Marine survey accuracy

Data published by the International Hydrographic Organisation shows up a surprising fact: the UK and Ireland are below Turkey in the league table of survey quality by area of national waters. Spain, Portugal and France score much higher than the UK.

  

Source : selected countries  from an International Hydrographic Organisation table.

 % of area at depths from zero to 200 metres which has been adequately surveyed

% which requires re-survey at larger scale or to modern standards

% which has never been systematically surveyed

Mediterranean

 

 

 

Monaco

100

0

0

Spain

97

3

0

France

95

4

1

Gibraltar

95

5

0

Turkey

88

12

0

Slovenia

80

20

0

Italy

70

25

5

Croatia

39

39

22

Greece

35

55

10

Morocco

30

0

70

Albania

25

45

30

Serbia Montenegro

0

100

0

Cyprus

0

100

0

 

Atlantic, NW Europe 

 

 

 

 

 

 

 

Portugal

100

0

0

Faeroes

100

0

0

Belgium

100

0

0

Germany, N Sea

96

4

0

Denmark

95

5

0

Canaries

95

5

0

Spain

94

6

0

France (Channel, North Sea)

89

0

11

France Atlantic

81

0

19

Norway

60

31

9

Azores

60

40

0

Netherlands

55

35

10

Iceland

52

48

0

UK

49

22

29

Ireland

26

74

0

 Greenland

25

25

50

Svalbard

10

1

89

Jan Mayen

0

0

100

 

Baltic

 

 

 

Germany

98

2

0

Finland

44

49

7

Poland

40

60

0

Sweden

25

74

1

Lithuania

16

84

0

Estonia

13

87

0

 

 

 

Checked January 2013

 There is one obvious reason why the UK’s position is relatively low; with a much larger area of shallow continental shelf, the British Isles has proportionately a far bigger survey to do than a country such as Turkey, where depths in many places reach 200 metres relatively close to shore.

Even so, it is widely known that there are cruising areas off the Turkish coast where chart accuracy is poor. Rod Heikell’s pilot warns that they can be out be by up to 2 minutes of longitude, considerably more than the warnings for anywhere on the British and Irish coasts.

 UKHO chart Q 6090 looks more deeply into the situation in the UK and Northern Ireland. It colour codes areas of the seabed by survey quality.  In the January 2013 edition, large parts of the coast of the Scottish mainland, Hebrides and northern islands, Wales, the Channel Islands, Lancashire and Northern Ireland are still marked as surveyed by leadline, or unsurveyed.

Follow this link to see UKHO chart Q6090

In an earlier 2006 version published in the AIB report on the Octopus (see Orkney Roulette page), the entire coast of  Ireland was marked as leadline surveyed. The republic’s coast has been left out of the latest Q6090, but the Irish government has now produced its own version of the chart, which shows a very large surveying effort since 2006.

Link to Ireland survey coverage chart

Interactive chart with local detail of Irish surveys

One result of the new surveys is that there have been new editions of 22 of the 60 or so admiralty charts for Irish waters since 2009, according to the Irish Cruising Club.

For practical decisions during a cruise, we have to rely on what electronic and paper chart publishers tell us about the underlying quality of their products, backed up, of course, by pilot book advice. This information can be pretty patchy. For example:

  • UKHO charts   have source data chartlets, a benchmark for quality.
  • Imray charts have no source data.  Some Imray charts do have general warnings on chart accuracy, eg for the Ionian and Turkey, where recent editions have quantified errors in the area as up to one minute and half a minute of longitude respectively.
  • Pilot books vary on the issue: Heikell has general warnings in his introductions of much larger errors in Greece and Turkey, of 1.5 minutes and 2 minutes longitude maximum respectively, but that covers a vast area.    
  • The Irish Cruising Club pilot’s latest edition for the West and South coasts of Ireland has gone much further, with localised chart accuracy information for different chapters, a good benchmark to aim for.  
  • Some other pilot books I have checked recently  do not seem to mention the accuracy issue at all, even where they cover cruising grounds which the tables above show have known  chart quality issues (for example parts of the Adriatic).
  • Many leisure electronic charts lack information on source data or other indications of underlying survey quality. They also lack last correction dates, and there is no detail of how comprehensive the updating is. Memory Map does reproduce source data diagrams on its raster charts but not edition dates, even though it is not hard to find UKHO charts for sale now whose most recent edition was three decades ago, for example on the West of Ireland.
  • To find comprehensive source information on an electronic  chart, you have to move to those used in Electronic Chart Display and Information Systems on ships, a different world,  where vessels equipped to a high enough standard are now allowed to dispense with paper charts altogether.

