New Rowperfect RP3 is shipping in September
boatie
shipping from mid-September.
Details on the UK website http://www.rowperfect.co.uk/rowperfect
and lots of photos on the USA site www.rowperfect3.com
We will have demo units available in the UK for clubs to try out.
He has worked hard to overcome some of the 'shortcomings' of the older
model including improved foot stretcher, lowered centre of mass,
flywheel resistance adjustment and some more subtle things like a cam
adjustment for the bar / main frame tensioning (very neat engineering
indeed).
drifting away
doesn't the monitor come with it. All rowing machines have a monitor
and for that price it should. I can't see what the extra money is for
compared to a C2 or Oartec.
Charles Carroll
For awhile now I have been looking at photographs of the prototype of
the new RowPerfect. It is good to see that Casper Rekers finally has
put it into production.
But I am still left with a question. Does the new RowPerfect have any
important advantages over a C2 on slides with a CorePerform seat?
I know one friend who already has ordered the RowPerfect. He points
out that his chief reason for going with RowPerfect is that it has a
smaller footprint than a C2 on slides.
If you can't fit a C2 on slides into the room in which you erg, than
of course a RowPerfect makes sense.
But are there any other reasons?
Cordially,
Charles
Sarah A Harbour
Economies of scale at a guess... (ooh look who's been doing too much
accountancy revision!)
Concept 2's are mass produced - stick them in gyms and let joe public
who can't row for toffee loose on them. Can't ever see gym rowers
using this Rowperfect... or actually, maybe I can - would be rather
amusing!
If I was going to buy a rowing machine, I'd get one. No point having a
personal C2 when I can nip down the boathouse or gym and use theirs.
Having said that, I don't think I could justify either the expense, or
the storage room at the moment. Better get back to the revision so I
can hopefully sort both of those obstructions out...
Sarah
boatie
> But I am still left with a question. Does the new RowPerfect have any
> important advantages over a C2 on slides with a CorePerform seat?
the advantages are
1 - it SIMULATES rowing and so the machine moves exactly like your
single
2 - the moving mass of the fly wheel section is 17kg and that is the
same weight as a 1x plus riggers / oars. So you are training on land
with the same mass of equipment as on water
3 - the software power curve shows in real time, precisely, how you
apply your power to move the boat (RP) and you will improve your power
application skills by working with this.
4 - The software is calibrated to give your "on water equivalent"
times so you can compare land and water training times (given near
perfect conditions and near perfect technique).
5 - anyone who trains on a fixed head ergo uses a technique on the
ergo that is not the same as rowing on the water. So you are training
the wrong muscle firing sequence with your indoor training
6 - in most cases, the first year an athlete trains on Rowperfect s/he
goes around 2-5% faster on water because of the above
7 - for crews, linking RPs together can help athletes combine to
better row together and deliver their power in the same way and make
the crew go faster
> I know one friend who already has ordered the RowPerfect. He points
> out that his chief reason for going with RowPerfect is that it has a
> smaller footprint than a C2 on slides.
I expect the US LW2x result at the world championships will convince a
few people of the advantages - they only use RPs AFAIK
thanks for asking!
Rebecca
Meredith Haff
indoor season 2010-2011). In case you haven't seen the details, there
are blog postings on the Concept2 website:
http://www.concept2.com/us/company/blog/default.asp
http://www.concept2.com/us/company/blog/default.asp?id=967232916
http://www.concept2.com/us/company/blog/default.asp?id=677444685
Sarah A Harbour
So with the Dynamic C2, you've got the same effective movement as the
RP, ie. keep the seat still and move the feet, but you don't have the
flywheel moving, so it won't actually be a similar weight that moves,
like in a single scull, as Rebecca mentions with the RP.
Has anyone tried one of these things? What does it feel like compared
to a RP, and a normal C2 for that matter?
Sarah
Jim Dwyer
with a monitor that also displays heartrate?
Thanks
Jim
"boatie" <reb...@caroe.com> wrote in message
news:e218721b-b8cb-4193...@s17g2000prh.googlegroups.com...
Jim Dwyer
Jim
"Sarah A Harbour" <saraha...@gmail.com> wrote in message
news:0e16fe4d-e8f0-498d...@x42g2000yqx.googlegroups.com...
Charles Carroll
Have you tried a RowPerfect or the new RP3? Does it feel different
from a CII on slides?
Cordially,
Charles
Jim Dwyer
on slides. I do a million meters/year on the ERG and I like the dynamic
ergs better than the stationalr ones.
Jim
"Charles Carroll" <charles...@comcast.net> wrote in message
news:8e85lt...@mid.individual.net...
Charles Carroll
While I don't erg a million miles a year, I do have a CII on slides
with a Coreperform seat. I, too, prefer -- indeed much prefer! -- a
dynamic erg to a static erg. There is really very little, if any,
comparison between the two.
It makes me wonder what Sarah meant when she asked whether anyone
could compare a Rowperfect with a "normal CII." By "normal CII" did
Sarah mean a CII off slides? Or did she mean a CII on slides?
If you are going to compare a CII off slides to a Rowperfect, the
Rowperfect will win hands down. But will the Rowperfect win if you
compare it to a CII on slides with a Coreperform seat?
Cordially,
Charles
Charles Carroll
Did you see the video of Ursula Grobler on the RP3?
http://www.youtube.com/user/rowperfect3
Was the video taken at a dock on Lake Sammish in Washington State here
on this side of the pond? I have been told that this is where Ms.
Grobler does most of her training .
Am I the only one who finds it more than a little ironic that this
young athlete is erging on a dock under a blue sky on an immensely
beautiful lake on a equally immensely beautiful day? The water next to
Ms. Grobler is mirror flat.
How many on r.s.r. have access to such water? Would you be erging in
her situation? I know I wouldn't.
Cordially,
Charles
Kit
> > But I am still left with a question. Does the new RowPerfect have any
> > important advantages over a C2 on slides with a CorePerform seat?
>
> the advantages are
> 1 - it SIMULATES rowing and so the machine moves exactly like your
> single
Hmm. How about "It engages most of the major muscles to the same
extent as in a rowing stroke". "SIMULATES" (with your emphasis)
implies in my mind all aspects of the rowing stroke including catch/
finish technique. I have no doubt the RP3 is a big improvement (as are
all dynamic ergs), but I'm not sure it goes that far.
I have mentioned this before, but an erg that requires good
coordination between hands and leg drive at the catch would be an
interesting innovation.
Kit
Rob Collings
wrote:
>
> If you are going to compare a CII off slides to a Rowperfect, the
> Rowperfect will win hands down. But will the Rowperfect win if you
> compare it to a CII on slides with a Coreperform seat?
I've used a Rowperfect and a C2 on slides and prefer the rowperfect.
The C2 on slides is heavier than the Rowperfect head and I get the
"almost but not quite" feeling from it. It's a world better than a
static C2 but not quite as good a match to the boat as a Rowperfect.
It still feels a little heavy. I've never tried the Coreperform seat.
I spoke to someone who saw the machine in Canada and apparently the
footplate is just a footplate and moves freely. That suggests that it
might be pretty light, but he wasn't sure. I suppose that will make it
a bit easier to row (technically) as the seat and body won't roll
around as much. I'm told C2 are pressing the space-saving angle pretty
hard and may be aiming this at the gym market.
Rob.
melha...@gmail.com
> the advantages are
> 1 - it SIMULATES rowing and so the machine moves exactly like your
> single
Now now, Rebecca. That's false advertising. You're making a misleading
claim about the product. Just looking at the components of the
movement parallel to the slides, you are roughly correct around the
catch, but definitely misleading people about the finish. No erg
accurately simulates the finish. Both a static ergo and any form of
dynamic ergo have a very similar handle speed profile through the
stroke, and they are both quite different to the handle speed profile
of a boat. See here:
http://www.biorow.com/RBN_en_2005_files/2005RowBiomNews03.pdf
Essentially, as Valery points out, the effective gearing changes
through the stroke, whereas on an C2, or RP, it stays constant through
the whole drive.
I'm not saying that RP is a bad tool. I believe it's a very good tool.
However I object to you making claims that are flat out wrong as part
of your advertising.
