Portsmouth Yardstick for rowing?

[bw1099]

Is there something equivalent to sailing's Portsmouth Yardstick for rowing? For those who aren't familiar with it, the Portsmouth Yardstick is a way of comparing the relative speeds of different types of sailboats so they can compete fairly in a single race.

What I am really interested in is a comparison between an erg and a single. Somewhere, I heard that the erg was calibrated to give times equivalent to a specific type of boat (4- or 4x, I think). When I compare my erg times to my otw times, there is a huge difference, on the order of 1 minute per 500 meters, for equivalent distances. I'd like to have a way to determine how much of this difference is me and how much is the equipment.

bw

[Byron Drachman]

You can get an approximation using the formula at the physics of rowing website that says if you double the number of rowers you expect an eight percent increase in speed. So if an ergometer is calibrated to approximate four rowers, two rowers should be about 8 percent slower than four, and a single rower should be another eight percent slower than two rowers, or about 16 to 17 percent slower than four rowers. So your on-the-water times should be about 16 to 17 percent slower using that formula.

Confession: My technique OTW in neutral conditions, warm water, etc. does not get me within 17 percent of my ergometer times.

See this reference for details and assumptions used in the mathematical model:

http://www.atm.ox.ac.uk/rowing/physics/ ... l#section6

I believe someone (Kleshnev?) produced a table based on experimental data on erg vs OTW times but I'm not sure about that. Does anybody have a reference?

[Ralph Earle]

Here's Valery Kleshnev's "app for that": http://www.biorow.com/RigChart.aspx

Based on my PB from 2003 and SB from 2012, it predicts an OTW time for 2K a little over 10% slower in calm water at 20°C.

Interestingly (to me anyway) when I plug in data for me and my 2X partner at 1K OTW, it gives an erg time of just 2 seconds faster, which is pretty much dead on. This comports with USRA handicaps, which are the same for a 2X as for a 4X/4-.

Data, however, from the few masters over 60 years old for whom I could find OTW and erg times, indicates about ~20s/500m difference; i.e., typical medalists' times are 4:00 - 4:20, while their erg times are 3:20-3:40. But 4:10/3:30 = 119%, which is about what Byron wrote.

The difference between Kleshnev's 10% and the masters-over-60's 19% is probably due to the fact that Kleshnev is working with world-class rowers, whose ages are either "Open", "Under 23" or "Juniors."

So, a la the USRA Handicaps, how about a "Honolulu Yardstick" of 10% + 0.25%x(Age-27)? That would be about 22% for you, Byron -- is that about right?

If the winds are still calm late this afternoon, I'll give it a go at 1K in a Maas 24.
My erg SB is 4:15.3, 24spm; the Honolulu Yardstick predicts 5:07.6, but I'll probably rate 22-23. So it should take me 115-116 strokes, which seems about right.

P. S. A little sleuthing in the rankings says you're 52 and have a 2K ~7:59. The HY predicts OTW ~9:17. Is that close?

[Byron Drachman]

Here's Valery Kleshnev's "app for that": http://www.biorow.com/RigChart.aspx

Based on my PB from 2003 and SB from 2012, it predicts an OTW time for 2K a little over 10% slower in calm water at 20°C.

Interestingly (to me anyway) when I plug in data for me and my 2X partner at 1K OTW, it gives an erg time of just 2 seconds faster, which is pretty much dead on. This comports with USRA handicaps, which are the same for a 2X as for a 4X/4-.

Data, however, from the few masters over 60 years old for whom I could find OTW and erg times, indicates about ~20s/500m difference; i.e., typical medalists' times are 4:00 - 4:20, while their erg times are 3:20-3:40. But 4:10/3:30 = 119%, which is about what Byron wrote.

The difference between Kleshnev's 10% and the masters-over-60's 19% is probably due to the fact that Kleshnev is working with world-class rowers, whose ages are either "Open", "Under 23" or "Juniors."

So, a la the USRA Handicaps, how about a "Honolulu Yardstick" of 10% + 0.25%x(Age-27)? That would be about 22% for you, Byron -- is that about right?

If the winds are still calm late this afternoon, I'll give it a go at 1K in a Maas 24.
My erg SB is 4:15.3, 24spm; the Honolulu Yardstick predicts 5:07.6, but I'll probably rate 22-23. So it should take me 115-116 strokes, which seems about right.

