The Chart Table

The Chart Table

Satellite navigation (’GPS’) has only been reasonably accurate for the last 15 years. People rely on it but there are flaws.

Traditional Navigation

What happens if you run your battery flat keeping the beer cold?
No GPS. It is a US Military constellation of satellites.

What if they choose to make it unavailable because they are invading somewhere?

What if the Russians or Chinese decide to shoot the US satellites down?

It isn’t unknown for someone to go to sea and return to find the world has tipped upside down…

In all these cases, we will need to navigate by the old instruments of hand compass and paper charts.

Given the world’s uncertainties and the uncertainties of being at sea, it would be silly to forget traditional navigation, and it is still taught in sailors’ academies the world over for this very reason.

Plotting your route

The table itself is big enough to hold the paper chart. You should select the chart that has the most detail for the trip you are doing – if you are sailing 30 nautical miles across the Saronic Gulf you won’t need a chart of the world’s oceans!

On the chart table you will see the following instruments:

  • Pencils and eraser
  • A parallel rule
  • Dividers
  • Portland Course Plotter
  • Hand compass

Under the table you will find the charts for your area of sailing. We will have discussed with you your sailing limits – stick within them as you are not insured to go beyond.

ACROPOLIS REGATTA 2019

Plotting your planned route

ALWAYS use pencil to plot your route. Charts cost €€€ to replace.

With the weather forecast you will know the wind direction and should be able to accurately judge whether you will need to tack to get up your route.

Take note of any channel markers and Cardinal marks. As a general rule the smaller the port the more you as a yacht will have to stay within the channel markers. The likes of Piraeus will have channel markers for huge ships and you can stay outside of them, though DO check the soundings on the chart where you plan to go outside the channel.

Remember that the Mediterranean has tides. Though a metre or two (nothing like the UK) this can determine whether you can come outside of the channel or whether you will go aground. Where tide times and currents aren’t so important here, just remember to leave plenty of water under your keel.

Plot your route with the pencil and parallel rule.

Dead Reckoning (DR) and Estimated Position (EP) are very good ways of getting a handle on where you are.

DR

If you are able to sail direct down the line of the route you have plotted (a very rare event) you can use your time and speed down that line to get a rough estimate of where you are through Dead Reckoning. This gives you a rough guess where you are.

EP

Estimated position is a DR, with any currents factored in.

If you are headed north at 5 knots and know there is a tidal current taking you east at 2 knots you use the DR spot and draw a line of length representing two knots east. That will give you a better idea where you are.

Currents, leeway, magnetic compass deviation and variation all make this inaccurate, so please don’t take EP as supremely accurate in any way.

Three point fix

This is the best way to accurately get a handle on where you are, and has been used for many hundreds of years before GPS satellites were launched.

Using DR on the chart, get an idea of three landmarks on the coast, ideally 90 degrees or more from each other. A perfect fix would be where you are surrounded by islands and can get three landmarks at 120 degrees apart but you’re unlikely to be so lucky!

The chart will tell you to look for – a lighthouse or church for example. Bring the hand compass on deck, and identify the three landmarks with your eyes so you know exactly what you are looking for. Now, aim the hand compass at all three targets and remember the angle they are relative to due north.

Run down to the chart table and using the Portland Course Plotter, draw a three point cross from the landmarks to a point. You may have what they call a ‘cocked hat’ triangle if you are slow in getting the angles with the hand compass. That at least puts you within ten – 15 metres of where you really are.

Bored kids?

Kids will be excited about going to sea, and given the chance to do real navigation in the old way will probably leap at the chance, particularly if they are too far offshore to get mobile signal and can’t access Twitter… Remember you’re sailing for the sake of sailing, not just on a slow bar crawl. There’s more to sailing than getting pickled in a new place at night!

Yacht’s interiorThe chart tableGeneral sailing tips


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