGN RATE.    

ALL THESE CAUSE ARE REFLECTING THE SAME TRUTH OF TURNING MANEUVERING

WIND

A SUCCESSFUL TURN MAY CONSIST OF THREE PARTS:

1. THE VESSEL HAS TURNED TO THE DESIRED DEGREE.
2. THE VESSEL HAS MAINTAINED THE DESIRED SPEED.
3. THE VESSEL HAS PLACED IN THE DESIRED POSITION

• THE DESIRED DEGREE MEANS THE NEW COURSE AND STEADY ON IT.
• THE DESIRED SPEED MEANS WE DIDN’T USE THE ENGINE SPEED TO HELP THE TURN.
• THE DESIRED POSITION MEANS THE VESSEL HAS KEEP IN THE CORRECT POSITION IN THE WATERWAY, NOT TURNING TOO EARLY OR TOO LATE. 

WHAT IS THE CORRECT POSITION IN THE WATERWAY? IT’S THE POSITION WHERE THE PRESSURE FIELD AROUND THE VESSEL ARE IN EQUIVALENT STATUS. THIS CORRECT POSITION IS IN THE CENTER OF THE RIVER WATER FLOW LINE, BUT NOT NECESSARY THE CENTER OF THE RIVER. FOR A NATURE RIVER DEPTH IS UNEVEN CAUSING THE WATER FLOW IN DIFFERENT SPEED. WHEN THE VESSEL CONDUCTING THE TURN IN OPEN WATER, THE PRESSURE FIELD CAUSED BY VESSEL SPEED HAVE THE INFLUENCE SHOWN ON THE SHIP TURNING CHARACTERISTIC. WHEN A VESSEL PROCEEDING ALONG THE RIVER OR CANAL WILL MAKE A TURNING IN DIFFERENT CHARACTERISTICS.

FOR A VESSEL TURNING TOO FAST, THE COUNTER MEASURES WILL BE :

• REDUCING THE RUDDER ANGLE BEEN USED.
• MISHIP THE RUDDER TO NEUTRALIZE THE RUDDER EFFECT
• USING THE COUNTER RUDDER TO STOP OR SLOW THE SWING.
• USING FULL COUNTER RUDDER TO INCREASING THE CHECKING.
• USING THE RESERVED ENGINE SPEED TO MAXIMUM THE CHEKING.

IT SHOULD BE CLEAR NOW THAT THE RUDDER ANGLE SHOULD BE USED FIRST TO SLOW DOWN THE TURNING. IN THIS TURNING TOO FAST SITUATION, WE HAVE MORE WIDE RUDDER ANGLE RANGE FROM EASE THE HELM TO MIDSHIP TO COUNTER RUUDER. THESE MEASURES ARE ALSO USED WHEN VESSEL HAVE FINISHED THE TURN BUT STILL CAN NOT STEADY ON THE NEW COURSE. WHEN WE USE THESE COUNTER MEASURES TO SLOW DOWN THE TURNING RATE, THE VESSEL IS STILL MOVING ALONG THE WATERWAY. AT THE CORRECT WOP, WE WILL HAVE TO CONTINUE THE TURN TO APPLY THE RUDDER EFFECT AGAIN. SO, THE TURNING IS A SERIES OF MANEUVERING TO AQUIRE THE SUCCESS TURN.

   THE COUNTER MEASURE FOR A VESSEL TURNING TOO SLOW WILL BE

WE CAN DERIVE SOME BASIC CONCEPT FROM THE FACTS ABOVE.

PREAMBLE

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.

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. 

COLREG Rule 7 Risk of Collision (a) Every vessel shall use all available means appropriate to the prevailing circumstances and conditions to determine if risk of collision exists. If there is any doubt such risk shall be deemed to exist. (b) Proper use shall be made of radar equipment if fitted and operational, including long-range scanning to obtain early warning of risk of collision and radar plotting or equivalent systematic observation of detected objects. (c) Assumptions shall not be made on the basis of scanty information, especially scanty radar information. (d) In determining if risk of collision exists the following considerations shall be among those taken into account: (I) such risk shall be deemed to exist if the compass bearing of an approaching vessel does not appreciably change; (ii) such risk may sometimes exist even when an appreciable bearing change is evident, particularly when approaching a very large vessel or a tow or when approaching a vessel at close range.  

In 7(a) If there is any doubt such risk shall be deemed to exist. The point is mainly aimed to encourage the give-way vessel to take proper action to avoid the collision when other vessel’s bearing change is not obvious. It is interest to note that in a study from the aviation industrial of the so called mid air collision. There is a phenomenon called blossom effect. If the image of a target getting bigger and bigger, it means the risk of the collision is imminent. When the image augment is more than the bearing change, the OOW will confuse of the risk of collision. This is the time the rule 7(a) apply.   

 AFTERMYTH OF A COLLISION CASE