How To Set Safety Contour On Ecdis
Assumptions – The following assumptions were made in creating the scenarios described in these slides.1.ECDIS allows the mariner to set the Safety Depth and the Safety Contour Depth independently.2.The mariner sets the Safety Contour Depth equal to the “Vessel Safety Draft,” which is calculated as: Vessel Safety Draft = Vessel Draft + Dynamic Squat + Safety Margin 3.Depths are considered “safe” if they are equal to or deeper than the Safety Contour Depth.4.Depths shoaler than the Safety Contour Depth are considered “unsafe.”

What is the safety contour setting?

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.

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. The default safety contour if not specified by the mariner is set to 30m. 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.

Safety depth value can be set as 10m. However, we haven’t yet considered the depth accuracy as per ZOC. 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. 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.

How is the safety contour always displayed in the charts?

The safety contour on the ENC display will default to the next deeper contour if the depth contour of the set value is not available in the displayed ENC source data. During route planning, an indication will be made if the route is planned to cross the ship’s safety contour.

How do you calculate 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.

  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.

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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 contour value?

ECDIS uses a ‘safety contour’ value to show an extra thick line for the depth contour that separates ‘safe water’ from shoaler areas. If the mariner does not set an own-ship safety contour value, ECDIS sets the value to 30m.

How to use 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.

The older the data are, the less accurate they will be, due to the limited technology equipment used in each time. A case study The Captain and the second officer are reviewing the passage plan. 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.

CatZoc Position Depth
A1 5 meters 0.5 meters + 1% of depth
A2 20 meters 1.0 meters + 2% of depth
B 50 meters 1.0 meters + 2% of depth
C 500 meters 2.0 meters + 5% of depth
D Over 500 meters Over 2.0 meters + 5% of depth
U (Not assessed)

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 Scamin in ECDIS?

Scale Minimum (SCAMIN) concept in ENCs – The ” SCAMIN ” value of an object determines the display scale below which the object is no longer visible on an ECDIS. The purpose of SCAMIN is to:

  1. reduce the amount of clutter displayed to the ECDIS user,
  2. to prioritize the display of objects and
  3. to improve display speed.

SCAMIN is a very powerful S-57 attribute that can be encoded on particular objects with the aim of reducing ECDIS screen clutter. When this attribute is used, ECDIS software can simplify and generalize detail as the ECDIS user zooms out and can bring in more and more detail as the user zooms in.

Where would you turn on the Catzoc in ECDIS?

CATZOC table – There is a more accurate tool available on ENC’s in comparison to paper charts. On the modern ECDIS S-57 compliant ENC (Electronic Navigational Chart) you can turn on the layer called “Accuracy”, or “Data quality”, or “Accuracy pattern”, etc.

ECDIS displays these CATZOC values in ENCs using a triangular or lozenge-shaped symbol pattern. The number of stars contained within these symbols denotes the CATZOC value. For example, six stars are given to the highest level of data quality (A1) and two stars to the lowest (D). A single star is not used to avoid possible confusion with a rock symbol.

Areas that have not been assessed for CATZOC are shown as the symbol (U) for unassessed. This layer doesn’t need to be displayed all the time. However, during passage planning, or when one wants to access the present situation and possible navigational risks the deck officer shall be able to understand the meaning of the accuracy pattern. You can download the pdf version of the CATZOC table here.

What are 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.

What is S 52 and S 57 in ECDIS?

