Dynamic vs Stationary

[Rockin Roland]

No. The ratchet on the C2 can be engaged in roughly 0.01 second. How much more instantaneous do you want or need? You don't get instantaneous catches in a boat either, as the blade does not reach proper depth instantaneously. You can row the blade in to try to apply power from the moment the bottom edge contacts the surface of the water but that's creates its own -- significant -- set of catch problems.

The difference at the catch between a RowPerfect and a static C2 is overwhelmingly the well-known difference between a dynamic erg and a static erg. That has to do with lowered inertial force on the footstretcher potentially affecting handle turnaround, >not< some significant difference in the clutch mechanisms.

Nav, I'm not sure how you row but I've always been taught to place the blade in the water just before you reach full compresion at the end of the recovery. Not after you've reached the catch position, which is how many people row inefficiently. That way the blade has already reached its ideal depth in the water before you start to push. Plus you don't risk hanging around at the catch like the bad habit that the static C2 erg gets you into.

Although Carlos can sometimes be over the top with his RP3 sell, have a look at his following explanation in the difference between the catches between a C2 and RP3 erg:

http://www.youtube.com/watch?v=ZTNdqyXA6sM

I would also like to ask you Nav if you have ever gone to the trouble of having a row on a Rowperfect erg to feel for the difference yourself? Wether it's the flywheel clutch, shock cord positioning or other design features. Make no mistake, the difference at the catch is there between the C2 and Rowperfect ergs. If you haven't rowed on one then it may be difficult to understand where I'm coming from on this issue.

[NavigationHazard]

I have rowed on a RowPerfect.

Assume for purposes of argument that erg handle and seat are perfectly connected by the rower. It follows that if you move handle and seat back on the drive at a speed sufficient to engage the ratchet/clutch you can supply power to the flywheel. It also follows that you can move the handle/seat back but not fast enough to engage the ratchet/clutch and allow you to accelerate the flywheel. It also follows that if you move the handle/seat back fast enough you can engage the ratchet/clutch virtually instantaneously.

At the catch on a RowPerfect, the inertial force on the footstretcher is damped such that rower mass effectively is removed from the equation. This leaves you with having to accelerate a mass roughly equivalent to that of a 1x (or however you have the machine set). That's probably anywhere from 4 to 8 times less mass that needs to be accelerated to the point where the ratchet/clutch engages and power can be supplied to the flywheel.

At the catch on a static C2, rower mass needs to be accelerated rather than nominal boat mass. If you're not capable of doing it quickly enough you will move the handle/seat back without immediately engaging the ratchet/clutch. That's the source of the slack feel you (and Carlos) are talking about. It has nothing to do with an actual slack chain. OTOH if you are capable of doing it quickly enough then the slack feel disappears. The RowPerfect argument, per Cam Rekkers, is that in order to accelerate the rower mass quickly enough on a static erg to avoid slack feel you need a steeper force curve and/or probably a higher peak force than you do on a dynamic erg. If you buy the claim, among other consequences the greater forces on the static erg tend to increase the (statistically very small) risk of lumbar injury. And if your force curve in a boat or on a RP is already steep and high, according to Rekkers, you may not be able to handle the increased requirements (verticality, amplitude) inherent in a static erg.

Be all of this as it may, it does NOT mean that slack feel can't be virtually eliminated on a static erg. I'm perfectly capable of accelerating my not inconsiderable mass quickly enough, and I suspect that most rowers actually are most of the time if they pay the right attention to their force curves. Moreover no one has ever explained to me why a well-timed, well-sequenced, initially steep, high force curve -- which you can get with a static erg if you work at it -- isn't ideal in a boat. I quite agree that caving in to slack feel on a static erg is a bad habit and leads to sluggish catches in a boat.

As for my catches, I'm taught to drop at full compression. A third variant involves dropping the blades such that they're not quite square and letting the water square them as they're going to full immersion. I think you have to be extraordinarily well timed to get that one right, especially on water that's not flat.

[Tinus]

Nav, I'm not sure how you row but I've always been taught to place the blade in the water just before you reach full compresion at the end of the recovery. Not after you've reached the catch position, which is how many people row inefficiently.

