Information Wants to be Free: Sandettie Lightship and the English Channel

Information Wants to be Free: Sandettie Lightship and the English Channel

(tl; dr — 10 years of English Channel weather data, in a single CSV file. And some fun charts.)

Weather can turn on a dime in the English Channel, and the dreams (and finances) of English Channel swimmers often turn on the weather.

sandettie lightship
Location of Sandettie Lightship in the English Channel

The most important source of information about that weather is a 156-foot lightvessel called Sandettie, which serves as both a floating lighthouse and a weather station. Here’s a nice photo.

Sandettie collects a variety of important meteorological data – air and sea temperatures, wind speed and direction, wave height and period, humidity, and barometric pressure. These data are then fed back to the UK Met Office, who publish the most recent 24 hours’ of observations on their website.

Anything before the last 24 hours are what the Met Office call “chargeable data” — at the rate of £6800 per 10 years, per two elements (e.g., air temp & sea temp). According to the today’s exchange rate, that converts to no less than $11,575 USD.

LOL! (And yes, I actually requested a quote from the Met Office.)

Just sayin': In the US, quality-controlled meteorological data are available from NOAA’s National Data Buoy Center — for free.


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.…


One year in the life of a marathon swimmers forum

One year in the life of a marathon swimmers forum

One year (and one week) ago, Donal and I launched the Marathon Swimmers Forum with the following mission statement:

  • To celebrate and promote the sport of marathon swimming.
  • To foster connections and information sharing among the global community of marathon swimmers.
  • To provide an educational resource for aspiring marathon swimmers.

Donal and I are both pretty proud of what’s happened since then. Just by the numbers, 565 confirmed members have contributed 5,437 posts in 400 separate discussion threads. Even better, the quality of the contributions has been gratifyingly high.

To celebrate the Forum’s first birthday, here’s a quick peek at the site analytics:

A Global (yet, to be honest, mostly anglophone) Community

Geographical distribution of visits by city

Geographical distribution by country, full year

Geographical distribution by country, first month
Geographical distribution by country, first month

Everybody Loves a Controversy

Top Threads, as measured by pageviews:

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?

search terms: “english channel” swim (blue) vs.

Santa Cruz Island Swim, Part 4: The Data

Santa Cruz Island Swim, Part 4: The Data

In case you missed it:

The shortest-line distance from Santa Cruz Island to the mainland is 16.4 nautical miles (18.9 statute) – starting at San Pedro Point, finishing at the southern end of Hollywood Beach, north of the entrance to Channel Islands Harbor. Capt. Forrest actually plugged in a slightly more distant waypoint – the resort at Mandalay Beach – which made it a 16.6-nautical mile swim. I don’t know why, but that’s what he did.

To break Ned’s record, I had to average 1.59 knots (2:02 per 100m, 2945m per hour) across the channel. To break 10 hours, I had to average 1.66 knots (1:57 per 100m, 3074m per hour). My neutral-condition (i.e., pool) pace for a swim of this distance, at my current fitness level, would be approximately 2.3 knots initially, fading gradually to ~2.05 knots.

My progress for the first five hours (corresponding to the nighttime portion of the swim) was as follows:

  • Hour 1 — 1.4 nautical miles
  • Hour 2 — 1.8 nmi
  • Hour 3 — 2.0 nmi
  • Hour 4 — 1.8 nmi
  • Hour 5 — 1.5 nmi

Given my average progress over hours 1-5 (1.69 knots), the conditions may have been as much as a 20-25% “tax” on my swim speed.…


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.…


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.…