Where do you set the safety depth?

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.

The UKC sets the minimum level of distance between the deepest point of a vessel and sea bottom. 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 ECDIS 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.

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.

1. 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.
2. Contours are present in the values of 5, 10, 15, 20, and 30 and so on.
3. 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.

What is the safety contour setting in the route planning tool used for?

The ECDIS revolution introduced a new way of navigating. The ENCs are fully customizable, the ECDIS anti-grounding alert function warns the mariner if the ship is approaching hazards to navigation or shallow waters. To get the most out of these amazing functions the navigator must properly set-up the system and, most importantly, must know also the limitations of some of them.

In this article we will discuss how having bathymetric lines every 5-meter will impact the identification of safe and unsafe waters. (To know more about the ECDIS Depth Contour function, read my previous article available here !) Normally, the Safety Contour is used to define the “No-Go” Areas, However, if the mariner sets a Safety Contour value not directly available in the ENC database the system will select the next available contour as the boundary between navigable and non-navigable waters as per IMO Resolution MSC.232(82):”ADOPTION OF THE REVISED PERFORMANCE STANDARDS FOR ECDIS” : “If Safety Contour value set by the operator is not available among the available depth contour of the ENC, then the ECDIS will select the next deepest available contour in the ENC ” (IMO, 2006),

In the best ENCs the mariner gets 5-10-15-20-50-100 meters depth contours but the safe draft (safe draft = dynamic draft + UKC requirement as per company policy) varies considerably. As one can imagine it is a very rare occurrence that the safe draft of a vessel coincides exactly with one of the available depth contours.

Instances will regularly occur where the ship must cross the Safety Contour selected by the ECDIS. Once the ship crosses the Safety Contour, the Safety Contour alarm is no longer available. This can affect the safety of navigation, situational awareness and decision making. The UKHO, in the Admiralty Guide to ECDIS Implementation, Policy and Procedures (NP232), explains two methods on how to configure the ECDIS to cross the Safety Contour.

Both of them include the manual drawing of “No-Go” areas, in order to clearly define the safe navigable area. If the ship approaches the “No-Go” area, the ECDIS will give a visible and audible alarm to the navigator (Anti-grounding alert function). Without drawing “No-Go” areas none of the below methods can be considered safe. In some cases, the ENC producer may have captured the ENC data from existing paper charts with depths measured in fathoms. The ENC Product Specification requires that depths on ENCs are always shown in meters. The conversion from fathoms to meters therefore results in unusual contour values.

• The picture shows the 5 fathom contour on the paper chart will convert to become the 9.1 meters contour equivalent ENC.
• NOTE : The fathom-to-meter conversion may induce some mariners to reduce the Safety Contour to a shallower value, i.e.
• To 9.1 meters, to avoid the ECDIS using the 18.2 meters contour if the calculated Safety Depth value is more than 9.1 meters.

Such a decision must be carefully evaluated and discussed, case by case, with the Captain to avoid this becoming a standard practice when setting up the ECDIS. The ENC in the below example derived from an existing paper chart with bathymetry every 5 fathoms. In other words the passage between the shallow patches is navigable but depicted as non-navigable by the ECDIS. In the picture below, in red is underlined what is realistically non-navigable and in yellow what the ECDIS shows as non-navigable. To overcome this issue the mariner can choose between two methods described hereunder.

Where is Catzoc in ECDIS?

Catzoc on ECDIS – On ECDIS, the CATZOC information is displayed as CATZOC symbols. These ECDIS symbols are in form of the number of stars. Each symbol represents a particular “zone of confidence” category. An ENC with six stars would mean that the information in this ENC is highly accurate. Let us see where to find this information on JRC ECDIS. To find this information on JRC ECDIS, go to Chart -> Chart Settings Then go to View 1. Under this ensure that option “Accuracy” is checked. This will show the CATZOC symbol on all the ENCs on the ECDIS. To get more information on the “zone of confidence” of a particular ENC, while the accuracy is still selected in the settings, right click on the ENC. Then go to S-57/C-MAP/ARCS Information. Click on the Quality of data and it will show the “Zone of Confidence” for that ENC. If you now go to “Chart Legend” tab, it will give you further information for that “Zone of confidence” like position accuracy and depth accuracy values.

