sliding riggers
c.a...@blueyonder.co.uk
on sporting boats and one of the displays was a sliding rigger 1x.
From its fittings - clogs and metal swivels and gates I'd have guessed
at 1960s vintage or older. I hadn't realized they'd been around so
long.
Eberhard Nabel
German Wikipedia: The principle of the sliding rigger for rowing boats
was invented by the English engineer James Pacher. He applied for a
patent on Dec. 11, 1893 at the Empire's Patent Office. At that time
Pacher could not solve the mechanical problems around the sliding
rigger.
Another mame I would like to metion is that of Georg von Opel, who
made a boat with sliding rigger in 1946 or 1948.
Eberhard
Eberhard Nabel
> On 3 Jul., 22:29, "c.an...@blueyonder.co.uk"
>
> <c.an...@blueyonder.co.uk> wrote:
> > In the maritime museum in Bremerhaven today there was a small section
> > on sporting boats and one of the displays was a sliding rigger 1x.
> > From its fittings - clogs and metal swivels and gates I'd have guessed
> > at 1960s vintage or older. I hadn't realized they'd been around so
> > long.
>
> German Wikipedia: The principle of the sliding rigger for rowing boats
> was invented by the English engineer James Pacher. He applied for a
Carl Douglas
But still the unscientific babble persists, such as the following from a
major vendor of sliding rigger kits:
"Not only does the rowers momentum work against the boat's run it works
against the power transmitted to the oars. A portion, small but
measurable, of the rower's power goes to starting and stopping his or
her body. When the rower weighs 180 pounds and the sliding rigger
mechanism weighs only eight pounds, it takes a lot less power to
accelerate the rigger than the rower's body, leaving more energy for the
oar."
That load of bollocks could only have been written by someone with a
near-zero grasp of Newton's laws of motion & who, at best, sees a boat
as inertially identical to a fixed ergometer.
However, the fact that rowers across the world are daily urged in all
seriousness to "accelerate the boat" each stroke confirms that blind
ignorance of the inertial dynamics of rowing is widespread.
This sport is inescapably involved in cyclic motions, interesting
inertial interactions & complex fluid dynamics. So why are those who
see, describe, coach & market its actions determined to do so in in such
blissful ignorance of these disciplines? It wouldn't be clever or
acceptable to ignore the relevant science when building or flying,
aircraft, or designing or sailing sail-boats. So why is such
fundamental ignorance acceptable in rowing?
Do we prefer bogus explanations because everyone else believes them too,
or because we think anything more cerebral than pulling harder is
cheating. Does collective blind faith save us from having to engage our
delicate brains and think more deeply about our rowing, even though that
collective failure also keeps us slower than we need be?
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)
Andrew Hodgkinson
> However, the fact that rowers across the world are daily urged in all
> seriousness to "accelerate the boat" each stroke confirms that blind
> ignorance of the inertial dynamics of rowing is widespread.
Due to friction, the boat will slow down relative to the water if nobody
takes any strokes and changes the situation. If someone does put an oar
in the water, the boat's speed can be made to increase for the duration
of their stroke. An increase in speed over time is called acceleration.
What, then, is your problem with "accelerate the boat"? Perhaps you refer
to the use of the phrase in a specific wider context?
> Do we prefer bogus explanations because everyone else believes them
> too, or because we think anything more cerebral than pulling harder
> is cheating. Does collective blind faith save us [ etc. etc. ]
Instead of just implying that everything everyone teaches is wrong and
expecting us to believe *you* on blind faith (however justified and
correct you might be), you could perhaps explain exactly *how* the
specific points you highlighted are incorrect and go on to provide advice
on the things coaches should be teaching instead.
With some constructive and specific criticism of existing coaching
methods, we could all start getting somewhere. I've always been short and
too weak to move a boat by brute force and ignorance, so I'm all for the
cerebral approach!
--
TTFN, Andrew Hodgkinson
Find some electronic music at: Photos, wallpaper, software and more:
http://pond.org.uk/music.html http://pond.org.uk/
zeke_hoskin
Carl's right. You're right. When you pull on the oars, you're
accelerating the boat/rower system, but you are accelerating yourself
wrt the
boat, so the boat itself may be speeding up, slowing down, or
maintaining speed. Any analysis of sliding seat rowing that neglects
this
fact is about equivalent to an analysis of orbits that neglects
gravity. But you know that. The balls that Carl was deriding seemed
to
mean that you are wasting energy speeding up/slowing down your body on
a boat with more or less steady speed,
which would be the case if the boat weight 5x as much as the crew
instead of vice versa.
To the best of my understanding, sliding rigger is faster because it
eliminates the weight shift and therefore the tendency of the
boat to hobbyhorse, and therefore allows the hull to be optimized for
low drag without consideration for weight shift, so that
boats designed for sliding rigger tend to be slow when converted to
sliding seat. I have a sliding rigger in my slow fat touring
boat and it does go better than with the sliding seat. (Piantedosi
RowWing rig, easily converted from one to t'other.)
Faster? I couldn't say for sure, because I myself am getting slower. //
Zeke Hoskin
Carl Douglas
Andrew may not have noticed - & no reason why he should, of course -
that I have in the past been quite specific on these matters. A spot of
googling might have helped avoid that misunderstanding, but today is too
hot & muggy to flog that particular horse in comprehensive detail.
As Zeke notes, the heaviest item around is you. The boat is 1/5 of your
weight, so it, not you, is already the most accelerated/decelerated
item. And the more that you cause its velocity to fluctuate by your
efforts to accelerate it, the less & less efficiently it moves.
