Metrics In Open Water: Measuring Distance

Now that open-water season is more widely opened up in the Northern Hemisphere we should discuss some ideas about translating pool practice into open-water.

It takes an adjustment in mindset to move from pool practice to open-water practice. When asked I let swimmers know that pool swimming and open-water swimming are related – but more like cousins rather than sisters. Pools are controlled environments = tame water. Open-water is outdoors, natural, uncontrolled = wild water. It takes different skills and different mindset to not just be safe but really enjoy it.

1406 Land Mammal

When training in open-water how do I measure distance?

When training in open-water the brain’s sense of distance is quite variable. I highly recommend setting up some sort of routine or course in the place you intend to swim most often.

Conveniently, Coach Terry has a 200 yard rope line in Lake Minnewaska where he swims in summer so he has a precise distance he can consistently measure himself by. He can count strokes and then know exactly what stroke length he is using. But he still has to deal with any conditions the weather sets up for him there.

In my stretch of the Mediterranean I don’t have a fixed rope line to help me on short distances. I most often use stroke counting to mark shorter segments of my practice and reference points on shore to mark the larger segements. I also have various routes I swim and therefore, from measuring and from experience, have a sense of how far, how long, or how many strokes it takes to go from point to point. Throw in some wind and waves, cool water or warm, early morning or mid-afternoon, and I readjust my expectations.

So there are two main ways I break down a long open-water swim into smaller, more easily measured pieces:
1) Use two known (and measured) points, or
2) Use stroke-count intervals.

Fixed Points

One simple approximate way is to pick two easily identifiable land marks and swim between those. Fixed boys, docks, rock outcrop, or something you can swim very close to – that won’t move around from day to day.

If you don’t have a GPS swim watch (I don’t), and the objects are big enough you can look up these two landmarks on Google Maps and use the measurement tool (they say it’s accurate to +/1 2 meters!). Keep in mind that in open-water, we likely never swim in a perfect straight line, but straight line is still what is used to officially measure open-water swim distances.

If you are confident in the Google Map or GPS measured distance, you can take the Distance of the Swim (DS) and divide by your Stroke Count (SPL) to get your Stroke Length (SL), that universal number need for comparison between swimmers.

DS / SPL = SL

By having some measurement for actual distance, now you can figure out SL, Tempo, and Pace using the simple algebra equation:

Pace = (SPL x Tempo) / 100 meters (to give you Pace / 100m)

Stroke-Count Intervals

This approach is more subjective because you can’t measure stroke distance precisely, but this is what I use while racing, and it is most often what I use while training.

Personally, I like to use 300-stroke intervals. I can count 300 of each arm stroke, or 150 of just one arm, or 100 bi-lateral breaths when breathing every 3 strokes.

But you can do intervals of any stoke count you like – 20, 50, 100, 200, 300, or more. It is just a matter of how much time you want between changing focal points. or how high you can go before losing track of your count!

Stroke-Count Intervals is more about dividing up the Time, rather than dividing up the Distance, through we can estimate that too.

Sometimes I swim with a Tempo Trainer and sometimes not. I often keep it tucked in the back of my swim cap, pre-set to an appropriate tempo, just in case I suddenly decide I want to use it. I specifically train with a Tempo trainer so that my sense of rhythm, and fine adjustments of it, gets so hard-wired I can swim without needing one.

So, without a Tempo Trainer I can track my tempo just by looking at splits on my watch. 300 strokes at 1.00 Tempo is exactly 5 minutes (300 seconds). 1.05 is 5 min 15 seconds, and 1.10 is 5 min 30 seconds. I just hit the start button at the beginning, then either stop and rest at 300 strokes, or I hit the split button in stroke at the end and take a quick glance at my watch to check that I am on Tempo. At that number of strokes it’s close enough for all practical purposes. 1.00 to 1.10 is is my current Tempo training range.

From years of training SPL in the pool, if I have strong imprinted feel for a specific SPL range – but, it does require check-up and tune-up, and salt water (or any differences in water chemistry, temperature and volume) can affect buoyance and viscocity – which affects how far I travel on each stroke. I can generally rely upon that muscle memory (up to a point) to let me know by feel if I am using an 18 SPL stroke (1.11 meters per stroke), a 17 SPL stroke (1.18 meters) or a 16 SPL stroke (1.25 meters).

For rough, conservative estimates of distance (which attempts to account for the many things in open-water that are likely shortening the stroke) I just assume 1 stroke = 1 meters.

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7 responses to “Metrics In Open Water: Measuring Distance

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