RCHtF
Lab.
Technische Hoschc,.'2'
y. Scheepoù*k.
Deift
The Case of the ÑANKAIMARU
Toshio HISHIDA -(Received November 30, 1964)
The circumstances under which the disaster over took the Nankai-Maru were examined. The matter of the first concern in this case is her stability against voilence of nature. The
wind and waves which attacked on her were examined and her behaviour among them was
discussed.
As the second problem, the progress from upset to sinkingwas infered and a calculation of the time of survival was tried.
1.
Introduction
Miss Nankai-Maru returned to Mother Sea together with all of 167 persons on board.
It was at dusk of Jun. 28, 1958. She had displayed her graceful figure extremely
stream-lined in the Wakayama-Komatsushima line.
Fig. 1. 1. Captain, wireless, wheel house, 2. Officers, 3. Ist. dass .pass.,4, 6, 8, 11. 2nd.
class pass., 5. Offlcers,toilets, 7. Crews, 9. Cargo, 10. Engine room, 12.Promenade
deck, 13. Upper deck, 14. Steering engine.
On the day, she had. to unmoor in Komatsushima for her third service in spite of the
warnings by the meteorological observatories that the wind force would grow strong and
be about '20 rn/sec or more at dusk. Although, at about half past 5 p.m. when she left the
harbour, the wind force had been already 10 rn/sec or more southerly in Wakayama and
Sumoto, it was not so strong in the Bay of Komatsushima which was moderately sheltered from southerly winds. However she prefered the course in stoimy weather, rounding the
north side of Nushima (island). When she got off the harbour area and headed for NE 3/4 E (the true course being about 480), she should suffer the direct wind and waves fairly
growni This is infered from the fact that her actual speed up to disaster was only 12.8 knots in spite of her cruising speed being 13.5 knots.
128 -t.
,&a
'1q 'o
'.
Komatsushima , Awaji Island Xê
(N 34-08.8 'E 1:34--46 T. HIsRIDA Ku Channel Fig. 2. StOr V WakayamaAbout one hour later from departure, or at 18:30, the Shipping Company received the wireless informing an emergency and, in succession, at 18:32 or 33 they caught SOS. On the other hand, the wrist watches and the ship chronometer, which were landed afterward,
had stopped at 32-33 minitues past 6. This tells that she would sink within a single
minute.
The most interesting problems in maritime disastrics in our case will be how she met with the disaster and how sank. Unfortunately, all the crews and passengers on board have
passed away. No one speaks about the circumstances. However, the problems will be perhaps related to ship stability and reserve of buoyancy. Let us examine the disaster
in these points of view.
2.
Estimation of the Loading Condition and the
Stability Curve of the Ship at the Disaster.
The loading condition at departure for the 3rd. service on the day is calculated in
Ap-pendix I, based on the examination of the Maritime Safety Headquarters in Kobe. From that the corresponding particulars are obtained as shown in Table 1, in which they are compared with those at the unloaded departure condition. The significant differences
between them are in trim and KG. These affect the stability curve. The stability curve
amended, regarding to KG, from the one at the unloaded departure condition which
is easily obtainable from the stability calculation sheets of the shipbuilding basin, is given
by the solid line (GZ1) in Fig. 3. But the discrepancy in trim is ignored for less effect.
0.2
The Case of the NANKAI-MARU 129
Tablet
i
,
0.4,1
-10 30 40 O (deg) Fig. 3.The differences in weights and their distributions at departure and atdisaster are also insignificant, because the consumable goods spent would be negligibly
small.
Thus, we take the solid curvein Fig. 3 for the one at disaster.
3.
Estimation of the Wind and Waves
It is supposed that she would be capsized by the actions of wind or gust and waves,
and sank in inflow of water. Then, at the first step, we must examinethe circumstances of the capsize.
(a)
Estimation of Wind For.
For example, the fuel consumption being 120 litters per hour.