That, Andrew, was the point to which I was, somewhat bluntly I admit,
alluding with my references to Newton & other things which seem
completely lost on so many in rowing. Rowing is _not_ about
accelerating the boat. The objective is to maximise the mean speed of
boat + crew &, since you sustain much the same average speed throughout
the race, every period of acceleration of the boat is matched by it
suffering a proportionate quantity of deceleration. You might like to
consider running shoes: the runner sustains as steady a velocity of
their C of G as he/she can manage, since surging & bobbing costs effort
& overload muscles (which causes premature fatigue), but the shoes
undergo cyclic accelerations & decelerations with every step. Yet
accelerating the shoes more or less (as with the boat) may have no
relevance to winning the race.
Anyway, I started the hare, you then asked some questions (a little
abruptly maybe?), & Zeke & I have tried to answer them. How did we do?
BTW, I never said "everyone", so let's avoid unwarranted extrapolations
which seek to convert what is thought to be common to what is universal.
I think my advice to consider Newton's laws of motion was all that was
necessary: I wanted to see who might rise to that spur, do a bit of
spade-work, accept the right always to challenge a popular orthodoxy &
then ask a few questions. I preferred not to spell it all out - which
gets so boring. And, as Zeke said, the fundamental falsity of that
stuff about supposed bodily accelerations is rather self-evident when
you stop for a moment to ponder it. In fact the boat moves slower than
the body from just before the catch to about the finish (depending on
what you do there) & faster than the body throughout the recovery. Only
just before the catch & finish do boat & body move, instantaneously, at
the same velocities.
There is one predominant repository of mass & kinetic energy in rowing,
& that is the rower. What we do during the stroke is to work to store
excess kinetic energy in the body by accelerating it a bit, as well as
doing non-stored work to overcome the continual drain of energy due to
fluid drag. During the recovery we recoup that excess of stored kinetic
energy from the moving body by making it decelerate by applying a force
through the legs to draw the stretcher towards us. Were we truly
clever, maybe by superior athleticism we could so manage our stroke &
recovery strategies as to eliminate all accelerations & decelerations of
the boat, with benefits in drag reduction. That hasn't happened yet, &
is unlikely to happen while we persist in deluding ourselves that the
boat is the heavy part of the system & demanding of ourselves that we
accelerate it.
As for the fluid dynamics: isn't it strange that, when trying to get
maximum efficiency in a wind turbine we invest the products of many
years of aerodynamic science into optimising blade design, while in
rowing we spout all sorts of crap about not looming, not going deep,
ensuring there's a hole behind the blade, delaying the main pull until
we feel the blade is loaded (how does it do that?), maximising effort
into the midstroke, "not squeezing the boat", etc. - all of it tosh, all
of it said with great faith, but all of it said without the faintest
clue as to how blade & water do actually interact.
When I tell you that maybe as much as 1/3 of your input effort gets lost
into generating a useless zone of turbulence around the puddle, maybe
you start to see why a slight acquaintance with fluid dynamics might
help us improve our boat propulsion. As you have noted, some of us need
all the help we can get!
Sometimes it's more constructive to challenge people with well-aimed
provocations than to spoon-feed them buckets of detailed advice.
Nothing stimulates reactions among those who hug orthodoxies better than
breaking a few of their favourite icons ;
On response to a point Zeke raised: There is no reason for the bow of a
boat with fixed rigger/sliding seat to dip at the finish - that is all
about how the finish & first part of the recovery are managed, which
again comes down to understanding the inertial effects. You can dip the
bow if you want to, but you don't need to.
zeke_hoskin
> Cheers -
> Carl
>
Okay, I'll bite. You've moved the center of mass toward the bow, which
is a reason to dip. You are accelerating a mass (wrt the hull) toward
the stern,
and since this mass is above the center of mass of the boat, you are
exerting a torque that is downwards at the bow. You are sitting up
from
your layback, rotating your torso in such a direction as to cause the
boat to rotate bow-down. Your oars are out of the water,
so there is no force from the water to compensate for the weight shift
and recovery torques. That certainly strikes me as a set of reasons
for the
bow to dip. I grant you that you might be able to counteract the
effect, for instance by laying back further, to remove some of your
weight from the
boat, until you dragged your mass back amidships, but I don't see that
actually happening.
And nevertheless, as Galileo remarked, it moves. Possibly there is an
inertial effect I'm missing. I observe the stern of my Maas 24 to dip
very little
at the catch compared to my shorter boat and conclude that the
difference is in hull design. If there is a technique to make there be
no reason to
dip the bow at the finish, I'm sure I'm not the only one who'd like to
understand it.//Zeke Hoskin
That said:
Charles Carroll
> ignorance of the inertial dynamics of rowing is widespread.
Carl,
Is it possible to maintain constant boat velocity during each stroke?
If it isn't, then doesn't this presuppose that during a stroke cycle a shell
going to reach a maximum velocity, then regress to a minimum velocity?
And if so, then how can we not conclude that the function of the drive is to
bring the shell from minimum velocity back up to maximum velocity, that is,
to produce "a time rate of change in velocity?"
It seems to me that the question is not whether we are trying to accelerate
the boat, but rather how we are trying to accelerate the boat.
How do we take the catch? How do we drive? "Thrust-stroke?" Or "solid stroke
with hard beginning?" Schubschlag? Or Kernschlag? Hasn't this been discussed
and argued for decades and decades?
Cordially,
Charles
Charles Carroll
> at the same velocities.
Carl,
Is this true? \
I can see it at the finish. There, if only for an instant, oars, boat, and
sculler all move at the same velocity.
