Industry stakeholders have discussed a lot about the pros and cons of paperless navigation concluding that ECDIS does have an edge over the traditional paper chart navigation. However, the question for the navigating officers remains the same. Can they steer the vessel, following a pre scheduled passage plan, within the safety margins that they set, from berth to berth, avoiding grounding? At this point, it is worth to mention the passage plan’s main purpose which is to use the available ‘navigational waters’ for the indented voyage so that the vessel could safely conduct the voyage.

– The ‘navigational waters’ can be mainly affected by the water depth, which is indicated both on paper charts and ENCs. Specifically, the depth measurement, as indicated, is the result of a relevant depth survey which varies in age and quality depending on the measurement techniques and the available technology.

Because priority for surveying is given to the major shipping routes, each navigator sailing into unfamiliar waters away from these routes should be able to interpret the various quality indicators that are, or should be, indicated on every chart. This is why many guides are available with best practices of navigation for commercial vessels and cruising yachts that help mariners to decide on how much confidence they should show on the marked depths.

1. However, a mariner should be always wary of any chart that does not feature these indicators, irrespective of whether it is a traditional paper chart, or an ENC.
2. ECDIS dispay vs traditional paper charts On the traditional paper charts, the Reliability Diagram (old charts) or Zone of Confidence diagram (new charts) indicate the depth accuracy based on surveys.

Navigators should carefully check the areas that they have chosen to sail, find the relevant indication on diagram and apply additional measures or safety features to protect the vessel from grounding. On ENCs the same policy is followed with the exception of the indication of accuracy which is well spread and marked on the chart with CATZOCs (Categories of zone of confidence). which indicates the accuracy of depth. This indication is subject to ON or OFF selection by the navigator, therefore, for an unfamiliar user the risk is increasing. In particular, there is risk of not displaying and checking the depth accuracy, resulting in unpleasant situations for the passage planning, thus, vessels to reach the depth limits (in accordance with calculated UKC) and finally to run aground because the depth result was not as accurate as the navigators expected to be.

Shallow Contour: Indicates the depth below a vessel could run aground and it is equal to vessel’s maximum static draft.Safety Depth = Maximum Draft(static) + UKC (Company’s Policy) + Squat(Maximum) – Height of TideSafety Contour: Is calculated same as per Safety depth AND activates ALARM when depth is lessDeep Contour: Indicates the limit of sea area where shallow water effects occur that can affect a vessel. It should be estimated twice or four times the draught of vessel (depending on the depth of water available)

Image 1: Areas of Navigational Waters ECDIS safe settings Although color code may vary in different ECDIS system displays, the generic idea remains the same. Another key issue to consider is to include the chart depth accuracy into UKC calculation or make a comparison between the CATZOC with the UKC (Under Keel Clearance) which is more common.

1. The UKC sets the minimum level of distance between the deepest point of a vessel and sea bottom.
2. In particular, it is a company-specific measurement, therefore, it is company’s responsibility to specify this distance and Masters must consider it during passage planning (especially in shallow waters).

Again, the depth accuracy emerges as an important issue for UKC calculations. For example, if a vessel has set the UKC to 0.5m but the chart accuracy has +/- 1 m, this may cause problem and the navigating officers are advised to take this issue into consideration.

• Table 1 shows UKC correction due to the different Zone of Confidence of ENCs.
• The Category D is worse than Category C; it cannot be trusted and large anomalies in the depth can be expected.
• Also, the Category U is the unassessed category; the quality of the bathymetric data is not yet assessed.
• In conclusion, Electronic charts and ECDIS are necessary tools for navigators in order to plan the route and monitor the position easier and faster.

Considering that these electronic means are based on human surveys and measurements, the possibility of false information regarding depths, heights etc cannot be excluded. This is an additional factor to be considered during e-navigation and therefore all mariners (navigators, OOW and Masters) are advised to be always alerted and stay focused when they use these means of navigation. Table 1: Recommended table of UKC correction due to different Zone of Confidence of ENCs.

What is the safety depth and safety contour on ECDIS?

ECDIS has become the essential tool for watchkeeping officers on ships. Navigating a ship with an ECDIS is fundamentally different from navigating with paper charts. It is important that the Masters, navigating officers, and ship-owners are aware of the benefits of managing the chart display, safety settings, and alarm system of ECDIS.

ECDIS equipped vessels have been involved in a number of groundings which may have been avoided had it not been for failures in the setup and use of ECDIS safety settings and alarm systems. Inappropriate settings are likely to render the safety contour alarms meaningless. The use of ECDIS safety settings has often been overlooked by navigating officers due to either ignorance or insufficient knowledge.

Deck officers may be unfamiliar with the setup and use of ECDIS alarms thereby increasing the risk of grounding in shallow waters and causing other unwanted situations. Related Read: Real Life Accident: Improper Use Of ECDIS Leads To Vessel Grounding Appropriate safety settings are of paramount importance for ECDIS display.