What are S52, S57, S63, IENC and AML ? The International Hydrographic Organization (IHO) has published a number of publications that standardize how ENC data should be encoded, visualized and protected:

S-57 (IHO Transfer Standard for Digital Hydrographic Data) is the standard used for the exchange of digital hydrographic data between national hydrographic offices and for its distribution to manufacturers, mariners and other data users. It defines how ENC cell data should be physically encoded to files. The S-57 implementation is based upon the IHO Transfer Standard for Digital Hydrographic Data – Special Publication No.57 – Edition 3.1 – November 2000. S-52 (Specifications for Chart Content and Display Aspects of ECDIS) specifies how ENCs should be visualized on a map. It provides a symbology set and a number of rules that rigorously define how each individual object in an ENC cell should be displayed, by specifying the symbol, color and line style. The S-52 implementation is based upon the Specifications for Chart Content and Display Aspects of ECDIS – Special Publication No.52, and the IHO Presentation Library User’s Manual – Edition 3.4 – January 2008. S-63 (IHO Data Protection Scheme) provides a mechanism to encrypt and protect ENC data from unauthorized use.

Parts of the S-52 specification are not freely available, but need to be purchased via the IHO office. Although S-57 was initially designed for the encoding of ENC data, the standard can also be used for the encoding of other products. One such product is Additional Military Layers ( AML ), which is used for the encoding of military nautical data.

Another is InlandECDIS ( IENC ), used for river navigation. The IENC feature and attribute resources, as well as the visualization rules, are based on the InlandECDIS specification version 2.4. You can use it to open IENC versions 2.0, 2.1, 2.2, 2.3 and 2.4. The AML feature and attribute resources are based upon the AML Feature and Attribute Catalogue version 3.0.1.

The visualization of AML is based on the AML Portrayal Specification version 3.0.0. Reference information on AML, including the Feature and Attribute Catalogue, can be downloaded at the following location: : What are S52, S57, S63, IENC and AML ?

What is s 101 in ECDIS?

What is S-101? S-101 is the latest product specification for ENCs. S-101 ENCs will provide a base chart layer upon which other interoperable S-100 based products can be overlaid, such as S-102 (Bathymetric Surface), S-104 (Water Level Information) and more.

Can a vessel cross a safety contour?