But is this true for the catch?
Cordially,
Charles
porter
wrote:
Charles, I think it MUST be true - with the proviso that the precise
moment may be quite tricky to determine.
Looking at it very crudely - but I think the principle will hold good
even if you get down to very fine calculation - during the
"recovery" [or whatever] phase your body moves [RELATIVE TO THE BOAT]
against the whole system's direction of travel; during the
"propulsion" phase it moves, relative to the boat, in the same
direction as the whole system is going.
I think there pretty much have to be a couple of transition points at
which the body ISN'T actually moving relative to the boat? At least
the body's centre of mass [even if say hands are moving one way and
some other body part the other?]
Richard
Reinder Verlinde
<f303773d-4318-4b72...@h11g2000yqb.googlegroups.com>,
porter <rdup...@hotmail.com> wrote:
> I think there pretty much have to be a couple of transition points at
> which the body ISN'T actually moving relative to the boat? At least
> the body's centre of mass [even if say hands are moving one way and
> some other body part the other?]
If you ignore the vertical and sideways velocities, that must be true.
You simply cannot go from moving forward relative to the boat to moving
backwards without going through zero (and, the mathematician in me must
say: keeping one's horizontal velocity greater than or smaller than that
of the boat at all times is not a realistic option, either)
Taking vertical and sideways velocities into account, it need not be
true, and probably isn't. You would, at some moment during the stroke,
have to either move at all, or make some movement without displacing you
center of mass.
Not moving at all is considere bad technique. That leaves the 'moving
without displacing your center of mass' part. I would say the only two
candidate places here are the catch and the release.
At the catch, I would think good rowers would start moving their arms up
(just so slightly) before they reach the point where horizontal movement
stops in order to have the blades just hit the water at that exact
moment (perhaps even slightly before that). So, exactly zero it will not
be. On the other hand it may well be practically zero.
I guess things are even closer at the release, but again I doubt there
will be a moment where there is zero movement.
In the end, it all turns down to the fact that, in 2-D or 3-D one can
easily make a U-turn without stopping, and that, I think, is what the
center of mass will do.
Reinder
Carl Douglas
Charles -
The boat is the junior partner in the team dynamics.
The boat is just a piece of lightweight kit, albeit the largest & most
important bit of it (or you'd be swimming). It moves always at about
the same speed as the balls of your feet. So, do you think about
accelerating the balls of your feet towards the finish line during the
stroke? I think not.
Acceleration is a much over-worked & misused term in rowing. It sounds
so important of itself that folk think it must mean something vital.
Acceleration (& its mirror, deceleration) are names we give to rates of
change of velocity. When launching a space probe, acceleration _is_
vital as without it you will not reach the velocity either to achieve
earth orbit, or to escape that orbit. When driving a race car,
acceleration is also vital, if we may ignore a host of other factors,
since it determines who gets ahead before the first corner, who can pass
whom & who may out-brake whom (deceleration). In rowing it only matters
for about the first 7 strokes - the time it takes to reach cruising
speed. Thereafter you will go no faster & will hope also to go no slower.
Sure, the boat's speed does vary about its mean cruising speed
throughout every stroke. But that's a reflection of teh fact that its
mass is so much less than that of the crew. The velocity of the
combined system's C of G varies by much less - because boat is more like
the shoes of the runner or the boots of a skater. Like them it serves
to support you above your chosen medium (land, ice or water) &, like
them (& so unlike the race car), it is a lightweight sub-component,
securely attached to your feet, with no choice but to go where your feet
go & thus to come along for the ride.
Which pinpoints one of the sadly ignorant ways in which rowing's
dynamics are misunderstood & mis-taught. Were your boat a 1 tonne mass,
& just suppose it incurred no more fluid drag than your single with you
sat upon it (which could not be true), you'd then be spending a lot of
the time & effort in each outing in just accelerating it gradually up to
race pace - because at that speed it'd be storing >71 times as much
kinetic energy as is averagely stored in your 14kg boat at the same
speed. (Since the combined mass of you + boat in this thought
experiment would be almost 13 x greater than normal, it would take you
>90 strokes to hit race pace). And, being so much heavier, the boat
would scarcely fluctuate in speed through each stroke. Crazy?
Yet that's exactly how all those folk who talk about needing to
"accelerate the boat each stroke" would seem, if logic intruded upon
their analyses, to view the relationship between boat & crew - as if the
boat was where all the mass was concentrated & the mass of the crew was
immaterial. As I've said elsewhere, who cares about accelerating the
running shoe? Or the skate, or even the rower's socks? So who, after
those first few strokes, should care about accelerating the boat?
Firstly, the boat is not the major mass component in the system, you
are. Secondly, after the catch it is an inescapable fact that you will
accelerate _more_ than the boat, otherwise you would not be moving away
from the stretcher.
So, if it ain't going to be possible to accelerate either you or the
boat to beyond a certain mean velocity, you need then to concentrate on
_reducing_ both the accelerations & decelerations in the boat's velocity
(&, of course, in yours) about that mean.
I never said that understanding the inertial interplays in rowing would
be straightforward. But that does not excuse the widespread, &
sometimes aggressively defended, misunderstandings of the dynamics of
the rowing stroke. Applying a bit of simple science might help clear
the air, leading to better insights &, perhaps, to better rowing &
reduced injury.
Carl Douglas
Let's break this down into its parts?
