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1 INTRODUCTION
Restricted water operations (e.g. rivers and ports)
require an autonomous boat to be capable of fast
response to avoid obstacles while maintaining its
course. A well-designed autonomous boat offers
solutions that contribute towards safer waterways
and higher economic yields. Such activities include
periodically patrolling the river for reconnaissance,
environmental monitoring, and transportation of
humans and goods. Currently, autonomous boats rely
heavily on several hardware devices such as global
positioning systems (GPS) [1], distance sensors [2],
radars [3], and cameras [4]. While such hardwares are
common for the construction of an autonomous boat,
several problems exist such as the high price of radar,
GPS multi-pathing which resulted due to high-
density vegetations, and expensive high-quality
cameras which also require frequent maintenance.
This leaves the autonomous boat with the use of
distance sensors, which may offer a robust [5] and
low-cost solution to assist in navigation and obstacle
avoidance tasks, driven by a well-trained artificial
intelligence system.
Fundamentally, an autonomous boat/autonomous
surface vehicle is a subclass of mobile robots.
Conceptually, a mobile robot consists of a control
system, sensors (distance sensors, light sensors, vision
sensors), and actuators (motors, servos) to respond to
its surrounding [6]. An autonomous mobile robot is
capable of sensing its surroundings and acting upon
Neuroevolutionary Autonomous Surface Vehicle
Simulation in Restricted Waters
A.F. Ayob, N.I. Jalal, M.H. Hassri, S.A. Rahman & S. Jamaludin
University of Malaysia, Terengganu, Malaysia
ABSTRACT: Safe, accurate, and predictable autonomous systems in marine vehicles are paramount. An
understanding of an intelligent system fitted inside a ship is critical to ensure an autonomous ship is safe to be
operated. Although the use of artificial intelligence in the design of the road-based vehicle has arrived at the
self-driving level, there exists a significant gap within the research of autonomous ship to operate in restricted
water (riverine and ports). Hence, this article shall discuss the relevant works of literature to set a preliminary
guiding principle for the design of an autonomous ship. We present a simple illustrative framework as a
starting point for ship designers to begin working in a simulated environment, which can be used as a
foundation before the physical autonomous-ships are constructed and tested in a real-world situation. The
framework consists of a virtual 3D environment and a surface vehicle with distance sensors, controlled by a
neuroevolution-based autonomous piloting system. In this work, two scenarios will be presented: navigation in
restricted waters, and obstacle avoidance capability of an autonomous ship. Results show that the resulting
autonomous surface vehicle (ASV) is also capable of performing obstacle avoidance in the test track, albeit not
being trained to do so in the training track. The work demonstrated in this paper is useful to the ship designers
and can be extended for scenario-based planning for autonomous ship design.
http://www.transnav.eu
the International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 14
Number 4
December 2020
DOI: 10.12716/1001.14.04.11
866
the surrounding based on its mission definition. In
the field of maritime technology, there are vast
potential use-cases for autonomous surface vehicle
robots. While the primary mission of an autonomous
surface vehicle varies (e.g. reconnaissance, patrol,
intercept, environmental monitoring), several
common themes constitute as the sub-tasks of such
autonomous surface vehicles such as manoeuvring
[7][10], cruise control [11][14] and collision
avoidance [9], [10], [15].
In this paper, we present a concise state of the art
5-years review on the application of
neuroevolutionary methods in maritime technology,
particularly in the ship design discipline. A
fundamental example using state-of-the-art tool is
presented, where an autonomous surface vehicle
(ASV) or an agent is shown to interact with an
uncertain environment (dynamic water response due
to buoyancy, uneven riverbank terrain, potential
collision situation with other floating objects) while
avoiding any collision situation through automated
steering and thruster control.