In preparation: articles on GPS accuracy and on what makes leisure charts unsafe compared with those used in ECDIS systems.

Med charter disaster?

Since looking into chart accuracy following the Orkney cruise (see previous article) I’ve spent a couple of months in the Mediterranean. It’s much worse there.

I vaguely knew that, but previous sailing in the Mediterranean had been without chartplotters and on the earliest occasions without GPS. More recently, chartplotters seem to be standard on charter boats as well as private yachts. We amused ourselves by doing some checking.

In the Ionian and South West Turkey (but only rarely on a cruise round the Peloponnese) we noted numerous position errors, often a tenth of a mile, and a couple of times as much as a quarter of a mile; there were very noticeable – almost random – variations in the size of position errors, measured by GPS, within the area of a single paper chart, so it was not a simple matter of the datum being wrongly set (which of course we checked, as well as satellite coverage.) The errors were clearly the result of using an accurate GPS on inaccurate paper and electronic charts based on old surveys.

Rod Heikell, the pilot book author, in a  talk at the Cruising Association in London in February 2013, amused the audience with a plot of a yacht track running up the hill behind a Mediterranean town as the boat approached the harbour. That was exactly the kind of anomaly we picked up, in one case in the Ionian with the boat moving down a road on the island we were coasting.

Now none of this is new to old hands in the Mediterranean, with some of whom I have recently discussed it on a Cruising Association forum. Charts based on old leadline surveys can miss underwater dangers and sometimes have large position errors, mainly of longitude.

The advice, of course, is that GPS should always come second to older methods of pilotage, using eyes, handbearing compass, clearing lines and depth sounders, because while the longitude on charts may be wrong, the relative positions within a single area of a chart – for example a bay and harbour – tend to be accurate. The best a chartplotter and GPS can do is get you out of somewhere by using a plot of the track, once you have safely got in by conventional means. The better equipped Med sailors also talk of radar and forward looking echo sounders. Pilot book authors give GPS waypoints they have checked themselves.

However, it is very different for new arrivals in an area, and for holiday charterers it can be positively dangerous. A couple of recent trips were on bareboat charters with a large UK operator. After a series of chartplotter and GPS checks at known chart positions for a week, we found large and variable errors.  But neither the technical staff at base nor a flotilla skipper we spoke to had any idea of the scale of the local chart errors.

When we checked the equipment on arrival at one base in Turkey, we found the plotter showed the boat nearly a quarter of a mile from the marina. The company sent a technician to rebase the chartplotter’s boat icon onto our pontoon in the marina. It was an older type of instrument which we had not come across before, which allowed recalibration. (This was not a datum adjustment, which we also checked). The technician announced that the plotter was now fine.

That night, 15 miles away, the plotter was a tenth of a mile out; for the rest of the cruise, the charted positions within a cruising range of no more than 50 miles fluctuated from zero to a tenth of a mile and in one case approaching a quarter of a mile, simply because the GPS was more accurate than the charts. Back at base at the end of the week, the error was zero, so there was nothing to show the next customer that there was a problem.

The base clearly thought we were imagining it. I got the impression they were not even conscious of Rod Heikell’s pilot book warning of the size of longitude errors in Turkey. Skipper briefing at the base did warn about chartplotters, but it was not specific to the area, and was the kind of routine mention you hear in the UK. Visiting charterers might well assume it meant the relatively modest range of inaccuracy found at home, rarely more than 100 metres.

One lesson is that specific warnings with numbers attached are vital for getting the message across: for example the Imray Ionian chart used to have a general note warning that there were longitude inaccuracies, and I suspect not much notice was taken. A quantified warning was recently added saying the errors could be up to a minute of longitude, which has a much greater impact. Suddenly you realise what you are up against. The errors could be as big as the gaps between some of the islands. In these circumstances, chartplotters are an accident waiting to happen for holiday charterers. It would be safer to switch them off.

Next, how do we find out more about survey accuracy and chart errors?

Orkney Roulette

Not long after a jack-up rig called Octopus ran aground in Stronsay Firth in the Orkneys in 2006, we were feeling our way into a bay at nearby Stronsay. We crept through shoals and reefs relying on chartplotter and echo sounder, in strong winds and bad visibility, confident that our plotter would get us through: after all, we had checked it frequently on our passage up the English and Irish coasts and through the Hebrides, and had been pleasantly surprised never to find the GPS positions more than 50 metres out on the chart.

So confident had we become in our first chartplotter that a few days earlier, in fog rolling off the island of Hoy so thick that the boat’s bow was only just visible, we used it, along with the depth sounder, to find our way at dusk into the harbour of Stromness, which involves a tight turn round a reef at a point where the tide can run at up to 8 knots into Scapa Flow, right across the entrance to the inlet leading to the town.

