of July, at 15:00 JST, the Typhoon Response Committee recommended preparing for evacuation by issuing the ﬁrst
warning. Moreover, because the strong wind area was predicted to reach the port within 24 hours, on the 24th, at
13:00, they issued the second warning. They recommended that ships in the port take strict precautionary measures bytaking shelter outside of the port and so on.
On the afternoon of July 23rd when the ﬁrst warning was issued, the Master had a meeting with the person in charge at
the local agent and decided to take shelter at Kagoshima Bay.
On the following day, July 24th, when the cargo was unloaded 17,194 tons, cargo handling was interrupted and the
Vessel C left the wharf at 10:40.
The Master was thinking that he had not experience with entering Kagoshima Bay, it would take 11 hours as a roundtrip and there was a risk of being close to the centre of the typhoon according to the forecast of the typhoon’s path,then. He also judged that the force would decay judging by the information from NAVTEX. Because there was ample
spare time until the typhoon approached, the Master decided to choose the anchorage according to the movement of
the typhoon from the following three choices as his original plan: ① head for Kagoshima Bay, ② stay anchored at
Shibushi Bay without navigating a direct course to Kagoshima Bay or ③ seek shelter oﬀshore. As a result, at 11.30, thevessel dropped her starboard anchor at 6 shackles <056> 2.0 nautical miles oﬀ of Birou Island and 2.1 nautical miles oﬀ
Shibushi south breakwater, light house <193>, where the sea bottom was sand with a water depth of around 25 metres.

July 24th 10:40
Left the wharf

Kagoshima

Souof th b
Sh re
ib ak
us
hi watPo errt

Wakahana
Whorf

Zen-noh Silo
Dolphin

5

10

July 25th 2１:11
Grounded

rl

im
i

t

Shibushi Bay

Shibushi Bay

Quarantine
anchorage

ha

rb

ou

×

Birou Island

20

<193>
2.1nautical miles

July 25th 20:30
Dragging anchor started

July 24th 11:30
Started anchoring

Shibushi Bay

Fig. 54

Afterwards, partly because a similar size of ship, Vessel M started anchoring at Shibushi Bay, Vessel C also continued
single anchor mooring with 6 shackles of anchor cable. However, contrary to expectation, the force of the typhoon
did not decrease and Shibushi Bay gradually entered the storm area and the right semicircle of the typhoon. Due to− 28 −

the violent storm and swell encroaching on the Bay, at 20:30
on July 25th, dragging anchor occurred and they grounded at
21:11.
Regarding the damage, cargo holds, between No. 5 and No. 6,
near the centre of the hull there was breakage and No. 2 Fuel
Oil Tank under No. 5 cargo hold was damaged. Immediately,at the same time as he activated the distress signal by operating
the EPIRB, the Master reported the distress to the Japan Coast
Guard via international VHF radio communications.
The Master judged that there would be a danger of thedamaged part of the hull ending up sideways. At 21:30, theMaster commanded all of the crew to wear helmets and life
vests in order to abandon the ship. Then they lowered thelifeboats outfitted on both sides of the deck respectively, allof the crew boarded the lifeboat on the starboard side (leewayside) and then they started to lower the lifeboat.

Photograph 55 EPIRB

However, the lifeboat was violently beaten against the shell
plating of Vessel C due to the gale force winds and highwaves while lowering. Also, some crew were injured when
their bodies were beaten in the lifeboat. Due to the constantbuffeting, all of the crew evacuated from the lifeboat andPhotograph 56 Breakage
jumped into the sea. As a result, although 15 out of 19 crew
members managed to swim to the nearby coast, 4 (one second engineer, two ABs and one C/Cook) were deceased.

Path of Typhoon No. 9 in 2002: Asian name is FENGSHEN
On the 14th of July 2002, a
tropical depression formed in thesea around the Marshall Islands
and changed into Typhoon
No. 9 accelerating in force
and heading north. She took awesterly path in the vicinity of
15 degrees north in latitude and,by the 20th, reached the vicinityof 200 nautical miles southwestof Minami-Tori-Shima islandand changed to a northwesterly
path nearing the Ogasawara
Bonin Islands while gradually
increasing in speed.
Fig. 57 Path of Typhoon No.9

− 29 −

（1）July 24th
Regarding Typhoon No.9, according to an observation at 00:00 JST, weather information provided by NAVTEX
announced that at 03:00, she was located in the vicinity of the northeast at 100 nautical miles away from Chichijima
Island of Ogasawara Bonin Islands. She developed into a “strong typhoon” with a central pressure of 945hPa and amaximum wind speed of 41m/s close to the centre. The storm area was 120 nautical miles moving northerly at 25m/s with a strong wind area of 250 nautical miles and a wind speed of more than 15m/s as she advanced into southern
Kyushu taking a westerly path at 15 knots.