Traditional method of passage planning on paper chart: Using a draft of 14 mtr and applying a 2 mtr safety margin, the second mate would mark off areas with depth 16 mtrs and less, on the navigational chart. These areas would then be highlighted, using a pencil, as a NO GO area and the passage would be planned keeping well clear of this area. Correspondingly on ECDIS When the safety contour value is set as 7 mtrs. ⦁ Safety contour is emphasized (bolder) than other contours. ⦁ If the safety contour specified by the mariner is not in the displayed SENC, the safety contour shown defaults to the next deeper contour. ⦁ ECDIS will give an alarm if, within a specified time set by the mariner, own ship crosses the safety contour. ⦁ Areas with depths lesser than the set safety contour is coloured blue and deeper depth area is coloured white. ⦁ Enabling the “shallow pattern” provides a cross hatch pattern to further emphasis the NO GO area as was done on paper charts. Hence like the traditional NoGo areas on a paper charts, on an ECDIS, ⦁ Blue area denotes NO GO areas ⦁ White area denotes the navigable area. If the entire planned passage upto the pilot station is through the “white” and the “Grey” areas, followed by a channel/river transit to the berth: Then at no point in the voyage, the vessel’s planned track is expected to cross into the blue areas. In this case ⦁ By setting safety contour setting ⦁ And enabling the shallow contour pattern, The No Go area is automatically marked by the ECDIS. There is, generally, no need to additionally mark NoGo areas using mariner info overlay. What should the OOW do an obtaining a safety contour alarm? OOW should call the master immediately and alter course back into grey/white zone if you are about to violate the NO-Go area. By just feeding in the safety contour setting, the ECDIS ENC display is sub-divided into blue (no-go) and white (navigable) zones. Changing over from 2 color mode to 4 color mode and by entering appropriate values for shallow contour setting and deep contour setting, we find that: ⦁ The blue area gets subdivided into dark blue and light blue areas. ⦁ The white area gets subdivided into grey and white. What does the colour indicates DARK BLUE ZONE: On inputting the shallow contour setting, areas on the ENC with depth value <= Shallow contour setting is displayed as dark blue zone. Example:- Assuming vessel static draft of 7.80 mtr With shallow contour setting at 5.00 mtrs Dark blue zone denotes grounding depths. LIGHT BLUE ZONE: On inputting the safety contour setting, areas of the ENC with depth value lesser<= Safety contour setting is displayed as light blue zone. Example:- Safety contour setting = (Static draft + all allowances + Minimum net UKC requirement for that area – Height of tide) Vessel is in congested waters, Height of tide as 1.5 mtrs, we take 0.50 mtrs as the minimum net UKC requirement. Giving us Safety contour setting = 7.8+3.0+0.5-1.3 = 10.0 meters With safety contour setting at 10.0 mtrs Light blue zone denotes an area where you are in non-compliance with the Minimum Net UKC policy of the company. GREY ZONE On inputting the deep contour setting, areas of the ENC with depth value <= Deep contour setting is displayed as Grey zone. Grey zone denotes an area of potential shallow water effects White zone is relatively safe waters No Go Area :- Dark Blue Zone and Light Blue Zone IMO "standard" display setting is the minimum ECDIS layers considered essential by IMO for safe navigation. The "standard" display des not include the sounding layer as the four colours shown on the ECDIS display provide sufficient data for anti-grounding purposes. Example:- The pilot station is situated within the light blue zone (No go area) of the ENC. We will use a vessel with draft of 12 mtrs. Dynamic Draft= 12+1.9 (all allowances ie. Squat, heel correction, density correction and others) = 13.9 m Safety Contour Settings = 13.9+0.5-0.4 = 14.0 m Safety depth = 14.0 m Shallow contour = 10.0 m Vessel has to pass the safety contour area to enter channel When the vessel first crosses the safety contour, the safety contour alarm will be generated to alert the navigator to a potential violation of the NO GO area. However no further Anti-grounding warnings will be generated, if for any reason, the vessel deviates off her planned route. Why ECDIS has this issue The ECDIS ENCs like the earlier paper charts, have sounding contour layers of 5/10/15 or 05/10/20 / 30 or 100/200/300 etc. Hence, when we set the safety contour setting as 14 mtrs, the ECDIS defaults to the next available contour which is 20 mtrs. So though the light blue area is a No-GO area as per the ECDIS display, technically we can navigate in waters with depths> the safety contour setting of 14 mtrs (highlighted as NAVIGABLE ) Depths <=14 mtrs (highlighted as NO GO and cross hatched with red lines ) are still No-Go depths as the vessel will likely be violating the UKC policy of the company. The risk associated with navigation in these safer areas within the light blue zones are: ⦁ Availaible sea room inside light blue area is generally confined or restricted for safe navigation ⦁ Soundings are not easily visible, more so in the night mode ⦁ No more alarms are generated once the vessel crosses the safety contour Configuring the ECDIS for crossing the safety contour As per above the safety depth setting is set at 14m, so all depths <=14 m will appear bold. Spot soundings with depth <= safety depth will appear bold. Note These are not required to generate any alarms as per the IMO performance standards Lets make some modification on ECDIS for more safe passage planning Using user maps (mariner info overlays), demark the no-go areas within the light blue zone. (only usermap lines with danger attribute will generate alarms when interrogated by the safety cone) Use warning lines to follow the virtual 14 mtrs (safety depth setting) contour indicated by the darker safety depths. Note: These warning lines will generate an alarm when interrogated by the vessel's look ahead (danger detection) cone Navigate within the light blue zone with the vessel look ahead (danger detection) cone activate. (Ensure that look ahead cone time or distance setting is carefully set to meet the particular circumstances. Note: If set too long it will create numerous alerts that may distract the navigator. Obstructions (dangerous to navigation) All obstructions (dangerous to navigation) with an attribute equal to or lesser than the safety contour setting will be highlighted with a Magenta Cross Head Symbol. Any obstructions (dangerous to navigation) with an attribute more than the safety contour setting will not be highlighted with a Magenta cross head symbol.