These settings control how the ECDIS presents depth information, making it easier to visualize areas of water that are safe for the vessel to navigate in from those which are not. This article will help to understand the best practice for handling safety settings on ECDIS which includes the Safety contour, safety depth, shallow contour, and deep water contour.

The model of ECDIS used for illustrations is Furuno. Related Read: Pros and Cons of ECDIS Or Paperless Navigation Of Ships These values can be entered in Furuno ECDIS by following the steps mentioned below:

Go to the main menu and select Chart display Select the Main Tab to display it.

Safety Contour: The safety contour is the most important parameter of all the safety settings for the display of unsafe water areas, detecting isolated dangers and triggering anti-grounding alarms. The safety contour is basically an outline which marks the division between safe and unsafe waters.

1. Related Read: Ship Stability – Understanding Intact Stability of Ships The colour blue is used to indicate the unsafe areas while white or grey for safe areas.
2. The default safety contour if not specified by the mariner is set to 30m.
3. The blue colour in a traditional paper chart does not provide a vivid picture of shallow water, i.e the depths mentioned in the blue part of a paper chart may be shallower for a deep draft vessel while safe for a vessel with a smaller draft.

Unlike paper charts ECDIS allows the officer to set safety parameters according to the ship’s static or dynamic particulars. The safety contour can be calculated as follows: SAFETY CONTOUR = SHIP’S DRAFT + SQUAT + UKC – HEIGHT OF TIDE Let us check an example. Let us consider that as per company policy UKC requirement is 10%. Please note that UKC calculation takes into account various factors such as sea conditions, density or increase in the draft due to rolling. It should be calculated as per company UKC calculation sheet.

UKC = 1.0m Consider SQUAT AT MAX SPEED = 1 m Height of tide = 1 m Safety contour value would, therefore, be equal to 11 m. Contours are present in the values of 5, 10, 15, 20, and 30 and so on. If the value set by the mariner is not available among the available depth contours, ECDIS selects the next deepest available contour in the ENC.

Related Read: What are the Methods To Update Navigation Charts On Board Ships? If within a specified time set by the user, the ship is about to cross the safety contour, an alarm will sound. Based on the value of safety contour, ECDIS displays the isolated danger symbol for underwater features and obstructions which may pose a danger to navigation. Safety Depth Setting: The sole purpose of the safety depth is to portray spot soundings either in gray for deeper depths or black for shallower depths compared to the safety depth value entered by the navigating officer thereby highlighting the potentially safe and unsafe areas.

The safety depth value has no effect on alarms or any other aspect of ECDIS. Safety depth is normally the ship’s draft + squat. Related Read: How Squat, Bank and Bank Cushion Effects Influence Ships? Now the question is why do we need to mention safety depth when safety contour can demarcate between safe and unsafe waters? It is also logically to select Safety Depth equal to Safety Contour.

Some soundings on the shoaler side of the safety contour will be gray because they are deeper than the safety depth set by the mariner, although shoaler than the safety contour selected by ECDIS. The depths below safety contour may not always be non-navigable,

Suppose for example if safety depth and safety contour are set to 11 m, the ECDIS will emphasize the depth contour equal or deeper than the selected contour which say is 20m, whichever is available in the ENC. Related Read: How ECDIS Can Be Further Improved – A 2nd Officer’s Perspective Thus we can see that water areas with depths between 11m to 20 m are navigable but are below the safety contour.

This provides the mariner with additional information about where the ship could most safely pass if crossing the safety contour is required (an alarm will still sound). This could provide additional maneuvering room in narrow passages where safe depths exist. In the picture above, safety depth value is 14m. You can see that depths equal to and below safety depth value are highlighted in bold. Zone Of Confidence Catzoc: In calculating safety depth it is also important to consider CATZOC features OR ZONE OF CONFIDENCE, Let us consider an example. Ship’s draft = 7.7m Squat = 1m Effective draft = 8.7m Required company UKC is 10% of the deepest draft which is 0.87 approximately 0.9m. Thus we see that the total safety depth required complying with company UKC policy is 9.6m.

1. Safety depth value can be set as 10m.
2. However, we haven’t yet considered the depth accuracy as per ZOC.
3. Let us consider that Catzoc in this area is category B which implies there can be an error of 1m + 2% of depth = 1.2m.
4. Therefore if catzoc error is allowed, the minimum depth required would be 10m + 1.2m = 11.2m.

As safety depth cannot be entered in decimals in ECDIS, we can enter 12 m as safety depth. During passage planning, it is essential that CATZOC is displayed and noted for all stages of the voyage. Catzoc Category B Shallow Contour: The shallow contour highlights the gradient of the seabed. It is considered to be the grounding depth i.e this is the depth below which the ship will definitely go aground. This value can be set equal to the ship’s draft, Therefore if ship’s draft is 7.7m, shallow contour value can be set as 8m.

