A better SWOLF formula

A better SWOLF formula

SWOLF (“swim golf”) is a drill that measures swimming efficiency. A SWOLF score is your time (in seconds) on one lap of the pool, added to the number of strokes you took. Lower scores = Higher efficiency. SWOLF is a fuzzy, indirect measure of efficiency, because stroke count doesn’t necessarily reflect effort. In my view, the most precise definition of SWOLF is that it identifies the most efficient stroke count for a given level of effort.

I originally wrote about SWOLF in April 2012, and the post has become – by a wide margin – the most widely-read in the history of this blog. In a subsequent post a month later – “Stroke Count Games” – I described how SWOLF doesn’t quite capture the most efficient stroke count. At least for me, using stroke cycles (number of strokes divided by two) produces better results.

I wondered if this was true for other swimmers, so I asked any interested readers to send me their own data, using a test set of 8×100. Three readers sent me their results.…

--READ MORE--

Marathon Swimming Rules Survey: Results and Analysis

Marathon Swimming Rules Survey: Results and Analysis

Marathon swimmers talk a lot about rules – what should and shouldn’t be allowed during a swim – but as far as I know, there has never been any systematic study of what marathon swimmers actually think, as a matter of public opinion.

Perhaps most would agree that goggles are OK, and fins are verboten… but what about swim streamers and stinger suits? Or drafting off the escort boat? If you only read blogs and forums, you might assume the most vocal opinions represent the majority. But do they really?

Earlier this month the SBCSA launched a survey to find out. Over 25 days, we received 175 responses from around the world.


First, a Summary of Findings (TL/DR). Click any of the following links to skip directly to the relevant section.

I. We received responses from a representative sample of marathon swimmers – current, former, and aspiring.

II(a). Marathon swimmers agree on basic channel-rules attire: traditional porous textile swimsuit (including jammers), goggles, one latex or silicone cap, ear plugs, and nose clips.…

--READ MORE--

Google search trends and open water swimming

Google search trends and open water swimming

Google has a fun tool that lets you visualize trends in search queries submitted by its users. Google is often the first place people go to find out more about a given topic, so it’s a powerful measure of the public’s “interest” in that topic. Below are a few Google Trends graphs related to open water swimming.

Is open water swimming “growing”? 

search term: “open water swimming”

Some observations:

  • Interest in open water swimming is highly cyclical, with summer peaks and winter troughs. (Obviously.)
  • Two big “spikes” corresponding to the Olympic Games in 2008 and 2012.
  • Aside from the seasonal cycles and Olympic spikes, the peaks and troughs do seem to rising slightly over time.

What about two sub-genres of open water swimming: marathon swimming and triathlon swimming?
search terms: “marathon swim” (blue) vs. “triathlon swim”

As expected, triathlon swimming is consistently bigger than marathon swimming. One exception: the surge of interest associated with the London Olympic 10K marathon swim.


What about the Triple Crown events: English Channel, Catalina Channel, and the Manhattan Island Marathon Swim?…

--READ MORE--

What is the speed advantage of a wetsuit?

What is the speed advantage of a wetsuit?

Everyone knows wetsuits help keep you warm in cold water. Lesser known among the general public (but well-known among triathletes) is that wetsuits also make you swim faster! The buoyant neoprene in a wetsuit floats a swimmer higher in the water, decreasing drag and thus increasing swim speed.

But how much faster is a wetsuit? I’ve heard various rules of thumb: 10% speed increase; 4-6 seconds per 100m; 1 minute per kilometer. I’ve also heard various caveats: it depends on the swimmer’s skill (better swimmers benefit less); it depends on the swimmer’s body-type (naturally floaty people benefit less); it depends on the quality of the wetsuit (you get what you pay for); it depends on the fit of the wetsuit; and so forth.

So the answer is: It depends. Because I’m usually disinclined to let things go at “it depends,” I decided to conduct a field experiment. Reef & Run, which I’ve written about previously, provided the perfect laboratory. Almost every Thursday evening between June 21 and yesterday, August 23, I swam one mile in the ocean at East Beach in Santa Barbara.…

--READ MORE--

Stroke count games

Stroke count games

What’s the fewest number of strokes you can take for a single length of the pool? (No streamlining past the flags; no more than three kicks per stroke.)

I can get down to 8 strokes per 25 SCY, but it’s tough to sustain for more than one length. 9 strokes per length (SPL) I can do pretty much indefinitely – but it’s incredibly inefficient. The inefficiency is readily apparent: a huge dead spot in my momentum as I glide (glide, glide…) after each stroke. The Swim Smooth guys have a term for this: Overgliding.

I swim most efficiently between 13 and 15 SPL, depending on pace. 13 for channel/marathon pace; 14 for “threshold” pace (from the mile up to about 5K); 15 for 200/500 pace. For an all-out sprint, I’ll add one more stroke (16 SPL).

Experienced pool swimmers have an intuitive feel for this… but what if you don’t? Is there a formula to identify the most efficient stroke count for a given pace? This question led me to try the following set:

8×100, as fast as possible, with about a minute rest between each.…

--READ MORE--

Fat vs. Fast

Fat vs. Fast

There’s an old saying about cold-water marathon swimming:

Either be fat, or be fast.

Is it oversimplified? Probably. Crass? Definitely. But there’s a kernel of truth worth examining. Thin swimmers have made it across the English Channel, but they’re usually fast. Slow swimmers have made it across the Channel, but they’re usually… carrying a healthy layer of bioprene.