As you reach the finish, the body should be brought to a halt WRT the
boat by the force of your hands pulling on the oars. In which case
there are no inertial consequences to resolve, only the much lesser
issue of the quite small change in location of rower's C of G from the
mean between astern & ahead. Inertial effect may sometimes intrude, as
in a small number of crews & scullers whose bodies do a bow-wards
genuflections just after or during the extraction. It surprises me that
this fault goes un-noticed by their coaches or, if noticed, is thought
OK, for its inertial consequence is to bounce the bows.
As for the statics, the levers & moments issue, at the finish. Even in
a 1x the difference between the location of the C of G at the finish &
that when sat up normally, as one does in a boat is surprisingly small.
The legs are extended in both cases, so no changes due there, & the
back does not go so very far from the vertical in most finishes. So the
difference in static trim between finish & hands fully away is very small.
Next consider the flow around the hull. Its parting around & under the
bow tends slightly to lift the forward part of the boat &, by acting at
the very end of the boat, has a large moment which can & does amply
support the modest shift in C of G just discussed.
Now to the recovery. There are those who rotate a straight body up &
out of the bow from the hips - which certainly has inertial consequences
tending to thrust the bow downwards. But is that necessary? I think
not. A good recovery lets the hands go first, it does not seek to raise
the height of the upper body's C of G but, rather, the head moves
towards the stern at a constant level & the back bends forwards, led
smoothly by the arms, then shoulders, then the lower back as the trunk
curls over. After all, the object is for the boat to run smooth &
level, so there's no point in recovering in a way which increases the
height of the C of G as that must always bounce the boat. Nor, for a
smooth & swift recovery, is there any ergonomic advantage in suddenly
moving the body out of the bows ('though we keep hearing of crews being
told to do just that, "Because it gets the weight out of the bows").
And the adverse consequences of bouncing the boat, in terms of energy
losses, are significant - as you see from the waves that spread if you
bounce a stationary boat by shrugging your upper body.
Now understand that at the recovery you are _not_ moving the body. The
rower, as we agree, is a relatively massive object. It is the major
mass of the entire system by far, with nothing (during recovery) of
sufficient mass against which to react with enough resistance to support
large sternwards accelerations of any significant part of the body.
Despiute how it appears superficially, in reality during recovery the
rower's body simply curls up from its extended into its contracted form
as the feet draw the boat underneath it.
One pair of varying force couples remain to be considered:
1. the interaction between the total drag force acting on the submerged
surface of the hull & the Newtonian reaction of that force summed over
every part of the body. But that couple applies during stroke &
recovery, being greatest at the finish (where the boat is moving fastest
& incurring most drag) & correspondingly least at the catch. You have
limited scope to alter it, but it would be worth understanding that it
exists.
2. The force acting across the blades during the stroke, which acts a
little bit lower in the water than the drag force on the hull & thus
introduces another couple of varying magnitude during the stroke,
reaching zero at the finish.
I'm sure I've missed something in that list, but I trust it helps to
explain my earlier statement?
Carl Douglas
We will agree that at no point are all parts of the body, boat & blades
not moving WRT each other, & that there may be vertical motions even
when there is almost no horizontal movement. There will, however, be
points where the relative motions are slight &, ignoring 2nd-order
effects, it is those that we take as points of zero relative motion.
Re hand movement at the catch: for there to be no check due to
back-watering, the blade must already be swinging around the pin at a
velocity approximating to the boat speed x the cosine of its angle ahead
of perpendicular, so hand velocity must always be greater than zero at
the catch & the hands must begin moving a little bit before the catch is
taken. Further: to get any load on the blade requires you to bend the
shaft, which requires more hand movement, such that hand speed
throughout the loading process exceeds what that simple equation
suggests. Even then, hand speed will continue to be influenced by the
blade's effective angle of attack WRT the shaft &, due to the shaft's
elasticity, by variations in the load at the hands.
At which point a further consideration intrudes: the higher the load,
the more the oar is bent backwards around the pin, which significantly
changes the blade's angle of attack WRT to water flow. But we never
give that the slightest consideration.
As I was indicating previously, while most try very hard to pretend that
things like these are immaterial to our performance, that cannot really
be true. Nor is it beyond the wit of science to analyse what is going
on & reach conclusions which could lead to improvements in technique &
performance.
Walter Martindale
wrote:
Hi
This might help... Refer to http://www.rowingnz.com/Resource.aspx?ID=56
The graph is on page 2.
The mish-mash of velocities at the finish part of these curves is most
likely due to the quality of the data collection (it's from 1981, and
from a really small image, digitized from a 16 mm film)
I don't have time to read Carl's stuff (below) as I'm packing to move
from Karapiro to Christchurch...
Walter
ATP*
"Carl Douglas" <ca...@carldouglas.co.uk> wrote in message
news:7bbpg4F...@mid.individual.net...
effect enhances the overall progress of the system is certainly
wrong-headed. However, it does seem that all other things being equal, a
shell equipped with a sliding rigger would be ever so slightly more
efficient if only due to the fact that the rower's torso is staying in the
same place relative to the hull.
Charles Carroll
I wonder if it isn't slightly overreaching to draw an analogy between
running shoes and a flat water racing single. I am having some trouble
finding similarities between them. Let me explain.
My brother-in-law, Gordon Campbell, was a significantly gifted athlete in
the late 1960s when he was at Carlmont High School, which is in Belmont.
Belmont is a small town about half way between Mike and me, that is, about
half way between San Francisco and Palo Alto.
Anyway my brother-in-law was a sprinter. I believe his events were the 100,
the 440, and the 880. By the time he was in his second year of high School,
about 15 years old, articles were being written about him in the San
Francisco Chronicle and other newspapers. He was immensely powerful, very
fast, and winning just every event he entered.