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Why do we need safety contour?

The safety contour is important visually because a thick black line is placed around the safety contour itself, thus highlighting safe water ; and as an alarm setting, because it is this contour that will generate an alarm based on the parameters set for approaching shallow water.

What are the no go areas on ECDIS?

4. NO GO Areas – We are required to mark the no-go areas along our route. These are the areas that are the danger to navigation and we must not navigate into. But let us say there is a wreck (or shallow waters) about 50NM from our planned route. Do we need to mark this as “No-Go area”? On a paper chart, the answer to this question was simple.

And the answer was, Yes, we do need to mark it as no go area if it is on voyage chart. But the ENCs on ECDIS are seamless and the same logic does not apply on ECDIS. So what is the maximum distance that we need to mark the no-go area upto? Well, ideally this distance should be provided in the company’s navigation manual.

Alas, most certainly you will not find it there. So, in the case, a distance can be decided by the master and the same communicated to the navigating officers. If we have decided the distance of 50NM, we need to mark the No-Go areas in the range of 50NM from our route.

It is not that we cannot cross the shallow contour. We can. The only thing we cannot do is run over the safety depth. And thus the shallow contour is not a no go area. Even if we consider this as a no go area, the distinction of this area is already visible with a different color. Why clutter the ENC further?

The marking for no go area needs to be done for something that the navigator could miss. Something like an isolated danger, wreck, depth area or an area like with oil rigs that vessel needs to avoid. We need to identify all such areas and mark these as “No-Go Areas”. To mark the no-go area, go to User Map -> User map editor and open the user map that you have created for the present voyage. By now, you should be able to create lines, shapes and add text in the user map. To mark the user map you need to use these lines and shapes to mark the area as a No-Go area. Use your artistic skills to decide which shape or line you need to use for marking of No-Go area. Once marked, go to the property and change the line color, thickness etc. Again use the color as something other than the course line color and thickness slightly lesser than the course line. Finally, write the text as a No-Go area around the marked area.

What is guard zone in ECDIS?

GROUNDINGS: HOW ECDIS HAS CONTRIBUTED – Alarm management One of the recurring aspects of reported groundings involving ECDIS is the use of audible alarms. There are often too many audible alarms, from ECDIS and from other equipment on the bridge, and this is a concern that has been raised by various marine investigators.

This has been addressed, at least in part, in the revised presentation library where it states that navigational alarms should be set to a minimum by the navigator, using his discretion or in accordance with company policy. This however does not impact on the number of system alarms, which still have potential to cause confusion and distraction.

In one example, there were frequent requests from the ship’s command to the managing company to disable the alarms. The company therefore sanctioned the disabling of alarms without informing class which had the effect of making the system non-compliant with IMO performance standards.

In another reported case, the visual navigation alarm indicated the ship was running into shallow water but it was not noticed by the navigator due to the fact that he was concentrating only on collision avoidance. The audible alarm was not connected and as such was not compliant with IMO performance standards.

Crucially, despite the lack of audible alarm the navigator appeared compliant, apparently still relying on the ECDIS to somehow alert him despite the lack of audible alarm. Too many alarms have been shown to cause alarm fatigue and to be a major distraction to competent watch keeping.

  1. However, disabling all ECDIS alarms prevents the system from functioning properly.
  2. This problem presents some challenges for the future development of performance standards for ECDIS, but for the time being the audible alarms must be connected and operable.
  3. Good installation enabling all inputs to be fully integrated can go a long way to reduce the number of alarms.

Correct use of ECDIS safety settings In most cases reviewed by the Club’s loss prevention department, one or more of the safety settings was incorrect. Depending on the type of ECDIS, the equipment will have a safety depth feature and some may also have a contour setting.

In either case, ECDIS has a safety guard zone. This is an area set by the navigator ahead and to angle on either bow for a safety depth in which an audible alarm should sound if a danger is identified within this guard zone. The safety depth should be used while planning the passage and a safety guard zone used for monitoring the passage.

