Mr. Pilot

Safety of Navigation in Narrow Straits

11 October 2012 - 07:51

Capt. Cahit İSTİKBAL[1]


In recent decades, increasing size of ships carrying dangerous cargoes such as crude oil and derivatives, chemicals, explosives and others;  together with increasing volume of maritime traffic, has increased the risk of catastrophic accidents. This risk realized in maritime disasters such as Atlantic Empress, Amoco Cadiz,        Torrey    Canyon    , Sea Empress and Independenta. While the risk in maritime transportation increased to a level that one single accident could cause catastrophic effect to the life, property and environment due to the huge sizes of modern vessels, the safety concerns have also increased. Within this picture, narrow waterways constitute the most vulnerable sea areas for such accidents. There are many reasons that make these areas vulnerable; dense population, close proximity of land and other traffic to be effected in case of accident, etc. This article intends to summarize the risks of navigation in narrow straits and possible ways to meet or avoid these risks.


According to Richard Goss, Professor of Maritime Economics at the      University  of    Wales    , “Perfect safety, like perfect behavior, may be attained in paradise; it cannot it can not be achieved here on earth. We must therefore aim at some acceptable level of safety”. “Absolute safety” which means “zero risk” is not an achievable goal. We can come to a conclusion that risk is something we have to accept to live with.  So what is risk, and if we can not eliminate it, what can we do with it?

                                Figure 1- The Hazard: Sharp bend in a narrow strait

According to Steve Pelecanos, vice-president of IMPA, “admitting that risk is inherent to all human activity is not fatalistic defeatism, it is accepting reality”.

Risk is a key element in marine safety philosophy, so it should be defined first. At any dictionary, risk is defined as “the source of danger”. But in marine terminology, risk is more complex than a simple definition.

                                Figure 2- The Risk: Vessel might go aground with insufficient rudder counter-effect to the currents pushing.

International Maritime Organization defines the risk as “The combination of the  frequency  and  the  severity  of  the consequence.[2]”  In this definition, “Consequence” represents “the outcome of an accident” and frequency represents “The number of occurrences per unit time”.

So we can formulate the risk as follows:


Risk =








A sharp bend in a narrow strait is a hazard. The risk in such a case is, how likely it is that a ship can not stop the turning after this sharp bend and how severe the consequences can be both for the ship and the environment if the ship goes aground. According to IMO definition again, hazard is “A potential to threaten human life, health, property or the environment.

In brief, in marine terminology, risk means a hazard that is proven as reason for accidents by the frequency and is proven intolerable by consequences.


Under the light of previous definitions, the following conclusions stand forward:

a.       We don’t have the option for a risk-free world and we have to accept risk.

b.       We can still handle the risk to diminish its consequences even though we can not eliminate it.

The second option is called as the “Risk Management”.

                                Figure 3- The Risk Management: Tug assistance and pilotage combination.

In managing the risk, there are four basic principles:

1)       Identify the hazards (What can go wrong?)

2)       Assess the risk (How likely is it and what are its consequences)

3)       Determine the control measures (Decide what is the best way to manage it)

4)       Apply and monitor the controls (Implement decision and evaluate its effectiveness)

There are many methods developed to apply these principles to organizations and to industry.  Recently IMO developed the Guidelines for Formal Safety Assessment (FSA). These guidelines were approved at the 74th Session of Maritime Safety Committee, in June 2001 and published to member governments as a circular. IMO defines the FSA as follows:

“Formal Safety Assessment  (FSA)  is  a  structured  and  systematic  methodology, aimed  at enhancing maritime safety, including protection of life, health, the marine environment and property, by using risk analysis and cost benefit assessment.” [3]

                                Figure 4- Flow chart of the IMO’s FSA Methodology

FSA aims to assist to decision-makers for their decisions to establish proper risk management tools in areas where necessary.


So far, we concentrated to define and analyze the risk in general. However, vessels navigating in a narrow channel or strait, or near harbor approaches have much more challenges to cope with, compared to a vessel navigating in the high seas.  Such sea areas generally called as “confined waters”. Following the steps in IMO’s FSA methodology, it is possible to make a safety assessment for narrow straits.

Step 1: Hazard Identification:

Navigation in a confined strait is highly dependent on shiphandling skills; while shiphandling in narrow channels is more an art form than a science and a kind of intuition is required to detect and balance the dynamic, yet often subtle, interactive forces acting on a vessel so as to maintain control over its movement[4].  Modern ships are often pose some disadvantage rather than advantage in the shiphandling field when a narrow strait is in case, because:

1.       Waterway improvements lag years behind changes in ship design and performance[5].

2.       Ship propulsion and steering systems may be designed for sea-efficiency rather than maneuvering performance[6].

3.       The general maneuvering behavior of ships in narrow straits and shallow water is known, but “actual” behavior is uncertain, especially where underkeel clearances are only a few feet (Gates, 1089).

