Trying to understand drag factor better

[Sandeman]

Ok, so I've read a lot about drag factor and seen quite a few youtube video's, but it's still a complex concept for me.

There are two things that seem to appear in most of the information I found:
1) A higher DF is like you're rowing a bigger (less streamlined) boat
2) A higher DF is like using a higher gear when you're on a bicycle

Ok, I get that. High DF means you have to work harder than with a low DF.

But now it becomes a bit fuzzy for me, because a bigger boat and a higher bicycle gear actually aren't the same.

If I perform a certain amount of work in a (less streamlined) boat, it would get me less far than the same amount of work in a sleak boat right?
But if I perform a certain amount of work on a bicycle it doesn't really matter which gear I'm in. High gear means hard to get the pedals around, but I go really fast doing so. Low gear means easy to paddle but it doesn't really go very fast.

Am I still on the right track here? Or is my perception of work vs distance for different types of boats wrong?

Assuming I'm on the right track, shouldn't there be a different analogy for drag factor? The plump vs sleak boat doesn't feel right.

I've been thinking about this and if all of the above is (somewhat) correct, I think we could (should?? ) use a paddle length analogy.

So we instead of picturing different kinds of boats for different dragfactors, we use the same boat all the time.
But we change the length of the paddles.

If I use a short paddle I have a very short lever and I don't have to work very hard to move them through the water.
But the distance I will travel at every stroke will be small. This feels like a low drag factor for me.

But if I use a very long paddle, I have a very long lever and with every stroke I get a huge distance through the water but I would have to exert a huge amount of force to do so. This feels like a high drag factor for me.

I'd appreciate if you could shed your light on this.
I could be very wrong, but the concept keeps bothering me.
A question I ask myself a lot is: "does any amount of work on DF 140 give a the same split as the same amount of work on DF 100?". I think the answer is yes, but I can't match this with the different boat sizes analogy.

Sorry for the long post, thanks for reading

[Carl Watts]

All I know is that a DF of between 110 and 130 tends to work best for most people with years of rowing experience.

I don't think you need to try and fully understand it because what works for someone else may not work for you. Its trial and error, people come in all shapes and sizes with a massive wide range of power and are different ages. Even what works for you will change over time.

Really not worth worrying about, just don't set it to high or set it to low. With a clean Erg my damper setting is a "4" which is a 125 drag factor on the monitor, pretty much never change it unless it for a short sprint event.

[JaapvanE]

Ok, so I've read a lot about drag factor and seen quite a few youtube video's, but it's still a complex concept for me.

There are two things that seem to appear in most of the information I found:
1) A higher DF is like you're rowing a bigger (less streamlined) boat
2) A higher DF is like using a higher gear when you're on a bicycle

Ok, I get that. High DF means you have to work harder than with a low DF.

But now it becomes a bit fuzzy for me, because a bigger boat and a higher bicycle gear actually aren't the same.

If you would be rowing a bigger or more sluggish boat, the ratio between power (Watts) and speed/pace would change: it would require more effort to travel the same distance at the same speed. Changing the DF does not do that, it behaves like a bicycle gear, you just switch from Aerobic (many drives) to Anaerobic (more force per drive).

A question I ask myself a lot is: "does any amount of work on DF 140 give a the same split as the same amount of work on DF 100?". I think the answer is yes, but I can't match this with the different boat sizes analogy.

In theory, yes. But in practice you are not able to sustain it.

To make the analogy with the bike complete (sorry, Dutchmen, love bikes). In theory you would produce the same power when cycling in 1st gear as you would in 21st gear. But going uphill, you can't physically produce or sustain the force required to do that in 21st gear, so you probably do that in 1st gear. Going downhill, you probably couldn't keep up in 1st gear, you would feel that you can't deliver your power, and 21st gear would be great to do that.

However, as we are all built differently, we tend to be better at sustaining a specific force at different drag factors. So where I like a DF of 130 to 140, others are much more comfortable at DF 125. But I've rowed 4K's at DF 225 as well, where I do get close to my normal times (but it is physically extremely demanding, can't recommend it unless you really are focussed on good technique).

[Tsnor]

1) A higher DF is like you're rowing a bigger (less streamlined) boat

Common, but not perfect analogy. Drag factor varies with boat speed.

When the shell is stopped and you start rowing the feel is like very high drag factor. Some coxswains even call the first few strokes of a race start "PRY...PRY" and the strokes are typically short -- no more than 1/2 or 3/4 on the slide. The oar handle moves very slowly.

As the boat gets moving faster your oar handle has to move faster. Every stroke as the boat goes faster has a lower drag factor than the previous stroke. Same power, faster handle = lower drag factor.

Once the boat is at it's steady state, it's the speed of the boat that determines the drag factor. The faster the boat (for a given oar setup) the lower the drag factor.

In a sprint the boat speed is higher still, and the DF is even lower.

[Dutch]

In theory you would produce the same power when cycling in 1st gear as you would in 21st gear. But going uphill, you can't physically produce or sustain the force required to do that in 21st gear, so you probably do that in 1st gear. Going downhill, you probably couldn't keep up in 1st gear, you would feel that you can't deliver your power, and 21st gear would be great to do that.

