The water's balmy come on in!

A common concern with triathletes taking to the sea/lakes here in Ireland is the cold.
It's definitely a reasonable concern, the water here doesn't exactly look warm!
It's not as cold as you think. People always think it's colder than it actually is.
Modern triathlon wetsuits are very good at keeping us warm. With a good suit heat loss through the body is low and should not be a concern for triathlon swims which are by open water swim standards, short. Consider that the standard distance for a swim marathon is 10km and and the longest tri swim is the ironman 3.8km. If anything, you're more likely to overheat in a suit than feel cold in a race.
We lose most of our heat in the water through our heads. Think about it, lots of blood supply and very little insulation in the form of fat or muscle. A good quality silicone hat will suffice to cut this heat loss off. If you get especially cold there are neoprene (wetsuit material) swim hats. I use these in early may while swimming but after that it's a standard silicone hat for me.
Another important piece of kit is ear plugs, cold water in the ear canal can lead to big problems in the long term, known as surfers ear, very painful surgery required to fix this. Ear plugs are €3 a pop and once they're in you forget they're there.
Some people wear swim socks but I'd steer clear unless you suffer unusually badly from the cold. It must be very difficult to kick properly in these and you can't wear them in a triathlon.
You just got to "suck it up" when it comes to your hands. I wear gloves while surfing in the winter. It's so much harder to paddle with them but it's just too cold not to wear them. For swimming in the summer you don't need them, end of. Pretty sure they're not race legal either.
I met club secretary Lynsey Dunne in the pool recently and we spoke about her training for her 2013 channel swim. She is taking to the water this weekend (18th March) to begin her cold water acclimitisation and will of course be minus a wetsuit. She cannot wear a suit for her channel swim for it to be officially recorded. Now Lynsey is tough and most of us couldn't do that but it puts swimming in a wetsuit in the summer into context, ie: it's not too bad. Her advice for dealing with the cold? "Just get on with it".
No matter the suit you will always feel a little cold as the water gets in at first, but this will quickly pass once you get moving.
I wouldn't get into the sea myself before May, it's still warming up and there's just no need.
Water temperature is surprisingly highest in Sligo in Autumn not Summer. The chart shows that the water temperature is out of sync with the air temperature and takes longer to warm up during the year. Who'd have thought November was warmer than May!! Temperature can vary from day to day somewhat depending on weather conditions. If the wind blows over the surface of the water it causes rotation with warm surface water going to the bottom and the colder water replacing it at the surface. This is called upswell, and you will notice it if you're in regularly.
On a hot sunny day the water doesn't heat up much as a result of the sunshine and it can actually feel colder as you go from the warm air to colder water.
Finally, if you're really feeling cold there is an old surfers trick where you pee into your suit to warm up! Maybe not a good idea with your nice tri suit on underneath however!
*Data is for malin head, we're a little warmer at say rosses point where you could probably add a degree.

Coach Shane's swim blog

Swimming advice and techniques for new and experienced triathletes from Shane O'Doherty

Caoimhe's tri blog

Follow the training and racing of top Sligo triathlete Caoimhe Ni Mhuruchu

Eamon McAndrew's racing blog

The training and racing diary of our club sponsored athlete Eamon 'mouse' McAndrew

Iron distance wall of fame!