LOADED VOYAGE - Bulk Carrier Practice

Departure from the loading port, choice of route, cargo ventilation, soundings, acidity of bilges, cargo temperatures, sampling of air in holds, checking and tightening of cargo lashings daily, inspections in fair and rough weather, conduct of the voyage in rough weather, reporting, arriving at the discharging port

Departure from the loading port

IN Chapter 12 it was noted that it is normal for all the hatches to be secured for sea and their securing checked by the chief mate before the vessel leaves the berth. An exception may be made when a vessel has a long passage to complete from the loading berth through sheltered waters before the open sea is reached. In these circumstances, if the paperwork can be completed promptly, time can be gained by completing the securing of the hatches after the vessel has left the berth. For Cape-sized vessels the ports of Kanogawa, Ponta Da Madeira and Dampier come into this category, and the grain loading port of New Orleans and the iron ore port of Narvik are two examples of ports where this approach is justifiable for Panamax-sized vessels. Many more examples could be quoted for handy-sized and mini-bulkers. If there is a high tide to catch or if daylight is required for the transit, there is an added reason for departing as quickly as possible and completing the work of securing whilst proceeding towards the sea.

Once the berth has been cleared and tugs have been released, mooring lines must be secured on their reels and covered or passed below decks into the rope stores.

Anchors must be secured when deep water is reached and there is no realistic possibility of using them.

Cargo residues lying on deck should not be washed or swept overboard whilst the vessel is in the port approaches or coastal waters. Light residues such as grain are liable to blow over the ship: they should be swept into piles between the hatches and damped down for disposal once international waters are reached. Heavy residues like iron ore can be left on deck to be swept or washed overboard in international waters. (The regulations for the disposal of cargo residues are described in Chapter 25.)

Essential cleaning should be done. For example, a clear path along the deck to the pilot ladder must be swept or washed, and if the pilot is to be discharged by helicopter the helicopter landing hatch cover and the two covers next to it must be washed down. This is to prevent dust being drawn into the helicopter engine, where it might cause failure, and to avoid the creation of a dust fog.

Choice of route for the loaded voyage The obvious first choice of route for the loaded voyage will be the most direct one and often this will be the best, but there are various reasons for considering alternatives. When choosing the route, the master should take into consideration the ship's loading and operational requirements, plus climatic and weather data.

Loading and operational requirements: A ship which has been soundly built and properly maintained ought to be able to face normal heavy weather without

suffering structural damage, but there is no benefit to be gained from meeting adverse weather on the direct route if more favourable conditions can be found on an alternative route. Furthermore, no master should let his vessel remain in the path of exceptional weather, such as is met near a tropical cyclone, when there is an alternative.

The ship's loading and operational requirements are dictated by such facts as the cargo the vessel is carrying and, where applicable, the way it is secured.

The master of a ship carrying a deck cargo of steel pipes, timber or woodpulp, or with holds loaded with steel coils lashed with strapping bands, for example, will want to avoid heavy adverse swell as far as possible. Heavy seas shipped on deck can dislodge deck cargo, and the ship's violent motion can cause steel coils to break adrift in the holds. If the cargo requires ventilation the master should try to avoid weather which makes it impossible to ventilate.

A strong case can also be made for choosing a route to avoid troubles. Coasts where civil strife has led to the shelling of passing ships, areas where pirates are known to operate and areas where large concentra- tions of fishing vessels can be expected are all well worth avoiding.

Climatic data: Climatic data include the observa- tions of currents and wind and wave height and direction taken over a period of years. In low latitudes within the tropics, the weather and wave conditions remain stable for long periods except when tropical cyclones occur, and these data published by hydro- graphic authorities are very reliable. In low latitudes a choice of route which takes account of prevailing currents, winds and swell conditions is likely to be suc- cessful. It is reasonable for a master to set courses which increase the distance over the ground, provided that the extra distance is outweighed by benefits such as a favourable current, or a better speed through the water.

If the arithmetic shows that on indirect route 'B' making good 14 knots, the vessel will arrive in port earlier than by direct route 'A' where only 13 knots can be expected, then the decision to use indirect route 'B' is justified.

It is climatic data which influence a shipmaster when he chooses an indirect route across the Arabian Sea during the SW monsoon or remains further from the South African coast when rounding the Cape from west to east to avoid the adverse effect of the Agulhas current.

The routes recommended in Ocean Passages of the World⁹⁰ are based on climatic data, and such data can be found in routeing charts, current atlases, tidal stream publications and sailing directions.

Weather forecasts: In higher latitudes the weather is less stable than in the tropics, being regularly dis- turbed by the depressions which cross the oceans. In

BULK CARRIER PRACTICE 179

these areas the use of weather forecasts is essential when choosing the best route to follow: swell and wind conditions can be very different over a distance of no more than a few hundred miles.

