Navigation & piloting questions & answers

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Navigation

The Dover Straits - English Channel

60 nautical (sea) miles = 1°of latitude

1 nautical (sea) mile = 1minute of latitude

1 nautical (sea) mile is 2000 yards - 1852 metres - 1.852 Kilometres.

0.1 of a nautical (sea) mile is 200 yards -- 185 metres

English Channel chart - Part of practice chart 5505. Reproduced by permission of the Admiralty charts & publications. This chart is not to scale and must not be used for navigation.



Q. How far do you swim to get from England to France?

A. The English Channel is approximately -

19 nautical miles (38000 yards) or
35 kilometres (35000 mtrs) - wide.
Its narrowest point is Shakespeare Beach, Dover to Cap Gris Nez, France which is 18.2 nm.
Most swims are a little longer so you can expect to swim about 20 nm - 37 km.

The Tides are strong and change direction ,approximately every 6 hours.
They flow to the North East from about 1.5 hours before high water to about 4.5 hours after high water (Flood tide).-

Then turn and flow South West from 4.5 hours after high water to 1.5 hours before high water (Ebb tide).
These tides can flow at up to 4 nautical miles per hour.
The tide gets later every day by about 30 to 50 mins and change in height and flow speed every tide.

The lowest flow/ height range is known as the NEAP TIDES and is the time most swimmers try to swim.

The highest flow/height range is the SPRING TIDES and require calm weather and good piloting for swims to be successful.

(Good spring tide swims are usually a little faster the neap swims but require a lot more planning an skill from the pilot).
See the channel chart above.


Q. How does the tide affect the swim?

A.Think of the English Channel as a river between two lumps of land.
Every 6.2 hours- approximate- the tide changes its direction by 180 degrees and flows back to where it came from.


From about 1.5 hours before High Water to about 4.5 hours after high water the tide flows towards the North East (from bottom left hand corner of chart to top right hand corner). This is known as the FLOOD TIDE


It then turns through 180 degrees and flows back from where it came. That's towards the South west. The South West flow is from about 4.5 hours after high water to 1.5 hours before High Water. This is known as the EBB TIDE.


To confuse matters more the gravitational pull on the water mass from the sun and the moon vary depending on the position of the moon.

This is a 14 day cycle and it produces what we call SPRING & NEAP Tides.

To be brief --- SPRING tides are when the moon and the sun are in line with each other.

This is at the NEW & FULL moons.
At this time the tidal movement is at its greatest. (The largest amount of water moving up and then down the Channel is when there is a new moon)

NEAP tides are when the sun and the moon are at right angles to each other. This is when there is a HALF moon.

At this time the tidal movement is at its lowest (the smallest amount of water moving up and down channel.

At Dover --- The top of the SPRING tides are when the tide table readings are about 6.8 metres or above for High Water and 0.8 metres or below for Low water.

That means that the water will rise and fall by 6 metres plus between Low - High - Low water approximately every 12.4 hours.
The bottom of the NEAP tides are when the tide table readings are about 5.3 metres or below for high water and 2 metres or below for LOW water. That means that the water will rise and fall by 3.3 metres or less between low - High - Low water every 12.4 hours.


As you can see there is nearly twice as much water moving on the top of the SPRING tide as there is at the bottom of the NEAP tide.

This change is gradual over the 7 days between SPRINGS & NEAPS The full cycle is every 28 days. (Neap - high spring - neap - low spring - neap)
This is a Lunar Month.
For Channel swimming purposes we consider


NEAP TIDES to be anything BELOW 6.1 metres
SPRING TIDES to be anything above 6.1 metres.

How does this affect the swim? - on a 5.3 metre NEAP tide the swimmer will be carried about 7 to 7.5 nm up Channel on the Flood tide and then come back 7.5 to 8 miles on the Ebb tide.
On a 6.8 metre SPRING tide the swimmer will be carried about 13 nm up Channel on the Flood tide and then come back 15 nm on the EBB tide.


You do not actually swim these distances as you are swimming across the tide but your course will be in a long curve, or curves, depending on the rate you swim at. The distance you travel up and down Channel is about the same and cancels each other out although the exact effect it has on your swim will depend on the skill of your pilot.

Q. When is the best time to swim -

A.The best time to swim is when the weather is stable and the sky is overcast giving a sea and land temperature that is about the same and when there is little or no wind.

That day is usually in mid December -- the rest of the year is compromise and suspect. The weather in the Dover Straits is a very fickle thing.

The Weather is the most important factor in any swim but it is hard to predict and many a swimmer has sat on the beach on a flat calm day because the forecast did not match what happened.

There are also the days when the forecast has been good and the weather terrible (ask Alison Streeter MBE, our CS&PF chairperson, about her 30th crossing -- her first unsuccessful swim in 43 crossings).

Most swimmers try to swim on the NEAP tides - these are the traditional swims - when the tides are slacker and the piloting much easier.

It was also the period (in days gone by) when the fishing was not that good.

The weather is often better on the SPRING tides but the piloting requires a lot more skill. The pilot and swimmer have to work together to get the course right as the pilot has to estimate the swim speed more accurately and know the tide runs to be in the right place at the right time.

The swimmer needs to be able to swim at about 1.6nm (3200 yards -- 3000 metres) + per hour for a fast time. Fast swimmers have produced faster times on SPRING swims. It is all very "Swings & Roundabouts" as we say. I think the mental attitude of the swimmer is very important as well. The right frame of mind is -- " have a go and be confident, do not worry about failure, just think success."
After many years at sea delivering boats all over Europe and teaching people to handle boats I have a little saying that I often have to quote to myself in times of need - it also applies to open water swimming :Before you make a decision -- assess your abilities -- respect your limitations -- never lie to yourself -- be positive and go for your "goal"
The effort is never easy -- the results will be a lifetimes of experience and your memories, good and bad
There is also a saying on the beach - which applies to a small number of failed swimmers comments.
Success is down to the swimmers ability - failure is the pilots and/or the weathers fault.

This document maintained by michael.oram@btinternet.com.
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