Departure condition Designed unloaded
Item in this case departure condition
Displacement (tons) Equivalent draft (m) Block coeft. 401.05 2.21 0.475 401.66 2.21 0.475 Fore draft (m) 1.57 1.37 Aft draft (m) 2.79 2.97
Mean draft (ni) 2.17 2.17
Trim (m) 1.22 1.60
KG (ni) 3.44 3.29
GM (m) 0.65 0.80
GZ (m)
GZ1: Under upper deck.
OE6 GZ2: Including superstructuresand deck-houses.
/
GZ3: Including only superstructureabove
W 401 tons promemade deck. F"
The change of wind force on the afternoon is shown ¡n Fig. 4, inwhich the forces
based on the recordings in the weather stations themselves and the informations sent from ships at sea are plofted against time t.
The data from the sources which are exposed to sea winds indicate that the mean
wind velocity in the Ku channel would be about 20 rn/sec SSE or S.
As to the gustiness of the wind velocity, none were informed. However, we have the data" analysed from the recordings in the meteorological observatories or stations
for so many years, in which the gustiness at a sea near a land is 1.4-1.5 in winds blowing into lows or fronts. This means the maximum velocity being about 30 rn/sec.
These velocities coincide well with the ones judged by the Maritime Meteorological Observatory in Kobe, the mean being 17-20 and the maximum' 25-30 rn/sec.
55W 8 16- 7
14-12- 6 8 9 - Litte sheltered.i
6' I/
SSE 6-v-j
-t
SE 4- 3 13 SSE I ;_ S S Sheltered. 0 Lighthnuse of Hinnmisaki. O .' « Muroto, X Shiono-misaki, Ø Weather station of Tokushima, s--
SSW sSw -- / S SE/
E,SSw
°S Ai i',
SSE./ __-r
ESE SE sE 14 15 Time (o'clock) S a as Fig. 4. (b) Estimation of Waves.Fig. 5 is obtained for the wave height, where the heights measured at the lighthouses of Muroto and Shionomisaki are annexed for comparison. Unfortunately, we could not
S a
fr
SSW./
SSW s SSw SSW 16 17 18A Wind recorder at Nusima. £ Ship. The Afurika-maru.
The Kyomei.marU. M Other ships, è Fishermen neighbouring.
as
sf
- -5E"% .SW tSSW'i t:
'(s
SSW SW 19 20 130 T. HISHIDA 24- 20-18-Wakayama. Letters in the figure
a
3
The Case of ¡he NANKAI-MARU
dA Information from ship, 'nearHinomisaki.
V
I, ..o
« " near Nushima,D Light house of Hinomisaki.
Shionomisaki.
t
Muroto;X Judged by the Mart ime Meteorolo
-gical Observatory in Kobe.
2.
1'
%t i
18
131
have any reliable information of the waves at the time of disaster.
For this, it must be estimated by another way, for example, by the Pierson method2
predicting waves. In the method waves are predicted according to the time of duration,
the fetch and the strength of wind there.
As the change of the wind force is fairly rapid as seen in Fig. 4, we set two stages,
the one from i to 4 p.m. and the other since 4. The waves at a half past 6p.m. are predicted
after the assumptions that the waves would grow from 3 to 4 or 5 in the wave scale, by
Table 2. 1/lo heighest wave height (m) Significant wave height (m)
Mean height (m)
Mean wave period (sec)
Mean wave length (m)
Mean wave speed (misec)
Mean steepness
Range of period of Sig. wave (sec)
Direction of waves 5.1 4.0 2.5 5.8 50 8.5 0.05 2.5-9.4 SSE
T. HISHIDA
the wind of 16 rn/sec in the meanspeed, during the former time interval, and that the mean
during the latter interval was 20 rn/sec.
The results thus predicted are listed in Table 2, and the change of the wave height, of
the significant wave as well as the1/10 highest wave, up to the time of disaster, is described
¡n Fig. 5. It is thought that these heights are in fairly good agreement with the observed
values which usually correspond to
the significant or the 1/10
highest. Whether thePierson method will suit this sea area or not, will be certified in Appendix II.
4. Remarks in Application of the Method of Stability Criterion
Whether she could be capsized by such a wind and waves as above or not, will be able
to judge by the method of stability criterion. However, in application, there are some
things to be mentioned, going back to the ground upon which the method has been
cons-tructed.