Now, you may ask, why write about the long ago glory days of my
brother-in-law? And the answer is because my brother-in-law didn't wear
running shoes. Gordon ran barefoot.
And now, if I may ask, have you ever heard of a sculler winning a race
without sculling his flat water racing single? Assume for the moment the
ridiculous. Visualize a sculler who can swim faster than anyone can scull.
Could this sculler/swimmer legitimately compete against other scullers and
claim to have beaten them by sculling faser than they can scull? Of course
not! But he can swim faser than they can scull.
Am I wrong, then, in thinking that a flat water racing single is much more
important to a sculler than a pair of running shoes is to a runner? You can
run without shoes. But can you scull without a scull?
In my hopelessly prosaic mind it seems to me that the point of sculling is
to move your boat faster than the guys next to you can move theirs. Running
may not be the art of moving your shoes, but how can anyone say that
sculling isn't the art of moving a scull?
Now, for the next point, it seems to me that our thinking about how to race
a flat water racing single is not all that different. For me the idea is
twofold. First, in the initial seven or so strokes get the shell up to an
average mean velocity that you can sustain for the rest of the race. And
second, within each stroke reduce as much as possible the difference between
maximum and minimum boat velocity.
But I believe, if I am not mistaken, that you have said all this many times
over the years.
So I will go on to my next concern, which is the idea that one should not
try to accelerate the boat. I have found a video of the 1956 Olympic 1x Men's
Final in Melbourne. I suspect you have seen it. It is the race where
Vyacheslav Ivanov won his first gold medal. He was 18 years old and was "in
fourth place at the 1,500 meter mark. With only 500 meters left, he began a
devastating sprint, first catching Poland's Teodor Kocerka, then American
John B. Kelly, Jr. Finally, with 200 meters to go, he blew past fellow
teenager Stuart Mackenzie of Australia who had led the entire race."
(Wikipedia) Vkyacheslav's devastating sprint begins about two minutes into
the video.
Try as I might I cannot watch this video without thinking that as Vyacheslav
rows through these three competitors he is producing "a time rate of change
in velocity."
Thus I keep coming back to the same question. If Vyacheslav wasn't
accelerating his shell, how could he row through these guys?
So, as you can see, I am still stuck in the same place that I was yesterday.
It still seems to me that the question is not whether to "accelerate" the
boat, but rather "how" to accelerate it.
So how does Vyacheslav accelerate his boat?
Does it accelerate it by pulling harder? Not from what I see in the video.
Quite the contrary, it looks to me that Vyacheslav doesn't actually change
anything about his drive. He remains long, the pressure he puts on the pins
remains constant, and, perhaps most importantly, he remains relaxed at the
catch and continues to stay relaxed through the entire drive.
Then what does Vyacheslav do to accelerate his boat?
To my eye the only thing he does is change the recovery, which he speeds up
significantly. Just look at his stroke rate compared to the guys he is
rowing through. So how does he get this stroke rate? He looks to me that
Vyacheslav produces it in the recovery.
But look at the video, Carl, and tell me what you see. I am always a little
afraid to comment on video. I seem to miss so many things that everyone else
on rsr sees.
In any event, I want to return to the point I tried to make yesterday. Are
we talking about whether Vyacheslav accelerates his boat? I don't think so.
It seems to me that acceleration is a given.
So if we are not concerned with whether Vyacheslav accelerates his boat,
then what are we concerned with? The only answer I can come up with is
"how." What I keep returning to is "how" Vyacheslav accelerates through
these three formidable competitors.
Cordially,
Charles
Alexander Lindsay
"Charles Carroll" <charles...@comcast.net> wrote in message
news:7bd37nF...@mid.individual.net...
> Carl,
>
snip
Charles
I am afraid there is a fundamental confusion between acceleration and
velocity. To overtake someone you need a higher velocity (i.e to go
faster). You don't have to be accelerating.
In outline, what you see on the video is at first all the scullers going at
roughly the same mean velocity, with zero mean acceleration.
Then Ivanov accelerates, probably for only two or three strokes, i.e. his
velocity increases to be greater than the others. That actually doesn't
take much effort: a slight increase in kinetic energy.
Then, because his velocity is greater, he overtakes them. He is not
accelerating, he is just going faster.
But that's the remarkable bit, because, by going faster he increases the
drag on his boat, and therefore must be working very much harder.
The point Carl is making, I think, is that to win you need to have a higher
velocity, not to be accelerating. Accelerating is, by definition, necessary
if you want to increase your velocity, as Ivanov did briefly, and as
everyone does at the start. But once you have reached your intended
velocity, you want as little acceleration as possible as variations in
velocity waste energy.
I suspect this would all be much easier to understand if we didn't call the
velocity pedal in our cars the "accelerator".
I will leave the shoe analogy to Carl.
Alexander
Carl Douglas
But only if that situation carried real advantage with it. We can posit
all manner of things which, because they have a pleasing aspect, we
think ought to be "right" (e.g. not looming), but unless we analyse them
and can quantify whatever benefits we suppose they may bring, they are
worth no more than any other such notion.
In an activity such as rowing, in which load is intermittently applied,
it may actually make more sense to operate an energy storage & return
system involving a sliding mass. In rowing, that sliding mass happens
to be you.
AFAIK, there is no statistical evidence to suggest that the sliding
rigger made for faster times in international competition. It'd be
pleasing to some of us if it did, but we must work with the evidence,
not our wishes.