The common factor: Core temperature must be preserved. Either generate heat, or retain it. Fast swimmers are good at generating heat. Fat swimmers are good at retaining it.

In the English Channel (from what I gather), it’s considered prudent for non-overweight swimmers to put on some weight, even if they’re “fast.” A Channel attempt is expensive and, unless your name is Petar Stoychev, just getting across is the main priority. Bioprene increases the probability of success.

But at what cost? How much does the extra weight slow you down? Swimming is a gravity-less activity, so obviously it matters less than in running or uphill cycling. Further, the flotational benefits of fat may improve your body position in the water.…

--READ MORE--

Water temperature in the Catalina Channel

Water temperature in the Catalina Channel

There are 14 years of publicly available data on the surface water temperature in the Catalina (a.k.a. San Pedro) Channel – via NOAA and CDIP. Unfortunately, that’s all it is – data. No summary statistics, no long-term charts – nothing particularly useful if you’re just looking for a simple, big-picture view of trends and cycles in sea temperature (perhaps to inform your upcoming swim across the channel).

So I decided to make one myself:

Catalina Channel water temperature, 1998-2012

NOAA buoys take readings every 30 minutes. Over 14 years, that works out to almost 239,000 observations. Don’t try this on an old computer! For a smoother line, I calculated a weekly average. Same data – just prettier.

If you really need more detail, I also made an interactive chart with daily-level resolution (5,044 observations). Keep in mind, Javascript is required to view the chart, and it probably won’t look good on mobile devices. If you’ve ever used Google Finance to view stock prices, the chart format will look familiar.

Summary Statistics by Day of Year

Sea temperature varies by season, but there are also year-to-year variations.…

--READ MORE--

Venus, Mars, and Catalina

Venus, Mars, and Catalina

Previously, we’ve looked at some general stats on Catalina Channel finishing times, and the growth in participation since George Young’s pioneering swim in 1927. What about gender differences? (Taking a page from Katie’s playbook…)

From 1927-2004, there were 90 successful swims by men and 44 successful swims by women (a ratio of 2.05 to 1). From 2005-2011, there were 80 successful swims by men and 49 successful swims by women (a ratio of 1.63 to 1). So, the gap is narrowing…a bit.

Here, again, it would interesting to see the data on failed swims. Is the ratio of men to women the same for failed swims as for successful swims?

Side note: I decided to split the data-set at 2005 because it offered similarly-sized groupings, and because this was the year when there was a surge in popularity of Catalina Channel swimming (possibly due to the advent of the “triple crown”).

And here are the average & median finish times for each group (C-M one-way crossings only):

Average Median
Men 1927-2004 13:14 12:14
Women 1927-2004 12:17 11:03
Men 2005-2011 11:23 10:51
Women 2005-2011 11:00 10:39

In both eras, women are faster – despite lower levels of participation.…

--READ MORE--

Catalina Channel stats: An epidemiological view

Catalina Channel stats: An epidemiological view

The second in a series of posts taking a statistical look at the history of Catalina Channel swimming. These analyses have not been validated or endorsed by the Catalina Channel Swimming Federation and should be considered “unofficial.” 2011 swims are included, but are unofficial until the ratification banquet on November 5.

CCSF’s official list of successful swims is available here. Penny Lee Dean’s authoritative history is here.

On January 15, 1927, George Young was the only one of 102 participants to finish the Wrigley Ocean Marathon, and in so doing, became the first person to swim across the Catalina Channel. For his achievement Young earned a $25,000 prize – approximately $325,000 in 2011 dollars, and richer (even in nominal dollars) than any current cash prize in professional marathon swimming.

Seven of the DNF’s in the Wrigley Ocean Marathon – four men and three women – returned later that year to try again; four finished. But Catalina Channel swimming didn’t catch on after this rousing first year. Over the next 25 years only two more swimmers added their names to the list.…

--READ MORE--

Catalina Channel: A history in numbers

Catalina Channel: A history in numbers

The first in a series of posts taking a statistical look at the history of Catalina Channel swimming. These analyses have not been validated or endorsed by the Catalina Channel Swimming Federation and should be considered “unofficial.” 2011 swims are included, but are unofficial until the ratification banquet on November 5. CCSF’s official list of successful swims is available here.

I should note that Penny Lee Dean did some similar statistical work in her authoritative History of the Catalina Channel Swims Since 1927. However, the book has not been updated in 1996, and in any case, the stats chapter seems to have been removed from the online version.

The Catalina Channel was first conquered in 1927 by George Young of Canada, in 15 hours, 44 minutes, 30 seconds. Since then (through September 2011) there have been 259 successful solo crossings by 220 individuals, including 7 double-crossings.

The short list of double-crossers includes some of the greatest marathon swimmers in history.

From the mainland (M-C-M):

  • John York – 16:42 in 1978
  • Dan Slosberg – 19:32 in 1978
  • Tina Neill – 22:02 in 2008
  • Cindy Cleveland – 24:30 in 1977

From Catalina (C-M-C):

  • Penny Lee Dean – 20:03 in 1977
  • Forrest Nelson – 23:01 in 2010
  • Greta Anderson – 26:53 in 1958

Of the 252 one-way crossings, only 19 went from the mainland to Catalina (M-C).…

--READ MORE--