Ship Handling Articles

Narrow passageways and fairways in rivers and canals with a navigable depth and width comparable small in relation to the draft and the breadth of passaging ships are called restricted waters. The maneuverability of ships navigating through such restricted waters will be affected by high hydrodynamic effects that are different from those when ships navigate in broad and deep waters. These peculiar hydrodynamic effects are the shallow water effects, ship squat, interaction and bank effect. Let us have a look into the shallow water effect and ship squat.

When a ship proceeds, the surrounding water is displaced toward the sides and bottom, making a relative flow against the ship’s advance. Advancing hull submerges deeper compared to when she is dead in the water; this changes the trim because the water around the hull flows a little faster compared with the ship’s speed and the hydraulic pressure decreases. This phenomenon is called ship squat; but why does this take place?

In shallow water, when the bottom clearance is comparatively small, the ratio of the horizontal flow along both sides of the ship increases because the current towards the bottom is restricted. The hydraulic pressure along both sides of the hull decreases, as the nearer hull is to the surface flow, the faster the rate accelerates and the water level around the ship drops considerably. For this reason, sinkage of the bow and stern and subsequent trim change become larger in shallow water than in deep water. We should be careful that sinkage of the bow and change of trim become greater when a ship runs in shallow water.

Now let us see how the depth of water affects the turning capability of the ship in shallow water. We will have a look at the data of the turning capability of the large ships. Every curve indicates the tactical diameter of a specific ship by the multiples of the ship’s length. There is another graph illustrating how the turning track of the ship differs as the depth of the water changes. Note that in both cases, the ratio of the water depth to draft is changed with all other parameters remaining same. Thus, we can estimate the tactical diameter of a ship running in restricted water as the multiples of its length, although the presented data are taken from the test results of the large ships, this method can also be applied to smaller ships.

In view of the maneuverability of a ship, the depth of water also affects course stability like the effects on turning ability. We shall study the difference of the effects on course stability in deep water and in shallow water from the results of the zigzag maneuver tests. In the zigzag maneuver test a ship’s rudder starts to swing alternately to port and starboard when the ship is set on the steady straight course. At first, the rudder is put to starboard ten degrees until her head swings starboard ten degrees from her original course. Immediately after the ship’s head swings ten degrees starboard, the rudder is changed to port ten degrees until her head appoints ten degrees port from her original course.

This alternate rudder operations are repeated several times making a ship run in a zigzag course. On the picture you can see the results of the zigzag tests conducted in deep and shallow water. The required time to turn a ship’s head port or starboard to a settled angle in shallow water become shorter with a smaller overshoot angle than that in deep water. This means that we can expect quicker rudder effect in shallow water compared to that in deep water.

A well-remembered case among several cases reported in the past is that of a large passenger ship navigating in shallow water without reducing the speed that hit her bottom severely on the rocks. When running in restricted water, it is essential to keep enough underkeel clearance to avoid the deterioration of the maneuverability and touch bottom damage.

Underkeel clearance means the space between the ship’s bottom and the sea bed. It equals the value when the ship’s draft is subtracted from the sum of chart datum and height of tide at that time. To maintain enough underkeel clearance, we have to consider the factors affecting the sinkage of the hull such as squat allowance, wave response allowance, possible error of chart datum, meteorological and oceanographic conditions, and other environmental conditions, and secure a safety allowance that eliminates ship handling difficulties.

The effects of sinkage and change of trim when a ship navigates in shallow water greatly affect the ship’s maneuverability. Enough knowledge of these effects in restricted waters will prevent accidents.

This short article is devoted to the practical use of ECDIS as an aid to navigation and the usage of the common features and functions in a safe and efficient way during the voyage of your vessel. The ECDIS system is only one of many complicated electronic navigation aids found on today’s modern ship bridges. To navigate his vessel safely and efficiently, the navigator must have a good navigational background, sufficient navigational practice, theoretical knowledge about the ECDIS system architecture, functions and features, and practical experience in the use of ECDIS systems.

An ECDIS system is a very impressive system even when seen through the eyes of the professional navigator. But no navigator should ever forget that all systems do have limitations and the fact that these limitations are very often well-hidden and/or not mentioned in the system manuals. The most important thing to know about modern computerized systems is their limitations. Knowledge concerning their functions and features is quickly accessible with a little interest and practice. The only way to get to know the limitations of the system is to study available material about the subject, system manuals, and by practical use under safe conditions.