A departure from the direct route (i.e., from the great circle route) in higher latitudes is most likely to result in a saving when the route runs easterly or west- erly because that is the direction in which the weather systems travel. It is mainly in east-west crossings of the North Atlantic, North Pacific and the three southern oceans that savings in time and/or fuel can be made by good route choice.

Experienced masters can learn to recognise the weather patterns over the oceans and to choose their route accordingly. During periods when conditions are favourable the planning of the route is easy, but ocean voyages may take 10-30 days and there can be few shipmasters who have the resources to plan optimum routes so far ahead through adverse conditions.

For the mariner the forecasting of swell height and direction is even more difficult than the predicting of wind, yet swell is the factor which has the greatest effect on ships' speed and movement. No long-term swell forecasts are broadcast. The difficulties for a shipmaster of forecasting, days in advance, the nature and effects of adverse weather on his ship and the desire for voyages completed economically and without losing time or damaging cargo, have led to the development over the last 25 years of ship routeing services. Improved communications and data proces- sing have made such services possible.

Ship routeing services: Ship routeing services serving the whole world or more limited areas are provided by several commercial organisations which have the resources to predict the weather and to forecast a ship's progress along alternative routes so that the most suitable one can be chosen. The size of their data bases and the power of their computers enables them to assess the options and choose the best route in a way that no mariner could hope to match consistently.

As an example, the Metroute organisation, part of the UK Meteorological Office with its considerable resources, can be quoted. It receives regular and frequent weather reports from numerous sources situated all round the world, including data from satel- lites, and uses operational computer models which produced (1993) detailed forecasts of winds and waves for five days ahead.

Metroute, like its competitors, asks the purpose of the routeing—to minimise fuel consumption, or to minimise adverse weather, for example—and recom- mends an appropriate route. The route is chosen by professional mariners working for Metroute on the basis of the forecast weather and the ship's anticipated performance. The ship's performance is forecast on the basis of her particulars and the experience which the forecasters have in their computerised records of routeing similar ships. The ship reports her position at intervals during the voyage so that her progress can be monitored and the route amended when changing conditions required it. Metroute also monitors sea ice and the recommended routes take vessels clear of ice infested waters.

After the voyage the routeing organisation provides

180 THE NAUTICAL INSTITUTE

a comparison between actual and possible alternative routes to demonstrate the benefits of the routeing advice. The routeing organisation can also provide comparisons between actual speeds achieved and charter speeds, after taking account of the weather and currents experienced. These comparisons can be provided regardless of whether or not the vessel was routed on the voyage in question. A fuel consumption monitoring service is provided as an optional extra and is used by many charterers.

When to use a ship routeing service: It is common for charterers to insist on the provision of a ship routeing service for the loaded voyage, particularly for east west crossings of the oceans outside the tropics.

However, although charterers instruct the master to be guided by the routeing service they usually also stipulate that the route taken is to have due regard to the safety of ship and cargo, thus requiring the master to continue to use his own judgement to ensure that the voyage is safely accomplished. The use of the ship routeing service enables the charterers to be satisfied at modest cost that the chartered ship has followed the optimum route.

When routeing is not a requirement of the charterers it is still open to the master to request owners or charterers for permission to use a routeing service and some owners and charterers will expect him to do so when benefits can be expected.

Individual cases must be judged on their merits, but routeing services for bulk carriers are likely to provide the biggest savings in fuel consumption, and/or the greatest reduction in damage, when one or more of the following conditions are met: voyage is outside the tropics: voyage is through the tropics during tropical cyclone season: voyage runs more east to west than north to south: the shortest route would take the vessel into very high latitudes: voyage is during bad weather period (e.g., winter or monsoons); ship is medium- or low-powered; ship is in ballast or has a deck cargo;

master has little experience of the region; ship's facili- ties for receiving weather data are poor.

Cargo ventilation

Speaking generally, bulk cargoes are ventilated to prevent the formation of cargo sweat or ship's sweat which could damage the cargo, to reduce the harmful heating of a cargo, and/or to remove hazardous gases from the cargo spaces. Ventilation in the wrong circumstances can do considerable harm and before a decision is made to ventilate a space it is necessary to consider the requirements of the cargo, the temperature and humidity within the holds and outside and the presence or absence of sea spray. The types and positions of ventilators with which the ship is provided must also be taken into account.

Hold ventilators: It is usual for any bulk carrier to be provided with two or four ventilation trunks per hold, with one or two situated at the fore end of the hold, and one or two at the after end. To avoid passing through the topside tanks the ventilator trunks are situated close to the ship's centreline. Within the hold each such trunk often terminates in a simple square, round or rectangular opening in the deckhead (Fig.

15.1). Alternatively trunking may continue down the bulkhead, with slots at intervals to admit air to the hold

FIG 15.1 VENTILATOR OPENING IN DECKHEAD at various levels. Portable plates can be put in place to close the lower slots, when ventilation at lower levels in the cargo is not wanted.