The ECDIS will then display the next depth contour available in the ENC. All of the areas between the 0m depth and the shallow contour is therefore not navigable at all and appears hatched. As I have already mentioned earlier that the division between safe and unsafe water is highlighted by chart colouring, with blue colour for indicating unsafe area while white or grey for safe areas.

The unsafe area is further defined with the selection of shallow contour showing dark blue in the shallow water and light blue between the shallow water and the safety contour when 4 shade display is selected.2 shade and 4 shade display is further explained below. ECDIS also gives the option of simple two colour shading. In this situation light blue and deep blue will merge into a single blue colour and grey and white will merge to a single white colour. If the value of the safety contour is changed, the boundary between two depth shades changes accordingly. The picture above shows that the four shade depth option is not selected. The pictures below show a comparison between two shade and four shade depth in daytime and night time. Day Time Night Time Watch Vector/Anti Grounding Function: The look ahead or watch vector actually compares the safety settings that have been entered by the navigating officer with the depth information contained in the ENC, and generates an indication or warning where the safety settings will be contravened.

• It provides advance warning of dangers/cautions, primarily intended to prevent grounding.
• It acts as a final layer of safety should a navigational danger be missed by the visual check or route scan.
• The scanned area is sometimes displayed as a cone or column on screen and should be set to a distance appropriate to the amount of navigable water ahead of the vessel.

This value should be determined for each stage of the voyage and noted in the passage plan. Many officers fail to realize the significance of the safety contour and do not make proper use of the look-ahead vector. This is how you can activate own ship check-in Furuno ECDIS.

Go to Chart menu and select Initial Settings

Open the menu displayed at the left and choose Chart Alert Parameters

Click the Check area tab. Set Ahead Time or Ahead distance The Around field allows the officer to set fixed areas.

Note that the chart alert always uses the largest scale chart available, which may not be the visualized chart. Note that the ‘Chart Alert’ feature should be highlighted so as to trigger the audible alarm whenever safety contour is breached. It is required to amend the alarm parameters from their previous settings when beginning a new voyage. The alarm parameters need adjustments throughout the voyage to ensure they are optimized for the prevailing circumstances and conditions.

ECDIS is a valuable asset in assisting navigators and providing them with more detailed situational awareness. However, until used accurately and properly, ECDIS may contribute to accidents rather than preventing them. Related Read: How to Order Electronic Navigation Charts and Keep Them Updated On Ships? Increased training and practical use will help to develop and create a better ECDIS mindset.

Trainee officers should be encouraged to understand the benefits that Ecdis provide and make the optimum use of the same. During route planning, a chart alert calculation should be done to detect any dangerous situation and the same should be modified as necessary.

A better understanding of ECDIS safety settings and their proper use can act as a potential barrier to the grounding of ships and any untoward situation. Disclaimer: The authors’ views expressed in this article do not necessarily reflect the views of Marine Insight. Data and charts, if used, in the article have been sourced from available information and have not been authenticated by any statutory authority.

The author and Marine Insight do not claim it to be accurate nor accept any responsibility for the same. The views constitute only the opinions and do not constitute any guidelines or recommendation on any course of action to be followed by the reader. Paromita has completed graduation in Nautical Science and is presently preparing for 2nd mate exams. Besides sailing, she loves to read books and travel. She has also won many awards in music.

What is the safety depth?

The depth, selected by the mariner, which defines own ship’s draught plus under-keel clearance which can be used by the ECDIS to indicate soundings on the display which may be equal or less than the defined value.

Can safety depth be less than safety contour?

At the same time it is seems to be unsafe to select Safety Depth shallower than Safety Contour since part of the spot soundings less than the selected Safety Contour in this case will not be emphasized and will not trigger anti-grounding alarm in ECDIS.

What determines the Catzoc of an ENC?

What is CATZOC or Zone of confidence – If the possible errors in depth and position where depth is marked were constant on the charts, it would have been easier to just apply a constant error. But these errors are not constant. As the technology advanced, the errors in these readings became marginalized and readings taken were more accurate. Each zone of confidence (CATZOC) has been assigned the maximum errors that it can have in depths and its positions marked on the charts. So if for a chart or ENC, the CATZOC is 4 star (zone of confidence B), this would mean that

the position of the depths and dangers marked on this ENC may be inaccurate for about 50 meters There may be an error in the depths for up to 1 meter + 2% of depth

So if at any place the charted depth is showing 20 meters, the error in this could be 1.4 Meters (1 meters + 2% of 20 meters).

How should ECDIS perform accurately all calculations?

11.1 The accuracy of all calculations performed by ECDIS should be independent of the characteristics of the output device and should be consistent with the SENC accuracy.

How do you calculate contour survey?