Contour setting: A safety contour is intended to show the navigator a distinction between safe and unsafe water. Most ECDIS systems are designed for the safety contour to default to 30 metres. At this setting many dangers will be obscured in the unsafe area.

  • For example, on a ship with a draught of 8 metres negotiating the Dover Strait with a default setting of 30 metres, the ECDIS would show much of the Straits as unsafe water.
  • Many shallow patches that the ship would go aground on would not be highlighted.
  • Thus a safety contour should be selected in the same manner as the safety depth described below.

Safety depth: This setting, if set correctly with the alarms functioning, will give an audible and visual warning if there is an obstruction less then the safety depth set. For this to work properly, an accurate chart must be used. Electronic navigations charts (ENC) are based on same the same information as paper charts with the same accuracy.

However in ENC this information is referred to as CATZOC (Zone of Confidence Category). For example, Category B has an accuracy of horizontal distance of +/- 20 metres and depth error of +/- 1.2 metres. It is extremely important that this is considered carefully when calculating the safety depth. In most cases reviewed, the safety depth was either not set or set incorrectly.

The safety depth should be calculated as follows: Safety depth = draught +minimum under keel clearance + allowance for squat + CATZOC depth correction + allowance for swell (if applicable) – height of tide. In some parts of the world the swell should be considered particularly when crossing a shoal or bar in an exposed location.

  • C ross track distances: This is the distance that the ship can deviate from the planned route before the alarm is activated.
  • This should be set to give a safety margin between the maximum off track distance and the point at which the vessel would cross an obstruction.
  • In one case the company had approved a series of routes without using cross track distance settings.

These settings are key to keeping the ship in safe water, particularly in coastal waters. System knowledge In all the grounding cases reviewed the ECDIS was not set up correctly for the prevailing circumstances which was compounded in most cases by the audible alarms being deactivated.

The navigators were heavily relying on ECDIS despite the reduced alarm capability imposed. The navigators were working in a misguided reliance on the ECDIS being a robust safety asset despite the reduced alarm capability they had imposed. It is extremely important that all who use the ECDIS are fully conversant with the safety features, that they know what they are and how to correctly calculate and set them in the system.

There is a need to understand how the structure of overlays work to create the picture on the screen and what features are removed/added with what particular setting. It is also vital to be on the most appropriate chart scale. Most ECDIS have an automatic optimum scale setting.

  1. This should be used and where necessary this can be zoomed in or out but always returning to the optimum setting.
  2. This is no different from using paper charts as the same logic applies.
  3. Chart corrections and warnings A major advantage of ECDIS is that electronic chart corrections can be updated by data input into the ECDIS.

However, temporary and preliminary notices have to be added manually. A review of recent cases has shown that, in many cases, those updating the charts have presumed that these notices are included in the weekly chart corrections as an automatic upload which is not always the case.

  1. Some chart providers do offer a service to cover this, however it is for the ship operator to ensure that these corrections are updated on the system by whatever means.
  2. Complacency In the cases reviewed there appears to be a general conception that ECDIS can be completely relied upon.
  3. However, like any other navigation aid, it is only as good as the user.

If the information is properly inputted and the safety parameters are correctly calculated then ECDIS is an excellent aid to navigation. Many previous developments such as ARPA were improvements on existing navigational aids such as RADAR. However, ECDIS is not just an improvement on paper charts but rather it requires a conceptual change to the way a bridge team operates because ECDIS consolidates all navigation information and allows for a many different ways to present and utilise that information.

What is XTD in ECDIS?

Cross-track distance (XTD), is set to a number of meters on the port and starboard side of the dotted track line. The corridor can then be automatically checked in ECDIS for under-keep clearance.

What is maximum static draft?

A ship’s safe maneuverability depends on the available water depth of the navigation area concerning the vessel’s draft. Water-depth limitations will considerably change the pressure distribution around a moving ship. They will mostly cause an increase of the hydrodynamic forces due to the ship’s motion through the water.