However, as we are all built differently, we tend to be better at sustaining a specific force at different drag factors. So where I like a DF of 130 to 140, others are much more comfortable at DF 125. But I've rowed 4K's at DF 225 as well, where I do get close to my normal times (but it is physically extremely demanding, can't recommend it unless you really are focussed on good technique).

Nicely quoted JaapvanE. Also just to add, the flywheel slows down quicker when the drag is higher and as JaapvanE has said, it is really physically demanding to try and keep it moving at high drags unless its a sprint. The reason we do sprints at higher drags is so we don't catch up the flywheel with the amount of extra spm.
Lighter people tend to use really low drags if they are not physically strong, as they are built more for speed and can use that speed to sort or make up for lack of power or they maybe shorter.
2ks and upwards are different from sprints, we wont catch up the flywheel as much because we are not using higher spm. There fore lower df can be used.
I hope that makes sense lol.

[Carl Watts]

Its just the same as gears on a bike. Taken to extremes the results is as follows.

To low a gear and you cannot rate up high enough or get enough leg speed to put on pace. This is like Drag factor less than 90 on the Erg.

To high a gear and you simply don't have the power to get the rating up high enough and you cannot put in the power for any length of time other than short sprints. This is like Drag factor 200+ on the Erg.

The ideal drag factor for steady state rows is the same as cycling on a flat road, there is an "Ideal" gear that both matches your target speed and cadence. So basically think of it like riding a fixed wheel bike with only one gear on a indoor velodrome, there is ONE gear that matches your cadence and speed but you have to be able to maintain that speed or you fall outside of the "Optimum" range for the gear.

Taken to the extreme on the Erg there is one drag factor that is perfect for you but finding it is quite hard because you do not have just 21 gears to choose from the setting on the damper is near infinite (like the CVT transmission in a car) and that DF still changes depending on what your doing on the Erg because of pace and distance.

Like I said, don't try and over think it, just use a setting to start with between 110 and 130 and row. The most important thing to know is that the damper position is NOT the important thing as dust build up inside the flywheel changes that, its the actual Drag factor number on the monitor that is important.

[Sandeman]

Thanks for all the replies, they are of much help.
I do tend to overthink stuff like this because I like to understand things that I work with.
So just selecting some setting without thinking about it (like everyone seems to do in gyms ) is not really for me.
Thanks again, I'll think about it some more (can't help it) and I'll try out some different drag factors to see which suits me best.

[jamesg]

Ok, so I've read a lot about drag factor and seen quite a few youtube videos, but it's still a complex concept for me.

Rowing is a power sport, needing a full length quick stroke that moves boats fast. At low rates this stroke gives us time to rest before the next one.

This full stroke can be imitated on the erg only by using low drag that lets the flywheel spin fast. So set the drag at 90 to 130 as to size, age and strength. Don't try to pull too many of them, if unfit; they are very hard work.

If in doubt, erging is done as shown here:
https://www.concept2.com/indoor-rowers/ ... que-videos

[Ombrax]

Here's how I think about the DF. (I'm going to switch back and forth from a "water drag" example to "air drag." I'm also going to ignore the inertia of the C2 erg's flywheel - let's assume that it and the person exercising have zero mass.)

Imagine you have in your hands a 1' x 1' piece of cardboard. You sweep it through the air with the large "face" of the sheet facing the direction of motion. You feel some resistance, but not a huge amount, since 1 ft^2 isn't that huge. You then take a different piece of cardboard that's 3' and sweep it through the air at the same speed as the first one. This time you feel a noticeable resistance, because all things being equal, the drag force is linearly proportional to area, and so 3 x 3 = nine times higher. That means that for the same motion as before you need to do more work. 1 ft^2 board has low drag compared to a 9 ft^2 board.

Now switch to the C2 erg. Since the erg measure the motion of the flywheel, it knows how the flywheel slows down over time, so they are able to calculate the drag. They can also measure how you accelerate the flywheel. Already knowing the drag and how the flywheel is accelerating they are able to calculate the force you must be applying at the handle over time. Work is force x distance, which allows them to calculate how much work done. This allows them give you credit for your effort whether you're pushing the 1'x1' board through the air, or the 3'x3' board through the air (or the equivalent for the flywheel drag). You have to run around the room with the 1x1 board a lot more or a lot faster to do significant work, compared to 3x3 board. Same thing at the erg handle. At low drag you can feel the difference as you pull the handle, compared to high drag. Chances are, you'll generate lower forces at the handle at a low DF, compared to a high DF (same as with the boards) but the erg knows that, so for the same handle motion you get more power displayed on the PM at the higher DF.

Bottom line, choose the DF you like best. If you really want to geek out, you could do some tests over time to see what DF allows you to do some given distance in a shorter period of time, but keep in mind that if you're a newbie you'll also be getting stronger and might also be improving your technique. Chances are, if you're like most people, your "best" DF for "normal" rowing (e.g. you aren't trying to set a WR in the 500m sprint) will be between 110 and 130.