In this work, autonomous control of a surface
vehicle is designed where an agent demonstrates
river navigation while avoiding obstacles in a
dynamic environment, using artificial neural network
(ANN), as shown in Figure 1. The desirable steering
and throttle control are achieved using ANN in which
the weight and biases of the ANN are found using the
unsupervised machine learning method. The
unsupervised machine learning method used in this
work is reinforcement learning, in which an agent is
rewarded based on the attainment of accumulated
checkpoints number in each simulation run. This is
achieved using Genetic Algorithm (GA), in which for
every simulation runs, the best designs shall be
retained to evolve in a search for the best design until
an arbitrary generation number achieved.
We evaluate the performance of the
neuroevolutionary ship control using computer
simulation, focusing on the ship’s capability to follow
the river path, while at the same time avoiding
collision with other floating objects such as weather
buoys.
The main contribution of this paper is the state-of-
the-art review of neuroevolutionary ship control and
the experimental results of an autonomous surface
vehicle operating in a highly dynamic environment.
The review of literature shall be elaborated in the next
section, followed by the methodology, experimental
results, discussion, and conclusion.
Figure 1. Neuroevolutionary ship manoeuvring control.
2 RELATED WORKS
Neuroevolutionary-based works in the literature
concerning ship steering or piloting remains lacking
as compared with autonomous cars. This is due to the
high volume of production of cars compared with
ships within consumer markets. Based on the
keyword search (Elsevier’s ScienceDirect) on research
and review articles of ‘autonomous car’ versus
‘autonomous ship’, a stark difference (50%
differences) in terms of volumes of literature can be
seen, as shown in Figure 2. Such preliminary search
has demonstrated a considerable research gap within
this discipline and requires attention as the industry
is moving toward the 4
th
Industrial Revolution.
Figure 2. Numbers of publications between Autonomous
Cars versus Autonomous Ships spanning across 20 years.
In this section, the related works available in the
literature concerning autonomous ship shall be
reported. The subsection shall be grouped into three
major topics, which are the application of
neuroevolution (evolutionary-based artificial neural
networks), the study of ship motion of autonomous
ships, and finally the safety-related works in
autonomous ship developments.
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2.1 Neuroevolutionary Works in Ship Steering/Piloting
Autonomous ship berthing study was presented by
[16], [17] where backpropagation (BP) neural network
was incorporated to study the propeller revolution
controller under gust wind disturbances. Through the
use of a feedforward neural network, the study was
extended in [18], [19], [20] to justify the network’s
real-time response within the context of safe distance.
Similar work using ANN controller for automatic
berthing in different ports was presented in [21] and
[22]. A neuroevolutionary neural network
constructed via the use of evolutionary algorithms
was proposed by [23] to perform the task of crossing
or overtaking the ship-based COLREGs rules. This
ensures the ship to manoeuvre safely and efficiently.
Within the same context, [24] compared the use of
direct and indirect encoding for neuroevolutionary-
based ship handling, which uncovered the ability of
indirect encoding to generalize and react to new
states without bias towards the learned patterns,
however noting that direct encoding method may
adapt faster to new sudden changes.
Path following is crucial to maintain the safe
cruise of a ship. The works presented in [25]
demonstrated the capability of a vessel to return the
course-keeping path of a ship on the routes efficiently
using the neuroevolutionary method. Reported by
[26], such an algorithm is independent enough to find
the most effective path by considering a list of
possible solutions.
It can be noted that most of the works presented in
the field of neuroevolutionary ship piloting are
within the scope of simulation works [27]. Ship
simulation is a very powerful method to represent
real-life situations, to train ship operators and
intelligent algorithms while at the same time
examining typical scenarios in real-world situations
[28].
2.2 Motion Study of Autonomous Ships
One of the challenging aspects of control system
development in marine discipline is the highly non-
linear motion of ships, compared with road-based
vehicles. [7] demonstrated the use of artificial
intelligence to steer ships in completing manoeuvring
tasks autonomously. A hybrid of fuzzy logic and
artificial neural network (ANN) to perform autopilot
ship navigation was demonstrated in the work of
[8], while [9] proposed the use of a recursive neural
network to perform tactical circles and zig-zag
motions. An innovative offshore autonomous rescue
vessel was introduced in the work of [11], [12] to
assist large ships in the search-and-rescue mission.