As of today, the Seafarers Training, Certification and Watchkeeping (STCW) Code does not specify any special training in the use of ECDIS. STCW table A-II/1 considers the ECDIS training to be a part of training in understanding a “chart”. As a modern ECDIS system is just as complicated as ARPA, this lack of detailed training requirements may pose a hazard to ships, sailing with ECDIS operated by untrained operators.

The reduction of presented information or proper selection of only relevant information is often an important task when setting up an ECDIS system. An ECDIS system which simultaneously presents all available information tends to be overloaded and therefore the important information may be less visible. A basic and very important thing to understand and take into account at all times when using ECDIS is the fact that no system is better than its weakest chain, that is, “rubbish in – rubbish out”. Vital information for any ECDIS system is own ship’s position. Whenever own position is wrong, ECDIS chart information is wrong. Simple as that!

information is wrong. Simple as that! ECDIS systems accept position input from a number of positioning devices as well as dead reckoning. Most ECDIS systems today are connected to a GPS and/or DGPS. This means that stable and good positioning can be expected most of the time. However, the navigator should never forget to check his position as often as practicable by all available means in order to detect any malfunction or inaccuracy in the navigation system used as an input to the ECDIS.

Positions are always referenced to “something” and this “something” is referred to as the chart datum and there are hundreds of different chart datums around. This means that the navigators at all times must know:

1. What chart datum does the ship’s positioning system connected to the ECDIS use
2. What chart datum does the actual ECDIS chart use
3. Whenever the datum used by the positioning system and the chart are different, known corrections must be taken into account.

Today, the ECDIS system is often connected to an integrated bridge system, of forms a part of an integrated bridge system, i.e. a system where the Radar, ARPA, Autopilot, Positioning, Routing, Log, Gyro, ECDIS etc. are connected and work as “one system”. Several options for “automatic sailing” become available to the navigator. Depending on the ship position, i.e. open sea, coastal or restricted waters, the navigator may select between several sailing options. The examples of possible sailing options found on an integrated ship bridge system include course mode, corrected course mode, and track mode.

Course mode is a sailing mode normally used in open waters and for long distance sailing, as this mode will give the shortest distance between two points. No correction for offset is made, but the ship will “home” to the destination.

Corrected course mode is used in waters where it is necessary to correct for wind and current. Correction for offset is made, but no attempt to follow the original planned track is made.

In track mode, the system will calculate the optimal path back to the original planned track. This mode is used in restricted waters whenever it is important to stay exactly on the planned track.

For a professional navigator, it is a matter of course that the route selected for actual sailing is properly checked before it is activated and used for actual sailing. Parameters used when planning the route must still be valid in order to maintain required safety margins. If not, the route may have to be changed before it can be used safely. Examples of parameters which may have changed after the selected route was programmed are ship draft, available position accuracy, engine and steering gear reliability etc.

Navigation with an ECDIS system, especially when the ECDIS is connected to an integrated bridge system, changes the work situation for the navigator a lot. Conventional navigation with manual plotting of ship position in the chart, heavy traffic, and manual course change in restricted waters is a task that puts a heavy workload on the navigator. A good working ECDIS reduces that workload a lot. So, the navigator’s role has changed from actually doing the tasks to monitoring them. From the safety point of view, this should be very good, as the navigator is given more time to check important parameters and monitor the traffic more closely.

Sailing with ECDIS requires a highly qualified navigator with a sound and positive skepticism towards computerized systems. Take the necessary time and effort to really get to know your ECDIS. This will definitely save you lot of work and trouble in the future; it may someday save your career or even your life.

The basic inspection regime for all the MOUs is the IMO conventions. These include the Load Lines, SOLAS, MARPOL, STCW, COLREG and Tonnage conventions. Some MOUs also examine compliance with the relevant ILO conventions. Ships can check each MOU’s website for the further requirements. Complications can arise because for all members of MOUs, their national legislation will take priority over the MOU agreements.

MOUs have different levels of inspection. The initial inspection usually takes about three hours. If there are clear grounds to concern, it may progress to a more detailed inspection, adding another hour or two. Ships with a poor inspection history may be subject to a more detailed inspection. If the Master believes that port state control inspection is likely, he should double check the gangway watch. An ineffective or absent gangway watch will start the inspection badly as it implies poor compliance with the ISM Code. A proper gangway watch must always be in place. The ISPS Code must be strictly kept to. Ships with high target scores, such as old bulk carriers, passenger ships, oil tankers and gas and chemical carriers, will be subjected to an expanded inspection which will take six to eight hours.