Mel
Carl Douglas
"Simulates" does not mean "exactly copies in every respect". All
simulations have limitations. The only thing to wholly replicate the
processes you wish to simulate is the original article, in this case the
rower in the boat on the water. All models are necessarily imperfect &
the more complex the process the less accurate the model, especially the
earlier models, may be.
I raise this also because I see the same conceptual difficulty raising
its head in parallel RSR discussions around blade dynamics. Similar
intellectual misunderstandings of the sometimes marked differences
between analogy & reality also infect most of rowing coaching & training.
A simulation only ever replicates itself. Thus, however good a
computational fluid dynamics model of a working oar-blade may be, it is
unlikely to give numerically perfect answers & will, most likely,
require tweaking & the use of what are unkindly called fudge factors.
That said, CFD models are very useful, if well constructed (the big
"if), for analysing & unpicking the innards of complex fluid flos
situations. And can be use to god effect in exploring the consequences
of changes in geometry or flow. But if something is ignored, or
incorrect assumptions are made, the model will be correspondingly more
defective.
Furthermore, in modelling the rowing stroke you add multiple layers of
complexity to an already complex task. First, you have transience
(nearly everything has to vary over the time of the stroke), the free
surface of the water (so you are working with air & water & a surface
influenced by gravity, internal pressures & fluid density), the
flexibility of the oar (so the alignment of the blade is load as well as
position dependent) & the variation of the load on the blade (dependent
on elasticity of oar as well as speed of rower's hand movement),
possible vibration of the oar, actual boat velocity, which depends on
what oar & rower are actually doing.
RP has always been an excellent rowing dynamics simulator. But it is
bound to be imperfect in some areas. It simulates the generality of
velocity-squared fluid resistance as an energy absorber with its
air-mashing fan. It simulates the basics of the dynamic interaction of
rower & seat with its juxtaposition of freely-suspended seat &
freely-suspended carriage. It doesn't simulate the continuous variation
of gearing within the rowing stroke between catch & finish (harder at
the ends, easier in the middle_. It doesn't simulate the off-axis
loadings of the upper body arising from the handle rotation about the
pin. It doesn't simulate the transitions in the stroke between lift &
stall. You get no blade entry/exit simulation. And there are other
areas of incomplete simulation. But it remains an excellent training
device/simulator. Just accept that there are limitations to any simulation.
Just a note: the seat on a dynamic erg does _not_ stay still. Sure, it
seems not to move much, but to prevent that movement will require large
forces, the rowing will be less fun & it will no longer be dynamic.
Cheers -
Carl
--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories
Write: Harris Boatyard, Laleham Reach, Chertsey KT16 8RP, UK
Find: http://tinyurl.com/2tqujf
Email: ca...@carldouglas.co.uk Tel: +44(0)1932-570946 Fax: -563682
URLs: www.carldouglas.co.uk (boats) & www.aerowing.co.uk (riggers)
Kit
> Kit wrote:
> > On 31 Aug, 20:10, boatie <rebe...@caroe.com> wrote:
> >>> But I am still left with a question. Does the new RowPerfect have any
> >>> important advantages over a C2 on slides with a CorePerform seat?
> >> the advantages are
> >> 1 - it SIMULATES rowing and so the machine moves exactly like your
> >> single
>
> > Hmm. How about "It engages most of the major muscles to the same
> > extent as in a rowing stroke". "SIMULATES" (with your emphasis)
> > implies in my mind all aspects of the rowing stroke including catch/
> > finish technique. I have no doubt the RP3 is a big improvement (as are
> > all dynamic ergs), but I'm not sure it goes that far.
>
> > I have mentioned this before, but an erg that requires good
> > coordination between hands and leg drive at the catch would be an
> > interesting innovation.
>
> > Kit
>
> "Simulates" does not mean "exactly copies in every respect". All
> simulations have limitations. The only thing to wholly replicate the
> processes you wish to simulate is the original article, in this case the
> rower in the boat on the water. All models are necessarily imperfect &
> the more complex the process the less accurate the model, especially the
> earlier models, may be.
>
Fair point. And indeed, in my response, I tried to narrow down the
limitation of the simulation.
What made me itch though were the words "SIMULATES" and "exactly" when
describing its "advantages" over a C2/Slides/CorePerform, as if to
imply that the latter combination was no simulation at all. But I
don't really want to knock RP. I know they are probably the best ergs
out there ATM.
Sarah A Harbour
I meant - how does the Dynamic C2 compare to a normal C2 on sliders?
I've used the latter and it doens't feel like a Rowperfect to me...
though that may just be me!
Sarah
Jim Dwyer
feel any difference between the two. I did not have any problems balancing
the Row perfect.
Jim
"Charles Carroll" <charles...@comcast.net> wrote in message
news:8e8fje...@mid.individual.net...
Anthony
This has been puzzling me - is it significant that the RP fan assembly
weighs roughly the same as a single? If so, why?
I ask because I have been educating myself to believe that the weight
of my single is a relatively unimportant factor in my performance in
it (I regularly sneer inwardly at those on TalkBullshit who big up the
Fluid on the doubtful grounds that it can be built well under weight,
and that this will confer a significant, if illegal, advantage on the
buyer.)
And my single moves in water, the RP fan assembly in air.
I await further enlightenment...
aj
Charles Carroll
Carl,
Ah yes! Between copy and reality falls the shadow!
Puts me in mind of Jorge Luis Borges's little parable "On Exactitude
in Science." Do you know it?
". . . In that Empire, the Art of Cartography attained such Perfection
that the map of a single Province occupied the entirety of a City, and
the map of the Empire, the entirety of a Province. In time, those
Unconscionable Maps no longer satisfied, and the Cartographers Guilds
struck a Map of the Empire whose size was that of the Empire, and
which coincided point for point with it. The following Generations,
who were not so fond of the study of Cartography as their Forebears
had been, saw that that vast Map was Useless, and not without some
Pitilessness was it, that they delivered it up to the Inclemencies of
Sun and Winters. In the Deserts of the West, still today, there are
Tattered ruins of that Map, inhabited by Animals and Beggars; in all
the Land there is no other Relic of the Disciplines of Geography."
(Suárez Miranda, Viajes de varones pruedentes, Libro IV, Cap. SLV,
Lérida, 1658)
Cordially (which is heartfelt and real),
Charles
Charles Carroll
> tool.
> However I object to you making claims that are flat out wrong as
> part
> of your advertising.
Mel,
Inflated claims are always disturbing, especially when associated with
something like a Rowperfect, which in and of itself is so good that it
shouldn't have to bother with exaggeration.
Maybe I am being excessively fussy, but I also found it a bit
disturbing that Ursula Grobler's Coach would publically credit
Rowperfect with playing an essential part in Ms. Grobler's winning
gold in the LW2x at the Rowing World Cup in Bled earlier this year
without also disclosing that he is in the business of selling
Rowperfects.
But as I say, maybe I am just being fussy.
Cordially,
Charles
Carl Douglas
>
> This has been puzzling me - is it significant that the RP fan assembly
> weighs roughly the same as a single? If so, why?
It is significant, in the same sense that it is significant that a
static erg is static.
When you move relative to your single, then there is an inertial
reaction between your mass and that of the boat - in which the way you
move & the way the boat moves (in the other direction) bear a calculable
& tangible interrelationship. To simulate this in an erg requires that
your body mass be freely suspended & interacts through a similar
connection at the foot against a freely suspended mass similar to that
of the boat. Change the mass & you significantly change the
interaction. Change the mass to that of your part of a tub pair & the
interaction will resemble that between you & tub pair. Reduce the mass
to zero & it will feel distinctly odd the other way.
Imperfections do insert themselves into the calculations, due to how the
hand load is connected into the boat-simulating mass, etc., but these
are of secondary degree.
>
> I ask because I have been educating myself to believe that the weight
> of my single is a relatively unimportant factor in my performance in
> it (I regularly sneer inwardly at those on TalkBullshit who big up the
> Fluid on the doubtful grounds that it can be built well under weight,
> and that this will confer a significant, if illegal, advantage on the
> buyer.)
You are, however, absolutely right to question the volumes of ordure
spouted about boat weights in bars & other newsgroups. Everyone, from
FISA down (they sharpened the axe for those obsessed by boat weight by
setting lower weight limits), jumps to confusions through simplistic
assumptions over hull drag which conveniently ignore the velocity
fluctuations of a boat generated by inertial effects discussed above, as
well as by rowing's cyclic application of load.
