With thanks, from www.channelswimming.net....
Channel swims differ from other swims of this distance by their complexity and the local environment. This is why it is one of the ultimate challenges. The swim takes place in cold water, 15°C to 18°C (hypothermia is a major consideration and cold water training is important) for between 10 to 20 hours.
The English Channel is one of the busiest shipping lanes in the world, with approximately
600 vessels moving up and down them every day, plus the ferries, sea-
The shortest distance across the Channel is from Shakespeare Beach, Dover, to Cap Gris Nez (the headland halfway between Calais and Boulogne). This distance is 18.2 nautical miles which is approximately 21 land miles. There are 2,000 yards or 1852 meters to a nautical mile. Most of the England/France swims start from Shakespeare Beach or from Abbotts Cliff between one hour before high water and one hour after high water, although the pilots do start at other times and places, depending on the tide, the weather conditions, and the swimmer's ability.
With the use of computerised plotting for course calculations and the modern electronics on the pilot boats, start times and places can be evaluated before the swimmer enters the water, and the best choice of route made. The more the pilot knows about the tides, weather and the swimmer's ability the more accurately the swim can be predicted.
The Channel has quite a lot of hazards such as seaweed and flotsam and jetsam (rubbish
and timbers, etc.). It usually has a swell and when the wind is in the opposite direction
to the tide it can turn quite choppy. The weather is always uncertain and local conditions
can change in a very short time (30 minutes). The swim is every bit a mental swim
as well as a very physical one, and the swimmer must be both mentally and physically
attuned. There is an element of luck involved in getting everything to fall right
on the day. The only real way to achieve success is to start with the idea that nothing
else matters except arriving on the other side. Start with the intention of finishing,
no matter what, then play the day as it comes. Success is sweet, but as is often
said on the beach while training -
Because of the movement of water from one place to another, the Dover Straits are prone to strong tidal flows, and a large rise and fall in water between high and low tide. To complicate things a little more, the position of the moon relative to the earth and the sun affects the gravitational pull that is moving the water. The FLOOD TIDE flows from the South West from 1.5 hours before HIGH WATER to 4.5 hours after HIGH WATER DOVER. That's up Channel towards Holland and the North Sea. The EBB TIDE flows from the North East from 4.5 hours after HIGH WATER to 2 hours before HIGH WATER DOVER. That's down Channel towards Folkestone and the Atlantic. As the tidal cycle is a little over 12 hours from one high water to next, the times of high water change every day getting later as the days progress. A good guide is high water Springs are at approximately midday and midnight(GMT), and high water Neaps are approximately 6am and 6pm (GMT). You must add one hour for British Summer Time to these times.
Most swims take place on the Neap tides. These are the slacker tides and show as a more direct line on the chart. The lower the tide, the longer the period of slack water when the tide turns, and the slower the tidal flow. Spring tide swims are becoming a regular occurrence with very little difference in times (some swims are even faster), although they require more planning by the pilot and good weather conditions the swimmer. The major factor on any swim is the weather and good weather on a Spring tide gives a chance a lot of people do not want to miss.
Because the tidal flow is parallel to the coast and the swimmer is swimming at 90° to the coast, the tides do not do a lot to either help or hinder the swimmer's progress, although they can appear to do so. The pilot's job is to guide you and put you in the right place at the right time. For this he needs to know your approximate swim rate over the period of the swim, in advance. There are places during the crossing where you can get a little help from the tide, and there are areas where the tide will hinder your progress. The idea is to get a balance between the two.
If you waste two minutes on each feed and you feed every half hour, then on a 12 hour swim you will have lost 48 minutes. This can be the difference between landing with the tide or having to swim for another 2/3/4/ hours
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