Radial basis function (RBF) neural network was
incorporated by [13] to approximate the unknown
non-linear terms of the non-linear ship course control
system. Via the use of similar techniques, [14]
demonstrated an approach to simulate and control
the ship’s motion which caters to environmental
disturbances. [29] recommended the use of recursive
neural networks (RNN) due to its flexibility in
counter-measuring ship dynamics where they give
useful perspectives for solving the problems in
control theory as well as applications in marine
systems.
In visual perception systems for autonomous
ships, [30] analyzed four artificial intelligent
algorithms and deep learning frameworks on the case
of object detection and tracking, namely; K-Nearest
Neighbor (K-NN), Artificial Neural Network (ANN),
Convolutional Neural Network (CNN) and Deep
Convolutional Neural Network (DCNN). In view of
automatic ship navigation systems with collision
avoidance, [31] proposed the use of potential field
method in terms of its effectiveness and practical
applications. Presented by [32], a Neural Network
Allocation (NNA) was used to provide the
transformation between the desirable generalized
forces as input and the individual thruster command
for the output.
2.3 Safety-Related Works
Convention on the International Regulations for
Preventing Collisions at Sea (COLREGs) is essential
to apply for the manned and unmanned vessel. To
comply with COLREGs rules, [10] presented the
application of neuroevolutionary methods in vessel
overtaking, head-on, and crossing scenarios using
artificial potential field (APF). However, [33] argued
that COLREGs regulation might fail in some instances
when both of the ships decide to take the same
decision, which may lead to ship collision. Therefore
it is suggested that any two vessels; (1) should not be
overtaking when there exists a crossing vessel, and (2)
an overtaking can be done by a faster vessel when
there is no crossing vessel in the area of proximity
[23].
A complete collision avoidance system should
consider certain factors (e.g. ship types, traffic status,
weather, and navigation technologies) [34]. Therefore,
to improve the collision avoidance system, [35]
proposed a reward function as the main component
of Concise Deep Reinforcement Learning Obstacle
Avoidance (CDRLOA) to act as a feedback data to the
system that evaluates the system performance of the
control behaviour at one scalar signal. [36] proposed
the dynamic predictive guidance technique to
address collision avoidance. It is agreed upon that
collision avoidance should meet the following
optimal rules; collision avoidance’s safety and
network availability, and the shortest navigation
distance during collision avoidance [37].
3 NEUROEVOLUTIONARY-BASED SHIP
STEERING/PILOTING
In this section, the methodology for
neuroevolutionary-based ship steering control shall
be presented. The basic concepts of genetic algorithm
shall be discussed, followed by the description of
agents (autonomous surface vehicle, ASV) and finally
the description of both the training track and testing
track incorporated in this work.
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3.1 Description of Neuroevolutionary-based Ship
Steering Control
An artificial neural network is considered as an
individual in a population generated by Evolutionary
Algorithms (EA) such as Genetic Algorithms (GA).
Each ANN can vary in terms of its structures, or its
weights and biases, which are incorporated into each
of the individual agents within an environment. In
this work, a Conventional Neuroevolution (CNE) is
incorporated, in which the sets of weights inside of a
fixed-structure ANN are evolved using GA [38] [39]
[40]. Such an environment which is being utilized as
a platform to investigate the response of the agent can
be set up in two ways, whether in a physical
environment or virtual simulations. The response of
the agents (e.g. distance to a potential collision, the
velocity of agents, hydrostatic/hydrodynamic
performance, distance to a target, current position of
the agent) can be used as the input (objective
functions, variables, constraints) for the EA, in which
assisting in providing for the next generation of the
population.
