You probably swim farther than the course says. The best measurement we have puts the average at about 9% extra distance, which is roughly 342 m and 6 minutes on an Ironman swim. That’s the distance tax: the metres you add by zig-zagging between buoys.
Here’s the catch. You’ll see “10-20% extra distance” all over the internet. No study backs that as an average. Let’s look at what the data does show.
What the Open Water Sighting Evidence Actually Says
Researchers at the University of Kent tracked 17 swimmers with GPS on set lake routes. On average, they swam about 9% more than the route required. That’s a university case study, not a peer-reviewed paper. The swimmers were general swimmers, not just triathletes.
Translation: if the course is 1,000 m, the average swimmer covered about 1,090 m.
Race tracks tell a messier story. One Swim Smooth analysis of a single athlete at Ironman Australia in 2010 found 4.13 km travelled on a 3.84 km straight line. That’s about 8% extra, and the author noted some of it was GPS and swell noise. Coaching sites claim far higher numbers for poor navigators, but they cite no data.
So here’s the honest range. Around 9% looks typical. Some swimmers lose more, perhaps over 20%. Nobody has measured the full spread.
Know your own number. Don’t borrow one.
What a 9% Detour Costs in Minutes
Percentages feel abstract. Minutes don’t. The table below is simple arithmetic on standard course lengths at a 1:45 per 100 m pace. These are illustrative, not measured.
| Course | 9% extra distance | Time at 1:45/100 m |
|---|---|---|
| Olympic swim, 1.5 km | 135 m | ~2.4 min |
| 70.3 swim, 1.9 km | 171 m | ~3.0 min |
| Ironman swim, 3.8 km | 342 m | ~6.0 min |
In short: on a long swim, bad navigation can cost you minutes that no amount of extra pool fitness will easily win back. That’s a decent reason to practice it.
Why Lifting Your Head Costs So Much
Think of your body as a canoe. Hips up and level, it glides. Lift the bow, and the stern drops into the water, and you drag a bucket behind you. Sighting does that to your stroke.
No study measures the cost of a sighting head-lift directly. Be wary of any blog giving a precise drag figure. The closest evidence is indirect. Water polo players swim head-up, and a 2010 proceedings study found higher resistance and higher heart rate at a given speed than in normal front crawl. A 2015 study of 10 elite 400 m swimmers also linked sideways head movement to extra drag.
Translation: a big, slow head-lift makes you sink, wobble and work harder. The goal isn’t to stop sighting. It’s to make each sight small and quick.
Sight less and you drift. Sight badly and you sink.
Drafting Helps, If You Follow the Right Feet
Drafting is the other half of the puzzle. In a study of 8 highly trained triathletes, swimming in another swimmer’s wake made a 400 m swim 3.2% faster (4:47.69 versus 4:57.25). Blood lactate and stroke rate were lower too.
The benefit shrinks as you speed up. Drag reduction fell from 26% at 1.1 m/s to 13% at 1.7 m/s. A later study found the best spot is within 0 to 50 cm of the lead swimmer’s toes.
Translation: the slower you swim, the more a good draft helps. It also lets you borrow someone’s eyes. But a lead swimmer who veers off-line takes you with them. Glance up every so often to check.
For more on how to get into a good draft early, see how swim start seeding changes your first 400 metres.
The Three Sighting Drills
Here’s the honest part. No controlled trial has tested these drills. They’re coaching consensus, used by swim coaches for years. They’re sensible. They’re not proven.
1. Crocodile eyes. Lift only your eyes to the waterline at the end of your pull, not your whole head. Keep your chin low and hips up. Then roll into your breath so one movement does both jobs.
2. Sight-every-N pool sets. Pick a target on deck, such as a kickboard or lane flag. Swim sets where you sight every 6, then 8, then 10 strokes. Close your eyes between sights if you want to feel how far you drift. Try 8 x 100 m, sighting every 8 strokes, with your phone filming your stroke. Your cadence should stay within about 5% of normal.
3. Tarzan reset. Swim head-up freestyle for 4 to 6 strokes. This trains a quick, high-cadence reset for when chop or a crowd throws you off. Use it in short bursts only. Swim head-up for long and your hips drop.
Pair these with bilateral breathing practice, because the side you breathe on decides how easily you can fold a sight into a breath.
Pick a Target You Can Actually See
The drills only work if you aim at the right thing. Don’t sight on the buoy you’re swimming to. A small orange marker can vanish in chop. Look past it for something big and tall instead. A building, a tree line, a church spire or a crane works well. Line the buoy up with that landmark, and you can hold your line even when the buoy ducks out of sight.
Chop changes the timing. Waves hide the target in the troughs. So lift your eyes as you rise on a swell, not as you drop into one. If you miss it, don’t hold your head up and hunt. Take two strokes and try again on the next crest.
Sun glare is the other trap. Low sun on the water can wash out the buoy completely. Pick a landmark that sits off to the side of the glare, and use tinted or mirrored goggles on race day. Test them in practice, since new gear on race morning is a gamble.
Practise all of this at your own lake before the race. Look for landmarks on the walk in.
A Case Study: Dana’s 70.3 Swim
Here’s an illustrative composite, not a real athlete. Call her Dana, 41, training for her second 70.3. In a June practice swim, her watch showed 2,070 m on a 1,900 m buoy loop. That’s about 9% extra, or roughly 3 minutes at her 1:45 pace. Her pool times said she should swim faster.
She spent six weeks on the three drills, twice a week, about 15 minutes each time. Her next two lake swims read 1,985 m and 1,960 m, or about 4% and 3% extra. The gain was roughly 1.5 minutes. Her stroke didn’t change. Her line did.
Her watch has GPS error, so she compared several swims, not one. That’s the right approach.
Measuring Your Own Penalty (With Honest Error Bars)
Divide your watch distance by the course distance, subtract one, and multiply by 100.
Sighting penalty % = (watch distance / true course distance - 1) * 100
Watches aren’t perfect in the water. Signal dropouts and swell can add 80 to 100 m on a 3.8 km swim. So don’t trust one swim. Track several, on similar courses, and watch the trend. A drop from 9% to 4% over weeks means more than any single reading.
AthleteOS makes this easy to track. It syncs each open-water swim from your watch into your training log, right next to the session it was planned for. Put the recorded distance beside the course distance, keep the GPS error in mind, and you can see the gap shrink block by block. Start your AthleteOS training plan and your swims turn into a trend line.
Keep the rest of your race in view too. Swim fatigue carries forward, which is why brick workouts matter for triathlon and why brick frequency in a 70.3 build is worth planning.
Fix the line first. Then chase speed.