P. S. A little sleuthing in the rankings says you're 52 and have a 2K ~7:59. The HY predicts OTW ~9:17. Is that close?

Hi Ralph,

10+0.25*(74-27), around 22 %, seems pretty close for me. I should do some testing but I spend almost all my time on the water, and I only erg when the river is frozen. Last winter we had a mild winter in Michigan so I didn't erg much.

I wonder if some of the highly skilled masters scullers such as Mike VB, Leadville, Nosmo, just to mention a few I have seen on video or in person, would be around the 10% factor.

Thanks for the link to Kleshnev's chart.

[mikvan52]

FWIW:

my recent data:
1k OTW in a 1x......= 3:40.x (straight course against a little tide but w/a bit of tail wind)
1k OTErg: = 3:18.x

approx. difference 22 seconds

[Byron Drachman]

FWIW:

my recent data:
1k OTW in a 1x......= 3:40.x (straight course against a little tide but w/a bit of tail wind)
1k OTErg: = 3:18.x

approx. difference 22 seconds

Ahah! Evidence that a skilled sculler can get close to the ten percent difference as predicted by Kleshnev.

[Nosmo]

There is a chart in one of the older bio row news letters that compares OTW an erg times.

The erg was calibrated for 100 Kg rowers. And I believe it was for an 8+ not a 4x (a 4x is just a bit slower than an 8+).

The relative difference in speed will depend on the weight of the rower. A 117 lb person should have the same erg times in a 1x and on the erg. For ~145 lbs rowers in a 2x the times should be about the same.

A 4x should be 8% faster then a 2x which in turn should be 8% faster then a 1x. Same relation holds for sweep boats without the coxwain. The speed change with adding a coxswain can be calculated if the weights are known using the standard formula of speed being proportional to the weight to the 2/9th power. (all of this assumes the boats are designed for the weight of the rower, a somewhat different exponent holds for a given c boat.)

I'll find the link to the chart and give a bit more background when I get a chance later today.

Don't have accurate enough times for me to compare my erg and OTW times. (My OTW 1x times are all of the map--I don't usually train with a speed coach and my races always seem to have wind and current) but I believe I am a several seconds slower then Mike both on the erg and on the water. Maybe a little closer on the water but I'm 10-12 lbs lighter.

[bw1099]

P. S. A little sleuthing in the rankings says you're 52 and have a 2K ~7:59. The HY predicts OTW ~9:17. Is that close?

9:17 OTW sure would be nice. Back when I used to do 2k in ~7:59 on the erg as my normal time, I could do 2k OTW in ~10:00. This year, my erg times for longer pieces have been in the range of 2:30/500m. OTW over a similar distance last weekend with similar effort (but somewhat crummy conditions) was about 3:30/500m. In good conditions it is closer to 2:55/500m.

[bw1099]

It seems like the Gold Medal Standard is the equivalent to the Portsmouth Yardstick.

I found Gold Medal Standard table online. I normalized the times to the erg and sorted them from high to low (for men, since I am a man) and plotted them. The results are kind of interesting. For men the erg does appear to be calibrated for 4 rowers. The 16-17% slower for a 1x that Byron came up with is right on. But it doesn't account for age, which is why we have the Honolulu Yardstick. Then there is how low the boat sits in the water, which is likely the cause of my slower than predicted OTW times...

GoldMedalStandard.jpg (31.63 KiB) Viewed 10838 times

[Nosmo]

Dr. Valery Kleshnev's chart showing OTW time vs erg score and weight can be found here:
http://www.biorow.com/RBN_en_2007_files ... News08.pdf

and the explanation of his methodology here:
http://www.biorow.com/RBN_en_2007_files ... News07.pdf

Using 72 kg for Mike Van B. the chart is with in a second or two of his reported times.

I had not remembered correctly, the chart shows that on the water times and erg times are the same for
approxametly 105kg people in a 4x, for 100kg rows in a 4-, and 62 kg rowers in a 2x.
The other boats fall outside the range of the charts, extrapolating it looks like:
130 kg for an 8+, and 43 kg for a 2-. for a 1x much lighter yet.