The pseudo-code of the CNE-based
neuroevolution case study for an autonomous mobile
robot operating on a water surface can be observed in
Algorithm 1 below. In this case study, the structure of
the ANN is fixed with input with the size of 10
neurons (9 distance sensor inputs and one velocity
input), a hidden layer with the size of 3 neurons, and
an output layer with the size of 2 neurons (turning
angle coefficient, thruster coefficient). Using the fixed
structure of the ANN, an initial set of weights and
biases are generated randomly which are assigned to
each of the agents (P(g=1)). Upon receiving the
neurons, the agent shall complete its task to maximize
the number of checkpoints (reward) by autonomously
piloting itself within a challenging test track. In a
situation where the agent collided with the riverbank
of the track, the agent shall be discarded (penalty) for
that generation (g). The following generation shall
continue where the offspring (Pc(g)) are generated
from the best agent from the previous generation
until the stopping criteria (e.g. number generations)
of the GA is achieved.
Algorithm 1. Pseudo-code for the genetic algorithm in the
neuroevolution case study
1 g = 1;
2 initialize P(g=1);
3 while isNotTerminated() do
4 evaluateFitness P((g));
5 sortFitnes P((g));
6 P(g) = selectIndividual(P(g));
7 P(g) = crossOver(P(g));
8 P(g) = mutation(P(g));
9 Pc(g) =selectParents(P(g));
10 P(g) = Pc(g); // Children population became the
parents for the next generation.
11 g = g + 1;
12 end
The experiment can be described as a highly non-
linear constrained optimization explained as below:
Objective function: Maximization of the number of
checkpoints f(x) = f(x1, , x10), where variable x1 to x9
is the array of distance measured from the riverbank
to the body of ASV, and variable x10 is the velocity of
the ASV during the time of measurement. Each
member of the population aims to maximize the
number of checkpoints achieved given a prescribed
time in seconds.
Constraint: A boolean data of {0,1} condition in
which the body of the ship should not touch the
riverbank or any floating object on the water. If the
body of the ship collided, the boolean would be set as
{1} which deemed unfit and discarded from the
remaining population of the agents, whereas {0}
means the agent is fit in which the fitness shall be
recorded for further evaluation of the next generation
run.
3.2 Description of Agents (ASV)
Autonomous Surface Vehicle (ASV) is a sub-
classification of Autonomous Mobile Robot, which
operates on the water surface. In this work, the ASV
is modelled using typical dimensions of working-
class Hydrographic Surveying ASV available in the
market [41], shown in Figure 3 and detailed in Table
1. In this work, the ASV is equipped with an array of
9 distance sensors with an interval of 20
o
, located
from the perpendicular of port-side to the starboard,
as shown in Figure 4.
The simulations conducted in this work
incorporated the commercial mesh-based physics
modelling codes [42] to model the ASV buoyancy
force (Equation (1)) and hydrodynamic force
(Equation (2)) in real-time. The simulation
environment is created within the Unity physics
engine, which suitable for fast physics modelling
(utilizing C# programming language) in the
preliminary design stage. In this work, the ASV shall
only rely on the input gathered from the distance
sensors and its velocity to decide its value of the
thruster coefficient and its rudder angle coefficient.
Figure 3. A typical working-class Hydrographic Surveying
ASV.
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Figure 4. An array of 9 distance sensors with an interval of
20 degrees is incorporated in the ASV.
Table 1. Principal particulars of a working-class
hydrographic surveying ASV used in this work
_______________________________________________
Particulars Dimension
_______________________________________________
Length 2.4 m
Beam 1.0 m
Draft 0.3 m
Weight 500 kg
Top speed 7 knots
Number of sensors 9 distance sensors
_______________________________________________
B
F gV
=
(1)
where,
FB : Buoyant force in N
: Fluid density in kg/m
3
V : Displaced body of fluid in m
3
g : Gravity constant, 9.81 m/s
2
2
D
D
cA
F

=
(2)
where,
FD : Drag force in N
cD : Drag coefficient
: Fluid density in kg/m
3
v : Velocity of ship in m/s
A : Surface area underwater in m
2
.
3.3 Description of Tracks (Training and Testing)
The training tracks incorporated in the simulation are
designed to mimic a very tight and challenging
restricted water scenario, as shown in Figure 5. The
training track consists of several characteristics, such
as:
1 one straight cruise
2 four sharp U-turns
3 one sharp 90
o
corner
4 the width of the riverbank is 10m
5 the dimension of the training track is 60m width
and 100m length
Figure 5. Training track shown from the Top-view, with the
‘checkpoints’ highlighted.