Unlike these sheep, I have bothered to conduct a mathematical analysis
of the cyclic speed issue. This shows that there is for any sculler of
any given technique a particular optimal & non-zero boat mass below
which the overall drag will stop falling & start progressively to
increase. So a boat can be too light, as well as too heavy. And, as
luck would have it, for a 85kg sculler with an assumed typical
technique, that minimum does hover around the 14kg-ish mark. Now
there's a funny thing!
>
> And my single moves in water, the RP fan assembly in air.
>
> I await further enlightenment...
>
> aj
>
RP tries to simulate the drag of your boat via the energy absorption &
slowing down of its fan, so the energy expended & the speed of hands
necessary to make the catch seem reasonable. It does that quite well
Cheers -
carl
Charles Carroll
You write that the C2 on slides is heavier than the Rowperfect head
and that you get an "almost but not quite" feeling from it. I am not
clear on which of the machines the "it" stands for. The C2? Or the
Rowperfect?
I looked at the video of Ursula Grobler on the Rowperfect, and then
went downstairs and ergged a few strokes on my C2 on slides. I was
struck not by the similiarities of the two machines, but by the
differences.
Consider Ms. Grobler on the Rowperfect.
Look at the seat with respect to the bow of the Rowperfect. The seat
scarcely moves at all, just a few inches. It seems to me that mostly
what she is doing is drawing the flywheel up to her.
Now look at the seat in the second video, the one of Ms. Grobler in
the boat. It is the video just to the left of the first. Sometimes the
two videos collide and their respective images are superimposed. It
seems to me that in both the drive and recovery her seat in the boat
moves a greater distance than does her seat on the RowPerfect. She is
drawing the boat underneath her.
Then I went downstairs to erg on the C2. I was a little surprised. The
moving image of myself in the wall length mirror to my side looked
very much like what happens in a boat when I scull. Looking at my seat
with respect to the bow of the C2, it definitely moved a greater
distance than Ursula Grobler's seat moves on the Rowperfect. But at
the same time the whole erg slid back and forth underneath me and
seemed to much more closely resemble way a boat moves when I scull.
Of course the C2 weighs 29.5 kg as opposed to the flywheel head on a
Rowperfect which weighs 17 kg. I am not sure what the additional 12.5
kg signifies. I have always used the drag factor adjustment on my C2
to adjust the heaviness or lightness of the pull.
I wonder if Carl has ever conducted a mathematical analysis of the
cyclic speed issue between the Rowperfect and the C2 on slides. Four
years ago I spent about ten minutes on a Rowperfect. Carl was
watching, I was very self-conscious, and I freely acknowledge that I
remember almost nothing about "the feel" of the machine, so I have no
basis upon which to form an opinion.
Cordially,
Charles
Tinus
wrote:
> Then I went downstairs to erg on the C2. I was a little surprised. The
> moving image of myself in the wall length mirror to my side looked
> very much like what happens in a boat when I scull. Looking at my seat
> with respect to the bow of the C2, it definitely moved a greater
> distance than Ursula Grobler's seat moves on the Rowperfect. But at
> the same time the whole erg slid back and forth underneath me and
> seemed to much more closely resemble way a boat moves when I scull.
The row perfect is able to move almost freely with only a piece of
string as major resistance. The boat does not move freely and is
susceptible to fluid drag forces and propulsive forces. As a result
when comparing rowing and a dynamic erg of the same weight, the
internal forces are not the the same for the same movement of the
rower. If I am not mistaken the row perfect lower weight is only a
better simulation of the internal forces between rower and machine
when the rower decelerates relative to the boat. I am not sure how
much additional weight would be the optimal simulation of those
external forces but for the start of the drive and the start of the
recovery the heavier concept2 (or oartec?) could possibly be a better
simulation.
I say the choice between ergs is more a matter of taste. Something
which might be more important for the feel are cog size and flywheel
weight. The ergs do allow a certain type of gearing by changing the
dragfactor but changing the drag is not the same as changing the
weight of the boat/crew of changing the inboard/outboard levers.
I am only able to measure dimensions of a c-model concept rowing
machine. Does anyone have data about differencec in flywheel
rotational inertia and cog sizes?
Jim Dwyer
> When you move relative to your single, then there is an inertial reaction
> between your mass and that of the boat - in which the way you move & the
> way the boat moves (in the other direction) bear a calculable & tangible
> interrelationship. To simulate this in an erg requires that your body
> mass be freely suspended & interacts through a similar connection at the
> foot against a freely suspended mass similar to that of the boat. Change
> the mass & you significantly change the interaction. Change the mass to
> that of your part of a tub pair & the interaction will resemble that
> between you & tub pair. Reduce the mass to zero & it will feel distinctly
> odd the other way.
I just tried the CII ERG at the FISA World masters Regatta.
It was the one in which the footstops move but the flywheel does not so the
mass was close to zero and it did feel odd.
It felt like I had to do a lot of work pulling my feet towards me to get
compression and good length at the catch.
The CII on slides or the rowperfect feel similar to rowing a boat because my
"body mass is freely suspended & interacts through a similar connection at
the foot against a freely suspended mass similar to that of the boat."
Jim
Charles Carroll
> It was the one in which the footstops move but the flywheel does not
> so the
> mass was close to zero and it did feel odd.
> It felt like I had to do a lot of work pulling my feet towards me to
> get
> compression and good length at the catch.
Jim,
Does CII use a shockcord or its equivalent on their new prototype erg?
I wonder if this might explain why it felt like a lot of work pulling
you feet towards you. I confess I have never been quite sure how the
shock cord works.
Cordially,
Charles
Jim Dwyer
forward into the catch. It was hard to get good compression without our
mass moving towards the footstops. In a boat you relax and glide up the
slide and compress due to your forward motion but on this machine you are
pulling the footstops toward you as your seat moves towards the footstops
during the recovery.
"Charles Carroll" <charles...@comcast.net> wrote in message
news:8eo2vh...@mid.individual.net...
Carl Douglas
>
> "Charles Carroll"<charles...@comcast.net> wrote in message
> news:8eo2vh...@mid.individual.net...
>>> I just tried the CII ERG at the FISA World masters Regatta.
>>> It was the one in which the footstops move but the flywheel does not
>>> so the
>>> mass was close to zero and it did feel odd.
>>> It felt like I had to do a lot of work pulling my feet towards me to
>>> get
>>> compression and good length at the catch.
>>
>> Jim,
>>
>> Does CII use a shockcord or its equivalent on their new prototype erg?
>> I wonder if this might explain why it felt like a lot of work pulling
>> you feet towards you. I confess I have never been quite sure how the
>> shock cord works.
>>
>> Cordially,
>>
>> Charles
>>
> It did not feel like a lot of work, it felt like there was no
> momentum going forward into the catch. It was hard to get good
> compression without our mass moving towards the footstops. In a boat
> you relax and glide up the slide and compress due to your forward
> motion but on this machine you are pulling the footstops toward you
> as your seat moves towards the footstops during the recovery.
>
Err... not quite, Jim.
As you "come forward", your inertia (see Newton) keeps your body mass
moving over the water towards the finish line, at constant velocity if
not subject to other forces. Meanwhile, fluid drag on the boat (which
acts throughout the stroke) exerts a sternwards force tending to slow
the boat, & anything attached thereto, towards zero velocity through the
water.
The inescapable consequence of this conflict is that, unless you _pull_
the stretcher towards your body throughout the recovery, you will not
reach frontstops. This means, also, that a) you have no "forward
motion" available for the compression process, b) your mass cannot help
you to compress & c) whatever it may feel like, we kid ourselves when we
talk of gliding up the slide as if we had sternwards momentum over which
to exercise control.
Like it or not (& I do know how counter-intuitive & contrary to popular
belief this is), compression at the catch is an active process requiring
work to be done by you, not the pleasant & controllable consequence of
our mass moving towards a resisting foot-stretcher that it is always
seen to be. The stretcher is trying to get away from us, quite opposite
to the popular conception that it is there to halt our imagined
sternwards motion.
Cheers -
Carl
Richard du P
> On 08/09/2010 02:55, Jim Dwyer wrote:
> > It did not feel like a lot of work, it felt like there was no
> > momentum going forward into the catch. It was hard to get good
> > compression without our mass moving towards the footstops. In a boat
> > you relax and glide up the slide and compress due to your forward
> > motion but on this machine you are pulling the footstops toward you
> > as your seat moves towards the footstops during the recovery.