MOUs have different levels of inspection. The initial inspection usually takes about three hours. If there are clear grounds to concern, it may progress to a more detailed inspection, adding another hour or two. Ships with a poor inspection history may be subject to a more detailed inspection. If the Master believes that port state control inspection is likely, he should double check the gangway watch. An ineffective or absent gangway watch will start the inspection badly as it implies poor compliance with the ISM Code. A proper gangway watch must always be in place. The ISPS Code must be strictly kept to. Ships with high target scores, such as old bulk carriers, passenger ships, oil tankers and gas and chemical carriers, will be subjected to an expanded inspection which will take six to eight hours.

Under the Paris MOU, the ship is obliged to inform the port if it believes that it is due for the mandatory annual inspection. The Paris MOU website lists the types of ship for which this is required. Always ensure that the PSC officer is escorted to the Master’s cabin. Be aware that the inspector will be looking around to see the state of the ship.

What is voyage planning, who is responsible, how do we comply with the rules and how do we utilize the features and functions available in an ECDIS? The purpose of voyage planning is to support the bridge team and ensure that the ship can be navigated safely between ports from berth to berth. A voyage plan should cover ocean, coastal and pilotage waters and according to STCW regulations be planned in advance. The voyage plan aim to establish the most favorable route while maintaining appropriate margins of safety and safe passing distances offshore.

The following factors are amongst those that should be taken into account:

• - The marine environment
• - The adequacy and reliability of charted hydrographic data along the route
• - The availability and reliability of navigation aids, coastal marks, lights and radar conspicuous targets for position fixing along the route
• - The type of cargo can influence route selection
• - Any routing constraints imposed by the ship, e.g. draught, type of cargo, etc.
• - If possible, avoid areas with dense traffic
• - Take into account weather forecasts, current, tide, wind, swell and visibility conditions
• - If possible, avoid areas with onshore set or areas where onshore set can be expected
• - Whenever possible, follow traffic separation schemes and follow ship reporting procedures
• - Check technical systems before departure and if possible, take into account previous experience of their reliability
• Take into account your own experience with the planned route and type of ship.

There are four main stages in the planning of a safe voyage:

• - Appraisal, i.e. the collection of information and validation of all relevant information;
• - Planning, i.e. the presentation of the raw data -into information and the strategy to be used;
• - The execution of tracking, voyage and communication control;
• - Monitoring, i.e. ensuring that the voyage plan is being followed.

Cargo operations are probably the most important ship operations. They vary enormously from petrochemicals where the discharge is controlled by the ship’s officers to containerships where the discharge and loading is organized and largely carried out by the shore stuff. From your training and experience you will know the requirements of your own ship’s cargo operations but, whatever the cargo, many of the principles remain the same.

Prompt and accurate reporting of any damage must be done within twenty-four hours. Cargo condition, speed of loading or discharging, any delay in operations all can have commercial consequences. The chief officer will know what is critical in your cargo operations and you should discuss the procedures with him. Much of the time cargo operations proceed according to pre-determined plan. It is when the unexpected occurs that the skill of the deck officer is really tested. By responding in the right way you can make a big difference to the commercial performance of your ship.

Make sure you know what can go wrong, what to do and whom to contact if it does. Good situational awareness is the basis for any effective response. Make sure you know what is going on at all times in port. This means being on deck most of the time, keeping your eyes open and communicating with the terminal staff. This will also help with another major task – making sure that the ship is safe.

Current, tide and the cargo operations can all move the ship in relation to the shore if the mooring ropes are slack. The ropes need to be checked regularly for tautness. If your ship has self-tensioning winches, these are best left on the brake and not left in tension once the ship is secured alongside. In an emergency, never release the brakes and attempt to pull a ship back alongside using the power of the winches alone. You must know the ship’s mooring equipment and be familiar with its operation and capabilities including the type of winch and brake, the size, type and length of lines.

Make sure you are aware of the tidal changes and keep an eye on a weather forecast. Sudden changes can have a big impact on cargo operations and additional mooring arrangements may be needed. Be aware of nearby ship movements, check the lines after any ship has arrived or left the next berth.