What Are the Formulas? – You can determine volume using contour lines in two ways:

Prismodial method: This method offers a precise way to get an estimate of the volume. The formula is generally known as Volume = L(A + the square root of (A*B) + B) divided by 3. Trapezoidal method: This method is also used in calculating volume with contour lines. The formula is Volume = L x 1/2 (A1 + A2) cubic meter.

How do you find the contour ratio?

Height and Slope – 1. Measuring heights on a contour map: – Find the point you want to know the height of. – Find the elevations of the contour lines on each side of it. – Estimate height of the point between those elevations. – Example: if a point is 1/4 of the way between the 250 m and 300 m contours, we estimate its height as 250 plus 1/4 of the contour interval (in this case 50 m).

= 250 + 50/4 or 262.5 m. – (as this is an estimate only, don’t suggest you know it to within 0.5 m; round to the nearest 10 m, and call it 260 m).1. Measuring slopes on a contour map: – Find the point at which you want to know the slope. – Find the elevations of the contour lines on each side of it. – Measure the distance between the contour lines (at right angles to the lines themselves).

– Slope = “rise over run”, or vertical height increase over horizontal distance. – Example: if two contour lines are 300 m apart (use map scale to find the distance between them!) and they represent elevations 50 m apart, then rise = 50 m, run = 300 m.

Slope = 50/300. But we don’t write it that way. – (1) Percentage slope: do the division, multiply by 100: (50/300) x 100 = 17% – (what does this mean? – for every 100 m you move horizontally, you climb 17 m higher.) – (2) slope as an angle: do the same division: 50/300 = 0.16667. This is the tangent of the angle of slope.

– We need the angle whose tangent is that number. On a calculator, having found that number, press INV TAN or 2ND TAN (or however your calculator gets to the “inverse tangent” function). – In this case the angle is 9.5 degrees. – NOTE: The ‘run’ can be the distance between any two points, not just between two contour lines.

What is the meaning of CatZoc in ECDIS?

The oceans account for approximately 70% of the planet Earth, where about 50,000 ships ply every day. But how is it secured that they ply in safe areas? The seabed is a complex surface that is likely to differ in depth at all points across the ship hull.

How has such a large area been measured and mapped accurately to make sure that the water depth is adequate? S hips’ navigation for the transport of goods has been present for thousands of years, with Britannica recording the first indications of waterborne vessels as early as 4000 BCE. Measuring the ocean depths is not a task that took place in one day and certainly remains a key task of the world’s hydrographic offices in each state.

Measuring the oceans’ depth In the past, the measuring of water level was carried out manually with ropes and acoustic signals. A more recent method included a wire being towed by two or more ships with weights sunk at a fixed depth. Any obstruction in the area the wire was being dragged would be detected by the wire being stretched.

With the technological advancements of today, the method of conducting these hydrographic surveys has changed. The modern approach for recording the oceans’ depth is using SONAR ( SO und N avigation A nd R anging). The SONAR technique is using sound propagation, to measure distances or detect objects underwater.

The data collected through SONAR are then processed in combination with other data, such as tide, to make the depth measurement as accurate as possible. However, the data shown on nautical charts and ENCs may have errors depending on how these data were measured and when they were measured.

1. The older the data are, the less accurate they will be, due to the limited technology equipment used in each time.
2. A case study The Captain and the second officer are reviewing the passage plan.
3. At some point, they realize that the under keel clearance – the vertical distance between the bottom of the ship and the seabed- is 1.5 meters which is more than enough under the company’s SMS.

But how trustworthy is this estimation? What if the depth is lower? Looking at it a bit further, they realize that the measurement provided for this point of the passage plan was made over a century ago. And while navigating on this route would be alright under the company’s procedures, it could prove catastrophic in practice.

• So how much of a range should the crew expect regarding the water depth? This is what CatZoc addresses.
• CatZoc and its importance for safe navigation As there are several parts of the water that were mapped years ago, with different technological means, it is expected to not trust all the measurements.

The main possible errors may concern the actual depth measurement, as well as the position at which the depth measurement is depicted. At the same time, the potential errors of these two variables are not constant. In this respect, a CATZOC (also known as Zone of Confidence) is a deviation that helps make sure which of these variables are accurate and to what extent errors are expected.

The zones of confidence above provide the maximum errors per depth and position. As such, CatZoc (Categories of Zone Of Confidence) is a rather simple aspect of understanding ECDIS and electronic nautical charts (ENCs). On ECDIS, the CatZocs are symbolized by a number of stars.

the location of depths marked on this chart may be inaccurate by approximately 50 meters; orthe possible error of the depth is 1 meter + 2% of the depth, e.g., if the mapped depth shows 20 meters, the error in that could be 1.4 meters (1 meter + 2% of 20 meters).

Did you know? The effects of shallow water on ships’ navigation can be not only disrupting but also dangerous. For example, a very big cruise ship, e.g., the size of the Costa Concordia, is unable to float if the water is less than 26ft deep. Usually, when a ship is navigating in shallow waters, maneuvering becomes more sluggish and the speed of the ship over water reduces.