MagnusBurbanks
> ATP* wrote:
> > "Carl Douglas" <c...@carldouglas.co.uk> wrote in message
> URLs: www.carldouglas.co.uk(boats) &www.aerowing.co.uk(riggers)- Hide quoted text -
>
> - Show quoted text -
To quote Carl:
“AFAIK, there is no statistical evidence to suggest that the sliding
rigger made for faster times in international competition. It'd be
pleasing to some of us if it did, but we must work with the evidence,
not our wishes.”
There may not be any data around about sliding rigger systems, but my
guess is that it’s mostly because at the time FISA outlawed them, the
internet did not exist. There are good theoretical reasons to suggest
that sliding rigger systems make for faster scullers, though.
Carl again:
“The boat is 1/5 of your weight, so it, not you, is already the most
accelerated/decelerated item. And the more that you cause its velocity
to fluctuate by your efforts to accelerate it, the less & less
efficiently it moves.”
Correspondingly, the *less* you cause the boat’s velocity to
fluctuate, the *more* efficiently it moves. With a sliding rigger
racing shell, the sliding rigger will weigh an order of magnitude less
than the boat, because ~90% of the system’s mass comprises the boat
which now includes the rower. So the acceleration/deceleration
resulting from momentum transfer from the sliding rigger to the boat
will be small. Thus, using Carl’s own line of reasoning, one should
expect the sliding rigger system to be more efficient.
Magnus
Carl Douglas
Charles -
I can't improve on what Alexander has said, but I can flannel on a bit
further ;)
In every stroke there are accelerations & compensating decelerations, so
that you return to the much same speed at the same point on every
stroke. So, no net acceleration there, just the exact cancellation of
the integrals over time of the positive & negative accelerations.
When you need to pass the guy with whom you are currently level-pegging,
there is only one way: you have to increase your average velocity for a
sufficient period to establish the lead you require. That is a minute
acceleration imposed on the boat/crew system as a whole, not on any one
part of that system which will demand, as Alexander has said, a
substantial & _sustained_ increase in your power output.
To put things into perspective:
During every stroke your boat experiences accelerations & decelerations
quite close to those imposed on a falling body by Earth's gravity, g -
as you see from the loads visibly encountered by coxes. In contrast, to
raise boat speed by 1% (say by 5 cm or 2" per second) over the period of
a single power stroke demands an acceleration by the system as a whole
of ~0.005g. That really is piddlingly minute. However, the price of
achieving this increase in mean speed is an increase of ~3% in your
power output.
Now you may think that a 1% increase in mean speed is trivial, but over
2k that amounts to 20m, or ~2 1/2 lengths of your single.
Just to complete the circle, if A gains 1 length on B over 5 strokes
(say 8 seconds) without B going any slower, that represents a step
change in speed of 1m/s. Since that's a good 20% increase in speed,
then for those 5 strokes he has to be working at an incredible >70%
harder than before his sprint. But even so, if that acceleration was
achieved over the period of 1 second, it imposed only 0.1g on the system
- & only for that 1 second.
Finally to kill, if I may, your preoccupation with boat accelerations:
If the boat accelerates over time more than you do, you will no longer
be sitting on it as it will have moved out to somewhere ahead of you.
So the time integral of its accelerations & decelerations has,
absolutely has, to match yours - if it accelerates more, it must also
decelerate more. Them's the rules!
I used the example of runners' socks & shoes as parallels for the boat &
you tried to wriggle out by reference to the barefoot runner. A nice
try, but bound to fail, I fear. May I now replace the footwear with the
foot itself? Again, the boat moves with the feet, & has no choice in
the matter.
Carl Douglas
> rigger made for faster times in international competition. It'd be
> pleasing to some of us if it did, but we must work with the evidence,
>
> There may not be any data around about sliding rigger systems, but my
> internet did not exist. There are good theoretical reasons to suggest
> that sliding rigger systems make for faster scullers, though.
We have paper records which are no less valid than the electronic data
that feeds the internet, & nowhere have I yet seen evidence of a step up
in boat speeds for the period in which the sliding rigger was used in
international competition, nor of a step down in speeds when its use ended.
>
> Carl again:
>
> �The boat is 1/5 of your weight, so it, not you, is already the most
> accelerated/decelerated item. And the more that you cause its velocity
> to fluctuate by your efforts to accelerate it, the less & less
> efficiently it moves.�
>
> Correspondingly, the *less* you cause the boat�s velocity to
> fluctuate, the *more* efficiently it moves. With a sliding rigger
> racing shell, the sliding rigger will weigh an order of magnitude less
> than the boat, because ~90% of the system�s mass comprises the boat
> which now includes the rower. So the acceleration/deceleration
> resulting from momentum transfer from the sliding rigger to the boat
> will be small. Thus, using Carl�s own line of reasoning, one should
> expect the sliding rigger system to be more efficient.
>
> Magnus
That argument I had already partly answered by pointing out that the
sliding seat gives you a cyclic energy storage system which is not
available (not to anything like the same extent) with the sliding
rigger. In both systems you have a period during which the blades are
doing no work. In the sliding seat, unlike the sliding rigger, system
you have the chance to make an intelligent work input by means of which
to sustain boat speed.
As I have said, the inertial interactions in rowing are somewhat complex....
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
MagnusBurbanks
>
> >> - Show quoted text -
>
> > To quote Carl:
>
> > rigger made for faster times in international competition. It'd be
> > pleasing to some of us if it did, but we must work with the evidence,
>
> > There may not be any data around about sliding rigger systems, but my
> > internet did not exist. There are good theoretical reasons to suggest
> > that sliding rigger systems make for faster scullers, though.