The critical value of the stability criterion was decided statistically from a series
of the work ratio, of the reserve of dynamical stability versus the work done by both the
standard wind and waves, in cases of a great number of ships either sunken or navigating
safely for a long time.
Effect of other actions besides the wind and waves, that is, steering, shifting of weights, incoming of seas and so on, each of all being in a usual magnitude in a statistical
meaning which almost the ships, regardless .of sunken or not, will suffer, is contained
implicitly within the critical value decided.
Therefore, even when she suffered these effects, they must not be taken in con-sideration, if their magnitudes are not especially unusual.
The steering of 6° aport, which was found later in dock, has little effect. As regards the other actions, it is not considered that they were so unusual. Moreover, only the wind and waves are already capable enough to make her capsize, as explained later.
In examination of her stability, we shall take the actual wind of the above strength, considering its direction at the same time, in place of 19 rn/sec wind abeam which is the standard one for coasting vessels.
As the gustiness, 1.5 is chosen in place of /i in the standard.
Waves, also, of the above strength, in irregular character and in the actual
on-coming direction, are taken into account.
The maximum amplitude among rollings caused by 50 irregular waves in succession likewise in the standard, is taken in calculation.
5.
EstimatIon of the Rolling Amplitude.
She laid at full length horizontally on the sea bottom about 40 rn deep, at a distance
of about 2.5 sea miles westery from the west side of Nushima, heeling 103° to the port and heading to NE, according to a diver's inspection.
This direction of heading may point out her course just before the disaster, for her
course before the steering of 6° aport also had been in the direction of 48°, nearly NE. The
The Case of the NANKAI-MARU 133 might have yawed away and back, on gòing to sink after steered, but this is too compli-cated to have been materialized. Again, the other traces worthy are a hollow over the starboard side wall of the steering engine room and the broken doors of the aft passenger room which were struck by waves. They will perhaps indicate that she had suffered the waves quarterly by starboard.
If the couse just before the disaster is assumed to have been NE, the angle (a) between
her heading and the direction of wave propagation which was NNW, is probably 700.
Her speed (u) at that time also is not definitely known.
Simultaneously weassume once that it was 12.8 knots.
However the influences of the deviations of a or u will be discussed later
Now, the energy density spectrum corresponding to the waves in Table 2 is given by the curve ,2 in Fig. 6, where, is an amplitude of an individual wave and 1/f its period or f the frequency. This wave system is not yet fully developed. Therefore, the r2-curve
is cut down sharply from f = 0.125 to 0.1062) as shown in the same figure, where the
0.1 02 0.3 0.4
f(1 /sec)
Fig. 6.
latter is equal to 0.125 x a correction factor (in this case, being
0.85) and the former,0.125, has been determined from the wind force and its duration.
On the other hand, it is estimated from the data in our laboratory that the magnification factor for the rolling among regular waves will be such as shown in Fig. 7 in which the
.4 1.2 Fig. 7. 1.0 12 1.4 1.6 1.8 Fig. 8. 1.4 1.6 1.8
abscissa w = Tj T, T, being the rolling period of the ship (9.65 seconds, estimated) and T, the period of encounter. Hence, the response amplitude operator (A) is determined
(Fig. 8).
T0 is given by the following formula,
T, = 1/(fs)
(1)
In this, s=u oes a/a (u=her speed of advance and
=the wave length). Thus T0 arecalculated for several f.
Reading A corresponding to each T,/T0 from Fig. 8, A2 is
plotted against f in Fig. 6. In this procedure, though A ought to vary with f, it is replaced uniformly by the mean A of Table 2 because of lacking in the data of relationship between
Aandf.
a
(deg.
The Case of the NANKAI-MARU 135
In Fig. 6, we have 4 curves of A2 for a =90°, 800, 70° and 60°. f values correspond-ing to the maxima of A2-curves are in a reversed order with magnitude of a. Drawing
r2A2-curves, each area surrounded by one of them and the f-axis gives the cumulative energy (R) of rolling.
The rolling amplitude O is proportional to /ï.