（2）July 25th
Source: courtesy of the Geospatial Information Authority of Japan (GSI) website

Shiono-misaki
Muroto-misaki

Ashizuri-misaki

0

60

120

180

240

nautical miles
300

Kagoshima Bay
Shibushi Bay
Approx.60 kms

967hPa 33m/s

970hPa 30m/s
21:00 JST

18:00 JST

15:00 JST

970hPa30m/s

965hPa 35m/s

12:00 JST
09:00 JST

06:00 JST

970hPa30m/s

03:00 JST

25th
00:00 JST

18:00 JST

15:00 JST

Fig. 58 Path of Tyhoon No.9

On the following day of the 25th, by 00:00, Typhoon No.9 was already in the vicinity of the east-southeast 350
nautical miles from Shibushi Bay, with a central pressure of 965hPa, a maximum wind speed of 35m/s, a storm area of
80 nautical miles and a strong wind area 250 nautical miles. She approached southern Kyushu taking a westerly pathand maintained a speed of 11 knots. At 06:00, she reached the vicinity of 240 nautical miles east-southeast of Shibushi
Bay and the bay was now in the strong wind area.
Later, by 09:00, Typhoon No.9 was located in the vicinity of <124> 191 nautical miles from the point where Vessel C
had anchored in Shibushi Bay and the force had more or less decayed with a central pressure of 970hPa, a maximum
wind speed of 30m/s, a storm area of 80 nautical miles and a strong wind area of 270 nautical miles. However, she
moved west-northwesterly at a speed of 17 knots and was predicted to pass 50 to 60 nautical miles south of Shibushi
Bay between 19:00 and 20:00, if she proceeded on the same path and at the same speed. There was even the possibility
Shibushi Bay would be exposed the storm area, in particular the “right semicircle of the typhoon”: “a Dangerous
semicircle”.
− 30 −

On the other hand, although the maximum wind speed was at 33m/s according to an observation at 06:00 by
NAVTEX, by 09:00, it had decayed to 30m/s, according to further observation. Due to this, the international notationof Typhoon No. 9 was changed from a “T” to an “STS” (one category down). The maximum wind speed was also
forecast to have decreased to 28m/s within the next 24 hours. (Note: please refer to the notes below)
Yet, the storm area of 80 nautical miles did not change, and, at 12:00, Typhoon No.9 was still located in the vicinity of<128> 135 nautical miles from the point where Vessel C had anchored. She proceeded west-northwest at 18 knots withincreasing speed, maintaining a central pressure of 970hPa and a maximum wind speed of 30m/s. Then, it was highly
likely that shortly Shibushi Bay would come in range of the 80 nautical mile storm area.
By 15:00, with the force of the typhoon still unabated and with a central pressure of 970hPa with a maximum windspeed of 30m/s, she approached the vicinity of <141> 93 nautical miles from the anchored point of the vessel. At
approximately 16:30, she reached the vicinity of <150> 80 nautical miles (estimated position) from the anchoredpoint, and the outer edge of the storm area encroached on Shibushi Bay.
At 18:00, Typhoon No.9 reached the vicinity of 30 nautical miles southeast of Tanegashima Island of Kagoshima
Prefecture which was in the vicinity of <162> 73 nautical miles from the anchored point. And then, she moved west.
At approximately 19:30, she passed the vicinity of <180> 67 nautical miles from the anchored point, the closest she
had been to Shibushi Bay. Furthermore, at 21:00, she reached Yakushima Island in the same prefecture.
Note: In Japan, as explained in page. 2 - 3, it is categorized as a “Typhoon” when its maximum wind speed isgreater than 17m/s (wind force 8) and as a “Tropical cyclone” when it is less than 17m/s. On the other hand,according to the international scale, typhoons and storms are classified into the following three categories.

①

The maximum wind speed is more than 33m/s (wind force 12):TYPHOON (T)②

The maximum wind speed is more than 25m/s (wind force 10) but less than 33m/s:

SEVERE TROPICAL STORM (STS)③

The maximum wind speed is more than 17m/s, but less than 25m/s:

TROPICAL STORM (TS)In addition, a tropical cyclone that has a maximum wind speed of less than 17m/s is categorized as a TROPICAL
DEPRESSION (TD).

− 31 −

Movement of Vessel C
July 21st

Vessel C arrived at Shibushi Bay. Anchored in the bay in order to adjust the time for berthing.

01：06
July 22nd

A pilot registered with the Kagoshima Licensed Pilot’s Association embarked.

06：34
07：36

Berthed at the quay of Zen-Noh Silo Corporation and started cargo discharging work.
Total of 9 crew members (the chief officer [Indian national] and 8 other members (Filipino
nationals) disembarked.
Total of 5 crew members (the successor chief officer [Indian national] and 4 other members [Filipino
nationals]) embarked.
Note: Decrease of four crew members

July 23rd

Because the strong wind area of Typhoon No.9 was predicted to reach Shibushi Bay within
48 hours, the Typhoon Response Committee issued the first warning and announced therecommendation of preparing for evacuation.
Later, the Master and the person in charge at the local agent discussed the following items in their
meeting.

