What's The Easiest Way To Take Ten Minutes Out Of Your Swim Split?

Here's some fascinating GPS data from one of our Perth squad members, Daniel Tarborsky. Dan raced with his Garmin GPS under his swim cap for three of his major races this season just gone, recording the exact path he took. Let's see how he got on:

Busselton Half Ironman, May 2010:


  • Distance travelled from Garmin (inc run in & out): 2.33km
  • Straight line distance (inc run in & out): 1.98km
  • Distance extra swam: 0.35km
  • Percentage extra swam: 18%
  • Calculated time lost from swimming extra distance: 10 minutes exactly!

Port MacQuarie Ironman Australia, April 2010:

  • Distance travelled from Garmin (inc run in & out): 4.13km
  • Straight line distance (inc run in & out): 3.84km
  • Distance extra swam: 0.29km
  • Percentage extra swam: 8%

Hillary's Sprint Triathlon, April 2010:


  • Distance travelled from Garmin (inc run in & out): 1.02km
  • Straight line distance (inc run in & out): 0.82km
  • Distance extra swam: 0.20km
  • Percentage extra swam: 24%

Wow - thanks to Dan's data, you can clearly see the huge scope for losing time from poor navigation in open water. Whilst some of the extra distance measured by the GPS may be due to swell motion, it's clear that most of it is from straying off course - we've seen other GPS data at the same races showing much better navigation.

Food for thought isn't it? If we wrote a blog post about an easy way to improve your stroke technique to take ten minutes out of your swim split you'd hang off our every word! And yet, most triathletes never develop or practice their navigation and sighting skills.

A swimmer can measure their 100m time or count their strokes per length in the pool and so spends a lot of training focus improving these metrics - "what gets measured gets done". Until now we've not been able to accurately track how a swimmer travels in open water - and this probably explains the lack of enthusiasm about developing open water skills.

We're now rapidly approaching the northern hemisphere race season. If you are looking to get the best out of yourself in the water we strongly recommend you devote one of your weekly swims towards open water skills. The ideal way to do this is to train in open water in a group, however you can do a pretty good job working on your sighting and drafting techniques in the pool too.

A big thank you from us to Dan for being a great sport and allowing us to share his navigation skills with the world!

Swim Smooth!


Unknown said...

Great article, and it really shows how important navigation is.

But I would really appreciate it if another shot would be presented of the same GPS device (under a Swimming Cap) when walking in a straight line. Let's say, just follow a road for 1km. I think such GPS device will always show extra distance and I am wondering how much (some gaps just can't be explained, why would Dan all of a sudden hop from left to right at the close up of Hillary's Sprint)

AlanM said...

Rowan's comment is a good one. I know from using my Garmin Edge 705 on my bike on a trainer in the winter (for heartrate, cadence, etc), that a plot of the "route" shows me jittering all over an area with a radius of about 6m. Over a two hour spin workout, this can add up to quite a bit.

Still, there's a lesson in Dan's findings... pay attention to navigation!

Anonymous said...

That's interesting data, and it's not often stuff like this is published, - nice one. I'd take it with at least a small pinch of salt though, recreational GPS units aren't quite as good as the marketing says they are. I'd also like to know how the organisers set out and measured the course. Just as an example, the lake where I swim has 3 loops set out, and permanently marked with buouys, - the owner took great care setting them out and checked and re-checked using a hand held GPS unit. Out of interest, and after a chat in the bar I measured the course accurately (with lasers and infra-red equipment). The 1500 loop was really 1380m, the 800 -878m and the 400 -350m. I can't believe Dan turned at right angles on occasion, and even sharper in a couple of places, - so it does give you an indication of how the GPS unit is not getting reliable fixes throughout. I think the bottom line is: - don't place too much faith in the GPS! (I wrote a bit about GPS accuracies here: http://www.kingstonwheelers.co.uk/kwccforum/viewtopic.php?t=3573
It would be great to get a really accurate track of a swimmer, - I'm still trying to figure out how to do it though!
Still a great article though chaps, - it's not only Swim Smooth, it's Swim Straight.
Cheers, Harry

Paul said...

This is all of course very true.

What was really interesting though was immediately after Dan submitted his GPS data to us, his mate also sent through his GPS file using the same watch on the same course and he managed to swim just 20m over-distance, compared to Dan's ~300m+ - his course profile looked like it had been drawn with a ruler compared to Dan's!

I don't doubt for a moment there will be some inaccuracies with the unit especially when Garmin often quote how it may lose a signal when submerged in the water. To clarify though Dan did wear the unit on his head under his swimming cap so hopefully this would should less inaccuracy than if he'd worn it on his wrist.

I think the biggest thing to point out though is what Dan's per 100m pace worked out at during the Busselton Half Ironman event taking the course he did - this was 2'12" per 100m. Dan's consistent, repeatable rep pace in the pool for threshold 100s with a ~15s rest would be in the region of 1'45" to 1'48" prior to the event. He had a demonstrated ability to comfortably swim at a pace of 1'56" per 100m for a 1500m continuous swim also (pool, non-wetsuit). Dan also swims significantly quicker in a wetsuit due to a typical lean triathlete build with sinky legs. All-in-all I would have expected him to have been able to swim at ~1:50 per 100m for the 1.9km swim, especially with good drafting technique. As it was he was well over 20s per 100m slower than this which set the alarm bells ringing as to how crooked he must have swum.

Like I say in the article, its all food for thought. One of the things that may explain some of the deviations at the Hillary's course is swell...this tends to be a little bit of an exposed swim course compared with say Busso or Port Mac and may help to explain some of the shifts at right angles...perhaps.

Get working on your sighting ability crew and of course the ability to swim straight!

Cheers and have a good weekend.


Anonymous said...

GPS inaccuracies aside, it would be interesting to note where Dan tangled with other swimmers in those events. In one OWS I got tangled up with other swimmers coming around a buoy (had my ankle grabbed & pulled down,etc.). Right after I thought I had my bearings and was swimming straight, but with first good sighting I realized I was swimming UP-course. In the contact I had been turned almost 180 degrees & did not realize it.

Francis Mallard said...

Definitely food for thought. I know I swim a lot slower in open water and I'm pretty sure it's because of navigation. I get turned around quite a bit. I would guess 8-10mins is pretty reasonable but what a huge change if I could site better. What unit fits under a swim cap BTW?

Steven Munatones said...

Notwithstanding the swell action, I wonder if any of the deviations from the absolute straight-line course were due to Dan following a pack or an escort boat or running into flotsam or getting stung by jellyfish (which is an EXCELLENT way to automatically swim at an angle to one's intended course)?

Peter Elliott said...

A large thanks to Dan and Paul for this. My open water training starts in a couple of weeks, and sighting is on the "to do" list.
I'll feel better about taking my time to sight properly and letting the pack follow their noses into oblivion.
Who would have thought the shortest distance between two points is a straight line!
I love this sport!!

Gregwh said...

Interesting study...I have heard it's still better to swim with the pack even if they are taking a scenic route. The benefit of drafting outweighs the benefit of swimming a straight line all alone. Just a thought.

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Dmarie said...

everyone has really good points here. I think there should be a rate of variable change when they run the stats. Of course no one is going to swim a perfectly straight line. you could us the same point while swimming in a pool lane. But like rowan said there is a very good lesson to this:) Love reading all your insightful posts.

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