4.       Determinations of natural changes in strait geometry are not always timely or conveniently available to vessel operators or pilots.

5.       Real-time data on environmental conditions including weather, currents, and tide and river stages are lacking[7].

Risk factors:

Hazards in a narrow strait often come along with the following risk factors[8]:

·         Physical factors

o    Strait geometry and configurations

o    Hydraulic and hydrologic conditions

o    Hydrography

o    Environmental Conditions (E.g. Currents, Wind, etc.)

·         Vessel Factors

o    Types

o    Sizes

o    Propulsion and steering systems

o    Hydrodynamics

o    Maneuvering behavior

o    Vessel status/Maintenance condition

·         Economic Factors

o    Ship scheduling

o    Cargo transfer operations

·         Transit Considerations

o    Cargoes

o    Marine traffic

o    Duration of exposure

o    Navigational aids and support systems,

o    Waterway management/Traffic systems

o    Subsystem support (Such as tugboats)

·         Potential Consequences to

o    Vessel

o    Human life

o    Environment

o    Economics

o    Property

·         Human Systems

o    Decision making

o    Suitability, qualifications and proficiency of

ü  Vessel operators

ü  Bridge team

ü  Support system personnel

o    Work environment

Restricting factors in a narrow strait:

In a narrow strait, good shiphandling is essential. But there are some factors that restrict or just obstruct ship handling. In hazard-identification process, it is necessary to have a look at some important restricting factors of ship’s maneuvering in a narrow strait:

a.       Squat: In 7 August 1992, huge cruise ship Queen Elizabeth II was outbound Vineyard Sound, Massachusetts, enroute to New York when it grounded on a shoal (charted at 12 Meters) 2.5 miles south-southeast of Cuttyhunk Island near Massachusetts.  Speed was approximately 25 knots. Damage was extensive, with 4 double-bottom tanks holed.  Repairs totaled $13.2 million and put the vessel out of service for two months. But interesting part was, the QE had a maximum draft of 9.80 meters only. So how possible she could go aground with an underkeel clearance that was more than 2 meters? An investigation was soon underway. How could the QE2 have run aground in waters known to be deep enough for her? The answer came after serious investigation. The conclusion had been drawn and it was the so-called 'squat' that was to blame. This phenomenon is created when larger vessels travel through water at higher speed. The shape and speed of the ship pushes the surrounding water away, literally digging a hole in the water for the ship. What was discovered during the QE2-investigation was that this effect was greatly increased while traveling at higher speeds, which the QE2 was doing at the moment of the grounding. The amount of water pushed away was simply larger than expected, and thereby the ship also had a lesser depth of water to sail in. Squat can simply be defined as “the sinking of ship’s hull into water due to speed in shallow water”. The ship squats in deep water as well, but it is much lesser than she does in shallow water. For instance, a container ship squats 2.5 meters in 12 meters depth, since she squats only 0.75 meters in 50 meters depth. Taking into account that many of the narrow straits has draft limitations, squat effect is there as a hazard to be aware of. But, in narrow straits there is another point of squat effect which is equally important: as the underkeel clearance is reduced, ship may lose control of the steering due to reaction between the ship and the bottom[9].

b.       Interaction between ships: Interaction between ships is an important factor in narrow straits because ships usually have to make close pass or overtake while navigating in such areas. The effect of the “faster moving water” close to a ship’s hull being less dense, besides causing ships to squat, can have other effects on ships. It can cause an interaction between two ships, so that the ships will be drawn each other, whether one ship is overtaking the other, or they are passing. (Williamson,2001, p.131)

c.        Reaction between a ship and the bottom: If a ship is navigating slowly in a channel with shallow water on one side of the ship and deeper water on the other side, then the ship will be pushed away from the shallow water towards the deeper water. But, if the ship is with high speed, then the effect will be on the contrary; the ship will be pushed towards the shallows. (Williamson, 2001, p.135, See Footnote 8)

d.       Increase in turning circle due to shallow water effect: Restricted bottom clearance in shallow water impedes the flow of water underneath the ship, causing a restricted lateral motion of the aftship. The less bottom clearance, the more build  up of water on the side that the stern moves toward and the lower the water level on the side that the ship moves away from, leading to a smaller drift angle and consequently a wider turn in shallow water[10]. Every narrow strait has not limitations in depth, but where it does, this is an important factor to take into account for shiphandler.

e.        Environmental conditions: In a narrow strait, environmental conditions are extremely important for safe navigation.  These conditions include:

§  State and height of tide.

§  Minimum under keel clearance at the turning points.