 

If only we had known more about the quality of the local charts ….. much later, I came across a Marine Accident Investigations Branch report on the grounding of the jack-up rig Octopus, under tow by the tug Harald, which popped up in a web search for something else. (MAIB Report 18 2007).

 

I glanced at the summary and realised we had been playing Russian (or Orkney) roulette in relying so heavily on the charts, chartplotter and GPS while cruising in the Orkneys. The charts on the west side of the islands, where Stromness is located, were fine, because the area had recently been resurveyed. Much of the rest of the Orkneys, including Stronsay and its sound, was a very different matter: it had last been surveyed by leadline in the mid-19th century.

 

The new surveys had reached parts of the north-central Orkneys, in a programme that had been stepped up because of the risks to cruise ships, which were calling in increasing numbers; but by extraordinarily bad luck the survey work had stopped 200 metres north of the uncharted shoal in Stronsay Sound on which the Octopus grounded. It also turned out that local fishermen knew about the danger, but they had not told anyone.

 

UKHO Chart 2250, covering the danger spot, looked modern, but it used leadline surveys overseen in 1843 and 1844 by Commander George Thomas on HMS Mastiff. The skipper of the tug was using Admiralty paper charts, which display a diagram of ‘source data’, showing the age of the underlying surveys; he also had a monochrome electronic vector chart plotter with Seatrack software, of a type “primarily aimed at the leisure market,” according to the report. The plotter would have used the same underlying data as the Admiralty chart.

 

Leisure electronic charts do not give source data, but there was information  on the paper charts about the age and quality of the surveys on which they are based. How many of us actually take it seriously enough?

 

One of the MAIB report’s key conclusions was that shipowners should “emphasise to shipmasters and navigating officers the need to carefully consider source data”.  Since reading the MAIB report, finding out about chart accuracy and survey age have shot up my own list of priorities; if a chart based on an old survey can cause such problems for an experienced local tugmaster, how many yacht skippers also fail to make enough allowances for the age and quality of their charts?

 

Next: It’s much worse in the Med

 


How to mimic big ship equipment

To cut back seriously on paper charts, the greater vulnerability of equipment on a small craft to accidental damage would have to be taken into account, including lightning strikes. For small boats it is already possible to buy, at a price, extremely robust electronic systems, including waterproof laptops that withstand impacts (costing several thousand pounds), and high capacity lithium battery back-up packs;  small back-up generators have also become cheaper in recent years and can be accommodated on many mid-sized cruising yachts.

At a cost, robust weather and shockproof  electronic navigation with reliable backup systems should therefore be quite close to achievable now on a yacht. Even if we fall well short of the rigorous standards of an ECDIS system, we will not be carrying 100,000 tonnes of crude oil or thousands of containers, so perhaps we can be allowed to be rather less tough on the backup specifications. Similarly with training: new courses may be necessary, but perhaps not the 40 hours plus specified for ECDIS for commercial ship deck officers.

 Here is our current navigation equipment list plus a few items we plan to get. We rely on maximising the number of independent systems, including some which can be isolated from the boat’s electrical and aerial systems ie reversing the current fashion for electronics integration. Whether isolated equipment can be protected enough to see us through a lightning strike is a question that we are still thinking about.

We also try where we can to use portable equipment that we have bought for other purposes, keeping down the boat budget, but we draw back from the high costs of top-end equipment such as water and shockproof computers and screens. Others may have very different and perhaps much better ideas – it would be good to hear them, and especially any thoughts on protection against lightning (we had a strike 12 years ago that burnt out some instruments but not all).

This list is for cruising British and nearby waters.

  • Basic cockpit chart plotter using vector charts.
  • A separate large screen chartplotter at the chart table is a good option. But we have stuck with a standard laptop in an easily removable protective mount. The laptop is plugged into the boat’s 12 V system; two advantages over the plotter are that it is programmable and could be very easily switched to a backup external battery specifically designed for it (see below).
  •   iPhone or similar with Navionics or C-Map charts in a waterproof case, kept fully charged.
  •  An old fashioned stand-alone GPS at the chart table, feeding the DSC radio.
  • An AIT system, with its own GPS, displaying ship positions on the cockpit chartplotter, where it is of most use, but with a USB connection to the laptop in case backup is needed.
  • Radar.