15：00

Should the typhoon pass thesouth of Shibushi Bay,
where is one to evacuate?

Shibushi Bay would not besuitable for sheltering anchorage.
Until now, large vessels
took refuge anchorageat Kagoshima Bay.

MasterAgent

As a result, the Master decided to leave the wharf on the following morning and shelter from thetyphoon in Kagoshima Bay. At the same time, in order to carry out draft adjustment, the Masterchanged the discharging plan in order to complete the cargo discharge of No.2 and No.6. He also
arranged for the ballast tanks to be filled so as to adjust departure condition fore draft 8.00m andaft 11.60m.
July 24th
10：40

After completing discharge of No.6 cargo, filling ballast was also completed. At the time when
17,194 tons had been unloaded, the cargo handling was interrupted in order for the ship to leave
the wharf (with a remaining 40,280 tons still loaded).

− 32 −

11：30

13：00

After the pilot disembarked, the Master decided to anchor at Shibushi Bay without taking a direct
course to Kagoshima Bay that was originally planned as a sea area of sheltering. The Master
decided to observe the movement of the typhoon and anchor using the starboard anchor at 6
shackles at 2.1 nautical miles from south of the breakwater. The water was at a depth of 25m andthe sand type was sea bottom sedimentary.
The reason for the change of plan, as mentioned above, was because the following threeanchoring methods were planned. Paying attention to the movement of the typhoon, the Master
decided to observe the situation while anchoring at Shibushi Bay.
● To anchor at Shibushi Bay●

Avoided sailing into the open sea to keep a distance between the ship and the typhoon●

To shelter at Kagoshima Bay

Because the strong wind area was predicted to reach Shibushi Bay within 24 hours, the Typhoon
Response Committee issued a second warning.
In the evening, the Master got to know that a ship of similar size, Vessel M (38,567 tons), left thewharf in a similar way and started anchoring at Shibushi Bay.

July 25rd
06:00(observed)

09：00(observed)

The strong wind area encroached on Shibushi Bay.
Typhoon No.9 was in the vicinity of <117> 243 nautical miles from the anchored point and she wasproceeding west-northwesterly at 16 knots. Because Shibushi Bay had entered the storm areaat 250 nautical miles, if she continued to proceed on course, it was estimated she would pass at
approximately 50 nautical miles south of Shibushi Bay between 19:00 to 20:00.
There was a possibility that Shibushi Bay would enter the storm area of the right semicircle of thetyphoon.
Typhoon No. 9 was proceeding west-northwesterly at 17 knots close to the vicinity of <124> 191
nautical miles from the anchored point and it was estimated that there was a possibility of Shibusi
Bay entering the storm area of the right semicircle of the typhoon.

The Master only used the typhoon information provided by NAVTEX. Although the Master wrote
down the position, path and speed of the typhoon on the nautical chart, he did not write down thefact that the ship was in a strong wind area or a storm area.
In addition, the Master obtained the following information from NAVTEX.

● Category of the typhoon was downgraded by one category from T to STS.
● It was forecast that the wind speed would decrease to 28m/s within the coming 24 hours.
Furthermore, because it was still observed that the wind speed was less than 10m/s and the wave
height was at 2m, the Master decided to stay sheltered at Shibushi Bay.

It would take at least 11 hours to navigate to Kagoshima Bay...
I have never experienced this before...
It is a ship of similar size, Vessel M which is also anchoring at
Shibushi Bay...
I should be able to manage this using the engine and rudder.

− 33 −

12：00(observed)

The Master obtained the information from NAVTEX that Typhoon No.9 was proceeding westnorthwesterly maintaining a force of 970hp and a storm area of more than 30m/s.

North wind suddenly became strong and the wind speed exceeded 15m/s. Also, the height of theswells which encroached the bay mouth increased. Anchoring watch was enforced, however, theMaster stayed sheltering at Shibushi Bay without evacuating to the open sea.
16：00
16：24

Started use of engine keeping 6 shackles of anchor cable.

16：30

Shibushi Bay entered the storm area at the right semicircle of the typhoon.

17：00

Wind direction changed to northeast. Wave height at 3 meters.

19：30

The typhoon moved the closest at this point, with a wind direction now changed to east-northeast.
Wind speed was 17m/s, maximum instantaneous wind speed was 28m/s and wave height was 5m.

