Sailed4seas的部落格

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.

THERE ARE THREE STABLE PRESSURE FIELDS AROUND THE CONSTANT SPEED VESSEL. THE DISPELLED WATER FROM THE SHIP BODY REFLECTS BACK AND FORTH FROM THE RIVER BANK WILL RAISE THE WATER LEVEL BETWEEN THE BANK AND SHIP BOW. AFTER THE BROADEST PARTS OF SHIP TRANSVERSE SECTION, THE RAISED WATER FLOW INTO SHIP STERN WITH ACCERLARATED SPEED TO FILL THE VACANCY SPACE LEFT BY SHIP’S BODY CAUSING THE WATER LEVEL TO DROP. AFTER THE VESSEL PASSED, THE WATER LEVEL RAISE UP TO ORIGINAL HIGH. THE HIGH PRESSURE AREA IN THE SHIP’S BOW IS MORE CONSPICIOUS WHEN THE RIVER WIDTH IS LESS THAN 2.5 TIMES OF SHIP’S WIDTH.

IF VESSEL IS NOT PROCEEDING ALONG THE CENTER FLOW OF THE RIVER, THE SIDE MORE CLOSER TO THE BANK WILL HAVE MORE HIGHER PRESSURE ON SHIP’S BOW COMPARE WITH THE OTHER SIDE. THIS EFFECT IS CALLED THE BANK CUSHION WHICH CAUSING THE SHIP BOW BEEN PUSH AWAY FROM THE CLOSER BANK. WHERE IN THE MIDSHIP PART OF THE LOW PRESSURE FIELD, THE WATER AROUND THE SIDE MORE CLOSE TO THE BANK WILL HAS MORE HIGHER SPEED THAN THE OTHER SIDE TO FILL THE SHIP’S BODY VACANCY. THE FASTER THE WATER SPEED, THE WEAKER THE WATER SIDE PRESSURE. THE INBALANCE OF TWO SIDE WATER SPEED CAUSE THE SIDE MORE CLOSE TO THE BANK HAVE LESS SIDE PRESSURE THAN THE OTHER SIDE. THIS PRESSURE INBALANCE IS CALLED THE BANK SUCTION WHICH PUSHES THE SHIP MIDSHIP SIDE TO THE CLOSER BANK.

THESE INTERACTIONS WITH THE RIVER BANK IS FROM THE WATER SURFACE DOWN TO THE SHIP’S BOTTOM. THE RIVER WIDTH IS IRREGULAR FROM THE VISIBLE WATER SURFACE. EACH SIDE OF THE RIVER BANK HAS DIFFERENT SLOPE DOWN TO THE BOTTOM. IN THE RIVER BED, IF IT’S NOT REGULARLY DREDGED, THE DEPTH IS ALSO UNEVEN. ALL THESE IRREGULARITY CAUSED THE PRESSURE FIELD AROUND THE SHIP BODY IN CONSTANT CHANGING STATUS IN A RIVER. HOWEVER IN AN ARTIFICIAL CANAL, THESE WIDTH, SLOPE AND DEPTH ARE RELATIVE UNDER CONTROLLED.    

HOW DO WE KNOW THAT THE VESSEL IS NAVIGATING ALONG THE CORRECT POSITION IN A RIVER? THE SIMPLE FACT IS THE RUDDER DIDN’T NEED TO COUNTER THE BANK CUSHION EFFECT IN A STRAIGHT LEG OF THE RIVER. WITH NO WIND CONDITION, IF VESSEL PROCEEDING WITH ONE SIDE OF RUDDER ANGLE BEEN FREQUENTLY USED TO KEEP THE SHIP’S COURSE, IT IS POSSIBLE THAT VESSEL IS NOT CORRECT POSITIONED. BY THE INTERACTION OF THE BANK CUSHION AND BANK SUCTION, THE VESSEL WILL MAKE THE TURNING AROUND A BEND WITOUT THE RUDDER BEEN USED TO INITIAL THE TURN. HOWEVER, THESE INTERACTION IS CLOSELY RELATED THE VESSEL’S SPEED. TOO FAST OR TOO SLOW WILL NEITHER FULFILL THE PURPOSE.

IT IS VERY IMPORTANT TO KEEP IN THE CORRECT CENTER OF THE RIVER BEFORE MAKING A TURN. IF ANY RUUDER ANGLE BEEN CONSTATLY USED TO COUNTER THE BANK EFFECT, THE RESERVED MANEUVERIBLILITY IS SOMEHOW DETEORATED

https://www.youtube.com/watch?v=AaIpPjxXtPw

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