Aids to Navigation Improvement to Optimize Ship Navigation

Abstract

Aids to navigation are established to assist vessels in the navigation with special importance in narrow channels, rivers, or areas with special dangers to navigation. Whether the design of the aids to navigation (AtoN) system is optimum depends on ship positioning, which is affected by several factors: waterway geometry, metocean conditions, design ship, pilotage, and the AtoN themselves, being a crucial part of the design of a waterway.

Optimizing the type of signals and the distance between them allows, not only for safer navigation, but to expand the limits of the waterway by assisting larger vessels to move safely along the waterway, as well as to minimize dredging costs and dredging area by optimizing simultaneously the design of both: the waterway and the Aids to Navigation. An equilibrium is required between the investment and maintenance costs, and therefore, this combined assessment and optimization allows to finally get both, technically and economically feasible projects without detriments on the safety of the waterway.

The use of fast time manoeuvring models and Real Time Simulations allows to check and verify the optimization and improvements in the waterway and in the aids to navigation system. Real Time Simulators and manoeuvring sessions are the perfect place for all stakeholders (Port Authorities, Pilots, Harbour Masters, waterway designers, shipowners, …) to interact, discuss, evaluate, and agree on the best option for the improvement of navigation conditions while preserving the safety of the operations, as it allows to verify the effectiveness of the improvements before implementing them in the reality.

1 Introduction

AtoN provide information on ships positioning along the waterway, increasing the safety of the navigation by showing the safe area for ships to navigate by using visual or instrumental references, either physical or virtual, PPUs… Nevertheless, the availability of AtoN implies a certain error positioning of the ship in a waterway, which varies (increases or decreases) depending on the type of aid, the local conditions (mainly related to visibility such as rain or fog), and the distance between consecutive signals.

It is possible to improve the AtoN to optimize the navigation. This is done by minimizing the positioning error, allowing an increase in ship dimensions while keeping the fairway width constant, always maintaining the safety of the manoeuvres. Nevertheless, it is important to understand that there is a point in which by increasing the AtoN, the effective area of ships is not further reduced. An optimum design point is to be found, or at least, an adequate one.

Two examples of the optimization or improvement of the Aids to Navigation to allow the access of larger vessels or reduce dredging costs are presented. For the assessment of the optimization in navigation conditions by improving aids to navigation, both Fast Time manoeuvring models and Real Time Manoeuvring Simulators have been used, as those are the most adequate tools to analyse in detail manoeuvring conditions of ships for waterways design.

The importance of assessing together the waterway design with the Aids to Navigation, and their optimization to reduce dredging costs or increase ship sizes on already existing areas, without reducing the safety of the maritime operations, is presented. The use of fast time manoeuvring models and Real Time Simulations, to check and verify the optimization and improvements in the waterway and in the navigation conditions, is of essence in these assessments as it allows to verify the effectiveness of the modifications before implementing them in reality. Real Time Simulators and manoeuvring sessions are the perfect place for all stakeholders (Port Authorities, Pilots, Harbour Masters, waterway designers, shipowners, …) to interact, discuss, evaluate, and agree on the best option for the improvement of navigation conditions while preserving the safety of the operations.

2 Aton Positioning Errors

All available guidelines and recommendations for waterway design, national or international, consider that aids to navigation, which are placed for the safety of the manoeuvres by allowing ships to position themselves along waterways, produce a certain type of positioning error on the ships, and therefore this is to be considered for the waterway design.

AtoN might be fixed or floating. And this aspect is to be considered as well. Fixed systems have no error on their position, but floating buoys are subjected to external forces which swing the buoy at anchor, introducing a position error of the buoy itself.

For the purpose of this paper, the focus will be only on the positioning error that AtoN introduce on the ship navigation due to the type and number of the signals, but not on the intrinsic error of the buoys.

Positioning errors increase as the distance between buoys increases, and at reduced distances as reference, the next pair of buoys is to be considered, as some 200 m before reaching a pair of buoys, the Captain or Pilot is already considering the following pair as a reference. The following image shows how a pair of buoys concentrates the tracks of ships, reducing the required width to almost half of the width from previous buoy, which is only on one side of the track (Fig. 1).

Fig. 1.

Ships tracks along a waterway. Reduced dispersion at the pair of buoys

National and international guidelines and recommendations consider these positioning errors on the fairway design. The following tables and figures show different references that can be applied for waterway design, with distinct levels of detail (Tables 1, 2 and Fig. 2):

Table 1. Additional width due to positioning errors. PIANC 121 «Harbour Approach Channels Design»

Table 2. Additional width due to positioning errors. ROM3.1-99 (Spanish national recommendation)

Fig. 2.

Positioning errors derived from a pair of buoys. “Design standard for fairway in next generation”

When several positioning references are available in the same area, such a pair of buoys and leading lines, the one which provides the minimum error in each section is to be considered. Based on the recommendations on the calculation of positioning errors of the above references, the following errors are obtained for a waterway (Fig. 3):

Fig. 3.

Visual errors for different sections of a waterway

The area occupied by the ships in a waterway does not depend only on the AtoN, but other factors, such as wind, current, UKC, … also affect the required width. Conclusions are therefore derived based on all factors together. To evaluate the importance of AtoN visual error on the global width occupied by the ships the following image is presented, where this relation for both straight and curved section is shown (Fig. 4):

Fig. 4.

Visual errors dispersion vs Mean occupied width

This graph shows a stronger relation for straight sections than for bends, which makes sense, as positioning the ship along a bend, and therefore the occupied area, is strongly linked to the response time and the human factor of the Pilot or Captain, and not the visual positioning when in a transitory phase.