Besides the expansion of the ship’s resistance, water-depth restrictions generally decrease her maneuverability. The dependency of the maneuverability in the lower Under Keel Clearance(UKC) range is very significant: a small reduction in UKC results in a considerable increase in the turning circle dimensions.

As a result, larger bend radii are required in shallow navigation channels. A ship’s directional stability and maneuverability change considerably as a function of the available UKC. Especially in natural waterways (rivers, estuaries) where the water extent may vary significantly, both over the channel and over the tidal cycle, a ship’s maneuvering characteristics may be subjected to essential changes transit through the canal.

  • Open Sea (FAOP): The minimum UKC in the dynamic condition is 50% of the static draft.
  • Restricted Waters/Port Approaches/Harbour Transits (SBE): The minimum UKC in the dynamic condition is 10% of the static draft.
  • Tankers Only SBM / CBM mooring: the minimum UKC is 50% of the static draft.
  • Alongside (1st Line Ashore to SBE): For vessels 20m breath: 1.5% of the ships beam

The Static Draft is the draft when the vessel is not making way or subject to sea, and swell influences, i.e., the maximum draft the ship has loaded to. (UKC is a percentage of the Static Draft) The Dynamic Draft is the draft when the vessel is making way and subject to squat, sea and swell state and increase of draft due to heel when turning. Calculating UKC The following specific factors must be taken into account during voyage planning and recorded prior to proceeding en route:

  1. Draft observations/calculations including estimates of hogging and sagging;
  2. Increase in draft due to heaving, pitching and rolling motions;
  3. The effects of squat
  4. Increase in draught due to change of water density;
  5. Minimum charted depth available;
  6. The predicted height of tide (minimum available during planned transit window);
  7. State of sea and swell;

Guided by local knowledge and experience, it may be necessary for the Master to factor in an additional safety margin to make an appropriate allowance for the following variables:

  1. the accuracy of the hydrographic data (references to reliability are often included on charts);
  2. the vessels size and handling characteristics;
  3. Changes in the predicted tidal height, caused by wind speed and direction and high or low barometric pressure;
  4. the nature and stability of the seabed i.e. sand waves, siltation, pipelines, obstructions etc.

Many ocean charts are still mainly based on sparse and inadequate sounding data obtained from a wide variety of sources of varying reliability and accuracy. Chart accuracy is best along well-frequented routes, but even in these waters, undetected dangers may still exist, especially for modern deep-draught vessels.

Very little of the Oceans have been thoroughly surveyed. Certain areas are subject to earthquakes and volcanic activity, which could cause shoals to build up even in those areas which have been well surveyed; live coral is continually growing. The approximate positions of many hazardous shallow patches have been charted; these must be given a wide berth.

The Mariner’s Handbook, Ocean Passages of the World, and relevant Sailing Directions must be consulted for further information on the dangers of overreliance on charts. Where a request has been made by charterers to decrease the above parameters, or it is known that the above criteria cannot be met (such as advice from port authorities or Pilot), the Master must notify and seek the ship’s approval’s DPA.

  • He should indicate the calculated UKC and comparing it to the Company policy.
  • This notification is to be accompanied by a suitable risk assessment carried out on the factors known to the Master.
  • This Risk Assessment should include relevant controls, such as additional bridge manning, minimum speed, tug assistance, soundings & position monitoring.
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The latest sounding information, including the nature of the bottom, should be ascertained directly from the local authorities or terminal. Approaches to Shallow Waters The bridge team must keep the engine room well appraised of the vessel’s progress.

The cooling water intake must be changed over to the high sea suction before the ship enters an area where the under-keel clearance is restricted. Considerable quantities of mud and debris can be drawn into the cooling system if this is not done in time. Alongside A minimum UKC while alongside, following the requirement above, must be noted in the Cargo Handling Plan.