Here, O
is described in Fig. 9, a and u being varied. A correction bas been
given to the amplitude, for the inclining moment of waves oncoming in the oblique direc-. tion of a is reduced to sin a-times apporxiniately as much as the same waves doing abeamand consequently the amplitude is reduced in the same proportion.
?
2 4 6 8 lo 12 14
u(knos)
Fig. 9.
From the figure, we see that. O ¡s ranging from 13° to 16° or more for a probable
a of 70°. If the speed is 12.8 knots,
again takes 13°-16° for a of several degreesaround 70°. But, when she was going near disaster, her speed would be considerably reduc-ed by the growing wind and waves. Therefore, the most probable value of O will be
150.
In the next calculation, however, three kinds of O, 13°, 15° and 17°, will be used.
6.
Stability Criterion
The stability criteria were calculated, taking the meanabsolute velocity of the wind = 20 m/sec, the absolute velocity of the gust =25-30 rn/sec.
Some of the results are
(u=12.8 kn) (a = 90°) .l?o 1.0 4. :%...
4°'....
Angle of inflow =41.60° = 31° 25 26 27 28 29 30Gust speed (misec)
Fig. 10.
Fig. 11.
(a=7O°)
27 28 29
Gust speed (misec)
136 T. HISIUDA
C
C
The Caoe of the NANKAI-MARI) 137
Fig. 12. Fig. 13.
,
.9 0.8/
I-/
/
/
E/
.E 0.6 0.4 70 80 90 100 110I.)
« (deg.) Passenger ship, Corgo ship, Fishing vessel. WrnaFig. 14.
with the wind moment ratio represented by the solid 1ine3 in Fig. 13. The ratio means the wind moment acting obliquely divided by that acting abeam (a = 900). Also, the wind velocity effective to the moment, of course, is the one relative to the moving ship.
Fig. 14 is an example of drawings in calculation of the criteria.
The critical value of the criterion is unity.
If the angle of inflow is 41.6°, at which the lower edges of the side windows of the compartments on the upper deck touch the water surface, the criteria sometimes break
down unity for the gust of about 30 rn/sec (Fig. 12). It does not immediately mean a capsize,
but rather a critical state.
However, she bad got the doors of the compartments open just before the capsize
at least on the port side which was leeward. In this case, the angle of inflòw is 31°, and the corresponding criteria decrease considerably as shown by the dotted lines in Figs.
10v-12. Evidently the probability of capsize gets very laige.
From the foregoing, it is supposed that when she had a hard sailing in the strong gale of 20 rn/sec or more and corresponding waves, although she trid to avoid themto
quartering by steering aport and then to avert a dangerous lurch, she would be at last
capsized by a sudden gust.
The effect of the tidal current on the waves can be neglected as its speed was only
0.5 knot.
As evident from the above example, we had better take the angle of inflow at which the
water surface cuts the lowest edge of the entrance coaming' than the one at which it cuts the lowest edge of the side windows, because it is very hard to hope all the entrances closed for such a small passenger coaster.
7.
Influence of Wrong with the Engine upon the
Stability Criterion.
In our case, a considarable problem does not appear. The detail is omitted for want
of space. 138 t-0.4 0.3 02 T. MisabA (vr-90 Ci.'. Wind speed 30 ;n.'scc 2g 25 s C o cv, 0.1 20
1
-0.102
6.5 1(Y 20 il(dcg.) 30 40 41.6The Case of the NANKAI-MARL/ 139
8.
Inference of the Behaviour after Capsize
The known things about the disaster arc that she sent SOS at 18:32 or 33, the wrist
wat-ches and the ship chronometer (in the wheel house) landed stopped at 32-33 minutes
past 6, the side wall of the steering engine room and the doors of the aft passenger room suffered panting of waves, and she laid horizontally at the sea bottom heeling 103° to the port.
We infer her behaviour.
She is flooded more or less in the compartments, the doors on which have
been broken by waves. The passages on decks are also soursed.
The stability is moderately reduced and it sometimes causes lurches. She feels
dangerous and sends SOS. She will be capsized to the port by a sudden gust just after
SOS.