> >
> The inescapable consequence of this conflict is that, unless you _pull_
> the stretcher towards your body throughout the recovery, you will not
> reach frontstops. This means, also, that a) you have no "forward
> motion" available for the compression process, b) your mass cannot help
> you to compress & c) whatever it may feel like, we kid ourselves when we
> talk of gliding up the slide as if we had sternwards momentum over which
> to exercise control.
>
> Like it or not (& I do know how counter-intuitive & contrary to popular
> belief this is), compression at the catch is an active process requiring
> work to be done by you, not the pleasant & controllable consequence of
> our mass moving towards a resisting foot-stretcher that it is always
> seen to be. The stretcher is trying to get away from us, quite opposite
> to the popular conception that it is there to halt our imagined
> sternwards motion.
>
Thanks Carl for not disappointing your loyal fanbase!
No, seriously, your argument is perfectly in tune with the Newtonian
Mechanics they taught me up to 1959 [fortunately I believe most of the
oarspersons I know are way too big and moving too slowly for quantum
theory to come into play; just as well in case] and no dispute from
me.
Even if I dared.
And I plead guilty to "buying" a fallacious model from various coaches
for nearly half a century.
NOW .......... why does it "feel" so different? ..... anyone?
Could it just be the psychological effect of being in that fine
machine, a single sculler, and being conscious of the shoreline moving
sternwards past you?
Is it that SOME of the things we are coached to do, fit with a
fallacious model, and seem to work?
Or is that the machine we've been discussing, just doesn't simulate
the waterborne experience as well as was hoped?
Richard du P
Charles Carroll
I, too, enjoy Carl's succinct and lucid monographs on the physics of
rowing. I cannot tell you how much I have benefited from them. Not
only are they entertaining and give me something to think about, they
just add immensely to whatever small understanding I may have about
the sculling and rowing.
I, however, share your question about the ergs under discussion. We
are trying to discern the differences between a Rowperfect3, a CII on
slides, and a prototype CII. Jim Dwyer is one of the few of us who
seems able to compare all three.
If I haven't misunderstood Jim, he says that there is a very small
difference between the Rowperfect and the CII on slides.
On the other hand Jim seems to think that there is a distinct
difference between the previous two machines and the prototype CII.
To quote Jim:
"I just tried the CII ERG at the FISA World masters Regatta. It was
the one in which the footstops move but the flywheel does not so the
mass was close to zero and it did feel odd. It felt like I had to do a
lot of work pulling my feet towards me to get compression and good
length at the catch."
Carl's explanation, it seems to me, addresses Jim's idea of "momentum
going forward into the catch."
If I have understood Carl, he is explaining that "momentum going
forward into the catch" is just the wrong idea of what is happening.
At the risk of being overly simplistic, let's see if I have understood
anything. I am sure Carl will correct me if I haven't.
After the release we are working with two momentums: the momentum of
the rower and the momentum of the boat. Both momentums are moving in a
sternwards direction. The job or the rower is to combine his momentum
with the momentum of the boat. He adds his momentum to the boat's
momentum by pulling the stretcher in a sternwards direction towards
him.
I am sure that is too simple, but at least I gave it a try.
Now getting back to Jim's original assertion about the difference in
feel between the CII prototype and the other two ergs. Why did the
prototype CII feel odd? It seems to me that we could still use a
little enlightenment on this question.
And then, while thinking about this, I came up with yet another
question.
On a CII on slides you pull the erg underneath you. On a RowPerfect
you pull the flywheel to you. Looking at the videos of people rowing
on each machine, I found myself wondering, does the Rowperfect better
simulate a shell equipped with sliding riggers, while the CII on
slides better simulates a boat equipped with conventional riggers?
Cordially,
Charles
Charles Carroll
> the rower and the momentum of the boat. Both momentums are moving in
> a
> sternwards direction. The job or the rower is to combine his
> momentum
> with the momentum of the boat. He adds his momentum to the boat's
> momentum by pulling the stretcher in a sternwards direction towards
> him.
Did I actually write that "both momentums are moving in a sternwards
direction?"
I can't believe that I could be so dumb. Would anyone be kind enough
to think of this as a typo?
Clearly at the release both momentums are moving in a "bowards"
direction. Bowards! Bowards! Bowards! Unless of course we are talking
about back up!
Carl Douglas
opposite of that which you wrote, Charles? ;) You were just testing our
pedant factors, of course.
At a first crude approximation we can almost ignore the momentum of the
boat & consider the boat is if it were a set of sticky skates or skis.
In which case, no need to discuss what part the boat's momentum plays in
the process of recovery. So you have no job to do in "combining
momentum". Just concentrate on the unspoken, largely denied but still
inescapable need, in coming to front-stops, to apply a pull on the feet
somewhat exceeding the drag on the boat (which is, again at 1st
approximation) the drag on the whole system).
This is where the dynamic erg falls a bit short. As I see it (& I could
be wrong) during recovery you have only an inertial reaction against the
mass of what's attached to the stretcher, not the fluid drag which the
boat experiences, to provide the load against which your feet must pull.
As said previously, every model of a real process is somewhat of an
approximation, & this use of the inertia of the machine's head as a
substitute for fluid drag makes a handy if improper approximation to
reality in its sensation. The flywheel fan can't introduce that missing
drag element in the correct way, even if its overall energy absorption
characteristics model the overall drag process well enough.
BTW, a well-designed fan (i.e. one designed specifically to blow air)
will not model the fluid drag characteristics of a boat too well.
That's because a typical fan is an aerodynamic device, optimised to work
efficiently in a narrow speed range, so its drag vs speed relationship
can fall a long way from the square-law function needed to provide a
passable analogy for a shell's drag. Something better described as an
air mincer is more suitable than a proper & well-behaved fan.
Now, where were we?
Cheers -
Carl
PS I know nothing about the new C-II machine so can't usefully comment
on its specifics.
Jim Dwyer
"Carl Douglas" <ca...@carldouglas.co.uk> wrote in message
news:8epe5e...@mid.individual.net...
Carl:
I don't know how you build boats but my boat has slides that are angled down
towards the footstops so after the recovery all I have to do is relax and I
glide toward the fotstops. I do pull myself toward the footstops after the
release when my trunk is swinging forward then relax and the angled slides
and momentum take care of the rest ofthe compression.
On the new CII ERG you must pull the footstops forward for the entire
recovery to get good compression at the catch.
Jim
Jim Dwyer
> feel between the CII prototype and the other two ergs. Why did the
> prototype CII feel odd? It seems to me that we could still use a
> little enlightenment on this question.
On sliding ERGS like the rowperfect and CII on slides you have more mass
moving towards you during the recovery than you do with the new CII
prototype. All that is moving towards you on the CII prorotype is a set of
footstops sliding on a rail. On the new CII prototype there was no feeling
of movement of my body towards the footstops and I needed use more energy to
pull the footstops toward me at the catch so that I could get full
compression.
Jim
Carl Douglas
>> gliding up the slide as if we had sternwards momentum over which to
>> exercise control.
>>
>> belief this is), compression at the catch is an active process requiring
>> mass moving towards a resisting foot-stretcher that it is always seen to
>> be. The stretcher is trying to get away from us, quite opposite to the
>> popular conception that it is there to halt our imagined sternwards
>> motion.
>>
>> Cheers -
>> Carl
>
> Carl:
>
> I don't know how you build boats but my boat has slides that are angled down
> towards the footstops so after the recovery all I have to do is relax and I
> glide toward the fotstops. I do pull myself toward the footstops after the
> release when my trunk is swinging forward then relax and the angled slides
> and momentum take care of the rest ofthe compression.
>
> On the new CII ERG you must pull the footstops forward for the entire
> recovery to get good compression at the catch.
>
> Jim
>
>
We build the same as others in respect of slide slope, Jim. Typically
the slope is less than 1.5 degrees, but let's take a 1.5 degree slope:
Sternwards force component = tan(1.5) x your weight, W
= 0.026 x W
Sternwards force (83kg crew) = 2.16kg f.
At the finish, hull drag, D = ~15kg f.
