Asking the right questions

01 Oct 2021 The Navigator

David Patraiko, Director of Projects at The Nautical Institute looks at the difference between data and information and examines which data sources you should be checking, and how to assess their reliability

There is a subtle difference between data and information. Data generally refers to known, collected and measured facts. These are not always useful, in and of themselves. Just knowing the depth of water stated on the chart might not be useful on its own. But once that data is enhanced by knowing the state of tide and draft of the vessel, it becomes very useful indeed.

Information is derived from data, but the way that data is interpreted, or the algorithms that are applied to it, can make it very valuable – or introduce errors which can be misleading.

If data is inaccurate, all the information derived from it will be unreliable. For example, if the speed input is wrong, the vectors and closest point of approach (CPA) / time to closest point of approach (TCPA) that are generated from it will be unreliable, too. Even if the data is accurate, it may not show the whole truth. For example, if you take a pair of hydrographic measurements, you might assume that points between those measurements will be around the average of those two – but that may not take into account anomalies of geology (peaks and troughs). This is something that might be assessed by the quality (or not) of the hydrographic survey.

Here are some pointers on how to identify where navigation data and information might be suspect. A good navigator will always seek to confirm the quality of their information and assess the risks of any decisions they may have to make using it.

Data from Global Navigation Satellite Systems (GNSS), such as GPS, is the primary position input into an integrated navigation system. When it works, it is extremely accurate, but the data can be subject to both intentional and unintentional jamming and spoofing. These events are reportedly happening more frequently in recent years. If you have more than one GNSS system available, you can check the validity of GNSS inputs against other fitted GNSS systems (e.g. Glonass, Galileo, BeiDou etc). However, even multiple satellite systems can still be in error as they can be jammed or spoofed the same way. Remember; non GNSS input, such as visual and radar bearings and depth contours, offers more resiliency due to its independence from satellites. Make sure you practise using these even when GNSS is available – not just so that you can spot errors, but so you are confident using them when it is not.

Radar is an excellent tool for situational awareness, both in terms of navigation and collision avoidance. It can be independent of any external inputs, but it does need skill in interpretation. Remember that radar images can be affected by physical obstructions, weather, sea state and high-density traffic. You can check the validity of radar data against AIS, visual observation and even advice from VTS – and likewise, you can use radar to check and confirm information from these sources.

Depth/Under Keel Clearance
Under Keel Clearance (UKC) is crucially important. If you have no water, you cannot move! Being sure of your UKC depends on a number of inputs. The accuracy of charted data should always be questioned. Check the date of the last survey and the category zone of confidence (CATZOC), which will tell you whether the data meets certain minimum standards. CATZOC ranges from A1/six stars (best/most reliable), to D/two stars (worst). Tide states and squat both need to be taken into account. Echo sounder readings should always be monitored visually and with appropriate alarm settings. Use visual observation, too. A change in the colour of the water, or breaking waves ahead have often alerted navigators in good time to trouble ahead.

It is very important to know your speed – both over ground and through the water. Speed over ground is best measured between fixes (of multiple types; don’t just rely on GNSS!) Speed through the water can be assessed by a speed log, or calculated from speed over ground if you know set and drift.

Establishing the direction of travel sounds simple enough, but it can be surprisingly complex. You need to take into account heading (true/magnetic), vector over ground or through the water. Heading is important not just for navigation but also for judging a ship’s aspect for application of the Colregs. Again, ask where your heading input is coming from. Is it being supplied by GNSS or Gyro? If so, is the GNSS accurate and have your gyros been checked? Comparing your heading with the course shown on the chart is not a useful check if both inputs are coming from the same source, but checking against leading marks is. If you are using a magnetic compass, when was it last swung?

Target tracking
Identifying targets is also essential information for navigators. The primary tools for this are visual observation, radar, AIS and VTS, all of which have their strengths and weaknesses. Visual input is excellent, if visibility is good, but it is subject to conditions of visibility and optical illusions. Radar is very reliable too, but can be subject to interference and misinterpretation. Finally, AIS is prone to inaccurate inputs, both manual and GNSS – and not all vessels or hazards have AIS.