Plus in due course:

  • An iPad or Samsung Galaxy 10 inch screen tablet, with full vector charts and navigation software, with a bracket to hold it at the chart table and a 12V charging lead. With a waterproof case, the tablet could also be used in the cockpit in reasonable weather for a few hours at a time, held in a bracket.
  • Two or more 8 amp hour lithium external batteries, kept full charged, capable of recharging the laptop, the phone and the Samsung if the boat’s electrics fail.
  • If laptops with separate screens improve, a screen mounted (removably) on a bulkhead at the chart table and a keyboard on the chart table connected by bluetooth would be an ideal replacement for the current standard laptop. It would have  the programmability and screen size of PCs and the convenience of tablets, while protecting the screen better than a normal laptop.
  • For those with a big enough boat (not us): a generator and electrical control equipment to feed a spare battery to provide a complete standby power system for emergency lights, radio and navigation equipment.

 With this level of backup, is a yacht safe if it leaves most of its paper charts behind (perhaps keeping just a few small scale charts covering a wide area)? Does it matter that it would be ignoring the legal warnings by using leisure charts in practice as the primary means of navigation?

This partly depends on how seriously we take the inadequacies, as C-Map and others describe their own products, of leisure charts, which is a whole new issue for another article.

Next, an example of paper and electronic chart inaccuracy: Orkney roulette

Paper-free chart tables

The idea of a paperless chart table is usually dismissed out of hand, and the very suggestion makes some old hands fume. But if a 100,000 ton bulk carrier can now be paperless, then it is hard to maintain that it will always be a mad idea for experienced yacht owners.

For a navigator on a yacht as much as on a ship, the advantages of knowing instantly where you are on a chart, and where you are going, are too obvious to dwell on. An old-time merchant navy officer would have spent many hours in junior officer days correcting paper charts. Tony, the retired master mariner with whom we share our boat, had to do exactly that in his early days. Electronics were therefore the answer to a mariner’s prayer: hundreds, indeed thousands, of charts on one machine, with corrections of the whole portfolio available in one simple operation over the internet. Yet even recently there have been published accounts of yacht cruises round Britain urging people to buy full portfolios of paper charts.

For our own round Britain cruising (the second time in the last six years), £3000 would buy fewer than 130 new UKHO charts, compared with the 850 which Memory Map says it incorporates in its UK and Ireland package. Even with a limited paper edition, we would never have a hope of keeping them all up to date unless we devoted weeks in the winter to correcting. If we bought second hand, even if we could find them all, the correction effort would be much greater.  

In contrast, the Memory Map charts on the laptop cost only £50 for the UK 2013 edition, which includes every chart for the British Isles.  Our c-Map charts for NW Europe, including the whole of the British Isles, cost £180 new and just over £100 a time to update, which can be done several times a year, rather more frequently than most sailors I know get round to updating far smaller paper chart portfolios in practice. Navionics on the iPhone (and shortly on a tablet) is even cheaper, and updates automatically.

The result is that for both round Britain cruises we have bought mainly small scale Imray paper charts and very few large scale UKHO ones. We do not yet rely primarily on electronic charts, because we do not have robust enough electrical and electronic backup systems; but in practice, partly for budget and partly because of the ease of correction, we’ve tipped the balance quite a long way away from reliance on paper. Judging by conversations with other leisure sailors, that is rapidly becoming the norm.

So what exactly is it that makes it safe for a modern 100,000 ton ship to go entirely electronic, when yachts are faced with warnings on their chart plotters and electronic charts that they should not be used for primary navigation? The C-Map licence, for example, says “Only up to date official government charts and notices to mariners contain all information needed for the safety of navigation…..Unless otherwise specified by national maritime authorities, the data licensed hereunder is inadequate as a primary means of navigation, and should be used only as a supplement to official government charts and traditional navigation methods.”

The key official conditions for dispensing with paper charts in the commercial world are:

·  The ship must have an Electronic Chart Display and Information System (ECDIS) approved and certified by its flag state, backed up by a second fully independent ECDIS system. For many ships, an ECDIS system is now mandatory, and it will soon be for all. (The “improved positional awareness”, as some professionals put it, far outweighs the risks of going electronic). Ships may back up an ECDIS with paper charts, but a second ECDIS system has the attraction of avoiding the confusion that can arise from trying to keep paper and electronic portfolios simultaneously up to date.

To go paperless, both systems must use  vector electronic charts, not raster electronic charts (which are basically facsimiles of paper charts); the vector charts must be government issued or authorised and reach a very high level of specification and be updated frequently. One of the many mandatory functions is to display chart quality information, an amplified version of the source data diagrams on UKHO charts. Charts sold with the “professional” label for smaller commercial craft and fishing boats do not meet this standard, and neither do leisure charts.

·Navigators must be trained to a high level in the use of the systems.

Superyachts may be able to afford all that today. But is it possible to get close to these strict conditions on a modest-sized cruising yacht?

Next article: ‘how to mimic big ships’