Passage Planning – Practical Aspects

Planning may be considered in two stages:

1. Ocean and open waters

2. Coastal and estuarial waters

Though at times these two stages will merge and overlap.

Charts

Collect together all the charts for the intended voyage, putting them into the correct order. Charts not absolutely necessary for the voyage but which are adjacent to the area to be traversed should be included, as should very large-scale charts, e.g. port plans on the coastal part of the voyage. Although it may not be necessary to actually use such charts, they may include information that will prove of use during the voyage. Ensure that all charts and publications have been corrected to the latest Notice to Mariners available and that any authentic Navigational warnings etc. received from any source are also included. Similar corrections may also have to be made during the voyage after the plan has been completed and the plan having to be subsequently modified.

No-Go Areas

Coastal and estuarial charts should be examined, and all areas where the ship CANNOT go must be carefully shown by highlighting or cross-hatching, care being taken to not obliterate information such as a navigation mark or a conspicuous object. Areas so marked are to be considered as no-go areas. In waters where the tidal range may not be very large, no-go areas will include all charted depths of less than the ship’s draught plus a safety margin. Such areas will vary according to the ship’s draught so will not necessarily be the same for both inward and outward passages. In general the line determining “no-go” areas will be not less than draught +10%, though this will need to be modified according to the prevailing circumstances. Draught +10% may well prove adequate in areas where the sea is smooth but will require a considerably higher figure if the ship is liable to pitch, roll or squat.

In confined waters, where the tidal height may have a large influence, such no-go areas will vary according to the time of passage. Initially all areas and dangers showing charted depths of less than the draught plus the safety margin should be considered no-go, though such no-go areas may be subsequently amended when the actual time of passage is known. Such areas will need to be carefully marked showing the times and state of tide at which they are safe.

Margins of Safety

Before tracks are marked on the chart the clearing distance from the no-go areas needs to be considered. When a fix is plotted on a chart it invariably represents the position of a certain part of the ship’s bridge at the time of the fix. With large ships, although the plotted fix at a certain time may be outside a no-go area, it is possible that another part of the ship may already be in it – with disastrous results. A safety margin is required around the no-go areas at a distance that, in the worst probable circumstances, the part of the ship being navigated (the bridge) will not pass. On occasion, the margins of safety can be readily monitored by eye, e.g. using buoys marking the safe limits of a channel or easily identified clearing bearings.

Among the factors, which need to be taken into account when deciding on the size of this «Margin of Safety», are the dimensions of the ship; the accuracy of the navigational systems to be used; tidal streams; the manoeuvring characteristics of the ship.

The Margins of Safety should be chosen so that they can be readily monitored. To achieve this they need to be related to one of the navigation systems in use.

Margins of Safety will show how far the ship can deviate from track, yet still remain in safe water. As a general rule the Margin of Safety will ensure that the ship remains in waters of depth contour greater than draught +20%. It is stressed that this is only a general rule. Circumstances may dictate that the 20% clearance will need to be considerably increased, e.g.:

1. When the survey is old or unreliable;

2. In situations where the ship is pitching or rolling;

3. Where there is a possibility that the ship may be experiencing squat;

4. When the ship may have increased the draught by passing into fresh water.

Safe Water

Areas where the ship may safely deviate are considered to be Safe Water and the limits of this safe water are bounded by the Margins of Safety.

Ocean and Open Water Tracks

Ocean and Open Water tracks should first be drawn on small-scale charts, according to the decisions made at the appraisal stage regarding the route to be taken. Great circle and composite great circle tracks will have to be calculated or obtained from the GPS or from great circle charts. Rhumb lines may be drawn straight onto the Mercator chart, but all tracks will have to conform to the limits determined at the appraisal stage.

Coastal and Estuarial Tracks

Coastal and Estuarial Tracks will also be constrained by the decisions made at the appraisal stage and should be first drawn on the small scale charts covering large portions of the coastline, preferably from the departure port approaches to the arrival port. This will depend upon proximity of the ports and the charts of the area. In many cases more than one chart will have to be used. These first tracks will form the basis of the plan and from them may be obtained distances and steaming times and when the departure time is known, the ETAs at the various waypoints en rote can be established.

The true direction of the track should be shown close to the track on the chart. This will not necessarily be the course steered to make this track; it only indicates the direction to make good. The course to steer will depend upon various factors at the time of making the passage, e.g. tidal set and drift, leeway, etc.

When completed, these tracks should be transferred to drawn on the large-scale charts of the area to be transversed. Transfer of a track from one chart to another must be done with great care.

To ensure that no mistakes are made, it is good practice to double check this operation by using a range and bearing of the transfer position from a readily identifiable object e.g. a light common to both charts. This can be further confirmed on both charts by checking the latitude and longitude of the transfer position.

2. Answer the following questions

1. What are two stages for planning?

2. What should be done in respect of charts for passage planning?

3. How can you explain notion “no-go areas”?

4. What are the margins of safety?

5. What waters may be considered safe?

3. Discuss the situation concerning who is responsible for passage planning?

4. Explain how the passage plan may be appraised?

5. Give the summary of the following description