There can be a large difference between the way people are being thought to row and the way they actually will row.

You should place the blade in the water at nearly the same velocity as the water itself.This requires a significant backwards motion of the handle and hence it must happen after full compression/reach. Many high speed video analyses have shown this type of movement.

[Tinus]

The reason for the differences at the catch between the C2s, Oartec Slider and Rowperfect is due to their flywheel clutch mechanism. The Rowperfect flywheel clutch is designed to give a feeling of instant resistance at the catch. Whereas the C2 flywheel clutch has more give in it. The Oartec Slider is somewhere in between the two.

As all three have different clutches you are going to experience different catches between them. I'm not sure if using the software associated with these ergs will clearly demostrate this as it depends on which point the software starts reading the signal from the flywheel.

Roland, thank you very much for that information, very helpful!

C2, if you're listening, how about an improvement in the clutch so there can be instant resistance at the catch.

In addition to improving the rowing mechanics, this would probably reduce injuries to the ribs.

Instant resistance is exactly the thing which is bad. The large perceived slack on a C2 is most likely due to a steep increase of force as handle speed increases. A better clutch is not going to improve this. Using some kind of spring system to allow lower (initial!) forces for a certain speed of the handle softens the slack. The same sort of thing happens in the boat. For a certain handle speed the force is initially low because hydrodynamic pressure initially needs to build up, the blade needs time to be fully buried and the oar shaft bends a little.

The problem of slack which is less perceived on a row perfect is that many people start to accelerate the body without keeping the body connected to the handle. They throw their body backwards and only when their arms are fully stretched and the chain is horizontal do they apply force. Yes, that's an awkwardly feeling slack which they get. On the rowperfect this effect is less strong because the inertial forces are smaller. But, if you don't row/erg in this way than the difference between rowperfect and c2 can be hardly noticed.

The clutch really isn't a problem. If someone does feel a problem with it than it is the human body itself acting as a bad clutch. See also... http://www.dumpert.nl/mediabase/1591411 ... _niet.html

[c2jonw]

Interesting discussion. Regarding the clutch, the original Model A used a bicycle gear cluster with a ratchet and pawl clutch. The number of teeth in the ratchet varied with the cluster manufacturer and we intentionally looked for the maximum number of ratchet teeth to minimize potential slip at the catch. I think the unit we ended up using had 16, which would mean that from the point when the power is applied at the catch and the sprocket is rotating in the same direction as the flywheel and at some greater angular velocity, there could be as much as 360/16 or 22.5 degrees of relative movement between the sprocket and the flywheel. On a 15 tooth 1/2" pitch sprocket that 22.5 degrees translates to a little less than 1/2" of "slip" before the pawl drops into the next ratchet tooth. This slip at the catch was noticed by many rowers, so with the model B we went to a Roller Clutch Bearing unit, which have virtually no backlash when going from freewheeling to lock-up. We've continued to use the roller clutch in the C,D,E, Dyno, SkiErg and Dynamic. I'm pretty certain that this is the type of clutch utilized by Oartech and Rowperfect because of its virtual zero backlash, simplicity and reliability. As Tinus implies, differences in feel at the catch, perceived slip, etc. are more likely attributable to factors other than the clutch. C2JonW

[johnlvs2run]

Instant resistance is exactly the thing which is bad.

Only when the initial resistance is delayed.
The more the delay, the greater the impact and the greater the shock to the ribs.

The large perceived slack on a C2 is most likely due to a steep increase of force as handle speed increases.

When the resistance is instantaneous, then there is no sharp force long after the beginning of the catch.
This is why an instant catch is much better, for anyone and for everyone.

Imagine if the oars did not engage the water until the hands reached the feet like on the C2 machines.
But there is no delay on the water. The oars engage the water instantaneously, shown here and here.

many people start to accelerate the body without keeping the body connected to the handle. They throw their body backwards and only when their arms are fully stretched and the chain is horizontal do they apply force.

First you said that the delay is good on C2 machines and in the next paragraph you're trying to say there is no delay or it's bad. Which one is it?