Started dragging anchor. Wind speed was 25m/s, the maximum instantaneous wind speed was
35 to 41m/s and the highest wave height was 8m.
20：30

20：40

21：11

21：30

Confirmed anchor dragging via radar. Started weighing the anchor, but this became constrained
when heaving the cable to 2 shackles of 6 shackles. It was because the cable was extremely
tense, even with the engine at full speeded ahead.
Tried to prevent drift by using the engine. Even if it was temporarily effective, it was not possible tostop it completely.
Aft part was grounded at the point of south <238> 1.9 nautical miles from the breakwater in
Shibushi Bay, water depth at 10m.
Immediately after this, cargo holds between No.5 and No.6 near the centre of the hull were broken
and the No.2 Fuel Oil Tank under the No.5 cargo hold was damaged.
The Master judged that there was a possibility that the damaged aft part might rollover. Then,
as was described above, at the same time of activating the distress signal via EPIRB, the Master
reported the distress to the Japan Coast Guard by VHF.
The Master commanded all crew to wear life vests and started abandoning ship with the lifeboat
outfitted on the starboard side (leeway side). However, the lifeboat was violently beaten anddamaged due to the gale and high waves. Because some were injured, all crew jumped into thesea, however, 4 crew members out of all 19 members were confirmed as deceased.

− 34 −

＝ Quoted from the Marine Accident Inquiry Agency (MAIA) determination ＝Provisional translation
The following were analyzed as main accident causes.

① Insufficient realization regarding the typhoon▶

Wishful observation that the typhoon’s force would decay because of the typhoon information provided by
NAVTEX.

▶

Lack of crisis consciousness regarding the entering of a storm area, changes of wind direction andencroachment of gale and high waves.

▶

Lack of awareness towards typhoons by the Master and each navigation officer② Insufficient information of sea area for sheltering etc.
The Master decided to take refuge at Kagoshima Bay, because when the Master and the local agent had ameeting, the Master of Vessel C asked the person in charge of the local agent where he should sheltering and he
was advised by that person that “Shibushi Bay was not suitable for sheltering anchorage. Until now, large vessels
took refuge anchorage at Kagoshima Bay”. In fact, as described above, the Master did not navigate to Kagoshima
Bay and stayed anchored at Shibushi Bay.
▶

The Master made his judgement based on only what the local agent told him and typhoon information
supplied by NAVTEX.

▶

Thus, there was insufficient typhoon information (such as the range of strong wind or storm areas, winddirection, wind speed etc.)▶

One of the reasons to keep anchoring at Shibushi Bay was that it would take an extra 11 hours to sail in thestorm to Kagoshima Bay and, once again, the vessel was to return the Shibushi Bay, if the typhoon was to
pass.

▶

The Maser was hesitant to enter Kagoshima Bay, as he was not familiar with the area.

▶

According to typhoon information provided by NAVTEX, the category of the typhoon was downgraded by
one rank to category “STS”. With this information, the Master judged that the typhoon would decay naturally,
however, the wind speed did not decrease and a large swell encroached into the bay again.

③ The Master had a false sense of security because a vessel whose size wassimilar was also anchoring.
▶

The Master felt a false sense of security, because a foreign registered Vessel M (38,567 tons) was anchoringat the Port of Fukushima off in the northeast part of Shibushi Bay.

▶

Vessel M was advised: “If there is a wind from the East, Fukushima port off in the northeastern area of
Shibushi Bay should be suitable” by their pilot, and conducted single anchor mooring with 9 to 10 shackles atthat port. Although she dragged anchor due to a violent storm and swell, she managed not to get grounded.

− 35 −

３−４

Questionnaire conducted by the Marine Accident Inquiry
Agency (MAIA) for Masters of the coastal vessels thatexperienced sheltering from the typhoon

When the Marine Accident Inquiry Agency (MAIA) at that time issued their Maritime Casualty Analysis Report (Vol.
6): “Typhoons and Marine Accidents”, they conducted a questionnaire for Masters of the coastal vessels that actuallyexperienced sheltering from typhoon. Some of them are introduced here, as there were many practical comments.

There were many comments, such as“Matters to note when sheltering from a typhoon”
Paying attention to the distance between one’s own vessel and the one anchored nearby, the Masterwas cautious regarding both the anchoring of his own ship and other ships.
While the typhoon was nearby, the Master was careful to observe changes in wind direction following
her passing and the strong wind that would be blowing back.
Because a foreign registered ship tends to conduct single anchor mooring and can easily drag anchor,
the Master tried not to anchor in the vicinity of those ships. He especially avoided being leeward in
relation to the position of those ships.
Using the engine, steering and thruster, the Master tried to stand bow against the wind.
Commenced anchoring watch and stand-by of the engine at an early stage.
Because a strong wind was predicted and there were many anchoring ships in a narrow anchorage,
in an attempt to not cause horsing (yawing and swaying), the Master conducted two-anchor mooringin order to increase the holding power.
The Master wrote down the vessel names of the anchoring ships nearby, in case there was an incidentof dragging anchor, it would have been possible to contact the other ships via VHF or telephone.
Estimated the wind direction at the time of maximum wind speed, and applied two-anchor mooringin that wind direction.

In addition, other speciﬁc comments will be introduced.

