Time, distance, drag

John Simpson · Post by **John Simpson** » January 14th, 2008, 7:59 am

I've just started using the Concept2 in anticipation of trials for next seasons Cornish Pilot Gig racing. So, I set the damper to max and did 2000m in 8:09, then went looking for something to measure this against. I couldn't find any reference to damper settings in any distance/time data on the web. I understand that the calorie count isn't affected by damper setting; the harder you pull the more calories you burn, even if you're going slower, but distance over time must be affected by drag/damper setting (at least in the real world), or is this also calculated from power rather than total stroke length?

Citroen · Post by **Citroen** » January 14th, 2008, 8:16 am

Get the PM2/PM3 or PM4 to give you a number for "drag factor". Rather than the damper lever position as that's less affected by external factors. Search on here for "drag factor".

The PM uses that DF number in the formulas documented here http://www.atm.ox.ac.uk/rowing/physics/ ... l#section6

PS. if you're in the UK you may want to look at http://concept2.co.uk/forum

John Simpson · Post by **John Simpson** » January 14th, 2008, 8:59 am

Thanks for the reference. Interesting to know the trouble that's gone too to calculate a consistent drag figure, but it just confuses me further.

On the concept2 site (which I can't reference directly) there are several instances where times are given for a fixed distance without drag factors. My confusion stems from the fact that I know that if I row a real boat over a fixed distance as hard as I can, then it will take me longer if I leave the fenders in the water.

The machine that we will be using will not have a performance monitor (I'm guessing) , but it will be the only one used for these trials so that at least will be fair. It will surely take me longer to row 2000m with the damper to set to max than to min.

Tyn · Post by **Tyn** » January 14th, 2008, 9:41 am

The machine that we will be using will not have a performance monitor (I'm guessing) , but it will be the only one used for these trials so that at least will be fair. It will surely take me longer to row 2000m with the damper to set to max than to min.

John ,

take some time to read some topics about Drag, drag factor and DF on the forum.

The PM is just a little computer/calculator which shows distance, time, speed, etc!

Happy Rowing!

John Simpson · Post by **John Simpson** » January 14th, 2008, 11:38 am

Yeah, I didn't know what the PM was, but I read a fair bit before I posted the question and the article referenced by Citroen in his posting says

"The split is derived from the mean fan rotational velocity w through the stroke, while the power is proportional to an average of w^3. "

This suggests to me that if the split is derived from the fans velocity then the less drag there is the faster the rower will be going for a given power and hence the time would reduce. But there is also a chart referenced in the same section giving a straight conversion between power and speed which is presumably what the PM uses.

However, I guess this is academic, someone would have noticed by now if speed varied with drag and everyone seems to be happy with the way things are.

I've nearly finished now.

This is counter-intuitive. Like I said, if you row with a sea-anchor or in a boat covered in Barnacles then it will take you longer (for the same effort) to cover the same distance. But for the rowing machine there is a direct conversion of all power to speed according to the cubic law (plus a few other bits). This wierdness may account for the number of postings on the subject. However (oh christ I haven't finished yet) , it may be that people are just happier with time and speed as the normal means of measuring their performance rather than calories (and their association with weight issues) or watts over 2000m .

I'll shut up now and just keep rowing.

J

Citroen · Post by **Citroen** » January 14th, 2008, 1:22 pm

John Simpson wrote: This is counter-intuitive. Like I said, if you row with a sea-anchor or in a boat covered in Barnacles then it will take you longer (for the same effort) to cover the same distance. But for the rowing machine there is a direct conversion of all power to speed [pace] according to the cubic law (plus a few other bits).

And that's why the PM2, PM3 or PM4 (PM == performance monitor) uses drag factor as part of the maths used to calculate WATTS. (The calories and pace are then derived from watts. Calories uses a very odd formula.)

If you stick the drag up to 205 then it's like rowing a big wooden boat.
If you stick the drag down somewhere between 125 and 135 it should be like a 4+ racing shell. I was rowing at 108 for a long time, I now use 125.

The original idea of the machine was that land based rowers could develop their rowing stroke (probably when the weather was crap) and later apply their dry training on the water (ignoring the tactics and gamesmanship that is used on water). Indoor rowing without the OTW component developed later.

The damper tends to affect the focus of your stroke. Higher damping means more arms, less legs. Lower damping turns that around. I'm sure I can pull a much better time on DF 125 than on DF 205 (despite being short, slow, old and struggling to get under 75Kg).

Nosmo · Post by **Nosmo** » January 14th, 2008, 5:49 pm

John Simpson wrote: "The split is derived from the mean fan rotational velocity w through the stroke, while the power is proportional to an average of w^3. "

Power is really what is measured. The proportionality factor changes with drag, in order to keep a one to one correspondence between power and speed.
You are correct that the analogy between a fast and slow boat is not ideal. An analogy of how the boat is rigged (longer outboard,less span =higher drag) may be better.

michaelb · Post by **michaelb** » January 14th, 2008, 6:35 pm

Since this is an indoor rowing forum, we might as well talk about indoor rowing, so I can't see any problem with what is covered so far in this thread. I also thought I understood this stuff, now maybe I am confused.

Is the power or watts was measured independently of the drag setting?

The PM measures the flywheel speed, and the drag is calculated based on how quickly the flywheel slows down each stroke. So you can produce 300 watts at high drag or low drag; at high drag the flywheel is heavy and slow and deaccelerates quickly between strokes; at low drag the flywheel is light and moving fast and doesn't slow down much between strokes. You can produce power either way: slow and heavy or fast and light.

PM converts the pace/speed from the power produced (watts) and drag setting, to create the illusion of movement of distance (meters) at for a period of time (pace).

I think this is and has been a marketing problem for C2 though, and the source of much confusion and misuse by users. It probably would have been better in the end to turn the numbers on the damper upside down and have 1 be open and 10 be closed. Of course, they should have also gone to 11.