I got back in the pool about a year ago ( after 25+ years without swim training!) after I realised that I was never going to run again due to a chronic injury.
I have done a few OW races since and I did my main OW race for this summer yesterday: 6K in 1h54 from the island of Tabarca to Santa Pola in Alicante, Spain. I was reasonably prepared (averaging around 11k a week this year) and had no qualms about the distance but I was not prepared for the sea conditions continuously changing. When I got out I felt like I used to after a particularly hard rugby match - I was completely knackered. I took about 15-20 minutes more than in a 25m pool to do the same distance and was far more tired at the end.
Based on what you have said here, I think that you are somewhat underprepared for these swims. That is not to say that you won't be able to do them - that is probably more a mindset issue - but you should set your expectations accordingly and expect to take the consequences afterwards.
Recommendations:
- Try and swim in the same place as the 6k race beforehand (1k the day before?) just to acclimatise yourself to the conditions (wind & wave directions, currents, seaweed, murkiness, etc.).
- If you expect to be in the water less than 2h30, nutrition should not be an issue. Just eat (carbs) and hydrate well in the days leading up to the race and don't make any experiments or radical changes in your usual diet.
- Keep calm during the swim. Above all else, this will help you finish - concentrate on breathing and technique. If somebody lands on top of you or swims into your path, ignore them. Nobody is out to get you and they either didn't see you or were put there by a wave.
- In tough sea conditions maintaining a rhythm is difficult. If you go out thinking that anything can happen between one stroke and the next it's easier to deal with when something unexpected happens - you can't breathe because of a wave breaking, your arm entry is truncated, etc. Try and maintain a rhythm but don't get nervous if you can't.
- Use vaseline or bodyglide on the back of you neck, under your arms and between your thighs - apply it with a plastic glove. This will enable you to put your googles on without smearing them! I can't give you advice on wetsuit issues as they have not been allowed in the OW swims I have done.
- Start from an appropriate position. If your aim is to finish, start at the side or at the back. 6K in rough water is a long way, don't make it harder on yourself by fighting with the elites to get the best position in the first 500m.
- Don't be disheartened if your time is way down from what you expected based on pool swims. Every sea swim is dependent on the water conditions and currents, you cannot compare times directly.
If you get through 6K in rough water, you should have no problems in the 10K in calm waters - apart from boredom. Good luck!
EDIT: Forgot to add a link to some good training sessions for longer distances.
Edited: 09/07/2012 at 18:45