TLDR version: Just set the damper handle at a position that gives you a DF around 120 and forget about it.

[PavelS]

I must say that the analogy of higher DF and bigger/heavier boat does not fully work for me either. When explaining the drag to clients of our group lessons I prefer using the bicycle analogy. I quite like the example of shorter/longer oars although it captures just the the drive, not the recovery (similarly to bicycle example).

[gvcormac]

Neither "bigger heavier boat" nor "longer oars" fit perfectly.

The angular mass of the flywheel is fixed, as is the gear ratio. So on your initial pull from stationary, it will feel equally heavy with equally long oars regardless of your damper setting. Only as speed increases will the damper setting have effect.

I note that Models A and B had gear clusters (though only two on the B ) so a taller gear could accurately model heavier boat and/or longer oars.

[JaapvanE]

The angular mass of the flywheel is fixed, as is the gear ratio. So on your initial pull from stationary, it will feel equally heavy with equally long oars regardless of your damper setting. Only as speed increases will the damper setting have effect.

Unfortunatly, your interpretation is incorrect. When you look at physics of ergometers, you see that in the official formula's the power supplied consists out of two parts: dE = I ( dω / dt ) dθ + k ω2 dθ, where P = E / t.

In more understandable terms: when speeding up the flywheel, you will need to overcome the dragforce. As the drag is dependent on speed, you will not notice it in the beginning, but it will still be there. So the drag will be there, and you really feel the difference between df 70 and df 250, especially near the end of the stroke.

As an aside, there is another factor there, which in steady state is irrelevant, except for the start: the dω. Concept2 has a known issue in its power calculation as it ignores the dω part.

[gvcormac]

The angular mass of the flywheel is fixed, as is the gear ratio. So on your initial pull from stationary, it will feel equally heavy with equally long oars regardless of your damper setting. Only as speed increases will the damper setting have effect.

Unfortunatly, your interpretation is incorrect. When you look at physics of ergometers, you see that in the official formula's the power supplied consists out of two parts: dE = I ( dω / dt ) dθ + k ω2 dθ, where P = E / t.

In more understandable terms: when speeding up the flywheel, you will need to overcome the dragforce. As the drag is dependent on speed, you will not notice it in the beginning, but it will still be there. So the drag will be there, and you really feel the difference between df 70 and df 250, especially near the end of the stroke.

As an aside, there is another factor there, which in steady state is irrelevant, except for the start: the dω. Concept2 has a known issue in its power calculation as it ignores the dω part.

"Incorrect" is a bit absolute. As you note, you will not notice the effect at the beginning of the stroke, and you will really feel it at the end. This is not the same as a heavier boat or a longer oar. In normal circumstances, the effect may be negligible. But when you see Crossfitters abusing the machines, the effect is very real.

[JaapvanE]

As you note, you will not notice the effect at the beginning of the stroke, and you will really feel it at the end.

You won't notice it at the beginning of the first stroke, as ω is 0. But as soon as it isn't (second stroke or later), you'll notice it's there as the dragforce will be present. As the dragforce to overcome is bigger, the accelerating during the drive will feel heavier as the flywheel loses more energy to air resistance during the drive (and recovery). The flywheel will catch more air, and it makes you feel it.

This is not the same as a heavier boat or a longer oar. In normal circumstances, the effect may be negligible.

A heavier boat will result in a different magic constant: you need more energy/power for the same linear speed. The PM5 isn't capable of doing that.

The bigger oar analogy is focussed on changing the force/speed ratio, not on the actual movement itself. In a boat, the forces on the oar are totally different anyway, as the angle across the water changes its resistance. And you push 90 kilo's around, instead of a 26 kilo boat. And movements aren't linear, so a RowErg shouldn't be compared to a boat in that way. It is a good training tool for a boat, but not an accurate simulation of its forces during the movement.

But when you see Crossfitters abusing the machines, the effect is very real.

Not really. Being inconsistent across strokes is incorrectly handled by the PM5's power calculation, I agree. But for speed there is a point to be made for the current algorithm. Their inconsistency makes them ineffective, what actually happens on a boat as well due to the exact same physics: dragforce is determined by a constant x velocity. Inconsistency in that system, or many variation in speed, is very ineffective.

[gvcormac]

dragforce is determined by a constant x velocity. Inconsistency in that system, or many variation in speed, is very ineffective.

To be pedantic, drag is not proportional (i.e. constant x) velocity. It is proportional to some power of velocity, and I think C2 uses square as the power, but I'd have to check before swearing to that.

But we're talking in circles. The flywheel has a certain moment of inertia, which doesn't change. Nor does the mechanical advantage of the rower. All that changes is drag, which increases with some superlinear factor of flywheel velocity. Increasing the drag coefficient will feel different from increasing the moment of inertia, and it will feel different from decreasing the mechanical advantage. I have no problem with you saying that it only feels very different in the first few strokes. I also agree with you that C2 dramatically underestimates power in the first few strokes, but that's a somewhat different issue.

To sum it up, I think my position is that they are different; yours is that they are almost the same (i.e. different).