Passage planning and publications
When you are passage planning or using publications to make navigation decisions, you must ensure that the publications are from a reputable source and are maintained up-to-date. Corrections and version numbers are generally available online. Critical data can also be obtained from agents, pilots and VTS. Weather routing advice must always be checked against your own observations and experience as well. If in doubt, consult another source of advice.

Human vision is an excellent source of data and information to assist with situational awareness and decision-making. However, even this is not without its challenges and seeing is not always believing! Obvious problems include poor visibility, e.g. in darkness, rain, fog, etc. A bridge that is too bright can result in poor night vision. Bright deck lights are another problem. Even shore lights can cause poor visibility or provide misleading input (is that red light a navigation mark or a building onshore?). Visual observations should be checked against radar, charts and objects identified in the passage plan. Your own vision can be improved with binoculars, but in the near future the ‘optical scene’ may be further enhanced with cameras, lowlight optics and Augmented Reality (AR).

Think twice
Safe navigation relies on good decisions that are not just based on ‘presented information’, but on skills, experience, risk assessment and even gut feeling. Today’s mariners are provided with a wealth of data and information. Some is very useful and reliable, and some is less so. Before any critical decisions are made, think twice (or more than twice). How trustworthy is your information and how critical is that information to safety? What actions can you take to mitigate that risk? Has the bridge team been involved, so that you can benefit from collective experience and knowledge? What are the contingency plans or abort points? As we enter a period of increased digitalisation, navigators must inform themselves about the quality of data and information presented to them and how to assess it. Navigators also need to think about how a digital world and an analogue world can coincide and the best practice of good seamanship going forward.

Marine Superintendent Sajith Babu AFNI shares some thoughts on maintaining data quality

How do you ensure that you are using data that is of the best quality?
Comparing data with multiple resources and confirming that everything is the same is the only way. On board a vessel, it is important to know the errors / limitations of the equipment we are using, along with the operational procedures. This is especially true of navigational equipment. Comparing GPS positions with radar fixes or visual fixes; comparing echo sounder depths with soundings present on the chart / ECDIS and comparing the CPA/TCPA of the same target on both available radars are all crucial procedures for all OOWs to complete, even when not in congested waters. Regular testing of all available equipment is equally important. Check the equipment is operating efficiently and according to the maker’s instructions and company guidelines. Data should always be suspected for errors and the best way we can do that is by keeping the equipment in good shape and checking or comparing all of the data we receive.

What have been some of your experiences with unreliable data at sea? 
Even though GPS / ECDIS / AIS / ARPA have all helped navigators in receiving information readily, errors associated with it are also on the rise. Reports of loss of GPS signals / jamming / spoofing have risen over the last couple of years, especially on exiting Suez Canal and entering the Mediterranean Sea. Vessels that we manage have also reported loss of GPS signals near Port Said. In one vessel, the problem persisted over three days. It is very tough when GPS signals are being lost every five minutes. Alarms tend to distract the OOW and might lead to an accident. A few vessels have also reported loss of GPS signals inside the Persian Gulf. Lack of high-quality data in ECDIS for the South China Sea is another example where the bridge team can face a great challenge. Overlapping ENC cells, coupled with the small-scale charts that are available in these areas, is a common issue. Personally, I used to keep paper charts of these areas open and readily available for the OOW (of course not all ships might have paper charts anymore).

Data should always be suspected for errors and the best wat we can do that is by keeping the equipment in good shape and checking or comparing all of the data we receive

How do you think data quality can be improved by the maritime industry in general? 
Now that we have collectively moved to the era of digitalised equipment, there is no going back. The solution to improving the data quality will be an ongoing process. Recognising how to use each piece of equipment correctly and understanding their limitations is key for any OOW. A fair outlook on the dangers associated with over-reliance on a single item of equipment will also motivate navigators in comparing data for its accuracy most of the time. We should also encourage feedback from Masters and OOWs on significant navigational information, including suspected dangers and changes to navigational aids. Hydrographic notes, or even the H-Note app, can be used for this task. As end users of equipment made for seafaring, we have a social responsibility to give constructive feedback to help improve the system, rather than simply criticising it.