People are perceiving the delayed catch correctly. The delayed catch is most obvious when rowing with straight arms, with all power coming from the legs and no movement at all from the arms or the body. If you want to see this then row a fast pace at 36spm with legs only, arms straight, and keep the damper at 110.

The result is worse with delayed resistance, because many rowers improperly go through contortions with the body and arms at low rates to try and nullify the delay, for example rowing most of the time no higher than 24 spm and even low rates for racing distances. This is an exact response to the break in the catch, which is much less or absent at low ratings, but that does not get rid of the problem.

[Tinus]

First you said that the delay is good on C2 machines and in the next paragraph you're trying to say there is no delay or it's bad. Which one is it?

John, you need to differentiate. First I started to say that the clutch isn't the relevant part which delays and in fact it would be good if it had a (smooth) delay by means of a spring. Then in the next paragraph I say that the perceived delay (or better slack because the machine doesn't really have a delay) is of a different kind and it is this different kind of delay which may be bad (but can be helped by better technique).

- The steep increase in force on an erg can be made clear by imagining the opposite: a low increase in force. Everyone knows the effect of pushing the blades too fast through the water. There must be some sense of first connecting before pulling fast. It is exactly this effect which is missing on an erg but it is intrinsic to the machine. If you pull the handle with speeds lower than the flywheel speed then little force is required. But once you want to pull the handle faster than the flywheel speed then a high force is required. You can't move the flywheel at a certain speed instantaneously and the speed for pulling the handle is bounded. The flywheel represents the mass of the entire boat plus rower. Accelerating it costs a lot of force. When rowing on water, the handle speed boundary is of a different kind. Pulling the handle the blade can slip and pulling faster does not necessarily mean that the rower and boat are moving faster. Because of that the rower can pull faster (not necessarily harder) much more easily and it is even such that resistance may drop at higher handle speeds (the drag coefficient drops but possibly the force as well).

- The different kind of slack which people perceive is due to the body acquiring a higher speed than the handle (note how this is different from the handle acquiring a higher speed than the flywheel). In rowing this is more easily absorbed. On the rowperfect or concept dynamic (but also on the water) the inertial forces are smaller. But on the classic concept both the handle speed is bounded and the body has high inertial energy. That's the slack.

So this explains: Better would be if the clutch had a delay (by means of some smooth spring system). Bad is the delay within the body causing the slack. The second delay makes the steep increase in force a problem. The first delay would reduce the steep increase in force.

Also a higher dragfactor often increases the slack perceived by many people. A higher dragfactor decreases the flywheel speed (for the same power input). It shows that it isn't a cluctch having problems with high speed but actually a human body having problems with low speed.

[Rockin Roland]

So this explains: Better would be if the clutch had a delay (by means of some smooth spring system).

You may or may not be aware that the Rowperfect "Indoor Sculler" (but not the RP3) already has this. It's a patented system called "Oarflex". It's not in the clutch though. It's a stiff spring connected to the chain which is housed within their timber handle. It allows for a progressive release of some of the handle force supposedly to mimic the behaviour of an oar moving through the water.

I find that this "Oarflex" technology is most noticable on my erg when I increase the handle force. It's felt from the catch to about midway through the stroke. Similar in a way to when I'm rowing hard on the water right up to the point where I can feel the oar bending in the water. After this point the spring has reached its max. length and slowly recoils.

[johnlvs2run]

Anyway, I had a another go on both Oartec and Dynamic at Goldie boathouse yesterday, and must correct my impression of less slack; both show it, albeit limited by Newtonian effects (less mass to accelerate, so it's quicker and hence shorter). It's less noticeable, because the stretcher moves rather than us, but there all the same.

As usual, the first pull from stationary has no slack at all.

The reason for the differences at the catch between the C2s, Oartec Slider and Rowperfect is due to their flywheel clutch mechanism. The Rowperfect flywheel clutch is designed to give a feeling of instant resistance at the catch. Whereas the C2 flywheel clutch has more give in it. The Oartec Slider is somewhere in between the two.