The testing track incorporated in the simulation is
a larger restricted water environment, e.g. an inland
water transport scenario, as shown in Figure 6.
Surrounded by typical objects in ports (buildings,
boats, weather buoys, and deck), the testing track
differs in terms of the size of the river with additional
obstacles to test the generalization capability of the
resulting ANN model. The training track can be
summarized as below:
1 three straight cruises
2 six sharp U-turns
3 two sharp 90
o
corners
4 the width of the riverbank is 20m
5 the dimension of the training track is 130m width
and 140m length
Figure 6. Testing track shown from the Perspective-view,
with the buoys and boats floating on the water to represent
obstacles.
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4 RESULTS AND DISCUSSIONS
In this section, the results that demonstrate
neuroevolutionary-based ship steering control shall
be presented. The manoeuvring characteristics of the
best agent shall be discussed concerning the training
track, followed by the observation of the obstacle
avoidance capability shown in the testing track.
4.1 Training Track Autonomous Manoeuvre
The autonomous manoeuvre of the ASV within the
training track is shown in Figure 7. It can be observed
that the ASV was able to negotiate turns successfully
using the CNE-based ANN. With respect to the
manoeuvring characteristics, three sharp corner
manoeuvres on the North-East of the training track is
highlighted in Figure 8 and highlighted in green
colour, together with its respective zone 1, 2 and 3.
As the ASV cruising from the bottom right (South-
West) of the training track, it can be understood that
the positive angle values of the rudder angle
represent the right turn, while the negative rudder
angle value represents the left turn. In this
experiment, as the ASV cruise via the assistance of
distance sensor (input), the ANN model evaluated
the sensor input to produce the best throttle
percentage and the rudder angle values, as shown in
Figure 9.
It can be observed in Figure 8, accompanied by
Figure 9, as the ASV enters Zone 1, the rudder tends
to turn the ASV to the right to follow the U-turn
curve to the right. The same pattern can be observed
in zone 3. While manoeuvring against zone 2, the
ASV heads to the left to comply with the left U-turn.
In all three zones, it can be observed that the throttle
and velocity value spikes up and down significantly
each time an aggressive manoeuvre is being executed,
which is a desired characteristic for a CNE-based
ANN model.
Figure 7. Overall autonomous manoeuvre at the training
track with the ASV’s path highlighted in black colour.
Figure 8. Autonomous sharp corner manoeuvre,
highlighted in green colour, with the zones labelled as ‘1’,
‘2’ and ‘3.
Figure 9. Rudder angle, throttle, and velocity responses
while negotiating with sharp corners as highlighted in
green colour.
4.2 Test Track Autonomous Manoeuvre
In the second experiment, the same ANN model
trained in Section A previously was incorporated to
investigate the capability of the model to generalize
the manoeuvring characteristics in an unfamiliar
surrounding using a test track. The top-view of the
test track (Figure 6) is presented in Figure 10,
depicting the successful autonomous manoeuvre of
the ASV using the ANN model. In this section, an
additional challenge vis-à-vis the training track is
incorporated, where six weather buoys were located
on the U-turns and sharp turns, together with two
boats and one deck situated on the North-East of the
training track.
Depicted in Figure 11, two zones were shown;
zone 1 for the boats and deck obstacle, while zone 2 is
for the weather buoy obstacle. It can be observed that
within both zones, two quick manoeuvres to the right
were observed where the ANN is preventing the ASV
from colliding with the boats and weather buoy by
performing quick rudder turn to the negative angle. It
can also be observed that the throttle and velocity
values significantly dropped each time an aggressive
871
manoeuvre is being executed. It is shown in Figure 12
that the ASV is experiencing steady control of the
rudder and speed in between the two zones depicting
that no unsteady manoeuvre is being performed in a
straight direction cruise.
Figure 10. Overall autonomous manoeuvre at the test track
with the ASV’s path highlighted in black colour.
Figure 11. Autonomous obstacle avoidance manoeuvre,
highlighted in green colour.