In the event of wind speed exceeding 35m/s, it is dangerous to carryout an anchoring work at foreward station. Thus, the Master judged it
would be difficult to heave up anchor because it was in excess of 40m/s.
Therefore, the Master weighed the anchor before the wind became strong
and heaved-to while keeping course so as to receive the wind at the rightahead with a headway speed to some extent. （Large ferry）

The Master dared to conduct single anchor mooring, because Hakodate Bay waspredicted to have high waves sooner or later. Because she dragged anchor at a wave
height of 3m, the Master managed to keep not getting pressed by using the engine.
Single anchor mooring is desirable, if we are to prevent collision accidents due toanother vessel’s dragging anchor. It is impossible to prevent accidents using twoanchor mooring. (4,000 G/T Coastal Tanker）− 36 −

Because the wind speed exceeded 20 m/s, the chief engineer was stationed inorder to prepare for S/B engine. While the hull was yawing in a “figure-of-eight”
movement, the angular velocity of blowing back was faster than that of thelarge cargo ship, thus it was originally a mistake to judge that the holding power
would be strong enough, which resulted in the subsequent response. At thatmoment, the Master should have judged that a strong wind force was to press
instantaneously on the side of the vessel and prepared the engine and thruster.
（Large ferry）

If the fore station operation was deemed to be dangerous at the time ofweighing the anchor, pressure could have been prevented by using theengine. When contacting the Japan Coast Guard regarding anchorage
location and to ascertain information about anchorage, they kindly
responded and even gave information about where the typhoon washeading.（3,552 G/T Coastal Tanker）

Judging from the path of the typhoon, the Master carefully judged as to whether
it was a suitable place to anchor by considering which direction the wind would
blow and condition of gales and waves that may affect where the ship wasplanning to anchor. After having anchored, the Master made sure to write down
the names, positions etc. of other ships nearby so that he may contact them
immediately in case of an emergency. Regarding how harsh nature can be, it isa must to always consider countermeasures because one can never be wellprepared enough.

Because the vessel was too concerned with cargo handling, the commencement ofsheltering was delayed. Cargo handling should have been suspended, and the crew
should have taken refuge earlier evacuating to Mutsu Bay if it was possible. Off thecoast of Kitaura (off the Oshika Peninsula) was not a suitable choice for anchorage
because the kind of sea bottom was too rocky for anchorage, and fishing equipment
was set up in the vicinity. Anchor as early as possible. It would be difficult to lower
anchor as planned after the typhoon had come into close proximity and the windforce had increased. Also, it would be constraining to find a suitable position in
relation to other ships. It is important to plan for anchoring not only for during thenight but also during the daytime.

− 37 −

§4

Mechanism of dragging anchor

The following are important extracts from our Loss Prevention Bulletin Vol.25 titled Preventing an
Anchor from Dragging which was published on the 13th July, 2013. For details, please refer tothis guide.

４−１ Accidents involving ships at anchor
Accidents involving ships at anchor usually occur when the anchor drags and the vessel drifts without holding power,
leading to collisions and/or groundings or strandings. The following considerations should be taken into account:①

It can take some time to realize the anchor is dragging, despite the fact that the ship isdrifting.

②

It takes some time to weigh the anchor and restore the ship to full manoeuvrable
condition, even though the ship may be drifting for that period.

③

During the period beginning with the detection of dragging to the time full control isachieved over the ship’s manoeuvrability, the vessel may run dangerously close aboard,
or into another ship or structure, or into shoal water.

Unless heavy weather causes the vessel to capsize, no serious accident should occur just because a ship is dragging
its anchor, provided there is enough space around it for manoeuvrability and enough time available. The above threeconsiderations may also be applied to the cases introduced in the previous chapter (excluding vessel capsize due toheavy weather).

− 38 −

４−２ The reasons as to why an anchor drags
A ship’s anchor drags due to the impact of external forces on it which exceed the holding power of the anchor andcable. That is, dragging anchor occurs as a result of a relatively simple reason: “When an external force exceeds thatof the anchor’s holding power, it will drag”.

Holding power ＜ External force ▶▶ Dragging anchor

Empirical or Rule of Thumb Methods for Assessing the Minimum Required Length of Anchor Cable
The following is a well-known method for assessing the Minimum Required Length of Anchor Cable, however,factors related to ship type, actual wind speed etc. are not found in this method. It can be considered that those factors
were consolidated in the process of formulating this method for the minimum required length of an anchor cable.
Japanese Publication Theory of Ship Operation● Fine weather： Ｌ＝ 3d ＋ 90m● Rough weather ： Ｌ＝ 4d ＋ 145m

United Kingdom Publication Theory of Ship Operation

L ＝ 39 ×d

Ｌ：Minimum required length of anchor cable(m)ｄ：Water depth(m): up to a wind speed of around 30 m/s.

According to the Marine Accident Inquiry Agency (MAIA), at that time the wind speed and wave height whichcorresponds to the Japanese theory are introduced as simulation results and actual statistical data regarding theanchoring situation of 700 coastal vessels, when the landed typhoons (10 typhoons) passed in 2004, are documented
in their publication titled Maritime Casualty Analysis Report (Vol. 6): Typhoons and marine accidents (in 2006). The
ﬁndings are as follows. Naturally, because this theory or guideline will vary depending on the type of sea bottom andanchorage conditions regarding one’s ship and the other ships, actual minimum required length of anchor cable is tobe determined, with safety being the priority.

