In a triathlon with an open water swim there are usually very large buoys (and if not then some other obvious visual aid) that you must pass (on a specific side) and then turn around at least one of them. If you are not first, you will probably be able to follow other people, however you still want to make sure that the person or people you are following are on course so that you don’t follow them well out of the way!
Looking up to see where you are going is called sighting – because you get sight of the buoy to ensure you are going the right direction or course correct if you are not.
I have learned a way to do this that is super easy, and I’m pretty sure I really don’t lose any, or at least not much speed. Now to see if I can adequately describe the technique I use.
The main trick is that you sight not when you are taking a breath, but as a separate movement just after breathing to the side. So, if breathing to the right, then you put your face back down, and just as your right hand is entering the water, look up directly in front of you – picking your head up just enough to get your eyes out of the water. Then you put your head back down about the time your right arm is pulling, and you continue swimming without any change to your swim and breathing pattern.
This can of course be done after a breath to the left – that part doesn’t matter. And – if you do not see the object you are looking for to figure out whether you are going in the right direction when you look up, don’t worry. Just keep swimming, and the very next breath (or two) take another peak and see if you can spot it. I suppose at some point if this keeps not working, you may need to get a better lay of the land and will have to pick your head up for longer – possibly stopping or switching to breaststroke until ready to go again.
This can easily be practiced in the pool. You can either pick out an item straight in front of you to look at each time, or pick something a little off center.
As for frequency, I don’t have any tips. I think it would depend on how often you veer off course, how many and who is around you, the conditions, and the course.
When I am in choppy ocean water this probably rarely works for me at all and I usually am picking my head up pretty high on a regular basis just to catch a breath above the waves. Conversely, sometimes there are landmarks that make sighting easier – such as the old course at Ironman Western Australia where you swim around a large pier, and can thus use that to help you tell where you are going as you breath – ensuring it is on the right side and in about the same place. In another race, the course was on a rowing course (leftover from the Sydney olympics) and there were literally lines under the water to follow. (This ended up being detrimental because I decided to stay too close to a direct route and there were waves. Quicker swimmers in waves behind me caught up and I got pummeled…but that was my own fault).