§  Wind direction and strength,

§  Current direction and strength.

§  Visibility.

§  Sea state and swell.

f.        Substandard Shipping:  Condition of a ship navigating in a narrow strait is important on many aspects. Substandard shipping is a problem of world fleet in recent years. OECD studies suggest that the substandard can undercut the reputable by 15%. Substandard shipping is often indicated with four “M”s; Metal, Machinery, Men and Management. It has been estimated that the human factor lies behind some 80% of shipping casualties.  If the ship fails in one or more of these “M”s, the navigation in a narrow strait will be extremely hazardous for her and for the environment. Effective port state control could help for the solution. In the Turkish Straits, for example, in order to improve the conditions of passing vessels, following requirements were set in Regulations which came in to force in 1994:

1.       Main and auxiliary engines shall be operational in normal condition and ready   for any-time maneuverings.

2.       Emergency generators shall be stand-by for operation at any time. Main and auxiliary steering gear, gyro compass and radar shall be operational in normal condition.

3.       The navigation bridge indicators such as RPM, rudder, and pitch shall be operational and illuminated.

4.       The whistle and navigational lights of the vessel shall be operational and navigation bridge equipment shall be complete.

5.       All communication systems primarily those that connect navigation bridge to the fore, aft, steering gear and engine control room and the alarm systems shall be operational.

6.       VHF equipment(s) shall be properly functioning.

7.       A projector and at least one good-functioning binocular shall be kept ready in the navigation bridge ready for day and night use.

8.       The windlass and its equipment shall be ready to drop both anchors and the crew for that operation shall stand-by.

9.       Vessels carrying dangerous cargo shall lower emergency wires for fire at the fore and aft sides. Other vessels shall keep a towing hawser and a heaving line ready to use at the fore and aft sides.

10.    A vessel shall not be with a trim by the aft so as to have negative effect on her ability to maneuver and steer; and no vessel shall enter to the Straits with a trim by the forward.

11.    The trim of the vessel shall be arranged as far as conditions permit so that the propeller is totally below the water-level; in case of forcing conditions the partition above the water-level shall not exceed the 5% of the total diameter of propeller.

12.    The vessel will be trimmed and loaded such that the forward of the vessel and the sea beyond shall be easily visible from the navigation bridge.

13.    Vessels shall have these Regulations and updated versions of charts of the Straits available on the navigation bridge.

14.    Qualifications of the officers and the crew of the vessels shall comply with the requirements of International Convention on Standards of Training, Certification and Watchkeeping for Seafarers (STCW-78).

g.        Current effect at the turning points: If the strait has sharp curves as it is the case in the Strait of Istanbul, particular attention should be paid to the current and/or wind effect at the turning points. In such. a case, current literally pushes the fore of the vessel and makes it very difficult for her to turn in the desired direction, or if pushing  from the aft, makes it difficult to stop turning (See figures 2 and 5)

                                Figure 5: Current effect at the narrowest part in the Strait of Istanbul: Current pushes the fore of the ship giving difficulty to alter course in to desired direction.

Step 2: Assessing the risk:

Risk in narrow straits varies according to channel dimensions, configurations, and length, hydrodynamics, commodity types and flows, vessel types, hull forms, sizes, propulsion and steering systems, vessel loading, traffic types, patterns, density, times of movement, tides etc. All of these factors are not identical at every narrow strait. A general statement can not be taken custom-made for every narrow strait. But, it gives an idea to make a strait-specific assessment and that is exactly our intention in this article.

“What can go wrong in narrow straits?” Long list above was the answer to that complicated question. The second step is “what is the likelihood of possible wrong-goings in a narrow strait and what the consequences can be?” To answer this question, we will analyze the likelihood in the      Strait  of    Istanbul    .

                                Figure 6: Reason of accidents in the Strait of Istanbul. (Based on analyze of 396 accidents between 1982-2000, Source: Turkish Maritime Pilots’ Association, )

Between 1982-2000, there were 396 accidents in the      Strait  of    Istanbul    , according to the records of Turkish Maritime Pilots’ Association. Reasons were shared as follows:

Improper Navigation 14%, Technical Failure 8%, Nature 29 %, Unknown 49 %

Records indicate that natural conditions, such as currents, wind, rain, snow etc. are the main factors for accident in the      Strait  of    Istanbul    .

The consequences of wrong-goings in a narrow strait: A catastrophic accident in a narrow strait can be disastrous, both from human life and environmental aspects. For instance, according to experts, in the case of a major tanker accident in the      Strait  of    Istanbul    , the followings may happen:

§  Thousands of people may be killed.

§  Such an accident will give irreplaceable damage to insurance, finance and production sectors, national and international level.