What is the depth contour in ECDIS?

The Deep Contour – The Deep Contour is depicted in the light grey line dividing the deeper water (white) from the area where the ship could be affected by squat (light grey). Crossing the Deep Contour does not trigger any alert. Usually overlooked, the Deep Contour, if set properly, can give a pretty good idea where speed reductions, to minimize the squat effect, should be planned. Final Considerations One of the most important ECDIS customization features available to the mariner is the possibility to set-up the Depth Contour values. We saw that, if carefully selected, Safety Contour and Safety Depth can help the mariner to discern the safe from the non navigable waters.

These features will trigger alerts and will control the visualization of the Generic Isolated Danger symbol. The mariner must be fully conversant with each of these functions, knowing how to calculate the values and the limitations of the ENCs in relation to available bathymetries. There is not a “fit-for-all” value good for any situation; the Depth Contours values must be calculated taking into considerations factors like ship’s draft, quality of the data, expected weather conditions and minimum UKC requirements.

The Depth Contours values must be planned and discussed with the bridge team before executing the plan because they play an important role in the safety of the voyage. References: IMO. (2006, December 5). RESOLUTION MSC.232(82) ADOPTION OF THE REVISED PERFORMANCE STANDARDS FOR ECDIS.

Retrieved April 7, 2020, from http://www.imo.org/en/KnowledgeCentre/IndexofIMOResolutions/Maritime-Safety-Committee-(MSC)/Documents/MSC.232(82).pdf UK Hydrographic Office. (2019). Safety Settings In ECDIS display. In U.H. Office (Ed.), Admiralty Guide to the Practical Use of ENCs (3 ed., p.45). Tauton: UK Hydrographic Office All the screenshots and pictures were taken by the author using a Wärtsilä NACOS Platinum version 2.1.14.02.

Disclaimer: the views expressed herein belong to the writer; they do not necessarily reflect the views of CSMART or Carnival Corp.

What are the 5 ECDIS mandatory alarms?

The five mandatory alarms (as per IMO ECDIS Performance standards) are: crossing safety contour, deviation from route, positioning system failure, approach to critical point and different geodetic datum.

How do you cross safety contour on ECDIS?

Crossing the Safety Contour, a real example – Below is a real example (Saint Petersburg – Russia) where the Safety Contour will not perform its regular function: to display the depth boundary between the safe and unsafe water (ship’s draft is 8.5 meters).

• Safety Depth = 10.9 m (real scenario using ENCs, Total tide and port info).
• To describe method 1 the Safety Contour has been set to 11 m.
• To describe method 2 Safety Contour has be set to 10 m,
• The differences are substantial, and the mariner can use both methods – bearing in mind the limitations and inherent risks.

METHOD 1: In this example the mariner sets the Safety Contour to 11 m and the ECDIS selected 15 m as the next available contour. The result is that the entire channel is “not navigable”, so the mariner must draw the Own Safety Line around spot soundings with depth less than the Safety Depth. METHOD 2: In the second example the mariner has set the Safety Contour to 10 m (less than the selected Safety Depth of 10.9 meters). The Own Safety Line has been used to highlight the spot soundings with depths less than Safety Depth (10.9 m), placed outside the Safety Contour of 10 m. A safety margin has also been added between the spot soundings and the Own Safety Line in order to allow for the CATZOC positional accuracy.

What are the 6 kinds of ENC scale in ECDIS?

Six ENC ‘usage bands’, roughly equivalent to scale ranges, have been defined: overview (1), general (2), coastal (3), approach (4), harbour (5) and berthing (6).

How do you check the accuracy of ENC from the ECDIS?

Once the M_QUAL is known, and the CATZOC zone is assigned to an area on the ENC, the navigator can view these symbols on the ENC usually in the ‘All / Other’ display function on their ECDIS. The greater the number of stars that appear in the symbol, the greater the level of accuracy for that area.

How do I correct ENC in ECDIS?

Permanent corrections – Correcting ENCs for permanent corrections is a three step process which is