− 39 −

Fine weather

Wind speed 20m/s and wave height up to 1ｍ

When, Ｌ ＝ 3ｄ ＋ 90m
Rough weather

Ferries etc. Wind speed 25m/s and wave height up to 2.5m

When, Ｌ ＝ 4ｄ ＋ 145m

OthersWind speed 30m/s and wave height up to 2.0m

The above guidelines will vary depending on the type of sea bottom and the condition ofsourrounding ships in anchorage.

In addition, in the publication of the Maritime Casualty Analysis Report, the simulation results are introduced andattempt to answer question regarding the diﬀerence in the anchoring limit between “being exposed to wind only” and“being exposed to wind and swell” concerning cases in (3-3) in reference to Vessel C.

When exposed toonly wind from the ahead

50

10

12

（Ton）

shackles100

9shacklesshackles8

shackles6

shacklesHolding power
External force(only wind)

0

5

10

15

20

wind speed
（m/s）

25

Fig. 59

As can be seen from the anchor holding power of the anchor and anchor chain, which will be referred to later, because
the bottom part of the anchor chain decreases when wind pressure increases, it was found that the anchor does not
drag until the wind speed is 25m/s and when the minimum required length of anchor chain in the water is more than 6
shackles, although anchor holding power does decrease.
12

100（Ton）

10

shacklesshackles9

shackles8

shackles6

shacklesHolding power

When exposed to windand swell (wave height
5m and wave length200m) from the ahead

50
Dragging Anchor
External force（external force exceeds
holding power）(wind and swell)

05
Fig. 60− 40 −

10

15

20

25

wind speed（m/s）

In the event that a swell is added, due to Wind pressure force + Wave drift force (the force at which a wave moves
a ﬂoating object), the anchor chain tension reaches approximately 50 tons at a wind speed of 10m/s and exceeds its
holding power at 6 shackles at this point in time. Also, it was revealed that the anchor drags at 8 shackles at a windspeed of 15 m/s and at 12 shackles at a wind speed of 25m/s.

Donʼ t underestimate “swell” and “wave height” which may cause ship motion during anchoring.

Watch out for wind and for waves ! !
◆ Be careful regarding changes in wind direction, when a typhoon or windy atmospheric depression approaches.
◆ At sea, where there are few structures against wind, it is estimated that the maximum wind speed will be
be1.5-2 times stronger than the average wind speed.
◆ The higher the swell becomes, the greater the danger of dragging anchor will be, remarkably. Anchor at a
position where the encroachment of a swell is expected is to be avoided. Occasionally, the maximum wave
KHLJKWPD\EHWLPHVRIWKDWRIWKHVLJQLĺFDQWZDYHKHLJKW  *1）Significant wave height (from the Japan Meteorological Agency website)
Wave length λDisplacement

Choose 1/3 of the wave observations (within a timeframeof 20 mins.) in descendingorder from the top. Of those,
the average wave height andperiod becomes the significant
wave. According to this definition, this is also referred to as
the “1/3 maximum wave”.

Wave length λ

A

Peak

Wave
heightｙh[m]ーTroughTroughDistance travelled per second m

Graph expressing waves: in the event that two waves are generated per second

(m)
3.0

(m)
3.0

2.5

2.5

2.0

2.0

1.5

1.5

1.0

1.0

0.5

0.5

0.0

1

2

3

4

5

6

7

8

Peak

Amplitude

0.0

9 10 11 12 13 14 15

Wave hight detected at a point(Irregularly changing)

Average value of 1/3 fromthe biggest wave hight

6LJQLğFDQWZDYHKHLJKW
14

6

5

11

8

1

3

15 10 134

72

Sort in descending order of wave height− 41 −

129

４−３ Detection of dragging anchor
There are conventional methods to check for anchor dragging:①

Check the ship’s position, to confirm whether it is locatedoutside of a turning circle (see Fig. 61).

Fig. 61

Turning Circle②

The bow cannot stand against the wind.

③

The ship's side against the wind has not changed.

④

Check to see that there is no slacking of chains, just before a ship’s side is about to turnagainst the wind.

⑤

Check as to whether there are extraordinarily large vibrations coming from the anchor
chains.

In the event that the course recorder does not show a sine curve movement.

⑥

Photograph 62 shows the course record
when being anchored while being exposed
to wind at a wind speed of 8 m/s, when theauthor was on board a Pure Car Carrier(PCC). It is difficult to tell if it is a sine curve
movement or not.

Photograph 62

The above methods remain well-tried but, of course, only confirm thatthe anchor is dragging. They do not predict when dragging is likely tocommence.

