Having looked at a bit of the history, we're now going to look at what we need to prepare for.
Acclimation - the onset of hypothermia is the main reason why most Channel swims fail. When your core body temperature is at risk, the body minimises the amount of blood pumped to the extremities to prevent heat loss which can lead to difficulties in swimming technique and exhaustion. It is essential that we are acclimated to the water. We will be swimming in wetsuits but we are also swimming in June which is pre-Channel swimming season, and the sea hasn't had the summer to warm up yet.
Choppy or surfy - we cannot expect to swim the Channel on glass. It is a micro-climate out there and what may seem flat in Dover may be a very different story 15 miles out to sea. There may be long rolling waves or there could be choppy, washing-machine type waves, it depends on what way the currents are going in relation to what way the wind is blowing. And remember the tide will change direction at least once during the swim so when it does we could suddenly have very different conditions.
Mental 'walls' - 13.5 hours is a long day at work. To spend it swimming continuously tests not just your physical endurance, but much more your mental endurance. Alison Streeter, MBE, says that "Channel swimming is 80% mental, 20% the rest". Sometimes when we're training and doing a 6 hour swim, we'll find that the 4th hour (for example) just won't end. Time stops and your will power is tested. It is essential for our success that we experience these walls, recognise them for what they are, and employ methods to deal with them (think about French wine and cheese when we arrive for example!).
Feeding - No-one has swum the Channel without ingesting 'energy' enroute. We need to maintain our blood sugar levels to ensure that we're not burning up a calorie deficit. We need to try and test different foods, powder energy drinks or whatever works in training so that we know exactly what to take on the day. We need to work out how often we need to feed, and get the time down to a fine art. If we feed every 30 minutes and it takes 2 minutes each time, then that's nearly an extra hour added onto our swim, which is no good.
Support team - We need people to feed us and encourage us! This aspect is really important. We need a team who know us well personally and 'swimmingly'. They should be able to recognise when we need a lift and how to best give that lift. They need to know the feeding routine and process blindfolded so that it can work like clockwork. Think of F1 and pitstops.
Night swimming - Depending on the tide, weather and our speed, the pilot may ask us to swim through the night. We must therefore be prepared for this eventuality. Being able to swim in a straight line is important here (of course it's pretty crucial generally). Some people find night swimming very disorientating and if it's choppy it's easy to swallow a lot of water. Others find it extremely relaxing, like gliding through space.
Things in the sea - When swimming the Channel we will no doubt come across some kinds of marine life, mainly jellyfish. When a pale, flabby, palpatating mass appears out of the dark gloom it can give you a bit of a shock. If it then stings you, it can give you an even bigger shock. There is also a lot of rubbish in the Channel and we're likely to come across flotillas of crap which we just have to accept.
Swim technique - On top of an efficient swimming technique there are a few additional things we should learn to do. 'Sighting' is important. Being able to lift the eyes just above the surface of the water and take a bearing without lifting your head so much your that your legs sink down, causing drag. As well as bilateral breathing (breathing to left and right) to maintain a balanced and symmetrical stroke, we should be able to breath to just one side, on both sides. If the chop/waves are hitting from the left then you'll want to breathe purely to the right so that you don't get a mouthful of salt water. We should also train to adapt our technique depending on the conditions. An elongated, gliding technique is more efficient in calm waters, but when the conditions are a bit choppier, a shorter, faster, more punchy technique may be more effective.
So there are quite a few things to take into consideration when swimming the Channel in addition to being able to swim a long way.