§  The waterway may be closed for an unpredictable period of time.

§      Black Sea countries which depend on the Straits for their vital imports will receive strong impact.

Step 3: Risk Control Options in Narrow Straits

1.       Pilotage: A pilot will be familiar with all the dangers in a narrow strait and the rules designed to ameliorate them. No one knows those places and situations that pose the most hazards than the pilots of a waterway. Pilots are most qualified, in most respects, to lay down guidelines for the safest manner in which to conduct the navigation of vessels in the area covered by their pilotage[11]. International Maritime Organization strongly recommends using pilots in narrow straits, such as the Turkish Straits[12]. IMO makes a general recommendation on pilotage in resolution A.159 (ES.IV) and strongly recommends pilotage in the straits such as Turkish Straits (Resolution A.827-19) Straits of Malacca and Singapore (Resolution A.375-10/Annex V) Torres Strait and the Great North East Channel (Resolution A.710-17) Euro-Channel and IJ-Channel (Resolution A.668-16) entrances to the Baltic Sea (Resolution A.620-15) North Sea, English Channel and Skagerrak (Resolution A.486-12). These are clear indications that IMO accepts pilotage as a major risk reducer in narrow straits and confined waters. According to the long term statistics in Turkish Straits, 85% of all accidents were done by vessels that were not using pilots. It can be presumed that pilots worth to be at the first rank in the list of risk eliminators in narrow straits.

2.       Escort Towage: In the case of technical difficulties of a vessel navigating in narrow channel, the escort tug would be a good option to put the vessel in the track again or to assist her reducing the speed.

3.       Traffic Control Systems (VTS, VTMIS, etc.): There are many available models to control and manage the traffic in narrow straits. Most common system is “Vessel Traffic Services” According to IMO definition, vessel traffic service (VTS)  is a service implemented by a competent authority, designed to improve the safety and efficiency of vessel traffic and to protect the environment. The service should have the capability to interact with the traffic and to respond to traffic situations developing in the VTS area[13]. Recent years, VTS systems proved successful in many confined sea areas including narrow straits. In the Turkish Straits, after the introduction of Vessel Traffic Regulations and Traffic Control System in 1994, number of accidents dramatically dropped.

4.       Universal AIS: The AIS is a shipboard broadcast system that acts like a transponder, operating in the VHF maritime band that is capable of handling well over 4,500 reports per minute and updates as often as every two seconds.  Display information previously available only to modern vessel traffic service operations centers could now be available to every AIS-equipped ship.  With this information, you could call any ship over VHF radiotelephone by name, rather than by "ship off my port bow" or some other imprecise means.   Or you could dial it up directly using GMDSS equipment.  Or you could send to the ship, or receive from it, short safety-related email messages. AIS is designed to improve marine safety and efficiency by providing the navigating officer and pilot with important additional navigation information; simplifying information exchange between ships and between the ship and the shore; and reducing verbal mandatory ship reporting to VTS Centers; and it has the potential to reduce overall operating costs. Within a phased-in carriage requirement program, all ships over 500 Gross Tonnage will be fitted with AIS equipment by July 2008. When fitted on all ships, there can be no doubt that AIS will enhance safety at sea, the efficiency of navigation and the protection of the marine environment.


For a captain of a ship who is navigating through narrow straits there's very little room for error. The risk is “intolerable” on many occasions. All available resources should be used and managed to minimize the risk. Briefly saying, “Human Error” and “Technical Failure” are the main reasons of accidents in the Straits. To my opinion, “use of pilot for every vessel and use of escort tug(s) for certain vessels” are essential safety measures; beside a modern VTMIS System. Eliminating the substandard ships and substandard shipping is also an important factor for reducing risks.  Following recommendations are my conclusion remarks for a safe passage through a narrow strait:

§  Vessels should be technically in good condition and manned by qualified crew. An effective regional port state control network could help to improve the conditions of passing vessels in narrow straits.

§  Vessels should use the service of a qualified pilot while passing narrow straits.

§  Vessels carrying a certain amount of dangerous cargo should be escorted by tractor tugs.

§  Traffic in the strait should be managed and monitored by an effective VTS or VTMIS system where pilots take part in the advice-giving process.

§  Vessels should take part in the reporting system.

“A superior seaman uses his superior skills to keep out of situations requiring his superior skills[14]” It is true; we all should try our best practices to prevent accidents. And I hope this paper helps in doing that.

Kucuksu,    01 October 2002



[1] Active pilot in the Strait of Istanbul, Secretary-General of Turkish Maritime Pilots’ Association, Vice President of International Maritime Pilots’ Association (IMPA)


[2] MSC/Circ.1023 “Guidelines for Formal Safety Assessment (FSA) for use in the IMO Rule-making Process “

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