1. Collect corrections from chartco
2. apply corrections to ENCs on ECDIS
3. Confirm corrections applied on Chartco

Collect corrections from chartco From start up-Menu (on the left bottom section in chartco), click on Corrections. Click on ENC (top bar) and corrections (Right side bar). This list will show you the pending corrections to your active cells. Click on the “Collect and transfer to ECDIS” at the bottom of the screen. On the pop up, ensure that both Master as well as Back up is selected and then click on “Write to Media”. This will write all the corrections in a pre-specified folder. This folder is usually located in C:/Chartco/Corrections but could be specified differently during chartco set up. In any case, on clicking the ‘Write to media” chartco will give the destination of the folder where corrections are transferred. If you see in above image there is an option of “Confirm as applied”. After you have applied to the correction to ENCs on ECDIS, which we will discuss below, you need to come to this screen again and click “Confirm as applied”. To apply these corrections to ECDIS, Copy these corrections onto USB drive (or CD). Again if you have two ECDIS you will see different folder for both ECDIS named Master and back up. You need to copy content of one folder at a time and apply the corrections to the corresponding ECDIS. Applying corrections to ENCs on ECDIS In the application Window, click on the “ENC and ARCS chart portfolio”. Plug in the USB drive containing the corrections. Click Auto Detect. With this You will see all the pending corrections. On clicking Auto detect you may get a message “Please select media type”. In this case go to tools -> options -> Advanced options and then select the location of USB drive (or CD drive) depending upon the media on which you have copied the corrections. Then again click the Auto detect tab. This will show you the corrections. Now to apply the corrections, click on the “Import/Update” tab. This will apply all the permanent corrections to ENCs on your ECDIS. You need to repeat this procedure on other ECDIS. But for that you need to delete the data from the USB Drive and copy the data from the corresponding folder of chartco. After applying the corrections, you need to click on log to see if there was any error while importing the corrections. Or if all the corrections were imported into the ECDIS. Any error in the log must be dealt with. In dealing with any error, you must exploit the tons of resources available to you. These resources can be support from chartco, chart provider, ECDIS manual, UKHO website or your company’s marine department.

2. Confirm corrections applied on Chartco
3. After you have applied these correction, you need to go to Chartco and click on “Confirm as applied” as discussed earlier in this post.

It is important that you collect the correction, apply the corrections to ECDIS and confirm same in Chartco within few minutes of one another. This will ensure that when you confirm in chartco of the correction applied, you do not inadvertently confirm the new correction received which were not actually collected and applied.

What are the 3 mandatory sensors of ECDIS?

Electronic chart display and information system (ECDIS) ECDIS is an integrated electronic navigation system which combines the data obtained from a number of electronic navigation sensors and displays it on a video display unit/monitor both in the form of a graphic image and alpha-numeric information. The sensors providing the data inputs to ECDIS are the following:

The global positioning system (GPS and/or DGPS). The automatic identification system (AIS). The radar and automatic radar plotting aid (ARPA). The ship’s gyro compass. The echo sounder. The ship’s log.

The system makes use of electronic (digital) navigation charts (ENC’s) in place of the normal paper charts which they are intended to replace. The position of the ship is plotted in real time and kept continuously up to date. The ship’s track can be planned and plotted on the electronic chart either by use of the computer “mouse” and cursor or alpha-numeric keyboard.

The voyage or passage plan can then be stored in the system’s memory and when retrieved and executed, provides the planned track as would be the case with a paper chart. Being in digital format, the track is plotted on a seamless series of charts. In the case of paper charts, the position would have to be transferred to the next chart in the series as the vessel proceeded along its planned track.

The system can be instructed to provide a plotted position at predetermined time intervals, as would be the case with paper charts when positions are plotted manually. One can also set other navigational parameters in the system, ie the maximum allowable deviation from the planned track, safety depth contours, arrivals at predetermined waypoints, alter course positions, etc.

1. When these parameters are breeched, or a vessel reaches the predetermined waypoints/positions, it activates a visual and audio alarm to alert the officer of the watch/ navigator.
2. The ship’s physical parameters (length, beam, draught, tonnage type and power of the engines, types of steering, manoeuvring characteristics, etc are also entered into the system so that it can predict the outcome of an intended manoeuvre, ie determining alter course positions.

Electronic charts can be constructed using either of two types of data, namely vector or raster. In the case of raster charts, a paper chart is scanned and converted to a digitised replica. This digitised image cannot be interrogated or changed, ie what is on the paper chart is displayed as is.

1. In the case of the vector chart, all the information and symbols on the chart as well as their characteristics are digitally encoded individually and stored in the system’s data base.
2. This enables the operator to decide what he wants displayed and the level of detail he requires.
3. This is to prevent the display being cluttered with unwanted or unnecessary data.

To make vector charts is more costly and more time consuming than raster charts. Because of this, it will still take some time before all charts are replaced with vector charts. Until then ECDIS will also allow the display of approved raster charts which comply with IMO performance standards.

Whereas chart corrections and updating was carried out manually, the correction of Electronic Navigation Charts can be done off-line (by CD-ROM or diskette) or on-line (via radio links or internet). In addition to the purely navigational aspect, the system is designed to allow the overlay of the radar/ARPA picture on the chart graphics.

The rest of the information provided by ARPA and the AIS system is displayed next to the graphic display in alpha-numeric format. By looking at one video display unit/monitor the navigator or officer of the watch can observe all the information provided by the various navigation sensors, instead of looking at the data displays of each one individually in different locations.