Above deck the ventilation trunks may stand alone, each fitted with a mushroom cowl which gives some protection from spray and from the direct force of any wind (Fig. 6.2), or they may be built into the struc- tures of the masthouses with openings situated in the masthouse sides, the masthouse top (Fig. 6.1), or at the masthead (Fig. 6.3).

Every ventilator must be provided with a means of closing so that all ventilation can be stopped in the event of fire. The means of closing may be in the form of a ventilator flap set within the vent trunk (Fig. 6.3) and operated by an external lever, or a watertight door (Fig. 6.1), or may consist of a cowl which can be screwed down into a closed position by the operation of a valve wheel (Fig. 6.2).

Some bulk carriers are provided with ventilator fans set in the trunks of ventilators. When fans are provided they are normally fitted in the ventilator or ventilators at one end of the hold. Ventilator fans can usually be run in both directions so that they can be used either to deliver air to the hold or to draw air from the hold. It may be possible to vary the speed of the fans, selecting full speed or half speed or a larger range of options. Ventilation assisted by fans is known as mechanical or forced draught ventilation, whilst ventilation which occurs as a result of natural movement of air is called natural ventilation. Natural ventilation can occur as a result of a wind blowing, the ship's motion, or the circulation of air resulting from temperature differences.

The Regina Oldendorffis provided with one ventilator at each end of each hold. These ventilators pass verti- cally through the masthouses with the forward ventilator in each hold being on the starboard side and the after ventilator on the port side. The ventilators termi- nate on top of the masthouses with grilles which face aft and are provided with watertight doors (Fig. 6.1).

No fans are provided, so the ventilation is natural.

In addition to the main hold ventilators already described, some bulk carriers are provided with

ventila-tors of the hinged-door type set into the hatch coamings, whilst portable ventilator cowls are also provided for some bulkers to be bolted in position on the hatch covers when blank plates have been removed. Such additional ventilators are necessary to provide surface ventilation within the hatch square when a ship is carrying a cargo which fills the hold to coaming level, thereby sealing off the hatch square from the rest of the compartment (Fig. 15.2).

Reasons for ventilating bulk cargoes: A number of difficult cargoes have special ventilation requirements to prevent overheating or to remove dangerous gases. In such cases masters and officers should be guided by an instructions provided by owners, charterers, shippers and/or the BC Guide²².

In Chapter 19 the carriage of several typical cargoes is described and these provide a good illustration of the varied reasons for ventilating. Coal is ventilated to remove heat and hazardous gases. With grain and steel a major object is to avoid the formation of sweat, which would damage the cargo. In addition there can be a need to remove heat from grain cargoes. Iron ore has no particular need for ventilation although it is desirable for access and to reduce corrosion to maintain a dry and healthy atmosphere in the holds.

When there is no special need to remove gases or heat, the reason for ventilating is to remove moist air and replace it with drier air to discourage the formation of sweat.

Sweat: Sweat is the name given by seamen to condensation which occurs in a ship's cargo spaces. There are two types of sweat, ship's sweat and cargo sweat.

For sweat to occur there must be moisture in the hold atmosphere and a difference of temperature between the air in the hold and the cargo or the ship's steelwork.

The temperature difference usually occurs as the ship moves from one climatic region to another or from a cold to a warm current or vice versa, and the larger the change in temperature the more likely is the formation of sweat.

Sources of moisture in cargo spaces: The most important source of moisture in a hold is the cargo.

Most commodities, particularly materials of vegetable origin, posses some natural moisture and create an atmosphere, known as the storage atmosphere, in any compartment in which they are stored⁵⁹. Moisture in a hold can also be the result of rainfall during loading and the air in a hold will be moist if conditions were moist when the hold was closed on completion of loading.

The amount of moisture in the air is measured by its dewpoint, which is the lowest temperature to which a mass of air can be reduced without condensation occurring. As condensation is a 'bad thing' it is helpful to remember that air with a high dewpoint is a 'bad thing'. Dewpoint is obtained from a table, entered with readings taken from the wet and dry bulb hygrometer.

Cargo sweat: Cargo sweat consists of condensation which forms on the surface of cold cargo when warm moist air comes in contact with it (Fig. 15.3). Cargo sweat will form when the dewpoint of the air in the hold is higher than the temperature of the cargo. This is most likely to occur when the ship has loaded a cargo

BULK CARRIER PRACTICE 181

in a cold region and air is admitted to the hold as the ship is travelling towards a warmer region.

To prevent cargo sweat when passing from a cold region to a warm region all ventilation should be stopped and the hold should be kept closed, with the air unchanged, as far as possible. The temperature of the cargo will only rise very slowly to equal the exter-

In document Bulk Carrier Practice (Page 179-189)