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1 INTRODUCTION
Currently, the second generation intact stability
criteria are being discussed at the International
Maritime Organization (IMO) (IMO 2015, 2018). The
criteria include a new concept, “operational measures
(OMs)” (IMO 2019), for ensuring safety of ships at sea
during ship operations. The implementation of the
OMs has never been addressed in the history of intact
stability criteria. Therefore, the rationality and
practicality of the OMs in terms of implementation
during actual ship operation must be carefully
investigated. To facilitate discussion of the OMs,
Hashimoto et al. presented a set of pioneering case
studies on the OMs using a voyage simulation for an
ocean-going container ship for a variety of scenarios
(Hashimoto et al. 2017). This voyage simulation was
developed based on a weather routing model
(Kobayashi et al. 2011, Kobayashi et al. 2015).
Regarding the decision making for voyage routing
during an actual voyage, captains consider fuel
consumption, voyage distance, and safety factors,
such as rolling and pitching effects on cargos
(Koshimizu & Ishizuka 1994). A weather routing
service, which considers above points, is commonly
used in actual navigation (Fujii et al. 2017). This
means that it is reasonable to develop a simulation
tool for the investigation of OMs, which simulates
practical navigation routes correctly, based on a
weather routing model. However, captains decide a
voyage route not only with the reference to a route
recommended by weather routing service but also the
safety margin especially when the rough weather is
expected. Reliable voyage simulations need to
simulate ship navigation routes with sufficient
similarity to actual routes decided, by accounting for
the preferred safety margin based on the weather
conditions. Therefore, the route decision-making
criterion of captains taking into account of the safety
margin needs to be clarified.
Comparison of Master’s Route Selection Criteria of
V
ehicle Carriers in North Pacific and North Atlantic
U
sing Satellite AIS and Ocean Wave Data
M. Fujii
Marine Technical College, Japan agency of Maritime Education and Training for Seafarers, Ashiya, Japan
H
. Hashimoto
Kobe Ocean
-Bottom Exploration Center, Kobe University, Kobe, Japan
Y
. Taniguchi
Graduate School of Maritime Sciences, Kobe University, Kobe, Japan
ABSTRACT: The operational measures in which a ship needs to avoid specified areas to escape ship stability
failures were discussed at the International Maritime Organization as a part of the second generation intact
stability criteria. It is necessary that the rationality and practicality of the operational measures are carefully
investigated. In this study, master’s route decision-making criteria of trans-ocean vehicle carriers have been
clarified by comparing the Pacific and the Atlantic data, derived from Satellite AIS and ocean wave data.
Features of voyage routes of each ocean were discussed, followed by analysis of the encountered wave
direction and height during a voyage. The master’s route selection criteria were defined by comparing the
probability densities of the wave heights that occurred in the navigable area and that of the actual encountered
waves. The navigation hours in a stormy area were also studied.
http://www.transn
av.eu
the
International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 14
Number 1
March 2020
DOI:
10.12716/1001.14.01.16
138
The wave criterion of navigators has been defined
by questionnaires and route planning experiments by
seafarers in the past (Hayashi & Ishida 2004).
However, it was derived from a limited amount of
data covering only the North Pacific and could be
significantly different from the universal criterion.
Another research discussed the relationship between
route selection and encountered wave height,
combined with satellite AIS data and ocean wave data
supplied by the National Centres for Environmental
Prediction (NCEP) (available at http://www.
cdc.noaa.gov/) (Fujii et al. 2019, Fujii et al. 2017). This
research demonstrated that the encountered wave
height during the voyage can be obtained as objective
data by combining the ship’s position obtained from
the satellite AIS data and the weather information at
the corresponding position and time. However, these
researches were focused on the container carrier or a
limited number of vehicle carriers only trans-Pacific.
In this study, the master’s route decision-making
criteria aimed at developing a reliable voyage
simulation for discussion of OMs has been clarified
by comparing the actual voyages of the trans-Pacific
and the Atlantic. Firstly, the features of voyage routes
of each ocean were discussed by using the ship’s
position from the Satellite AIS data. Secondly, the
encountered wave direction and height during a
voyage were analysed by data combined with satellite
AIS data and ocean wave data. Thirdly, the master’s
route selection criteria were obtained by comparing
the probability densities of wave heights that
occurred in the navigable area with that of the actual
encountered waves. Finally, the calculation result of
navigation time, which is duration hours between
entering and exiting a stormy area, was determined.
2 DETAILS OF THE ANALYSIS DATA
Currently, the automatic identification system (AIS)
equipment is required to be installed on all ships,
including the vehicle carriers over 300 GT, on
international voyages. The signal is continuously
transmitting during a voyage in the ocean. In this
study, the ship’s position data from the AIS, for a
large number of vehicle carriers, were collected and
analysed. The AIS data were purchased from
exactEarth (https://www.exactearth.com), and
collected by several satellites from December 2015 to
February 2016. Figure 1 shows the received position
of the AIS signal by the satellites in the purchased
data. Nowadays, with the improvement in the AIS
service, and increase in the number of satellites, the
quality of data is becoming better year by year. The
purchased data included a large number of received
AIS data, as shown in Figure 1.
Figure 1. Received position of AIS signal by the satellites
This study is focused on the masters judgment in
a rough sea, especially the Pacific Ocean and the
Atlantic Ocean in winter. Therefore, the AIS data for
analysis was picked up from the purchased data
which contained the worldwide data. Analysis data
for the Pacific Ocean was picked up from the received
data between latitude 0 °N to 70 °N and longitude 100
°E to 100 °W, and for the Atlantic Ocean between
latitude 10 °N to 70 °N and longitude 0 °E to 80 °W.
For exclusion of error data in the AIS ship position,
the speed between neighbouring positions was
calculated from the position and received time. If the
speed was greater than the speed limit (24.7 kn), the
corresponding data were omitted as error data (Fujii
et al. 2017). In addition, voyages that were not
received within 24 hours were excluded from the
analysis due to poor reliability. Secondly, the trans-
ocean voyages were picked up from the data in the
designated area. The definitional lines were set on
both the eastern and western sides of the North
Pacific for the definition of the term “trans-Pacific”, as
shown in Figure 2. Similarly, the lines were set for the
North Atlantic in reference to the major routes (Vettor
& Soares 2015). Here, east-bound voyage means that a
ship departs from westerly of the west side
definitional line to easterly of the east side definitional
line, west-bond voyage is opposite.
Figure 2. Definitional line for trans-ocean in the (a) Pacific
and the (b) Atlantic
From these steps, the analysis voyages were
picked up, the details of which are shown in Table 1.
The number of ships was 174 in the Pacific Ocean and
124 in the Atlantic Ocean. The number of voyages was
198 in the Atlantic Ocean and 257(1.3 times more) in
the Pacific Ocean. However, this number is more
significant than the previous research (Fujii et al.
2017) and sufficient to analyse.
Table 1. Number of analysed ships and voyages
_______________________________________________
Number Number of Voyages
of ships East-bound West-bound Total
_______________________________________________
Pacific Ocean 174 151 106 257
Atlantic Ocean 124 108 90 198
_______________________________________________
The AIS data includes a ships position, the time of
transition, and more. However, the wave height at
that point is not included. Therefore, weather data has
to be imported from a different source while
analysing the height and direction of the encountered
wave. In this study, the oceanic data corresponding to
the ship’s position during the navigation was
obtained from the ocean wave data supplied by the
National Centers for Environmental Prediction
(NCEP). The encountered wave height and direction
are defined by combining the received ship’s position
data and the oceanic data. The ships position every 3