How is a safety depth contour seen on ECDIS?

Safety Depth setting – So far we have only been talking about contours. We have not said anything about the actual safe depth. Safety depth is the only depth setting on ECDIS. Safety depth is the depth of the water we can safely navigate upon. And it might sound repetitive but it is the depth that satisfies the UKC policy of the company.

In ECDIS we need to enter this minimum depth. It is same what we calculated as a simple example in safety contour setting. And as I said in that section, we need to follow the UKC calculation form of the company which may account for number of factors to calculate the safety depth required. But the question is why do we need safety depth settings when we can navigate in waters above the safety contours ? This is because of two straight forward reasons i) The depth above safety contour may not always be navigable.

This is in case of a shallow depth at one point in the navigable waters. Although we might be navigating in area above safety contour, this isolated depth pose a danger. Safety depth highlights this danger. ii) The depths below safety contour may not always be non-navigable.

We can understand this If you allow me to again go through the safety contour value we entered. We entered the value of 11 meters and when we enter this value the ECDIS will take next available contour. This will be 15 meter contour. Now the depths between 11 and 15 meters are navigable for us but it will show below the safety contour.

So in the area between shallow contour and safety contour, safety depth will show the depth on which we can navigate. Let us say we set the safety depth to 16 meters. On the ECDIS, all depths below 16 metes will be shown more prominently (in Black compared to others in grey color).

What are the carriage requirements of ECDIS as per Solas convention?

ECDIS carriage requirements – The amended SOLAS regulation V/19 requires all newly built passenger ships of 500 gross tonnage and upwards, as well as newly built cargo ships of 3,000 gross tonnage and upwards engaged on international voyages to be fitted with ECDIS.

What is base display in ECDIS?

Define SENC as applicable to ECDIS: – System Electronic Navigational Chart (SENC) means a database resulting from the transformation of the ENC (a vector chart) by ECDIS for appropriate use, updates to the ENC by appropriate means and other data added by the mariner.

• It is the database that is actually accessed by ECDIS for the display generation and other navigational functions and is the equivalent to an up-to-date paper chart.
• The SENC may also contain information from other sources.
• Define Standard Display as applicable to ECDIS: Standard Display means the SENC information that should be shown when a chart is first displayed on ECDIS.

Depending upon the needs of the mariner, the level of the information it provides for route planning or route monitoring may be modified by the mariner. Define Display Base as applicable to ECDIS: Display Base means the level of SENC information which cannot be removed from the display, consisting of information which is required at all times in all geographic areas and all circumstances.

• It is not intended to be sufficient for safe navigation.
• Define Vector Chart as applicable to ECDIS: A vector chart is a digital database of all the objects (points, lines, areas, etc.) represented on a chart.
• Vector charts store information, such as isolated dangers, depths, depth contours, coastline features, cables and pipelines etc in separate layers which can be displayed as per the user’s requirements.

Vector charts are also referred to as intelligent charts as they can be interrogated for information not displayed but stored in it’s memory. Define Raster Chart as applicable to ECDIS: Raster Chart data is created by scanning the information on a paper chart and storing this information in the form of pixels.

Many thousands of pixels together make a flat digital image. Each pixel contains all the data for a particular point: colour, brightness etc. They are also geographically referenced which makes the raster chart identical in every way to the paper chart on which it is based. Raster charts cannot be manipulated or queried.

Also referred to as the Raster Chart Display System (RCDS), the information is contained in one single layer only. Information can only be added to this type of chart.

What is AIO in ECDIS?

Admiralty Information Overlay – The Admiralty Information Overlay (AIO) is a data set that contains additional navigation information to mariners. The Admiralty Information Overlay is designed to be displayed overtop of electronic navigation charts (ENCs) on an ECDIS display screen and is unique only to Admiralty ENCs.

Navigation information, including all Admiralty temporary and preliminary Notices to Mariners (NTMs) and additional information that is specific to an ENC location such as navigational hazards is included to provide mariners with the most up-to-date and accurate information. AIO compatibility is dependable on what ECDIS/ECS is being used.