1. As in the case of the navigational mode, the system can be set to provide visual and audible alarms when a dangerous situation develops, ie a vessel on a collision course or having a CPA closer than.
2. It is a wonderful navigational tool which will save the officer of the watch much time, especially in a congested seaway where he can apply himself more efficiently in keeping a proper lookout of his environment.

There is always a danger, however, that he or she becomes complacent and relies too heavily on the system for watchkeeping, instead of using it as an aid to or enhancement of his/her physical/visual watchkeeping. The phenomenon when a collision has occurred despite the availability of electronic navigation systems has been referred to as an “electronically assisted collision”.

One must always be aware of the possibility of a malfunction in the system and regular checks by an independentnavigational source must be conducted. One should also continuously reconcile the electronic picture with that obtained visually by the watchkeeper. The International Maritime Organisation (IMO) decided that it will be mandatory for all seagoing commercial vessels to carry ECDIS.

Implementation was carried out in phases commencing 1 July 2012. It should be noted that not all Electronic chart Systems (ECS) are ECDIS and only an ECDIS approved by the IMO is approved for navigational use. It is also an IMOrequirement that a suitable and independent back=up navigation system be available in addition to the ECDIS. Side by side displays of the radar picture and the electronic chart display. : Electronic chart display and information system (ECDIS)

What are the 3 display modes of the ECDIS?

ECDIS displays have different color schemes (‘modes’) to accommodate variations in the ambient light conditions; the coding scheme should be effective whether the quality of data is to be advised in day-or nighttime using either of the three mandatory ECDIS modes ( day, dusk, night ) shown in Figure 4.

What datum is used in ECDIS?

WGS 84 is the Geodetic Datum used by GPS, ECDIS and ENCs.

What is the difference between safety depth and safety contour?

Industry stakeholders have discussed a lot about the pros and cons of paperless navigation concluding that ECDIS does have an edge over the traditional paper chart navigation. However, the question for the navigating officers remains the same. Can they steer the vessel, following a pre scheduled passage plan, within the safety margins that they set, from berth to berth, avoiding grounding? At this point, it is worth to mention the passage plan’s main purpose which is to use the available ‘navigational waters’ for the indented voyage so that the vessel could safely conduct the voyage.

• The ‘navigational waters’ can be mainly affected by the water depth, which is indicated both on paper charts and ENCs.
• Specifically, the depth measurement, as indicated, is the result of a relevant depth survey which varies in age and quality depending on the measurement techniques and the available technology.

Because priority for surveying is given to the major shipping routes, each navigator sailing into unfamiliar waters away from these routes should be able to interpret the various quality indicators that are, or should be, indicated on every chart. This is why many guides are available with best practices of navigation for commercial vessels and cruising yachts that help mariners to decide on how much confidence they should show on the marked depths.

However, a mariner should be always wary of any chart that does not feature these indicators, irrespective of whether it is a traditional paper chart, or an ENC. ECDIS dispay vs traditional paper charts On the traditional paper charts, the Reliability Diagram (old charts) or Zone of Confidence diagram (new charts) indicate the depth accuracy based on surveys.

Navigators should carefully check the areas that they have chosen to sail, find the relevant indication on diagram and apply additional measures or safety features to protect the vessel from grounding. On ENCs the same policy is followed with the exception of the indication of accuracy which is well spread and marked on the chart with CATZOCs (Categories of zone of confidence). which indicates the accuracy of depth. This indication is subject to ON or OFF selection by the navigator, therefore, for an unfamiliar user the risk is increasing. In particular, there is risk of not displaying and checking the depth accuracy, resulting in unpleasant situations for the passage planning, thus, vessels to reach the depth limits (in accordance with calculated UKC) and finally to run aground because the depth result was not as accurate as the navigators expected to be.

Shallow Contour: Indicates the depth below a vessel could run aground and it is equal to vessel’s maximum static draft.Safety Depth = Maximum Draft(static) + UKC (Company’s Policy) + Squat(Maximum) – Height of TideSafety Contour: Is calculated same as per Safety depth AND activates ALARM when depth is lessDeep Contour: Indicates the limit of sea area where shallow water effects occur that can affect a vessel. It should be estimated twice or four times the draught of vessel (depending on the depth of water available)

Image 1: Areas of Navigational Waters ECDIS safe settings Although color code may vary in different ECDIS system displays, the generic idea remains the same. Another key issue to consider is to include the chart depth accuracy into UKC calculation or make a comparison between the CATZOC with the UKC (Under Keel Clearance) which is more common.

1. The UKC sets the minimum level of distance between the deepest point of a vessel and sea bottom.
2. In particular, it is a company-specific measurement, therefore, it is company’s responsibility to specify this distance and Masters must consider it during passage planning (especially in shallow waters).

Again, the depth accuracy emerges as an important issue for UKC calculations. For example, if a vessel has set the UKC to 0.5m but the chart accuracy has +/- 1 m, this may cause problem and the navigating officers are advised to take this issue into consideration.

