rowing physics

The training

Last time I did this workout, 4x2km with 5 minutes rest, was on April 29th. Then I managed a 2:12.2 average, so today I was shooting for “faster than 2:12”.

In line with my plan, this would be the final “long interval” session of this OTW season. After today, it’s “so long, long intervals” until some time in September. 🙂

As I have a day off, I also wanted to take the time and experiment with the footstretcher location. After watching my video, several people suggested to move the footstretcher slightly sternward. So I did, but not immediately. The plan was to row the first two 2kms with the old rigging, and then change. I would take a bit more time between intervals #2 and #3 to move the stretcher and to get a bit more rest, so that hopefully fatigue would not influence the experimental results too much.

Wind was between 1 and 2 m/s varying between North and NorthWest, according to SportTracks, and it was between 2.5 m/s and 3.5 m/s NNW according to WindFinder’s prediction. On the water, I definitely noticed that the wind was growing. Between the tailwind intervals #1 and #3 there was definitely a stronger tailwind in #3, but also the water changed from “ripples” to “small chop”, and I wasn’t faster in #3 (with the new footstretcher setting). For the headwind intervals #2 and #4, pace went down by 3 seconds (from 2:09 to 2:12) with #4 being the slowest interval. Definitely a interval #4 was the hardest battle seeing the slowest splits at some points. I also noticed that interval #4 got quite sloppy in one point. When I realized it, with about 500m to go, I started to focus more on technique, which gave me a few seconds of split in the right direction (it could also have been the effect of a slight turn in the course, which made the wind less head-on and more cross-wind).

More about wind in the second half of this blog. First, the plots:

And the stats:


Workout Summary - media/20160628-105331-2016-06-28-0805.CSV
--|Total|-Total-|--Avg--|Avg-|-Avg-|-Max-|-Avg
--|Dist-|-Time--|-Pace--|SPM-|-HR--|-HR--|-DPS
--|13528|62:39.0|02:17.3|23.9|153.4|163.9|09.2
Workout Details
#-|SDist|-Split-|-SPace-|SPM-|AvgHR|MaxHR|DPS-
01|02980| 15:08 |02:31.5|19.6|131.0|161.0|10.1
02|02000| 08:06 |02:01.5|27.0|165.0|173.0|09.1 | tailwind standing start
03|02000| 08:35 |02:08.9|27.2|172.0|177.0|08.5 | headwind rolling start
04|00781| 04:30 |02:36.2|19.9|134.0|144.0|09.6 | tailwind standing start, footstretcher moved
05|02000| 08:06 |02:01.7|28.2|169.0|176.0|08.7 | headwind rolling start
06|02000| 08:49 |02:12.5|27.4|171.0|177.0|08.3
07|01767| 09:25 |02:40.1|18.1|132.0|139.0|10.3


You can see more on the workout page or the interactive plot on rowsandall.com.

After the session I did some rigging measurements, just to make sure I had all the data, and also to compare with on-line rigging charts for single sculls. The problem of course was that I never measured “work-through” myself, so I measured this differently than the tables. What I measured:

• Measured distance between stern (“front”) side of front stops and the line connecting the oarlock pins: 18.0cm, with front stops being more sternward.
• Measured distance between “ball of foot” location on footstretcher and the line connecting the oarlock pins: 57.8cm

What people measure:

• Distance between knee and the line connecting the oarlock pins at “half stroke” (between -2cm and +2cm recommended)
• Measure hip joint position vs that same line at catch position

I am actually not sure how people measure this without help, and I am not sure how accurate these measurements are … OK, will do more measurements tomorrow. Also, I forgot to measure footstretcher height and angle.

I will keep the footstretcher at the new position for a while. Boat didn’t feel significantly heavier at the catch.

Uploading trainings to Concept2 and comparing trainings

Regular readers know that I have been building a website to support creating those colorful plots that I show in my blogs. The site is at rowsandall.com. There has been quite an evolution over the past few weeks, probably because I put a lot of my free time into it. So here is an overview of the functionality:

• Upload data files for OTE and OTW rows (Painsled, ErgData, ErgStick, CrewNerd, RiM, SpeedCoach) and make plot image files or use interactive plots
• Synchronize your data (including heart rate, stroke rate, pace vs distance and time) to the Concept2 logbook
• Import your data from the Concept2 logbook for advanced plotting and sharing. Concept2 doesn’t allow to see the rows of other people. Rowsandall.com allows you to overcome that.
• Synchronize (import and export) your data with Strava and SportTracks
• Comparing workouts

Actually, everything I do on this blog is now going through that site. Bugs are starting to get relatively minor and seldom, so I encourage you to take a look, register, and try it out. Comments here or on rowsandall.slack.com.

That last functionality, comparing workouts, is relatively new, but quite interesting. Here are a few example plots for today’s workout vs the same workout done on April 29th:

The distance axis is not completely similar between the two workouts, because I took more time and distance for the warming up. Still it is clear that I managed significantly higher stroke rates and faster paces today. I call that progress (and perhaps the effect of the low i sculls). It cannot be only due to the warming up of the water …

Geeky stuff

Another thing that I am working on is correction for wind. The trouble is of course to get good wind data. Must develop a portable data logging wind meter for rowers …

Using the GPS track (and some data smoothing) you can calculate the boat’s bearing, and thus its angle with respect to the wind. Decomposing that wind into head/tailwind and crosswind components is then child’s play. Here’s my track of today:

Here is the wind according to SportTracks, taking data from nearby amateur weather stations:

Taking the prediction from WindFinder, the same plot looks like this:

Both plots were generated directly on rowsandall.com using the wind editor. I haven’t implemented wind correction on the site yet, but I have it working on the desktop. Please don’t look at the “Erg Power” and “Erg Pace” lines. They are off and I know it. That’s the next step. As the whole calculation takes about 10 minutes, I need to program this as a “background task”, enabling the users to come back to the calculations once they are done (and sending them a message when that is the case).

As you can see from the second plot, the calculation sometimes fails. Need to look into this a bit more.

Comparing the tailwind section’s comparisons, I think the truth is somewhere between the two plots.