As all three have different clutches you are going to experience different catches between them. I'm not sure if using the software associated with these ergs will clearly demostrate this as it depends on which point the software starts reading the signal from the flywheel.

the unit we ended up using had 16, which would mean that from the point when the power is applied at the catch and the sprocket is rotating in the same direction as the flywheel and at some greater angular velocity, there could be as much as 360/16 or 22.5 degrees of relative movement between the sprocket and the flywheel. On a 15 tooth 1/2" pitch sprocket that 22.5 degrees translates to a little less than 1/2" of "slip" before the pawl drops into the next ratchet tooth.

It doesn't make sense to me that the chain would slip through from one cog to another with each transition from recovery to the drive. Maybe someone can explain how that worked. So the chain used to skip a cog every time?

This slip at the catch was noticed by many rowers, so with the model B we went to a Roller Clutch Bearing unit, which have virtually no backlash when going from freewheeling to lock-up.

Which does not explain what people have observed.

We've continued to use the roller clutch in the C,D,E, Dyno, SkiErg and Dynamic. I'm pretty certain that this is the type of clutch utilized by Oartech and Rowperfect because of its virtual zero backlash, simplicity and reliability. As Tinus implies, differences in feel at the catch, perceived slip, etc. are more likely attributable to factors other than the clutch.

I used to perceive that the railing was sloped. Now I perceive that it's level.

[c2jonw]

It doesn't make sense to me that the chain would slip through from one cog to another with each transition from recovery to the drive. Maybe someone can explain how that worked. So the chain used to skip a cog every time?

No, the chain didn't skip. The slip or skip occured inside the freewheel and was a function of how many teeth there were in the ratchet for the pawls to engage. This system is used on most bicycle freewheels. C2JonW

[johnlvs2run]

No, the chain didn't skip. The slip or skip occured inside the freewheel and was a function of how many teeth there were in the ratchet for the pawls to engage. This system is used on most bicycle freewheels. C2JonW

Thanks for the clarification.

This slip at the catch was noticed by many rowers, so with the model B we went to a Roller Clutch Bearing unit, which have virtually no backlash when going from freewheeling to lock-up.

How can there be no delay, when the flywheel is moving much faster than the cogwheel; and that many people see, feel, and/or perceive a delay. Are you saying there IS no delay? Have you noticed that the cord returns and engages the flywheel faster than the chain? It would be nice to see some discussion of how the dynamic internal construction differs from the static ergometers. If there is no difference then we might as well stay on static machines.

[johnlvs2run]

One thing that is not made clear is why the efficiency drop between the Dynamic (D) and Static (S) machines. To me the reason is that on the D one has to use more muscle to keep the load at the same level as on the S, hense the V02 increase. This increase may be directly proportional to the increase in muscle utilization on the D. I do keep my SR about 4-6 higher on the D compare with when I am on the S machine for about the same load rating.

Have you noticed a difference in your scores between a dynamic vs static?

[Bob S.]

Have you noticed a difference in your scores between a dynamic vs static?

After a year and a half of using slides, I find that my scores are much worse than they were on the grounded erg. Of course I guess that most folks would just attribute that to the fact that I am that much older.

Bob S.

[slwiser]

I am now completing my third month of Dynamic use. It took me about three months to transition from static to slides. So I am nearing the term that I gave myself to be able to say something solid concerning the difference. I think the Dynamic is much harder to hold a load over a longer period. I still attribute this to having the muscles (legs and glut) work differently (harder) compared with either the slides or static which allowed me to throw more inertia into the compression and lay back of the finish with each giving me a little more length compared with the Dynamic. I am finding that an additional four to five strokes per minute is required to equal my static performance over the long term, greater than 30 minutes. Maybe this is a strength issue that will eventually go away with more work. I hope so.

[Byron Drachman]

Nav, I'm not sure how you row but I've always been taught to place the blade in the water just before you reach full compresion at the end of the recovery. Not after you've reached the catch position, which is how many people row inefficiently.

There can be a large difference between the way people are being thought to row and the way they actually will row.

You should place the blade in the water at nearly the same velocity as the water itself.This requires a significant backwards motion of the handle and hence it must happen after full compression/reach. Many high speed video analyses have shown this type of movement.

Tinus, I always find your postings interesting. When you say backwards motion of the handle do you mean toward the bow?