Figure 12. Rudder angle, throttle, and velocity responses
while negotiating with an obstacle. Obstacle avoidance is
highlighted in green colour.
4.3 Discussions: Comparative Handling Characteristics
between Human and Autonomous System
The performance of the trained ANN model as
evaluated in Section A and Section B has indicated
that the ASV is capable of performing safe
autonomous cruising, while at the same time
avoiding obstacles. Such findings are further
strengthened with the observation that the ASV is
competent to perform safe navigation in an
unfamiliar setting, as evaluated in Section B. While
such capability is very desirable in the realm of
control, it can be hypothesized that such ASV is
capable of performing better than a human operator.
Taking into account that the ASV is equipped with
nine distance sensors (Figure 4), the data of human-
controlled vessel navigating the training track is
recorded (Figure 13) to compare the efficiency of the
autonomous system between both human and the
ASV.
As depicted in Figure 14, a 50m straight-line
cruising operation was captured for 10 seconds are
compared between a human operator and the ASV. It
can be observed that a human operator who relies on
visual perception are more relaxed during the
straight-line course-keeping operation. Whereas, for
an autonomous system equipped with nine distance
sensors, the ASV actively measures the safe distance,
which in turn beneficial for active obstacle avoidance.
In real life operation, such an autonomous system
might perform abrupt adjustments to maintain its
distance from dangers/obstacles, therefore sacrificing
the comfort of the passengers.
A 90-degree manoeuvre performance comparison
between a human operator and the ASV is shown in
Figure 15. It can be observed that as the vessel made a
90-degree right turn (positive angle), the human
operator carefully adjusted the response of the rudder
accordingly, which resulted in a more relaxed
cornering manoeuvre. As of the ANN model, in order
to compensate with the probability to drift during
cornering manoeuvre, the autonomous system can be
seen as attempting to actively controlling its steering
response to maintain its distance to the vertical bank
of the river.
The comparative assessment discussed above
between a human operator, and the autonomous
system has raised a discussion with regard to the
element of accuracy bias and comfort in vessel
handling. For a human operator, comfort factor in
handling is very important to maintain longer
endurance of work; however, for an autonomous
system, accuracy is more important to reduce the
probability of hitting an obstacle as trained in the
experimental setup. It can be recommended that such
an element of bias and comfort can serve as the
potential works in the future.
872
Figure 13. Straight Line Manoeuvre Human Operator
view.
Figure 14. Straight Line Manoeuvre - rudder angle
comparison between a Human Operator and Autonomous
System.
Figure 15. 90-Degree Manoeuvre - rudder angle
comparison between a Human Operator and Autonomous
System.
5 CONCLUSIONS
Presented in this work are the state-of-the-art review
and experimental analysis of the use of
neuroevolutionary methods in ship design discipline,
particularly within the scope of autonomous handling
scenarios. Although autonomous vehicles have been
progressing rapidly for the land-based vehicles, the
research for self-driving in restricted waters (riverine
and ports) still possess a significant gap despite its
economic and safety impacts. In this work, an
illustrative example has been presented using a
simplified ship model in a restricted water scenario
(vertical riverbank) which reveals that the
preliminary neuroevolutionary model is not only
good for navigation in restricted water but also
capable for avoiding obstacle within the proximity of
the distance sensors. Using the end-to-end
unsupervised reinforcement learning, the artificial
neural network can predict the best steering angle
and throttle responses while avoiding collision with
other floating objects and riverbanks. Additionally,
the handling performance of the ship has been
compared between a human operator and the
autonomous system (ANN model) The future works
may include the consideration of comfort factor in
ship handling within the ANN training to ensure that
the ASV is not only capable of performing a safe
manoeuvre operation, but also comfortable handling
for human passengers.
ACKNOWLEDGEMENTS
The work presented in this research article is funded by
Universiti Malaysia Terengganu (Research Intensified
Grant Scheme, RIGS, Grant Number: 55192/12) under the
theme of Technology & Engineering (Infrastructure and
Transportation).
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