It must include instructions outlining the maximum draft, trim, and list. Taking the Ground There may be occasions where, through the nature of the port, smaller vessels are required to ‘take the ground,’ i.e., sit on the bottom. In such circumstances, the ship should be certified by class for ground loading / discharging.

  • The effects of stress and stability;
  • The nature and level of the bottom;
  • Vessel requirements for maintaining services such as fire-fighting and engine cooling water.

Based on this risk assessment, Critical Operations Checklists should be developed for taking the ground and subsequent re-floating, and these should be referenced in the cargo plan. Squat and Interaction The squat is the bodily sinkage of a ship in the water when making headway.

It varies from ship to ship. The amount of squat will depend upon several factors but in certain conditions may be as much as two meters. If not factored appropriately, this could lead to grounding, loss of steering, and/or collision. When navigating in channels or areas with restricted depth, increased draught due to squat must be taken into account.

It must be borne in mind that this effect will increase with speed and is greater when the channel is also restricted in breadth. The handling characteristics of the vessel may appreciably deteriorate when navigating in shallow water, in narrow channels or when navigating close to other vessels.

The squat can occur with a moored vessel, in an ebb tide, alongside a jetty. Tide speed along the stationary vessel produces components of bodily sinkage and trimming effects. The two combined give ship squat for a stationary ship. It should be considered when calculating UKC alongside. Particular allowance should be given to the impact of sea and swell when the vessel is engaged in operations at an offshore mooring such as an SBM.

The UKC calculation record must be shown to the Pilot during the Master-Pilot information exchange discussion. See Attached Documents for factors governing ship squat and how to calculate squat. Squat information relevant to the vessel for both loaded and ballast passages should be displayed on the wheelhouse poster compliant with IMO Res.A.601(15) and included on the Ship to Shore Master/Pilot Information Exchange provided to the Pilot.

  1. More ship’s power is absorbed by the water due to increased friction.
  2. Usually sinkage is greater forward than aft for ships of tanker speed and displacement in any depth.
  3. Turbulence interferes with rudder and propeller effectiveness. Signs that the ship has entered shallow water conditions can be:
  4. Wave making increases at the ford end of the ship.
  5. Ship becomes more sluggish to manoeuvre.
  6. RPM indication will show a decrease. If the ship is in “open water” conditions, i.e., without breadth restrictions, this decrease maybe 15% of the service rpm. If the ship is in a confined channel, this decrease in rpm can be about 20% of the service rpm.
  7. There will be a drop in speed, If the ship is in “open water” conditions, it may amount to a drop of 60% of the service speed.
  8. The ship may start to vibrate suddenly because of the entrained water effect causing the natural hull frequency to become resonant with another frequency.
  9. Pitching reduces, due to cushioning effect of water under the keel

Related Information Collecting Information and Data for Passage Planning Ships trial- turning circle diameters Definitions of various tide terms and related guideline Ships navigation -Factors Affecting Turning circle diameter More info pages

  1. Ships motion at sea and required precautions Ships are affected by movement in six degrees of freedom; rolling, pitching, heaving, swaying, surging and yawing. Of these, rolling, pitching and heaving generate the highest forces during heavy weather. Read more.
  2. Stress and Stability Calculation,draft, trim & free surface effect The Master shall ensure that the conditions of stability, hull strength, draft and trim of the vessel at sea and on arrival / departure at / from port and during loading / unloading cargo, bunkering and water ballast exchange, have been worked out, to secure safety of the vessel. He shall confirm the safety of the vessel by proper GM, stress and other factors as being within appropriate Limits. Read more.
  3. Passage planning requirement for safe navigation at sea Before proceeding to sea, the Master shall carefully check the Passage Plan, made after receiving the voyage instruction from the Charterer or the Company. Read more.
  4. Safe anchoring practice Anchoring into “Deep water” which is defined depth of water is beyond 50 meter, must be carried out with “Walk-back Style, however, on the VLCC operation there exists such a big inertia, Master can treat with Walking-back style even in the anchorage where water depth less than 50m, if following conditions are to be forecasted. Read more.