>
> We have paper records which are no less valid than the electronic data
> that feeds the internet, & nowhere have I yet seen evidence of a step up
> in boat speeds for the period in which the sliding rigger was used in
> international competition, nor of a step down in speeds when its use ended.
>
>
>
>
>
>
>
> > Carl again:
>
> > accelerated/decelerated item. And the more that you cause its velocity
> > to fluctuate by your efforts to accelerate it, the less & less
>
> > Correspondingly, the *less* you cause the boat’s velocity to
> > fluctuate, the *more* efficiently it moves. With a sliding rigger
> > racing shell, the sliding rigger will weigh an order of magnitude less
> > which now includes the rower. So the acceleration/deceleration
> > resulting from momentum transfer from the sliding rigger to the boat
> > expect the sliding rigger system to be more efficient.
>
> > Magnus
>
> That argument I had already partly answered by pointing out that the
> sliding seat gives you a cyclic energy storage system which is not
> available (not to anything like the same extent) with the sliding
> rigger. In both systems you have a period during which the blades are
> doing no work. In the sliding seat, unlike the sliding rigger, system
> you have the chance to make an intelligent work input by means of which
> to sustain boat speed.
>
> As I have said, the inertial interactions in rowing are somewhat complex....
>
> 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
> URLs: www.carldouglas.co.uk(boats) &www.aerowing.co.uk(riggers)- Hide quoted text -
>
>
> - Show quoted text -
I admit that I have seen no data, but I know that testing even a very
simple change to boat set-up to identify a marginal change in average
velocity is notoriously difficult as it's impossible to guarantee a
rower will repeat him/herself from piece to piece.
I stand by my use of your arguments re efficiency. The point about the
greater efficiency of sliding rigger vs sliding seat is that with the
sliding seat, it's the smaller-mass / much-greater-velocity-
fluctuation part that is in contact with the water and producing the
scaled-with-velocity-squared (cubed? I forget) energy losses. By
largely eliminating this source of water-contact velocity fluctuation,
a significant amount of energy loss is prevented.
I don't fully understand when you write "In the sliding seat, unlike
the sliding rigger, system you have the chance to make an intelligent
work input by means of which to sustain boat speed" but I interpret
that you are saying that energy savings from the reduced velocity
fluctuation would be offset by intelligent movement management with
the sliding seat?
However, I can quite see that there may well have been significant
frictional energy losses given the engineering of the late 70s/early
80s, the lack of development money involved and the clunkiness of the
sliding rigger setups.
Yours all out of hyphens, Magnus
MagnusBurbanks
zeke_hoskin
>
> >> - Show quoted text -
>
> > To quote Carl:
>
> > rigger made for faster times in international competition. It'd be
> > pleasing to some of us if it did, but we must work with the evidence,
>
> > There may not be any data around about sliding rigger systems, but my
> > internet did not exist. There are good theoretical reasons to suggest
> > that sliding rigger systems make for faster scullers, though.
>
> We have paper records which are no less valid than the electronic data
> that feeds the internet, & nowhere have I yet seen evidence of a step up
> in boat speeds for the period in which the sliding rigger was used in
> international competition, nor of a step down in speeds when its use ended.
>
>
>
>
>
> > Carl again:
>
> > accelerated/decelerated item. And the more that you cause its velocity
> > to fluctuate by your efforts to accelerate it, the less & less
>
> > Correspondingly, the *less* you cause the boat’s velocity to
> > fluctuate, the *more* efficiently it moves. With a sliding rigger
> > racing shell, the sliding rigger will weigh an order of magnitude less
> > which now includes the rower. So the acceleration/deceleration
> > resulting from momentum transfer from the sliding rigger to the boat
> > expect the sliding rigger system to be more efficient.
>
> > Magnus
>
> That argument I had already partly answered by pointing out that the
> sliding seat gives you a cyclic energy storage system which is not
> available (not to anything like the same extent) with the sliding
> rigger. In both systems you have a period during which the blades are
> doing no work. In the sliding seat, unlike the sliding rigger, system
> you have the chance to make an intelligent work input by means of which
> to sustain boat speed.
>
> As I have said, the inertial interactions in rowing are somewhat complex....
>
> 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
> URLs: www.carldouglas.co.uk(boats) &www.aerowing.co.uk(riggers)
Sliding seat has the advantage, as Carl points out, of much of the
hull's
velocity fluctuations being canceled out because the rower moves
backwards
wrt the hull during the time of no net power input.
Sliding rigger has the advantage of much lower center-of-mass
fluctuation,
to the extent that it is markedly and, undoubtedly, measurably
superior in a
short boat. (And, I'd guess, would work with hydrofoils).
Short boats have a huge advantage off the water, which is after all
where they
spend most of the time being stored or transported. I would personally
love
it if the powers that be ruled that sliding rigger boats were legal,
but
restricted to, say, 5.5 meters for singles.//Zeke
Mike De Petris
> Sliding rigger has the advantage of much lower center-of-mass
> fluctuation,
> to the extent that it is markedly and, undoubtedly, measurably
> superior in a
> short boat. (And, I'd guess, would work with hydrofoils).
>
> Short boats have a huge advantage off the water, which is after all
> where they
> spend most of the time being stored or transported. I would personally
> love
> it if the powers that be ruled that sliding rigger boats were legal,
> but
> restricted to, say, 5.5 meters for singles.//Zeke
will we see sliding rigger as best setup for coastal rowing?
boat mass is much bigger and lenght is shorter, so it seems to suggest
it would be great, not to tell about keeping your mass center while
riding big waves!!