See the table below for a list of compatible ECDIS/ECS systems. Mariners planning routes may take advantage of information contained in AIO to make necessary changes to avoid any universal hazards. Many ECDIS systems produced before 2011 require an available upgrade to display AIO.

All in force temporary and preliminary Notices to Mariners are displayed in the Admiralty Information Overlay. Each notice to mariners is displayed as a red polygon with red hatched fill indicating the area where the Notice to Mariners is in effect. The Notice to Mariner number assigned in the Admiralty Information Overlay is the same as the number assigned in the Admiralty Notice to Mariners.

Associate diagrams in Notices to Mariners may be accessed through using “Pick Report.” While all ENC services provide compliance only the Admiralty and the Admiralty Information Overlay provides mariners with the latest and most accurate information to sail confidently and safely in the toughest marine environments.

What is the Catzoc on ENC?

CATZOC (Category of Zone of Confidence) – Knowledge Of Sea CATZOC on the ENC in simple terms refers to the Quality and Accuracy of survey data and the applicable error in chart datum that sometimes can greatly affect vessel’s UKC calculations. Zone of Confidence (ZOC) has 6 Categories named A1, A2, B, C, D and U as shown below: Bridge watchkeepers should be aware of the ECDIS function to activate the CATZOC symbol on ENC. This data may be used to ascertain the contour settings on the chart.For example – if the data is unreliable, vessel may need to keep a larger safety contour margin.

• Eep this ON only during Passage Planning.
• While monitoring this is to be kept off to avoid unnecessary clutter on the ENC.
• The knowledge CATZOC is all the more important when vessel is passing a shallow depth area.
• These values can greatly affect the vessel’s UKC calculation and must be considered where the depths are shallow.

As a basic thumb rule the Master should plan vessel’s passage by keeping the vessel inareas shown by the triangles i.e CATZOC – A1, A2 and B and staying away from the areas covered by rectangles i.e CATZOC- C, D and U.

Where the vessel can’t keep clear from passing close to the rectangles, cautions notes should be posted on the ENC using the User Maps option instructing the navigator to “Keep Echo Sounder on”and “Monitor UKC Continuously”.Ship’s staff should factor in the value associated with these categories. This can be seen in the example below:If the depth marked on ENC is 10 meters, the actual depth of that area may differ depending upon the CATZOC shown on ENC.

For area with CATZOC A1, Actual depth may be: 10-(0.5+0.1) = 9.4 mtr. For area with CATZOC A2, Actual depth may be:10-(1+0.2) = 8.8 mtr. For area with CATZOC B, Actual depth may be:10-(1+0.2) = 8.8 mtr. For area with CATZOC C, Actual depth may be:10-(2+0.5) = 7.5 mtr (Although A2 and B have the same depth accuracy what differs is the positional accuracy.) For areas with CATZOC – D & U- The error is not specified or unassessed and should therefore be avoided as far as possible specially when in shallow waters.

How is the safety contour displayed in the chart area?

The Safety Contour – The Safety contour is the thick bold line on the screen that divides the navigable waters from non-navigable areas, Unfortunately, this concept does not fully reflect the reality (unless High Density Bathymetric ENCs are then used).

• Usually, the ENCs are compiled with standards contours; 5, 10, 15, 20, 50, 100 meters.
• Therefore, it can often happen that the Safety Contour value selected by the operator and entered in the ECDIS does not coincide with one of the contours embedded into the ENC’s cell.
• For example, if 11 meters value has been entered as Safety Contour in the Depth Contour page, the system will select the next deeper available contour, most likely the 15-meters contour.

As per IMO Resolution MSC.232(82):”ADOPTION OF THE REVISED PERFORMANCE STANDARDS FOR ECDIS” : “If Safety Contour value set by the operator is not available among the available depth contour of the ENC, then the ECDIS will select the next deepest available contour in the ENC” (IMO, 2006),

In turn, this creates a situation where the ship can safely navigate in an area deeper than 11 meters but the ECDIS will mark non-navigable from 15 meters to the shore, limiting the sea room available. At a first glance, this seems to be a good idea, a way to enhance safety allowing for an extra margin.

Unfortunately, in most cases a ship cannot approach the port or an anchorage area because such area are located inside the Safety Contour.

Jack Gloop