Safety and Security at Sea

D S Bist

• Publisher: Routledge
• Year: 2013
• ISBN:
  9781136078217
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Geography
• Index: Geography

Safety and Security at Sea is concerned with the safe operation of ships and consequently with preventing errors and oversights. This book contributes to safety where it is most effective - right at the site of work, on board the ship itself. It is here, indisputably, that it will prevent accidents and save lives. It translates theory into practice besides covering several new and current topics. This book is aimed at every deck officer - at every rank and on all ships. The book also attends to other manifest needs and discusses piracy, stowaways, management of crew on board and several other new and current topics in the interest of safety.All deck officers will find, when preparing for professional examinations, that the area which the oral section of these examinations at any level (Class One, Two or Three) cover - safety - is the one in which this book specialises. It will be an invaluable aid in passing these exams. By discussing essential details in every part of a voyage, parts that form different subjects in the theoretical section, it becomes an excellent reference book for them. In addition, it will also asist the staff of shipping companies in compiling ship operation manuals.This book includes the advice of various notices from the Marine Safety Agency and of guidelines from the International Maritime Organisation. It explains their requirements - International safety management code, emergency pollution control plans and others.In order to deal with ship board work thoroughly, this book takes an entire voyage into account. That is the reason for the sequence of its chapters to correspond to the progress of an actual voyage. The book begins with a ship embarking on a voyage and, in succession, conveys its message in a comfortable language. The last chapter leaves the reader at the beginning of another, but a safer, voyage.A summary is included at the end of each chapter.

Part one Preparation

1 Understanding the vessel

DOI: 10.4324/9780080516523-1

When a ship embarks on a voyage it is expected that all on board will fulfil their duties irrespective of whether they have just become part of the crew or they have been on board for a long time. This demands a complete understanding of the peculiarities of the given vessel: an apparently inconsequential lack of understanding at an inappropriate time is capable of leading a ship into difficulties.

When an accident is investigated, hindsight generally reveals the cause and suggests ways in which it may have been avoided. Sometimes it turns out that all that was necessary to avert the danger was a firm push at the correct moment on a simple control button. However, there is no single magical button that can prevent all dangers. Any control or switch, such as the emergency engine stop, the general alarm or the steering changeover switch, may be the one to avert danger on a given occasion, if used in time. This is because every accident has a point of no return, beyond which it changes from a possibility to a certainty. Only foresight brings an awareness of the right time and the correct action. It comes with a good understanding of equipment, controls and the characteristics of the vessel. Foresight does not guarantee immunity from accidents but it goes a long way to preventing them.

Familiarity with a vessel is easily attainable. The process begins with the hand-over instructions from the officer being relieved. Information that is necessary for immediate use and for emergency duties must take precedence, but it is necessary to become familiar with other controls and equipment in the following priority order:

1. Navigation
2. Safety
3. Cargo and ballast work
4. Efficient running of ship

Navigation is controlled by steering and propulsion, and familiarization appropriately begins with these.

1.1 Steering system

Proper understanding of the exact procedure for changing from automatic pilot to hand steering and of the workings of all controls in the system is a prerequisite for any navigational watch. Confidence in their operation, as well as developing with their regular use, comes from knowledge of the principles on which the system works.

An electrohydraulic system uses electrical signals to control a hydraulic mechanism to position the rudder. The steering stand on the bridge provides the electrical signals, and hydraulic pumps in the steering machinery supply the power. Usually a set of two pumps is available for use, either together for added reliability and quicker response at critical times, or individually. An electric motor drives a rotary displacement pump continuously in the same direction while signals from the bridge, converted to mechanical movements, determine the way in which the mineral oil acts. In some makes of machinery the signals control the movement of a plate inside the pump which reverses the suction and discharge of the pump when it moves from one side to the other, but allows neither when in mid-position. In others the rotary pump is pushed out of plane with the drive shaft to one side or the other to begin the flow of oil in one or other (opposite) path, or both remain in plane to give no transmission of oil. The fact that at this point the electrical signal from the bridge changes to a mechanical action to control the direction in which the oil pressure acts and hence the direction in which the rudder turns, allows the installation of a mechanical emergency steering system at this location. This easily and instantly takes over with the simple transfer of a locking pin and enables operation of the rudder from the steering gear room if the bridge system fails.

When the steering wheel on the bridge is turned, this angular movement is converted to an electrical signal which travels to the steering gear. There it changes to a proportional mechanical movement and starts the flow of oil from one hydraulic cylinder to another. The hydraulic ram of the cylinder receiving the pumped oil rotates the rudderstock to the desired side while the other ram, which is also connected to the stock, moves back into its cylinder from which the pump is withdrawing oil. As the rudder turns, another lever attached to the stock reduces the amount of mechanical displacement to control the flow of oil and eventually nullifies it when the rudder is at the required angle. There is no displacement of the control rod and hence no flow of oil when the rudder remains at the angle dictated by the steering control at the bridge.

On the bridge, steering signals originate from either the autopilot or the hand operated controls. A selector switch indicates the method in current use and it usually has three positions:

1. Follow-up
2. Non-follow-up
3. Automatic

1.1.1 Follow-up hand steering

Use of the helm or wheel is termed the follow-up hand steering mode because the rudder angle follows the steering wheel as it turns to one side or the other. If the helm turns to starboard so that the wheel indicator shows 25°, then this angle is converted to an electrical current which is applied to the steering gear where a proportional mechanical movement commences to pump oil in the correct direction to turn the rudder until it comes to rest at an angle of 25° to starboard.

In this mode, the rudder continues to follow-up the bridge wheel angle. Follow-up is the preferred method to use because it follows helm orders more accurately, but if it malfunctions, then the non-follow-up mode still allows steering by hand.

