Deep water anchoring safe practice by VLCC
VLCC in deep water
Anchoring into "Deep water" which is defined depth of water is beyond 50 meter, must be carried out with "Walk-back Style, however, on the VLCC operation there exists such a big inertia, Master can treat with Walking-back style even in the anchorage where water depth less than 50m, if following conditions are to be forecasted.
a) Strong wind / current effect
b) High density anchorage or anchorage with restricted area
c) Indistinct depth of water or bottom material
If the area where water is depth beyond 50m, master should be considered he is going to anchor into the "deep water", all chains must be drawn out by "Walk-back Style".
Ship's heading before commencing Walk-back chains
Ship's heading on final approaching should be faced into the Wind and Current which can provide good advantage to control good ship's pose (heading) when Anchor just Folding and also for Minimizing of Swinging rate to windward or current-ward.
Ship's speed during Walk-back chains
Ship's speed during Walk-back chain must be controlled as "0" with speed over the ground by GPS and/or Doppler Sonar, or less than speed of Windlass Walk-back Capacity (Speed).
The status of brought-up anchor should be confirmed as holding chains by windlass brake after drawn out required length of chains.
Although, on R-FPP (Right turn Fixed Pitch Propeller) vessels, when ship is propelling with astern engine, ship's head turns to right as on theoretical, however, it's to be affected greatly by the primary inertia.
Swing-way shall be estimated totally with following factors
a) Character of movement while using astern engine on FPR vessels
b) Character that ships heading turns to windward
This factor is remarkable as in ballast condition
c) Drifting value of wind and/or current to lee side
This factor is remarkable while ship's proceeding with low speed.
d) Trend of Wind / Current direction which ship's heading will follow.
e) Since in each case, Final inertia -way prior to anchoring is most affected to movement during Walk-back chains, this inertia can be managed occasionally with One Kick of Ahead Engine with Hard Angle of Rudder.
To plan as a gradual decrease as to secure remaining speed over the ground "0" by GPS speed when commencing to "Walking back Chains" by means of operating main engine to ahead and astern.
Including anchoring at strong current area, it's required to confirm if the ship has been stationary with O.G. speed by GPS and/or Doppler Sonar, also by all means of followings.
For the sake to be sure if ship has stopped moving completely, the master should check with following signs totally, even if no landmarks and signals are available to use.
a) Reports by Bow anchor watchmen with observing the condition of the cutwater on stem (and/or the anchor chain).
b) Same as above, it's a good practice to use Hand-lead to check the fine movement.
c) GPS speed monitor on ARPA showing slight positive speed with the Owned cursor directing towards almost vertically with ship's heading.
d) Astern propelled wave has reached to forward of living quarter.
Walk Back speed
On the standard, the weighing chain speed is 15cm / second (= one shackle 27.5 meter / 3 minutes). Its corresponding to 0.3 kts of ship's speed.
It means ships speed with combining turning rate and drifting to wind and current lee side should be controlled less than 0.3 kts against direction anchor chain is going.
Do not use propelling beyond maneuvering Half Ahead / Astern Engine, except in emergency cases, once walk back is commenced.
Communication between commander in wheel house and bow anchor watchmen
For the good image as macro-wise to actual ship's pose and condition of anchoring progress, Bow watchmen must report following to the Commander on the Bridge.
a) Approaching speed should follow a gradual decrease plan
Before arriving at anchorage, Eye estimation speed by bow watchmen should be verified with GPS or Doppler log.
b) Reducing speed for anchoring
Please note ship's speed is corresponded as follows
1.0 kts = aprx. 50cm / sec
0.5 kts = aprx. 25cm / sec
0.2 kts = aprx. 10cm / sec
c) Anchoring speed (Going walk-back)
If ship is stationary just prior to anchoring with observing cutwater at stem and anchor chains in water
d) Status chain number have been drawn on each shackle interval
It is preferable to report as "XX shackles in the water" in order for the commander to easily visualize Length of chains being in the water and can estimate timing of touching anchor with bottom.
both commander and bow watchmen must acknowledge the length of anchor shank when taking account length of cable.
e) Anchor chain direction and tightness after bottom touch
Report shall be combination of following factor
For Horizontal direction:
"clockwise" and "straight down" (or upright)
For Vertical direction :
"as Long hand (of the clock)"
"as Short hand (of the clock) "
For Tightness :
"Strong tight", "Moderate tight, "Easy tight" and "Slack"
Ex. Chain - 2 o'clock - as short hand - with moderate tight
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