− 42 −

＝ Actual ship movement at the time of anchor dragging ＝With GPS now being commonplace, a recent study analysis shows that anchor dragging is a phenomenon thatconsists of two diﬀerent stages. This study points out that anchor dragging started before it was detectable, prior toconventional methods of dragging anchor detection today (the ﬁrst stage: dragging anchor with yaw and sway). (Note:
this is not applicable when the anchored point is precisely written down, whereby even a slight change in the ship’s
position can be grasped.)

The first stage: dragging anchor with yaw and swayWind

The yaw and sway motion of a ship during anchoring is often
compared to a “figure-of-eight” pattern. (Part “A” in the diagram to
the right shows that the anchor is not dragging.) It has been foundthat as wind pressure force begins to exceed the anchor’s holding

Anchor chain

power, the ship yaws and is pressed transversely, as shown inarea “B” in the diagram. Also, it should be relatively easy to controlA

the manoeuvrability of a ship and weigh the anchor).

The second stage: Anchor dragging caused by

B
Path of Anchor

wind pressure
Where wind pressure force gradually becomes stronger, oneside of the ship turns against the wind and is then pressed andCmoves transversely at a certain speed, as shown in area “C” in the
diagram. The conventional method of detecting anchor dragging
takes place at this stage. At this stage, it is getting difficult(more time is needed) to weigh the anchor and if weighing theanchor cannot be accomplished, it is almost impossible to start

Hull
Fig. 63

manoeuvring.

Using tracking devices that display location information such as GPS, ECDIS and RADAR, it is now easy to detectanchor dragging during the ﬁrst stage. When an anchor does drag now, in addition to the usual methods of detection
concerning dragging anchor, it is desirable that “early prediction” and “early detection” of a dragging anchor be thenorm and that “safety countermeasures are taken as early as possible”.

− 43 −

Photographs 64, 65 and 66 are actual displays of the ECDIS and RADAR when the author was on board the Pure Car
Carrier (PCC). It was possible to grasp the actual ship’s movement using the ship’s position record and the electronic
displays.

Display of ECDIS and RADAR
Using the ECDIS display, it is possible to viewthe full size of the hull by narrowing in on thedisplay range. Also, GPS tracks are shown for
approximately 60 minutes.
This helps us understand the first stage inmore detail: Dragging Anchor with Yaw and
Sway.

Photograph 64

Similarly, the RADAR range was set to 0.75
nautical miles and the track of the GPS was
set for 60 minutes.
This helps to solidify understanding of thefirst stage: Dragging Anchor with Yaw and
Sway.

Photograph 65

Because there were no other vessels atanchorage, an anchor dragging wind pressure
experiment was conducted. The hull faced
sideways to the wind direction instantly andwas pressed at a speed of 3 to 4 knots, thus
more time was required for weighing theanchor.

Photograph 66− 44 −

４−４ Wind pressure force
In order to have a grasp of the external forces that cause anchor dragging, we must have an understanding of the windpressure force. Wind pressure force can be calculated with the following “Hughes Formula”.

Hughes Formula
Ra =

1
2

×ρ× CRa × Va2 ×（A cos2 θ＋Ｂ sin2 θ）/1000（ton）
θ

Relative winddirection from bow（θ）

Length frombow to wind аpressure centre（Relative Wind Direction）
Wind speed

Va（m/sec）

θα：Wind direction from bow ［degree］

Wind pressure
force angle

Va
ρ
A
B
a
Ra

：Headwind speed ［m/sec］：Air density ［0.125 kg ・ sec /ｍ４］
：Shipʼs projected area from bow above waterline ［㎡］：Shipʼs projected area from side above waterline ［㎡］：Length from bow to wind pressure center［m］（Point of Action）：Resultant wind pressure force［kg］→ divided by 1,000 to be "ton"（Total Wind Force）

α ：Wind pressure force angle［degree］（Angle of Action）
CRa ：Wind pressure force coeﬃcient（this can be calculated
Resultant windpressure force

by the following formula）

CRa：This varies for diﬀerent ship types, as follows.
Passenger, PCC, Ctnr ：1.142−0.142cos2θ−0.367cos4θ−0.133cos6θ
General cargo ：1.325−0.050cos2θ−0.350cos4θ−0.175cos6θ
Tanker & bulk carrier ：1.200−0.083cos2θ−0.250cos4θ−0.117cos6θ

Resultant wind pressure force is proportional to the square of wind speed.

It is diﬃcult to calculate for wind pressure force at a speciﬁc time instantly when manually calculating. However, it
is easy to calculate the wind pressure force once the formula has been input into a PC. Examples for reference using
Excel are shown in Table 67.