Weight of boat & blades = ~17kg
Total system mass = 100kg
Now proportion total drag force between the 2 inert masses of boat & crew:
Drag force on crew = 15 x (83/100) = 12.45kg f
So, just to leave backstops you must pull against the boat (i.e. the
stretcher with (12.45 - 2.16) = 10.29kg f
That's 4x the force available from the slide slope.
Let's look at it another way. Forget the inconvenient drag forces
causing deceleration of the boat. Assume only that your mass is
starting from zero velocity to roll on frictionless bearings down a 1.5
degree slope. How long will it take to reach frontstops?
Slide travel, S = 0.65m
Acceleration, A = 0.026 x gravity = 0.255 m/sec^2
Initial velocity down slide = 0
If time to cover Slide travel is T, then we know:
S = 0.5 x A x T^2
So: T = sqrt(2 x S/A) = 2.26 sec
This means that, in this completely unreal fiction where, unaided, the
boat somehow sustains constant velocity, & you do nothing to check your
gradual acceleration down the slide (doing that would greatly increase
time to reach front-stops), it'll take you about 2.26 sec to reach
front-stops, your rate will never exceed 18 to 19 spm, & you'll hit
front-stops at about 0.58 m/sec.
I hope that these separate explanations dispel the notion that slide
slope is able to get you to front-stops without you having to do most of
the necessary work?
Cheers -
Carl
PS I'm intrigued as to what you are pulling in the new C-II. Is there
an attached mass, are you pulling your own body weight up a slope (of a
lot more than 1.5 degrees), or are you pulling against a spring or
frictional load?
C
Jim Dwyer
> PS I'm intrigued as to what you are pulling in the new C-II. Is there
> an attached mass, are you pulling your own body weight up a slope (of a
> lot more than 1.5 degrees), or are you pulling against a spring or
> frictional load?
http://www.concept2.com/us/company/blog/default.asp?id=677444685
Scroll down to the video to watch.
The math is impressive but you misunderstood my point.
I understand that I have to pull to move myself towards the footstops. This
happens after the release when your arms are straightened and you swing your
trunk forward. Once you are moving forward your momentum, the slope of the
slides, and the fact that the boat is moving under you allows you to glide
up the slide with very little effort. This is why you are able to row with
your feet out of the footstops. Your forward momentum towards the footstops
helps your body compress at the catch in a boat and on static ERGS. On a
dynamic ERG the mass of the ERG moving towards you gives a similar effect.
On the new CII ERG there is no forward momentum of your body, there is no
ERG mass moving towards you and therefore you have to pull the footstops
forward under you to get full compression.
Jim
Carl Douglas
Actually, Jim, I did not misunderstand. And the maths has continuing
relevance right throughout your recovery, not something to be lightly
discarded as a fancy trick or of only passing relevance. But I do fully
understand the conceptual barriers - what I'm saying here is opposed to
what most of us have always been told is true, so it is tough to adjust
to. Iconoclasm is always unseemly.
Suppose you have started down the slide? The boat is still experiencing
the full decelerating force of its fluid drag. That force is pulling it
back, away from you. So, if it has no continuing pull from your feet,
let alone enough pull to help it to more than overcome that drag enough
to catch up with you before you need to take the net catch, it will run
back away from you.
The boat is much lighter than you are, & you do not acquire sternwards
momentum except at the cost of much greater bow-wards movement (&
consequently increased fluid drag) for the boat. Immediately you stop
pulling on your feet, the drag on the boat pulls it back out from under
you again - because the boat has all of the drag, little of the mass &
knows nothing about your supposed (but illusory) sternwards motion. That
it can move under you ensures that you cannot, except by your own
continuing physical effort, glide towards front-stops. And in any case
it is front-stops which come to you - just as you see happening on a
dynamic ergometer.
Finally, it is an old, well-tried but rusty saw to quote feet-out rowing
as proof of the absence of a heel pull. Were there no down-force into
the heels of the shoes or clogs, you'd roll over backwards. So there
has to be at first a small downward load (which is why feet-out finishes
tend to be more upright & shorter than normal finishes) & as you
approach front-stops (i.e. as they approach you ;) ) the down-force into
the heels must inevitably increase. Even with no heel down-force, your
heels won't pull out of the shoes because there's a significant
mechanical engagement between heel & shoe, despite the feet being
otherwise free.
No, the mass of the boat cannot help you to compress at the catch,
although the mass of the Earth most definitely does this for you on the
fixed erg. If the boat is decelerating, as it must if you don't pull it
towards you, then even for you to stay at one point on the slide needs
you to pull on the stretcher. If that's not the case, please explain
what massive forward-moving object exists in _your_ boat against which
you can react your (supposedly, but not really) sternwards moving body
mass in such a way as to generate a compression of the feet towards the
body?
Cheers -
Carl
Charles Carroll
It occurs to me that the one part of the body that always moves at the
same velocity as the boat are the feet. They are the only part of the
body that is irrevocably attached to the boat.
Pull the feet bowards and the boat must move with them.
Such a movement has a very distinct feeling. I can feel it both in my
boat and on my CII with slides. I imagine it can also be felt on a
Rowperfect.
But can you simulate an equivalent sensation on the prototype CII?
I noticed on CII's blog that the engineers are very pleased with the
feel of the drive. I think they mentioned that the drive has gotten
even better on this build of the prototype.
But we're talking about the recovery. And I get no sense of how the
recovery might feel on the new prototype. From the video it looks as
if the only weight being pulled bowards is the combined weight of the
feet and the footplate. That can't be very much.
When you were on the new CII prototype could you feel any resistance
when you pulled your feet bowards?
By the way, isn't this one of Rowperfect's main contentions? Doesn't
Rowperfect claim that their erg is better because it more accurately
simulates the recovery? As I understand it, the argument is that when
the sculler pulls the Rowperfect footplate sternwards he pulls only
the weight of the flywheel, which is 17 kg, a weight that closely
approximates the weight of a flat water racing single. On a CII he has
to pull a much heavier weight, almost 30 kg.
Or have I gotten this all wrong?
Cordially,
Charles
Charles Carroll
> the sculler pulls the Rowperfect footplate sternwards
Damnitall! I did it again. Bowards! Not sternwards!
Obviously it is time to call it quits.
Kit
wrote:
Charles,
Have you had a look at http://www.frontrower.com/ ?
It may help ... ;)
Kit
Tinus
> No, the mass of the boat cannot help you to compress at the catch,
> although the mass of the Earth most definitely does this for you on the
> fixed erg. If the boat is decelerating, as it must if you don't pull it
> towards you, then even for you to stay at one point on the slide needs
> you to pull on the stretcher. If that's not the case, please explain
> what massive forward-moving object exists in _your_ boat against which
> you can react your (supposedly, but not really) sternwards moving body
> mass in such a way as to generate a compression of the feet towards the
> body?
I don't want to make a claim that compression is due to negative work
because I don't believe it is the most important factor.
However, I do want to make the point that there certainly is a small
amount of negative work done by the body (which means that compression
is assisted by exchange of mechanical energy). Also, it's magnitude is
higher then expected when assuming a two body system in which boat and
rower move as two solid bodies. If you model the rower's body parts
separately then calculations will return a higher (and more realistic)
amount of (negative) work done.
The massive objects existing in your boat are your lower limps. During
the recovery their speed is somewhere between the speed of the trunk
and the boat and this internal kinetic energy contributes in
compressing the legs at the catch. This contribution is highest at the
final part of compression. Therefore, the feeling doesn't surprise me.
The feeling is not described as problems with compression but instead
as problems with full compression. This means that the problem mainly
exist in the final part of the compression phase, the part during
which the kinetic energy contribution is highest.
MagnusBurbanks
> "Carl Douglas" <c...@carldouglas.co.uk> wrote in message
>
> news:8epe5e...@mid.individual.net...
>
>
>
>
>
> > On 08/09/2010 02:55, Jim Dwyer wrote:
>
>
> - Show quoted text -
Although the slides _appear_ to be sloping, in a certain sense they
are not. Correct me if I am wrong, Carl, but I always thought the
slope of the slide was there to counteract the trim of the boat as you
alternately move the stern towards and away from you. Taking into
account this trim, you will actually be sliding very nearly level.
Magnus
Charles Carroll
So Kit,
After having seen this video how could anyone argue that rowing is a
backwards sport averse to new ideas and innovative technology?