• Table 1 shows UKC correction due to the different Zone of Confidence of ENCs.
• The Category D is worse than Category C; it cannot be trusted and large anomalies in the depth can be expected.
• Also, the Category U is the unassessed category; the quality of the bathymetric data is not yet assessed.
• In conclusion, Electronic charts and ECDIS are necessary tools for navigators in order to plan the route and monitor the position easier and faster.

Considering that these electronic means are based on human surveys and measurements, the possibility of false information regarding depths, heights etc cannot be excluded. This is an additional factor to be considered during e-navigation and therefore all mariners (navigators, OOW and Masters) are advised to be always alerted and stay focused when they use these means of navigation. Table 1: Recommended table of UKC correction due to different Zone of Confidence of ENCs.

What is the effect of the safety depth setting on ECDIS?

RESPONSE – From Andy Norris MNI, author of ECDIS and Positioning Similarly to paper charts, ECDIS has two methods of indicating depth- contours and spot soundings. Contours are ascertained by the surveying hydrographic office from the detailed soundings of the original survey used to compile the ENC.

The contours are put onto the ENC in two separate ways. Firstly, as a curve that represents the depth contour and secondly as an area with a depth that lies within a defined range of values- effectively the values between the adjacent depth contours. Not surprisingly, the depth contour is a line object, the depth area is an area object and soundings are put onto the ENC as point objects.

On ECDIS the user needs to select a safety contour. If a safety contour is entered that is not available on the particular ENC in use then the system will use the next deepest available contour. Areas that are deeper than the safety contour will have a grey or white background in the normal daytime viewing mode, depending whether in two or four colour depth area indication settings.

• If within a specified time set by the user, the ship is about to cross the safety contour an alarm will sound.
• If equipment follows the IMO requirements on this, the alarm should only need a single acknowledgement and should not alarm again, except (perhaps) when about to recross the safety contour.
• However, it is possible that this is implemented differently on different machines and feedback to the ECDIS Forum concerning this would be appreciated.

The user also needs to set a safety depth. This affects the indication of spot soundings when selected to be displayed on ECDIS. They will appear as bold numerals when the spot sounding is less than the safety depth, highlighting the potentially unsafe areas.

However, the safety depth feature does not trigger an alarm but it may provide an indication. There is an IMO requirement that “An indication shall be given to the mariner if, continuing on its present course and speed, over a specified look-ahead time or distance set by the mariner, own ship will pass closer than a user-specified distance from a danger (e.g.

obstruction, wreck, rock) that is shallower than the mariner’s safety contour or an aid to navigation”. It is to be hoped that no design interprets this as applying to soundings that are less than the selected safety contour. A sensible approach here would be either to give no indication or to base the indication on the selected safety depth.

In fact, it is unlikely that any ECDIS does provide distance-specific indications on soundings that are less than the safety depth but feedback to the ECDIS Forum if such a feature is available on specific equipment would be appreciated. As mentioned in the enquiry, depth contours on some ENCs can be relatively far apart, and sometimes do not permit their simple use when navigating close to shallow waters, such as on port entry.

In such areas soundings enhanced by appropriately set safety depths must be used. However, providing the ECDIS in use does not trigger a recurrent alarm that needs continuous acknowledgement, it should not be necessary to change the safety contour when navigating in such waters.

Instead, the ECDIS will continue to provide a visual reminder on the chart that the situation requires care, simply because own ship will be displayed in an area that is coloured blue, indicating that the waters are shallower than the safety contour. It is, of course, good practice to make a note of this impending situation on the passage plan.

In such waters close and regular inspection of the chart is always necessary, whether using paper or ECDIS. However, if the ship is kept away from depth soundings displayed in bold numerals then there should be sufficient water, providing an appropriate safety depth has been entered.

Many port areas have more closely spaced depth contours than in the quoted example. For instance, Harwich has them at 2, 5, 10, 15 and 20 metres. It is always worth lobbying the hydrographic office responsible for the compilation of the ENC data if it is considered that insufficient contours are available.

However, as described above, safe navigation is still quite possible where there are few contours- providing there are sufficient soundings, that they are turned on and an appropriate safety depth has been set. Also, on many systems user-specified lines and areas can be generated and used to highlight a rough approximation to the required safety contour and can also be set to alarm if the vessel approaches the boundary- but the safe navigator never relies on alarms! : Safety contours

What is margins of safety and safe water in navigation?

Margins of safety will show how far the ship can deviate from track, yet still remain in safe water (see below). As a general rule the margin of safety will ensure that the ship remains in waters of a depth greater than draught + 20%.

What are the 4 ECDIS alarm requirements?

The five mandatory alarms (as per IMO ECDIS Performance standards) are: crossing safety contour, deviation from route, positioning system failure, approach to critical point and different geodetic datum.

Jack Gloop