chartplotter – tide by tide

Coming soon on your phone – one metre accuracy

It seems that while my phone is accurate to an error of considerably less than 10 metres, the industry is heading to even better precision of a tenth of that level, and soon. This post looks at why that means satellite accuracy on all devices including smartphones is reaching levels where there are diminishing returns for small boat sailors.

In general, 5 metre satellite accuracy has been available on smartphones for a considerable time now. I give links at the end to industry, US government, academic and consumer articles that give more detail on how accuracy has been developing (and see also my earlier post ‘and a phone to steer her by’).

One of the secrets of the top performers such as the high-end Samsung phones, which can achieve 2 metres, is that they now have dual frequency satellite aerials so they can make the best use of the latest improvements not only in the US GPS, but the Russian Glonass, European Galileo and Chinese Beidou satellite systems. Nowadays, phones will often have as many as 40 satellites in the sky from which to choose the best signals.

Relearning old navigation lessons

Two letters in the latest issue of the excellent Cruising Association magazine* claim it is now safe to rely entirely on electronic charts because backups to the boat’s main chartplotter are so cheaply available. You can leave your old paper charts abandoned in the bottom of a locker somewhere, the argument goes.

However, while researching updates for the yachtmaster book I mentioned last month, I’ve been re-reading intensively about old fashioned navigation techniques I learnt a long time ago, some of which were beginning to fade from memory. It has reinforced for me how important it is to avoid total reliance on electronics and have a portfolio of navigation skills including the old ones. Continue reading “Relearning old navigation lessons”

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. Continue reading “Marine survey accuracy”

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. Continue reading “Med charter disaster?”

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).

Continue reading “Orkney Roulette”

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.
Continue reading “How to mimic big ship equipment”

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.

Continue reading “Paper-free chart tables”