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What is a good contour interval?

What is Contour Interval? – A contour interval in surveying is the vertical distance or the difference in the elevation between the two contour lines in a topographical map. Usually there are different contour intervals for the different maps. Considering the size of the area to be mapped, contour intervals are assumed.

What is minimum contour interval?

The minimum contour interval is the double vertical error (RMSE or standard deviation) of the height model. You can find that for ASTER GDEM in: Lang, R. Harold, and Roy Welch.1999. “Algorithm theoretical basis document for ASTER digital elevation models.” It’s defined by the “United States National Map Accuracy Standards (NMAS)” For example: If your DHM have a resolution of 2x2m, and the vertical error is 4m, you can extract contours of a minimum of 8m. PolyGeo ♦ 64.8k 29 gold badges 107 silver badges 327 bronze badges answered May 4, 2012 at 9:14 MartinMap MartinMap 8,146 6 gold badges 47 silver badges 105 bronze badges 0 I would say this depends on your knowledge of the data and how it was collected as well as how the DTM was generated from the raw data (regular grid vs interpolated from irregular points or other sources) I don’t think there is a rule of thumb. 0

What is contour ratio?

It is the ratio of width to height of bounding rect of the object.

What are the 5 mandatory alarms of ECDIS?

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.

What CatZoc means?

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.

CatZoc Position Depth
A1 5 meters 0.5 meters + 1% of depth
A2 20 meters 1.0 meters + 2% of depth
B 50 meters 1.0 meters + 2% of depth
C 500 meters 2.0 meters + 5% of depth
D Over 500 meters Over 2.0 meters + 5% of depth
U (Not assessed)

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.

Should it be possible for the mariner to select a safety contour from the depth contours provided by the SENC?

It should not be possible to remove information contained in the Display Base.3.6 It should be possible for the mariner to select a safety contour from the depth contours provided by the SENC. ECDIS should emphasize the safety contour over other contours on the display.

What is a user entered depth that ideally coincides with the contours giving an adequate safety allowance for the dynamic draft of the vessel?

CRITICAL ALARMS AND ALARM SETTING GUIDANCE – When using ENCs, an alert will be given when charted hazards enter the safety domain, even if the hazard is not visible on the displayed portion of the ENC. The alarms listed below should be kept activated at all times.

Alarms are to be set by the navigating officer at the time of passage planning and once the Master has reviewed the passage / alarm settings, they should be locked where such a facility is available. The alert will be an alarm or indication, depending on the circumstances and user settings. During passage, if any of the below alarm is received, O.O.W.

should immediately inform Master: 1. Crossing Safety Contours / Depth

There are generally three contour settings available to the user for highlighting available depth. The contours are differentiated by colours and if a guard zone touches the safety contour it will give an alarm. The contour will be selected only for that value for which a contour exists on the ENC. If any other value is selected, it will then select the next available contour.

i. Safety Contour: This is a user entered depth that ideally coincides with the contours, giving an adequate safety allowance for the dynamic draft of the vessel. ii. Deep Contour: This is user entered depth that will affect the appearance of spot soundings.

Safety Depth: This function is primarily used for the route check and an alarm will be generated upon encountering shallower depth in look-ahead area. The spot soundings below the specified values will appear bold.

My Company ECDIS Safety Settings :- Minimum Settings: Setting should be based on vessel’s dynamic draft. Dynamic draft = Present maximum static draft + All allowances ( Squat + Sinkage due to Density Allowance for Sea State + Heel Correction + Seasonal variation + other allowances) Shallow Contour >= Dynamic draft Safety Contour >= Dynamic draft + minimum net UKC requirement for that area + 2 meters (safety margin) Safety Depth >= Dynamic draft + minimum net UKC requirement for that area Safety Height: Air draft of the vessel + 1 meter. Deep Contour >= 50 meters