It is considered from the stability curve (GZJ of Fig. 3 that her heeling just after
capsized will be about 48°. In the figure the dotted line (GZ2) stands for the stability
(measured in experiments) when the superstructures above the upper deck are assumed to
be watertight.
Though the supersturctures are not watertight in the norm qualified by the regula-tions (the stability curve in this case is shown by the solid line, GZ1), it may be teated as tight within a short time after capsize because time is required to inflow of water. Thus she will be thrown in the ravine of GZ2-curve.
As some of doors on the port side (leeward) of the compartments between the decks, upper and promenade, will be opened for emergency, the compartments will be
flooded soon after capsize. But those on the promenade deck have no door on the side
but only side windows, the leak of water through which is much more gradual.
Therefore, though the stability curve gets near GZ3, the heeling angle will little alter during sinking.
The water will flow into the spaces under the upper deck from the openings on it, (passenger rooms, hold, engine space, and crew's quarters). The inflow may be regarded as a flow beyond a weir in hydraulics.
As the center of the water flowed in is near the vertical through the oentre of gravity of
the ship itself, the change of heeling due to the water will be little. The trim also will rem2in almost unaltered because the flooding covers the fore, aft and middle-part of the
ship.
On sinking, the direction of the ship centre line may be turned by the waves. As
the stabilities, both transverse and longitwIinl, are moderately weekened by the flooding, the periods of rolling and pitching will be more increased than synchronism with that of
waves. So they are, such a ship in waves has a tendency to be parallel with the wave
Going on sinking ñeary parallel to the water surface by the continued flowing
of water, she will vanish under water within a single minute after capsize.
The time of survival, (according to a trial calculation), is 60-70 seconds. In Fig. 15 the residue of the buoyancy which must be counteracted by the water in order to have her sink up to a water line (the horizontal scale indicating the number of water lines i m apárt),
70 60 50
140
l-30
10 600 400 200 o o .0 e -140 T. HISrnDA O i 2 3 4 5Water line no. or Sinkage (m)
Fig. 15.
and the time from capsize to the water line are plotted. The displacement at capsize will be more or less larger than 401 tons not containing flooded water, for she has been flooded to some extent before capsize. However the increment is neglected simply, for the water on the deck will fall down at the large heeling and the amount of water in compartments is unknown though it will be not so much.
The total amount of the residual buoyancy is neary 650 tons.
If the water of 650 tons or more floods, she submerges beneath the water surface.
Here, a void space occupied by the air corresponding to the volume of about 400 m3 must
be left in the hull under the upper deck. However, before submergence, when she sinks up to the 2k-water line, all the openings on the upper deck sink under the water surface.
Almost all the air contained in the hull at this stage, the volume of which is about 600 n?, will remain enclosed hence force. Therefore the volume of about 200 n3 which must be
displaced hereafter by the water is obtained by compressing the enclosed air.
The time required to each i m-sinkage is very long at the initial stage and decreases rapidly with the progress of sinking. The time of survival, from capsize up to a total sinking, is almost occupied by the time required to the ist. I m-sinkage. This is due to the increase in number as well as in the area of the openings, through which the water
flows, in accompaning with the increasing sinkage.
In calculating the time of survival, the inertia of the ship has been neglected because
the ist. i m-sinkage takes a moderately long time, and the following stages do not play
such significant parts as control the time regardless of taking into account of inertia or not. As the coefficient in the rate of flow beyond a weir, Rehbock, Oki or Omori's formula
was used. That for an orifice, when an opening is covered by water is assumed to be 0.65. In Fig. 15, two cases, where the initial heel is assumed as 48° aport and then as 60°, are shown.
The Case of the NANKAJ-MARU 141
(h) In the hull submerged, there remains the air on the starboard side under the
upper deck. As, on the other hand, the superstructures have been all flooded, the heeling aport will increase to about 90°. Going to sink, approximately horizontally, she will set on the oozy bottom of 40 m deep. She sustains little dam2ge on either the bow or the stern.
The time during sinking is calculated to be about 20 seconds, in which the water rs-tance proportinal to the square of the sinking speed is taken into account.
