As you know, I just got the Mar/Apr 2011 copy of the USMS Swimmer magazine. In the issue, there was an article entitled "Open Water Buoy Turns: The Four Ss of the 90 Degree Turn." The four Ss are Sight, Stretch, Spin, and Strike. All four of these Ss make sense, except maybe Spin.
Of course you must sight the buoy; without knowing exactly where you are in the race and where the buoy is, you could be losing valuable seconds. (Or in my case, with my horrible navigation skills, minutes.) The authors suggest you stretch the arm closest to the buoy right after passing the buoy. Once you're stretched, you start a barrel-roll around the buoy. That's the spin. Once you've spun and completed your 90 degree turn (or 180, which might require two spins), you strike out with powerful pulls and kicks to regain momentum.
I really wish I had access to open water and the requisite buoy so I can practice this. At my Cyprus 5K, I used the technique I learned in Fran Crippen's DVD, Go Swim Open Water with Fran Crippen. (Sadly, the Cyprus 5K was the same weekend Fran died, so I haven't been able to rewatch the DVD.) Fran's technique involves getting as close to the buoy as possible. Once you get just past the buoy, you stroke with only your outside arm, which helps spin you around the buoy. It seemed to work for me in Cyprus. Granted, I've only gotten to try it out that one time...
The USMS Swimmer magazine article gives buoy drills for the pool. However, the drills help with everything but actually turning around a buoy. They include two sighting drills, a "spin" drill, and a couple of strike drills. But all the drills are swum in a swim lane. None deal with turning around a buoy. The only way I see drilling buoy turns is to remove some lane lines and swim in a group around an actual buoy. I think that's called POW.

In my experience the technique described in Swimmer mag works well if you're making 90-degree turns, or if you have a very good sense of what the angles are at each turn. But sometimes you don't always know what the exact angles are, especially if you haven't swum the course before. I find that if I try to barrel-roll around a buoy without knowing the angle dead-on, it's easy to get disoriented. That's why I think Fran's technique is preferable under most circumstances.
Posted by: evan | 12 April 2011 at 00:32
Thinking back to my limited experience, the Jim McDonnell lake swim in Reston had a few turns that would have worked. The Copenhagen one was in a naturally round canal, so no need. The Cyprus one was all 180 degree turns, so I did Fran's method.
Posted by: IronMike | 12 April 2011 at 09:25