1.1.2 Non-follow-up hand steering

This is generally done using a spring-loaded lever or switch, and is called Non-follow-up because as long as the lever is pushed to one side of its mid-position, port or starboard, it continues to generate an electrical signal to turn the rudder to that side. When it is released it springs back to mid-position and the rudder stops turning remaining in the acquired position.

To bring the rudder to say 15° to port, the helmsman must press and hold the switch to port and release it just before the desired position is reached so that the rudder comes to a stop close to 15° to port. To bring the rudder back to amidships the switch must be pressed to starboard and released a few degrees before the turning rudder comes to amidships so that it stops near that position.

With a little practice it is possible to follow helm orders closely. Athough not as accurate as the follow-up mode, it is always available if the bridge wheel is not. Checking the non-follow-up system is an integral part of the obligatory testing of the steering gear.

1.1.3 Automatic pilot

An autopilot maintains a course by electronically reading the difference between its course selector line and ship's head and generating correcting steering signals. When first installed it needs initial adjustment to the steering qualities and characteristics of the particular vessel. To adapt to deadweight, speed, trim and weather, which are changeable, the device comes with certain controls. They may have various names given to them by different manufacturers, but whatever they are called, basically they provide three adjustments.

The initial rudder angle controls the amount of rudder applied when a vessel begins to deviate from the set course or changes the direction of swing. When a vessel is heavier more effort is needed (and hence more rudder angle) to turn. Consequently, more deadweight requires a higher setting. This control is active only when the ship initially goes off course.

Counter rudder varies the amount of rudder that an autopilot gives to counteract a swing by taking the angular speed of turn into account. It opposes the movement continuously as long as the ship continues to swing, unlike initial rudder, which acts only initially.

The yaw or weather adjustment alters sensitivity when maintaining a constant heading in order to avoid continuous rudder movements and undue stress on the steering gear in rough seas and in swell. It varies the angle by which a vessel can veer off the desired course before activating a correction.

A few versions may also have a damping control which, instead of delaying action according to the allowed angle of movement, may introduce an adjustable time delay before correcting a yaw. Some makes may have an additional provision to control weather helm when steering a set course. This makes an allowance for the prevailing environmental conditions and simply alters course by an amount corresponding to the setting.

In very bad weather hand steering gives the best control of heading and the least load on the steering gear.

1.1.4 Change from autopilot to hand steering

A simple twist of a selector switch changes steering control from automatic to hand follow-up, or non-follow-up if the helm is malfunctioning. Although this is straightforward, the precise procedure before operating the switch may vary from one device to another. Some makes need the rudder to be amidships before making the change from automatic to hand steering or vice versa. The operating manual of any system should indicate whether the rudder must be amidships or if it follows up to the position of helm after switching from automatic to follow-up hand steering. The correct procedure must be posted near the steering console.

Regulations say that a change from autopilot to hand steering or vice versa should be made by an officer or the master, or under their supervision. Regulations also advise that the autopilot should not be used in heavy traffic, restricted visibility, or in any hazardous situation unless a helmsman is available to take over steering within 30 seconds. Furthermore, a navigator must test hand steering after 24 hours on autopilot and before entering an area where hand steering may be needed.

1.1.5 Emergency steering

If for some reason the electrical control for all three systems — autopilot, follow-up and non-follow-up — fails, and steering is inoperable from the bridge, then the emergency steering system in the steering machinery room must be used. The exact procedure to be followed should be on display at the platform from where the emergency steering system is operated.

Generally, a trick wheel at the end of a screw shaft which runs through a threaded bore in a block so that the block moves along the shaft when the trick wheel rotates, provides the mechanical displacement required to control the flow of oil from the hydraulic pumps. The shift of control to this trick wheel is made by aligning a slot in the block of the screw shaft with a slot in the mechanical linkage of the steering gear and transferring a locking pin so that it couples the mechanical linkage to the block. In this way rotations of the trick wheel move the block and as a result the mechanical linkage and the rudder. It is possible to have accurate control over rudder angles as these are marked beside the length of the screw shaft on which the block moves. A display of compass headings at the control position provides further assistance.

With these indicators, good communication between the bridge and the emergency steering platform and a little practice during drills, it is possible to steer reasonably well from this position if the bridge steering console fails.

1.1.6 Steering failure

As soon as a malfunction becomes apparent while navigating, the first step is to assess whether circumstances demand stopping the engines, reversing, or in extreme cases in order to kill speed, the use of anchors. In traffic steering failure endangers other vessels and they need warning by use of the appropriate signals.

Simultaneously, in addition to informing the engine room, the situation also requires quick checks on the steering console to determine the extent of the failure, as duplicate systems are present for safety reasons, and it may be possible to bypass the fault. Each step in the checks needs to be confirmed first with one and then the other of the two pumps, steering motors and any other duplicate equipment present, progressing, if steering is not restored, to the next step in the order:

1. If the autopilot fails, switch to second automatic system if there is one.
2. Change to follow-up hand steering.
3. Switch to non-follow-up hand steering, and if this too is ineffective,
4. operate emergency steering and steer with helm orders from the bridge received over the communication system that is present.

However, the emergency steering also requires working hydraulic pumps in the steering machinery and if all pumps are inoperative then the ship is without steering and is not under command. This requires that the engines be immediately stopped, continued use of signals, and if urgent, reversing of engines and use of anchors.

1.2 Emergency stop of propulsion

Ships either have reciprocating engines or turbines. Turbines are suitable for controllable pitch propellers. The purpose of the engine emergency stop button is to cut off torque to the propeller and thus the propulsive power. On a reciprocating engine this is effected by pulling the countershaft for the fuel pumps to the stop position, cutting off the fuel supply and stopping the engines. With a controllable pitch propeller the stop button may declutch ...