− 45 −Wind Pressure Force Cal.：Just Reference
12
3

Relative winddirection from bow（θ）

This formula calculates the wind force of your vessel at the wind speed.
The wind force coeﬃcient in each kind of ship is calculated automatically.
Input the following data
200

（Projected area（Front）
）
（m2）
（A）

800

（Projected area（Side）
）
（m2）
（B）

5,800

（Wind Speed ）（m/s）

19.5 （Ave.Wind Speed × 1.25 or 1.50）（Kind of ship）（Passenger, PCC, Ctnr:1 General Cargo：2 Tanker, Bulker: 3）＊θLoa（m）

Input Wind Speed by below ref. data
Less than 8 m/s
Strong Wind : 8 〜 13m/sec
Storm Wind : More than 13m/sec

Length frombow to wind аpressure centre

Wind speed

Va（m/sec）

αWind pressure
force angle

1

Resultant windpressure force：Ave. Wind Speed：Ave. Wind Speed × 1.25
：Ave. Wind Speed × 1.50

RESULTS（θ）
Wind direction
from bow (deg)（Ra ）Total wind force (t)（RL）
Longitudinal(t)（RT ）Transverse(t)

（a ）
（α ）
Point of action(m) Angle of action(deg)（CRa）
Factor（Ｃ R ａ）

0

14.26

14.26

0.00

58.20

0.00

0.75

10

20.84

18.50

9.60

62.80

27.43

0.92

1

2

3

20

43.23

30.23

30.90

67.40

45.62

1.31

0.500000

0.750000

0.750000

30

80.39

40.60

69.38

72.00

59.67

1.65

0.660925

0.922400

0.87199440

118.0140.06

111.01

76.60

70.15

1.73

1.035993

1.313421

1.151506

50139.7829.83

136.56

81.20

77.68

1.58

1.387500

1.650000

1.40050060

145.9818.21

144.84

85.80

82.83

1.35

1.528709

1.732710

1.47901070

150.599.95

150.26

90.40

86.21

1.22

1.445025

1.575075

1.39083680

159.95

4.46

159.89

95.00

88.40

1.19

1.263500

1.350000

1.24950090（Impact）

165.4185.56

0.00
165.41
99.60
90.00
Wind Force on Front（θ＝０）×６, Tanker/Bulker × 4））

1.20

1.120549

1.215025

1.161670

1.060798

1.191369

1.144983

1.050000

1.200000

1.150000

Impact Force :Wind Force on Front × 5 〜 6 for PCC/CTNR/Passenger ship, × 3 〜 4 for Tanker/Bulker

Table 67

Regarding the calculating formula in the table, the following were used.

Calculation Formula in Above table
Total Wind Force

Ra = 1 × ρ × CRa x Va2 ×（A cos2 θ＋ B sin2 θ）/ 1000（ton）
2

Longitudinal Force

RL ＝ Ra × Cos α
Transverse Force

RT ＝ Ra × Sin αaPoint of Actiona ＝（0.291 ＋ 0.0023 ×θ）× Loa

α Angle of Action
α ＝｛ 1 − 0.15 ×（1 −θ /90）− 0.8 ×（1 −θ / 90）3 ｝× 90
Wind Pressure Co-eﬃciency（CRa）
1

1.142−0.142cos2θ−0.367cos4θ−0.133cos6θ（Passenger Ship / PCC / Container）

2

1.325−0.050cos2θ−0.350cos4θ−0.175cos6θ（General Cargo）

3

1.200−0.083cos2θ−0.250cos4θ−0.117cos6θ（Tanker / Bulker）

Impact Force
PCC/CTNR/Passenger Ship

Wind Pressure on Front × 6

BulkerWind Pressure on Front × 4− 46 −

４−５ Holding power created by anchor and anchor cable
Holding power created by anchor and anchor cable

H (Holding power created by anchor and anchor cable) = Ha + Hc = λ a x Waʼ + λ c x Wcʼ x
H：Holding Power Created by Anchor and Anchor cable （kgs）

Ha ：Holding Power Created by Anchor（kgs）
Hc ：Holding Power Created by Anchor cable（kgs）
Wa ：Anchor Weight in Air（kgs）
Wc ：Anchor Chain Weight per m in Air（kgs）
Wa' ：Anchor Weight in Water（kgs）＝ 0.87×Wa（kgs）
Wc' ：Anchor Chain Weight per m in Water（kgs） ＝ 0.87×Wc（kgs）
l：Minimum Required Length of Anchor cable（ｍ）

λa ：Anchor Holding Factor
λc ：Anchor Holding Factor

Anchor holding power during anchoring is the sum of “holding power by anchor” and “frictional force of anchor cablelying on the sea bottom”.
The holding factor of an anchor or anchor cable (λ a and λ c ) is diﬀerent depending on the type of anchor or typeof sea bottom. The anchor holding factor (λ a ) and anchor cable holding factor (λc ) of a JIS type or AC14 type areshown in Tables 68 and 69 respectively.

λ a：Anchor Holding Factor
Type of Anchor

Sand

Mud

Dragging
Anchor

JIS

3.5

3.2

1.5

AC14

7.0

10.6

2.0

Table 68

λ c：Anchor Chain Holding Factor
Holding

Dragging

λc

Sand

Mud

0.75

0.60

0.75 〜 1.0
Table 69

− 47 −

JIS

AC14