Cordially,
Charles
Jim Dwyer
I don't want to make a claim that compression is due to negative work
because I don't believe it is the most important factor.
However, I do want to make the point that there certainly is a small
amount of negative work done by the body (which means that compression
is assisted by exchange of mechanical energy). Also, it's magnitude is
higher then expected when assuming a two body system in which boat and
rower move as two solid bodies. If you model the rower's body parts
separately then calculations will return a higher (and more realistic)
amount of (negative) work done.
The massive objects existing in your boat are your lower limps. During
the recovery their speed is somewhere between the speed of the trunk
and the boat and this internal kinetic energy contributes in
compressing the legs at the catch. This contribution is highest at the
final part of compression. Therefore, the feeling doesn't surprise me.
The feeling is not described as problems with compression but instead
as problems with full compression. This means that the problem mainly
exist in the final part of the compression phase, the part during
which the kinetic energy contribution is highest.
Thanks Tinus!
That is the difference that I can feel between rowing in a boat and rowing
on the new CII ERG.
To get full compression on this ERG I have to pull my feet towards my butt
at the catch. In the boat as you are slowing down to take the catch you can
feel the mass of the boat on your feet pushing against you and helping with
full compression.
Jim
MagnusBurbanks
> feel the mass of the boat on your feet pushing against you and helping with
> full compression.
In a shell I agree you can indeed feel a little bit of pressure as you
approach full compression, if you slow the shell coming towards you
with greater force than the fluid drag already acting to resist it.
But that under-foot feeling is NOTHING compared to the same feeling on
a fixed-head erg.
To quote from my own thoughts at http://www.slidingseat.net/accel/accel.html#fixedheadVSscull
on this subject:
"... next time you're sitting on an erg and pulling some strokes, as
you approach frontstops take particular notice of the TREMENDOUS build-
up of pressure under your feet, and note also that this pressure
builds up well before the catch.
"This huge under-foot pressure before the catch simply doesn't happen
in a properly-rowed boat, where in fact most of the recovery should be
spent with feet pulling not pushing (see also here for more about the
recovery and how critical it is). Just before the catch in a boat, the
foot-pull briefly turns into a small "push" as the mass of the boat
needs to be decelerated to the same speed as the rower."
Magnus
Carl Douglas
We row for fun, & should never lose sight of the right to disagree.
However, Jim, Tinus is not telling you that the boat, even plus the
secondary masses of the links of your lower limbs (which are still
moving with the body to pull the boat forward between finish & catch) is
in any way pushing against you. As I said, the maths still applies &,
dead simple though it be, I have not seen it challenged so it cannot be
dismissed. And please note that in my maths, to simplify the analysis
in a way which results in understating my case, I made no allowance for
the fact that the body's CofG moves further & hence faster than the
seat. This, if included, would not enhance your case for the recovery
being all down to slide slope
I'd welcome any correction to the simple sums I formulated. Similarly
to my reply to your challenge over feet-out rowing. A discussion is
more useful when we evaluate the relevance of each proposed element of
our different models of the rowing action before seeking other ways to
hop over the wall.
Only at the instant just preceding the catch, when none of us can manage
a smooth enough engagement & loading of the blades to prevent it, do the
feet stop pulling & the feet impact upon stretcher. That imperfect
reversal of the former pull on the feet is immediately evident, of
course, as a measurable check on the boat.
Drawing in Magnus' comment on slide slope - my answer is that I just
don't know. It seems to be there because it's what folk like to have.
They may believe the slope is there to help you to the catch, & sure
it helps a little bit, as my simple arithmetic showed, but only a little
bit, so it seems unlikely you'd want to reverse that slope. But I'd not
previously heard the suggestion that Magnus advances - were that
applicable, then I suppose you'd want the slides to follow a long arc
about a point high above the boat. Mmmmm.
Charles Carroll
> you approach frontstops take particular notice of the TREMENDOUS
> build-
> up of pressure under your feet, and note also that this pressure
> builds up well before the catch.
Magnus,
But of course!
By definition on a fixed head erg the head is fixed. It doesn't move.
What moves is the person erging, who at the finish has to accelerate
his body towards the fixed head , i.e. the flywheel, then as he
approaches this fixed head is forced to come to a stop and
re-accelerate, i.e. push, in the reverse direction. This is a motion
that is guaranteed to be very hard on the back, particularly the lower
back. The only thing that moves on a fixed head erg is the person
erging.
Considering the array of inexpensive dynamic ergs available today, I
am beginning to wonder why anyone would train on a fixed head erg. But
then again, perhaps my back is just more delicate than most people's.
Cordially,
Charles
Chris Kerr
> We build the same as others in respect of slide slope, Jim. Typically
> the slope is less than 1.5 degrees, but let's take a 1.5 degree slope:
>
> Sternwards force component = tan(1.5) x your weight, W
> = 0.026 x W
> Sternwards force (83kg crew) = 2.16kg f.
>
> At the finish, hull drag, D = ~15kg f.
> Weight of boat & blades = ~17kg
> Total system mass = 100kg
>
> Now proportion total drag force between the 2 inert masses of boat & crew:
> Drag force on crew = 15 x (83/100) = 12.45kg f
>
> So, just to leave backstops you must pull against the boat (i.e. the
> stretcher with (12.45 - 2.16) = 10.29kg f
> That's 4x the force available from the slide slope.
>
> Let's look at it another way. Forget the inconvenient drag forces
> causing deceleration of the boat. Assume only that your mass is
> starting from zero velocity to roll on frictionless bearings down a 1.5
> degree slope. How long will it take to reach frontstops?
>
> Slide travel, S = 0.65m
> Acceleration, A = 0.026 x gravity = 0.255 m/sec^2
> Initial velocity down slide = 0
> If time to cover Slide travel is T, then we know:
> S = 0.5 x A x T^2
> So: T = sqrt(2 x S/A) = 2.26 sec
I'm not disagreeing with the main force of your argument here, but just to
be pedantic:
In the idealised 'frictionless' case of rolling down the slide just under
the influence of gravity, Newton's third law means that the same ~21N
component of the reaction force pushing you towards the stern pushes the
boat forwards. The overall acceleration relative to the boat is 21N divided
by the reduced mass 1/(1/17 + 1/83) ~= 14kg so around 1.5 m/s^2, giving a
travel time of just under 1s.
Carl Douglas
> Carl Douglas wrote:
>
>> We build the same as others in respect of slide slope, Jim. Typically
>> the slope is less than 1.5 degrees, but let's take a 1.5 degree slope:
>>
>> Sternwards force component = tan(1.5) x your weight, W
>> = 0.026 x W
>> Sternwards force (83kg crew) = 2.16kg f.
>>
>> At the finish, hull drag, D = ~15kg f.
>> Total system mass = 100kg
>>
>> Drag force on crew = 15 x (83/100) = 12.45kg f
>>
>> So, just to leave backstops you must pull against the boat (i.e. the
>> stretcher with (12.45 - 2.16) = 10.29kg f
>> That's 4x the force available from the slide slope.
>>
>> Let's look at it another way. Forget the inconvenient drag forces
>> causing deceleration of the boat. Assume only that your mass is
>> starting from zero velocity to roll on frictionless bearings down a 1.5
>> degree slope. How long will it take to reach frontstops?
>>
>> Slide travel, S = 0.65m
>> Acceleration, A = 0.026 x gravity = 0.255 m/sec^2
>> Initial velocity down slide = 0
>> If time to cover Slide travel is T, then we know:
>> S = 0.5 x A x T^2
>> So: T = sqrt(2 x S/A) = 2.26 sec
>
> I'm not disagreeing with the main force of your argument here, but just to
> be pedantic:
> In the idealised 'frictionless' case of rolling down the slide just under
> the influence of gravity, Newton's third law means that the same ~21N
> component of the reaction force pushing you towards the stern pushes the
> boat forwards. The overall acceleration relative to the boat is 21N divided
> by the reduced mass 1/(1/17 + 1/83) ~= 14kg so around 1.5 m/s^2, giving a
> travel time of just under 1s.
Chris, that's a fascinating analysis! But I suspect it is flawed ;)
How? Well, obviously every action demands an equal & opposite reaction.
So clearly the force which assists you down the slide must react
equally on the boat - no dispute there. But this is already accounted for:
1. The boat does not accelerate, it slows down, so your supposed
acceleration of this inferior mass does not happen.