The volume of the air enclosed in the hull just before setting on the bottom hasbeen
compressed to about 200 m3 (at neary 4.4 atm), if the change was adiabatic. The centre of
this air lies on the vertical through the centre of gravity of the ship itself at a heeing of
neary 110°, (Fig. 16), in which the mean permeability of the spaces containing the air was
assumed to be 0.85, but the shifting of weights caused by the greatheel was not taken in.
Fig. 16.
8. Acknowledgement
.
The author expresses his heartful thanks to Mr. S. Kurita, the then chief of the
polic-ing branch in the 5th. Maritime Safety Headquarters, for his preparation of a minute protocol, and to Mr. T. Gohara, the then chief of the policing section in the same Head-quarters, for his kind presentation of the observational data of waves.
References
JSRA: "Researches on the stability of ships among waves", 1957.
W.J.Pierson and others: 'Practical method for observing and forecasting ocean waves", 1955.
M.Kinoshita and others: On the wind effçct on the maneuverability of a bonito and tunny
G being abaft Ø positive.
The weight of the spare anchor is contained in the light weight.
The gravel ballast of 15 to,s in weight also is contained in thelight weight.
A test of Pierson's method predicting waves.
We shall test how closely the method may suit to the sea of the disaster.
Observations of waves at the sea were worked out by the Hydrographic Division
in the last decade of March, 1958, about two months after the disaster.
The observed values are compared with those predicted by the method in Table 3. The former was obtained by reading a scale with the eye along which the wave surface
went up and down. In calculating the latter theassumptions had been made thit the mean wind velocity had been 7m/sec (the actual, 6-8 m/sec), the time of duration 5 hours or more (fully developed) and the fetch 13 km (that is, from the narrowest part of the Naruto Strait to the point of observation).
Items Weight (:on)I GØ (m) KG (m)
Light weight 334.13 0.82 3.54
Crews and effects (28 persons) 2.80
- 4.78
5.22 Passengers, special Ist. (8 persons) 0.48-14.-
6.90ist. (28 persons) 1.68
- 8.55
6.85 ist. ( 3 persons) 0.18- 3.75
6.80 2nd. (20 persons) 1.20 -11.40 4.85 2nd. (25 persons) 1.50 11.45 4.80 2nd. ( 5 persons) 0.30 16.65 4.90 2nd. (40 persons) 2.40- 9.-
2.85 2nd. (10 persons) 0.60 14.60 2.90 provisions 0.25 5.25 4.64Fuel No.1 F.O.T. 2.57
- 0.75
0.59No.2 F.O.T. 2.36 3.45 0.59 Fresh water 6.08 6.17 0.50 Fresh water 0.50
- 1.45
8.10 Sanitary Water 0.51- 2.15
8.10 Cargoes, Checked 0.05 9.10 3.85 Compressor 0.40 9.- 1.80 Steel Wire 2.90 8.- 1.50 Stores 3.- 1.68 3.92 Mail . 0.05 6.65 4.52Fluid in engine room 1.92 0.79 4.90
Ballast', F.P.T.
12.15 -21.34 2.66A.P.T. 23.04 21.34 3.11
TOTAL 401.05 1.05' 3.44
142 T. HISHIDA
APPENDIX
Calculation table of the load condition at
departure for the 3rd. service on the day
The Case of the NANKAI-MARU 143
Table 3
We see in Table 3 the both series of wave characteristics are in a good agreement.
The observed ones of such lower means as the total mean or the mean of significant waves,
are heigher than those predicted. This often appears in observational data with the eye and will be oeused by the fact that they often overlook lower waves.
An analysis on the power spectrum of another set of data made by the Division also
proves an agreement.
Hence, it may be concluded that the predictionmethod is approximately applicable to the sea without any correctionfor locality.
Observed Estimated
Mean wave height (m) 0.26 0.21
Significant wave height (m) 0.36 0.33
1/10 heighest wave height (m) 0.42 0.42
Mean periód (sec) 2.2 1.9
Mean wave length (m) 5.0 4.9
Mean wave speed (m/sec) 2.5 2.6
