Dynamics/slides -- understanding why they replicate OTW closer?

[DelurkMode]

I've posted about my experience with ankle problems and getting slides here viewtopic.php?f=4&t=208622.

I do enjoy the erg doing most of the moving rather than me. It feels more rhythmic and I really like not having my head going back and forwards as much, but what I'm having a hard time grasping (and I've never rowed OTW) is exactly why the experience is closer to OTW. I've watched a fair bit of youtube to try to figure it out (including another manufacturer's demonstration) and read and pondered, but the whole thing isn't fully clicking. This is more out of curiosity than anything, but I would like to understand it.

What I have come up with so far is that as the flywheel moves towards you on recovery, this is like the boat coming towards you as it is moving against the direction that you are facing and your recovery on the water is largely passive as you coil your body for the catch. Is this right?

If that's right, then the bit that's eluding me is the drive on slides -- pushing the flywheel away from you. In a boat, are you pushing yourself up the slide as you drive? It seems like you are from videos. Does that mean that in a boat the drive is basically the same as on a static machine, but to simulate the OTW recovery the flywheel (or the footplate on a C2 dynamic) needs to move, so the drive on slides by pushing the flywheel away is dictated by the mechanics of the recovery simulation? I'm finding it hard to explain my thinking exactly here, but that's the closest I can come to it.

Thanks in advance for any insight, and apologies if all this sounds ridiculous!

[Cyclist2]

You basically have it right. Here is an article about the physics of rowing. The section on "propulsion" briefly describes the drive and recovery.

https://eodg.atm.ox.ac.uk/user/dudhia/r ... rowing.pdf. His first statement, "Relatively little is known about the exact mechanisms that explain the motion of rowing boats" kind of says it all...

So pushing the fan away from you is like imparting power to the boat through those levers called oars. Spinning up the fan is like overcoming the resistance of the boat through the water.

Glad you're having fun, you can solve those equations as you row to overcome the boredom

[gvcormac]

On the water there are two principal inertial masses: the boat and your body. On the drive, you accelerate both in the direction of travel, and on the recovery, you negatively accelerate the body a bit relative to the boat, while at the same time positively accelerating the boat a bit.

On a static rower, the principal intertial masses are the flywheel and your body. On the drive you accelerate both, and on the recovery, you negatively accelerate the body, with no effect on the flywheel.

On slides or a dynamic rower, you have flywheel, rower, and body. On the drive you accelerate the flywheel and the body a bit, while negatively accelerating the rower a bit. On recovery, you negatively accelerate the body a bit, and positively accelerate the rower a bit.

Neither rower perfectly emulates the dynamics of a boat. Arguably, slides or dynamic are a bit better because there is less deadweight accelerating/decelerating of the body. Rather than the body moving back and forth for the full stroke, the rower goes one way and the body the other. So the work consumed in moving the body/rower is about half -- each moves half the distance and weighs (about) half as much. So each does (about) 1/4 the work, for a total of 1/2 for both together vs static. You might argue that the rower (particularly dynamic) mass is less than bodyweight. You can adjust the calculations accordingly, but it still comes out a win for the slides/dynamic.

That said, there is some learned skill involved (which is not precisely the same skill as rowing on water) which is slide/dynamic pace isn't necessarily better than static.

[DelurkMode]

Thanks both! There's a lot going on! I have a bit better grasp of it now.

The main thing is that the slides do seem gentler on my suboptimal ankles/ligaments/tendons than the static so far. Bit frustrating -- my engine is better than my chassis.

Again, thanks!