2. And that's because I'd already accounted for this opposing reaction
by deducting the relevant ~21N or 21.6kg f from the total pull the rower
needs to exert to make it to front-stops.
How's that?
Cheers -
Carl
Jim Dwyer
towards the footstops and the footstops are moving towards me (action
reaction forces). When I start to slow down my forward movement to take the
catch the boat (footstops) push against my feet and I get better
compression. This does not happen on the CII ERG because all that is moving
towards me is a set of footstops on a runner. It felt that I needed to
actively pull the footstops towards me at the catch to get full compression.
Jim
"Carl Douglas" <ca...@carldouglas.co.uk> wrote in message
news:8esh6s...@mid.individual.net...
Carl Douglas
> The way that I look at it is that as I am approaching the catch I am moving
> towards the footstops and the footstops are moving towards me (action
> reaction forces). When I start to slow down my forward movement to take the
> catch the boat (footstops) push against my feet and I get better
> compression. This does not happen on the CII ERG because all that is moving
> towards me is a set of footstops on a runner. It felt that I needed to
> actively pull the footstops towards me at the catch to get full compression.
>
> Jim
>
>
>
I think between us all we've narrowed this down significantly. I think
Magnus, Tinus & I will all agree with you that, at the end of the
recovery, there's a coming together of crew & boat which, without the
continuing frictional drag on the hull, would induce a mutual relative
deceleration. From what we see when decelerations are measured at the
catch, that short-term hull deceleration is pretty sharp. But in good
scullers it is also rather brief.
If the hull's deceleration in the check at the catch exceeds about 0.5
g, which corresponds to its likely drag-induced deceleration if detached
from the crew but still supporting crew weight - a complicated but
necessary concept! - only then will there be some inertially-induced
compression of the legs.
Under those conditions, we're all in agreement on that point :) I'm
unsure how much help, if any, this really is in achieving the last bit
of compression.
This is, of course, different from the much greater part of of the
recovery - which was how we began.
On how the C-II dynamic erg works I am still none the wiser. I can
imagine all manner of ways of changing the foot-to-stretcher tension
during recovery, but what Concept actually do I just don't know. No
question, though, that dynamic ergs will feel a lot more like real
rowing or sculling than fixed ones. Tthat's because they do not make
you generate your recovery by hauling yourself off the finish, or your
catch by first slamming on the anchors or letting your sternwards
momentum suddenly scrunch you up & then having to get the body moving to
backstops before you can get any load onto the handle.
That sort of a change has to be good for you &d good for your rowing.
Bbut rowing, especially sculling, has to best of all.
Chris Kerr
>
> Chris, that's a fascinating analysis! But I suspect it is flawed ;)
>
> How? Well, obviously every action demands an equal & opposite reaction.
> So clearly the force which assists you down the slide must react
> equally on the boat - no dispute there. But this is already accounted
> for: 1. The boat does not accelerate, it slows down, so your supposed
> acceleration of this inferior mass does not happen.
> 2. And that's because I'd already accounted for this opposing reaction
> by deducting the relevant ~21N or 21.6kg f from the total pull the rower
> needs to exert to make it to front-stops.
>
> How's that?
>
> Cheers -
> Carl
>
Sorry, I obviously didn't make myself clear enough. By "the idealised
'frictionless' case" I was referring to the passage quoted below: the
hypothetical case where there is no/negligible drag on the boat (the closest
real-life situation to this is coming forward for the first stroke when
paddling off from backstops). In this case my reduced-mass analysis still
holds, while your 2.6 seconds is the time it will take to reach frontstops
on a static erg if you sit on the seat and roll forwards.
>> Let's look at it another way. Forget the inconvenient drag forces
>> causing deceleration of the boat. Assume only that your mass is
>> starting from zero velocity to roll on frictionless bearings down a 1.5
>> degree slope. How long will it take to reach frontstops?
Similarly, after taking the drag into account, any amount you pull on your
feet in excess of 10.29 kgf must be divided by 14kg and not 83kg to find
your acceleration relative to the boat.
This prompts an interesting question: supposing you accelerate your centre-
of-mass up to a maximum speed at the beginning of the recovery by rocking
your body forwards, then exert no further force on the foot stretcher until
taking the catch (as advocated by some coaches), what is the recovery time
then, and how fast do you need to rock forwards?
(Alternatively, taking the same problem in reverse, if you took a stroke
then were somehow teleported to frontstops, how long would it take to roll
back up to backstops and how fast would you be going when you got there?)
The acceleration relative to the boat will be 10.29 kgf / 14kg ~= 7 m/s^2
i.e. you would take 0.4 seconds on the slide (not including time taken for
arms away and body over) and require a starting speed of 3 m/s.
The acceleration required to bring your body up to that speed while rocking
forwards through a distance of 10cm is a = v^2 / 2*d = 45 m/s^2, which
sounds a lot until you remember that this is the acceleration of the
reduced-mass system and translates to a force of 45*14 = 630 N, which is
about twice the force you need to do a sit-up against gravity - probably
achievable for a few strokes during an exercise but not for the whole of a
240 stroke race.
Of course my analysis gets more and more tenuous towards the end there,
particularly the entirely arbitrary figure of 10cm.
Tinus
> ...sounds a lot until you remember that this is the acceleration of the
> reduced-mass system and translates to a force of 45*14 = 630 N, which is
> about twice the force you need to do a sit-up against gravity - probably
> achievable for a few strokes during an exercise but not for the whole of a
> 240 stroke race.
The analysis is indeed an interesting case and the description
completely correct (although the assumption of a two body system
overestimates the acceleration). But, a sit up is performed at much
lower contraction speeds.
Also this type of stroke would result in higher boat speed variation
and as a result a higher drag. It is purely a thought experiment or
hypothetical situation instead of something to be seen during a race.
Another note, one could arrive at a stop in compressed position
entirely by having the boat decelerate. Up to a certain extend this
might have some advantages however one is able to get to the front
stops faster if maintaining speed on the slides and have a (fast)
deceleration only at the very end. This might also have some
advantages. For one the compression is higher. Secondly a plyometric
motion is able to generate higher power.
Tinus
> Under those conditions, we're all in agreement on that point :) I'm
> unsure how much help, if any, this really is in achieving the last bit
> of compression.
It is much like in dynamic stretching. The last bit of compression or
stretching (what we call compression in rowing is actually a
stretching) is by definition only a small piece of compression.
Therefore it is not difficult for small effects to have large impact
on this last bit. Maybe the impact on power output is not large. But,
for the feeling of the rower the difference is large because the
feeling is only the feeling of this very last bit. Simply do the
following experiment move your arm slowly backwards and try to stretch
as far as possible now do it again but dynamically.... I believe that
at least the feeling is much different.
Charles Carroll
> simulations have limitations.
Carl,
At first reading this strikes me as completely obvious and therefore
true.
But the "obvious trueness" of an assertion becomes an invitation to
question.
Could an off-water training device be designed and built that so
accurately simulated the "feel" of on-water sculling that it would
become all but indistinguishable from the act of sculling on water?
Consider the cello. The Davidov Stradivarius produces a sound that
many people believe is unique and for this reason is impossible to
simulate.
But how many of us have heard it live? I daresay we lucky few are a
very small percentage of the world's population.
Yet how many of us would argue that we are not listening to real music
when we listen to its sound copied and reproduced in a digital medium?
Cordially,
Charles
Carl Douglas
>> "Simulates" does not mean "exactly copies in every respect". All
>> simulations have limitations.
>
> Carl,
>
> At first reading this strikes me as completely obvious and therefore
> true.
>
> But the "obvious trueness" of an assertion becomes an invitation to
> question.
>
> Could an off-water training device be designed and built that so
> accurately simulated the "feel" of on-water sculling that it would
> become all but indistinguishable from the act of sculling on water?
Yes, I am sure it could, & I know how it can be done. The price would
depend only on the quality of the simulation. Would I be right in
supposing that a high-quality simulator might fetch a price similar to
that of a top-quality single scull?
>
> Consider the cello. The Davidov Stradivarius produces a sound that
> many people believe is unique and for this reason is impossible to
> simulate.
>
> But how many of us have heard it live? I daresay we lucky few are a
> very small percentage of the world's population.