3 Optimization by Fast Time Manoeuvre Simulations

Fast Time Manoeuvre Simulators allow to perform a large number of manoeuvres in a short time combining many different parameters. A methodology to evaluate AtoN improvements in large areas of waterways is established by means of performing randomized manoeuvre simulations with autopilot models combined with the statistical determination of the safe manoeuvring area as per PIANC 121.

Based on preliminary assessments, and as described in Sect. 2, the positioning error along a waterway due to the AtoN can be estimated.

With these positioning errors Fast Time Manoeuvre simulations are performed in a randomized way, in which the waypoints of the track-keeping autopilot are randomly varied, linked to a mean and standard deviation of the positioning errors in each stretch of the waterway.

Considering AtoN improvements, in the most critical areas identified, the positioning error can be reduced and therefore the randomized manoeuvres are repeated by reducing the dispersion in waypoints.

The comparison of the statistically determined safe navigable areas with and without AtoN improvements allows to preliminarily evaluate whether larger ships can be accommodated in already existing areas, or if an optimization of the required dredging areas is possible to allow safe navigation in narrow areas by increasing the positioning performance of the ships by improved AtoN.

Fast Time Manoeuvring Models allow to define the most critical areas for navigation, with larger potential for improvement in long waterways or rivers. These critical areas can be later evaluated in detail using Real Time Manoeuvre Simulators, where AtoN improvements are incorporated. Pilots and Captains performing the manoeuvres introduce the human factor, which is the missing factor when using Fast Time autopilot models.

4 Optimization by Using Real Time Manoeuvre Simulators

Real Time Manoeuvre Simulators are the best tool to assess the improvements of the AtoN. They allow to determine whether the modifications allow larger vessels to safely navigate through the fairway, as well as to verify the potential dredging optimizations due to an improvement of the AtoN.

Real Time Simulators involve the participation of expert Captains and Pilots which perform the manoeuvres in a virtual environment including all features and aids required for navigation, allowing therefore Captains and Pilots to evaluate AtoN improvement before implementing modifications. Most important, incorporating the human factor (perception and decision making) absent in the Fast Time Manoeuvring Models.

The following images show a narrow channel in the Real Time Simulator with the AtoN that allow large ships to be safely handled (Figs. 5, 6 and 7):

Fig. 5.

Real Time Simulation view of an approach to a narrow channel, leading lights, and buoys

Fig. 6.

Real Time Simulation visual image of a bulkcarrier approaching during night-time

Fig. 7.

Real Time Simulation view of the departure of a bulkcarrier with the AtoN that mark channel limits

The next example shows a study conducted in phases to determine both the feasibility and the optimized dredging requirements to allow New-Panamax container vessels in an existing terminal, in a fairway initially designed for smaller ships. In this project a statistical assessment of manoeuvres based on PIANC WG121 report was performed to finally determine the feasibility of the manoeuvre strategy and the dredging requirements in combination with the AtoN design. Local conditions in the area are mild, which allows for a larger optimization of the waterway in combination with the AtoN. Initially the project consisted of the access of New-Panamax containerships of 366.0 m in length and 48.2 m in beam with restricted draught along a 1.5 nautical miles narrow channel leading to a swinging basin in front of the terminal, and with a predefined AtoN and compulsory use of PPU (Fig. 8).

Fig. 8.

Channel layout for the New Panamax containership assessment

Years later, the requirement to assess Maxi New Panamax containerships of 369.0 m in length and 52.1 m in beam with restricted draught was considered. During this assessment, the same methodology was applied, and it was found that, at the basin entrance, more space was required for the New Panamax container vessel compared to the Maxi New Panamax (with larger beam) for the same weather conditions and tug formation.

There was only one difference that justified the reduced area for the larger ships, and it consisted of the differences in the AtoN of the channel at the basin entrance, moreover when in this narrow channel buoys are the main visual reference to position the vessel during the transit. Considering the different results of navigable areas, it was concluded that buoys V-57 (in front of R-58) and V-59 are beneficial to reduce the required navigable areas by allowing the Pilot to position the vessel with a very low error (Fig. 9).

Fig. 9.

Layout and required widths during the Maxi New Panamax containership assessment

Additionally, it was concluded that installing a new buoy in the south area of the basin entrance, paired with V-59, could reduce, or even avoid, the interference identified in this area for departures starboard side alongside (sailing astern) to help the vessel to position precisely and maintain a distance to this shallow area. This solution could avoid dredging this area to allow safe departures of this vessel under the strategy mentioned (Fig. 10).

Fig. 10.

Additional proposed AtoN to potentially reduce dredging requirements

5 Conclusions

This paper presents the importance of jointly assessing the waterway design with the Aids to Navigation system. This combined assessment allows to optimize navigable areas and therefore reduce dredging costs or increase ship sizes acceptable on already existing areas, without reducing the safety of the maritime operations.

The use of Fast Time and Real Time Manoeuvre Simulators allows to check and verify the optimization and improvements in the waterway and in the navigation conditions. These tools are of essence in these type of assessments as they allow to verify the effectiveness of the modifications before implementing them in reality. Unlike with Fast Time models, Real Time Simulations increase the accuracy and detail as the human factor (perception and decision making) is directly included in the assessment.

Real Time Simulators and manoeuvring sessions are the perfect place for all stakeholders (Port Authorities, Pilots, Harbour Masters, waterway designers, shipowners, …) to interact, discuss, evaluate, and agree on the best option for the improvement of navigation conditions while preserving the safety of the operations.