>
> Yet how many of us would argue that we are not listening to real music
> when we listen to its sound copied and reproduced in a digital medium?
>
> Cordially,
>
> Charles
>
The sound from the cello must pass through the air, bounce off walls &
other objects, be focussed by our external ear into the inner ear & then
be subject to our own hearing processes & the brain's interpretation of
the resulting signals. Most folk start to experience impairment of
hearing before middle age. So what, really, do each of us hear when the
player passes bow over string? How much of the spectrum of pressure
vibrations which left the cello gets lost on the way, & how much
extraneous junk - noise & other distortions & signals - gets added?
I'll tread on some toes if I cast aspersions into the domain of the
Hi-fi enthusiasts & their concerns about heavy platforms & special
grades of copper cable, but I am aware that the player can matter a lot
more than the instrument. I fear that obsessing over particular
instruments can mean a loss of objectivity when, I suppose, the music &
its interpretation matter most. I used to be a (pretty poor) oboe
player - much more interested in the whys & wherefores of wind
instruments than in endless hours of practice. But I acquired an
interest in how much of the quality of the instrument related to its
materials & how much to its shape & quality of construction. Thus I
learned about papier-mache bassoons & nylon clarinets, not to mention
metal woodwinds of various types. How amazing that anyone can believe
that a flute made of gold must play better than one of wood or
nickel-plated brass - except for the superior care & accuracy built into
the more costly product?
The bassoon is a wonderful piece of furniture, but I learned of the
logical bassoon and one day was fortunate enough to encounter one. The
bassoon is a wonderful example of the instrument-maker's ingenuity: to
sound different notes the main bore must be vented at otherwise closed
holes set at the proper intervals along the pipe. But its a long
conical pipe that's too long to have straight so it's bent double & the
reed at the narrow end feeds its pressure pulses through a narrow pipe
shaped like a shepherd's crook. That's why the name in Italian is that
for a bundle of sticks - fagotto. Because we have only so many fingers
& these are attached to only 2 hands, it'd be a pig to have to cover &
uncover holes in all the right places, especially before there was much
in the way of keywork. So the venting holes were drilled on long
diagonals from where finger could reach them to where vents were needed.
A lot of compromises resulted, although few would doubt these
contribute to this beautifully sonorous & expressive instrument's
mystique, as well as to its cost.
But it needn't be so. And one day an Englishman cut up an old mahogany
sideboard. Onto one flat slab he laid out a labyrinth of upstanding
strips of wood to create a continuously widening passage of the
necessary length. Then he laid another slab on top to convert this
labyrinth into a tapered duct. Holes were drilled through the upper
slab in just the accoustically correct places, & keywork added to
control the opening of these holes, & a crook for the reed. The cost
was a fraction of that of a beautiful French or German instrument. To
my ear it played darned well & sounded very good. But I don't think
it's going to find favour among the cognoscenti.
So how good a simulator do you want, Charles?
Walter Martindale
> The way that I look at it is that as I am approaching the catch I am moving
> towards the footstops and the footstops are moving towards me (action
> reaction forces). When I start to slow down my forward movement to take the
> catch the boat (footstops) push against my feet and I get better
> compression. This does not happen on the CII ERG because all that is moving
> towards me is a set of footstops on a runner. It felt that I needed to
> actively pull the footstops towards me at the catch to get full compression.
>
> Jim
>
Hi Jim,
A couple of minor(?) things about the recovery - First is that with
the exception of the first stroke in which your boat is held
stationary in the water, your body never goes towards the starting
line - only towards the finish line. You can confirm this on the
water by looking down at the water that you are going past in your
boat - you (unless you're a really crap sculler which I sincerely
doubt) are always moving forward (toward the bow) through/over the
water. During the recovery, the boat goes forward (in the direction
of travel) faster than your body goes. The only way this can happen
is by applying force to the boat, because - if you think about it -
the water through which the boat travels is trying to stop the boat -
or make it go slower... To overcome the resistance from the water,
you HAVE TO pull on the boat, either by exerting one heck of a lot of
torque on the scull-handles to lever the boat forward through the
water (we know this isn't the case) or by pulling on it at the foot
stretchers.
Now - Carl has calculated and Richard Smith (a researcher in
Australia) has measured that in a single there is about 10 or so kgf,
or 100 or so Newtons of force in the direction of travel for the boat
- or about 5 kg per foot - which most of us don't perceive as being
much of a force, considering that when we run, we're applying more
than our body-weight worth of force each time we stride.
With respect to the feet out exercise - Try doing it where there is no
heel cup for you to sink your heels into - You'll either bang your
heels on the bulkhead at the bow end of the foot-well, or you'll have
to hook your toes over the top of the stretcher, because you won't be
able to recover the boat. Time is running out in Canada to do this
experiment, because I can see people getting immersed if they do try
it. It's sort of like what happens to a guy in a boat when the screws
holding his shoes to the stretcher let go, or when the bolts holding
the stretcher to the boat let go - whee, body continues toward the
bow, drag makes the boat slow down and slip out from under the
sculler.
One world famous coach says "sit there and bring your feet to you" or
something very similar to that.
With respect to the sloped-slide issue - Zibi has only recently put
slide-wedges under his slides and reports (personal communication)
that it is much easier to scull. However, I've tried this myself -
one club where I coached had some boats with flat deck and no wedges
under the slides - People complained that the boats were hard to row.
Went out myself to prove that they were wrong, and had a horrible time
of it - it felt like I was pulling myself up hill on the recovery -
hamstrings took a beating. Had a parent at the rowing club cut a
couple of wedges to put under the slides - they were about 10mm
different in height from one end to the other. With the wedges under
the slides it felt a whole lot more like what I remembered sculling to
feel like. The logic and mechanics of it has been touched on by
someone else in this discussion - when you are at the finish, your
body mass is forward (in the boat) with a pitching downward of the bow
of the boat - making the decking of the boat slope down toward the bow
- to recover (pull the boat forward under you) you have to pull the
boat under your weight with a motion that would have the effect of
shoving the boat further under water (because your body mass would
have to be lifted up the slope) - with the sloped slide, you counter
the pitch forward of the boat, and can simply slide the boat under you
and the only resistance is the drag from the water.
Whew.
Better go - time to go for my workout..
Walter
Zbigniew A.
> When I start to slow down my forward movement to take
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> the catch the boat (footstops) push against my feet and I get better
> compression. This does not happen on the CII ERG because all that is
> moving
> towards me is a set of footstops on a runner. It felt that I needed to
> actively pull the footstops towards me at the catch to get full
> compression.
Here i need some clarification, what you mean, cause the way i see it is
exactly opposite:
First, on a (relatively light) rowing boat one need to actively pull the
footrest in order to make a compression. One has to overcome the inertia
force pushing the body towards the bow, cause the drag is making the whole
system to slow down. If you don't actively pull the footstretcher, you make
no compression.
(That is felt most clearly on a single sculled in a race pace. On a crew
boat, especially when others are rushing the slide, you sometimes *may* have
the impression that the boat is "coming under" you by itself.)
On a traditional, stationary C2 what is moving is *you* , your body *mass* .
during the compression it is you moving forward. Towards the end of
recovery you stop actively pulling but your body is still moving (forward).
It is relatively easier to execute full compression on a stationery C2
machine.
Here comes the biggest, IMHO most important difference between stationary C2
and the boat:
On a C2 machine you stop actively pulling (yourself towards the
footstretcher) but -- beacue of the inertia of your body mass -- you are
still moving forward. Actually, you start pushing with your legs but for a
moment your body is still moving forward, only slowing down. You push
harder, then your body stops, and while you are still pushing for some time
now then your body mass starts to move in the opposite direction.
On a real rowing boat, as long as you actively make compression, you are
puling the boat underneath you. When you are ready for the catch, you stop
puling and start pushing -- and having your oars planted in the water at the
same time you momentarily start the drive phase.
Why would you "slow down the forward movement"? The way i see it, the less
you slow down the compression, "anticipating" the catch, the better.
That's why rowers who rely on *stationary* C2 machines a lot during winter,
when they start rowing on water in springtime they have their catch messed
up. They need quite some time on water to sort it out.
And that is why somebody invented Rowperfect, and that is why Concept2 is
working on a Dynamic Erg.
Please somebody tell me if / where i am wrong. Thank you in advance! :-)
Yours Virtually, Zibi