Andrew Hodgkinson
> The boat is just a piece of lightweight kit [...but imagine it were
> much heavier...] that's exactly how all those folk who talk about
> needing to "accelerate the boat each stroke" would seem, if logic
> intruded upon their analyses, to view the relationship between boat&
> crew - as if the boat was where all the mass was concentrated [...]
I've only ever had coaches mention "accelerating the boat" when talking
about ways to best deliver power through the stroke. A popular given
analogy is that of spinning the wheel of an upturned bike. To get the
best speed, one would not grab the wheel, stopping it, then spin it, then
stop, then spin and so-on. Instead, one would keep tapping the wheel to
keep its velocity up, letting it free-wheel (for minimum deceleration)
between the taps.
Not everyone may like that analogy, but if rowers understand it, then it
seems a reasonable way of explaining the thing you ask for - with which I
completely agree, by the way:
> So, if it ain't going to be possible to accelerate either you or the
> boat to beyond a certain mean velocity, you need then to concentrate
> on _reducing_ both the accelerations& decelerations in the boat's
> velocity (&, of course, in yours) about that mean.
Broadly, that's just how I've been coached. Associated with this are
topics such as avoiding check with a fast catch, how to best move the
body from finish back to catch again and so-on. This then turns into a
multitude of heavily debated topics concerning rowing technique, the
attempted perfection of which keeps the sport interesting for many of
its participants I suspect.
I've not been coached by anybody who seems to think that the boat is
constantly accelerating and that all efforts must be put into lugging
through as big a stroke as possible and hang the consequences - quite
the contrary. So perhaps coaching in general isn't in quite such an
unsatisfactory state as this thread might lead a casual reader to believe?
> Applying a bit of simple science might help clear the air, leading to
> better insights&, perhaps, to better rowing& reduced injury.
I can't imagine anyone arguing with you there! Thing is, though, I think
that's what most of the coaches I've met really *are* trying to do.
Walter Martindale
I speak about "accelerate the handles" during the drive. Or, "Hang on
for dear life at the catch while you load up with pressure on the foot
stretcher, and then make the handles go faster and faster all through
the stroke until you take the blades out." but I don't use "accelerate
the boat." How about "feel the boat moving under/with you"
If you look at point of view - the sliding rigger is either attached
to your hull or sliding around independent of the hull. Your feet
move the rigger back and forth wrt you whether it's attached to the
boat or sliding around on the boat, and your butt on the seat moves
back and forth wrt the rigger whether it's attached to wheels or
attached to the hull. AFAICF (can figure) the only difference between
the two movements is the displacement or non-displacement of the
sculler's centre of mass during the drive/recovery, which contributes
more or less, respectively, to the boat pitching at each end of the
stroke.
Gotta go - still packing to move house...
What's the point, really, of going on about sliding riggers? They're
not permitted in international competition, so athletes with ambitions
for international competition should learn to be the most efficient
they can be in a sliding seat, fixed rigger boat. To do otherwise is
to waste valuable training time.
IMO, anyway.
Walter
Carl Douglas
Magnus -
I've got a bag of hyphens hiding away somewhere. When I find them, I'll
send you a few ;)
There is one objective test of what is the most effective equipment -
does it lead to faster race times. If it does not seem to do so, the
jury can deliver no verdict better than the Scottish "Not Proven".
There is much emotional attachment within rowing to the twin ideas that
a) the sliding rigger was a faster way to scull & b) it was cruelly done
to death for that reason. I believe there is no evidence in favour of
proposition a), while proposition b) is quite untrue. It was dropped
because it was paraphernalia which, while interesting, gave no apparent
benefits. We can construct all manner of arguments to the contrary, but
it does seem that these must fail the test.
Now you suggest that equipment used in making sliding riggers in the
early '80s must have been clunky & an energy sink. Absolutely not!
Recirculating linear ball-bearing systems were used whose energy losses
were low then & could not be significantly lower now, if at all.
So let me try to explain this a little better:
During the whole stroke you do sufficient work to overcome a certain
average level of fluid resistance whose value at any instant is
(roughly) proportional to the square of boat velocity (sure there are
other non-linear resistance terms, including those due to wave-making,
wind resistance & to the inertia of the mass of fluid in the boundary
layer which is interacting with the fluctuating boat speed to modify
fluid drag). Whether you have a sliding rig or a sliding seat, you only
do propulsive work against the water for <50% of the total stroke cycle.
So for the other >50%, you & the boat are coasting, being decelerated
by that same non-linear drag force & in effect just running down.
In a sliding rig boat, since you can move no meaningful mass during the
recovery you can do nothing at all to alter that rate of run-down. With
a sliding seat, to bring the frontstops to you (not that I don't talk
about sliding up to frontstops) you can & must pull on your feet with
more than the force that, through the boat's deceleration & Newton's
laws, holds you at backstops. If you do that, you do work which will to
some degree sustain the motion of the boat as you draw it past your own
C of G. In that way you have the opportunity, if you get that recovery
right & don't blow it all by a sloppy or delayed catch, by interacting
inertially with your large mass, to reduce & not increase the range of
the boat's speed fluctuations.
I am not proposing that you will do any more work (although it is at
least plausible that you will, since you are using different muscle sets
to make your recovery by drawing on your feet) but that here you do have
the chance, not available with the sliding rigger, to control your
movements in such a way as to iron out your boat's velocity
fluctuations. Which ought, as they say in "1066 and All That", to be a
Good Thing.
I was one of those rather disappointed by the failure of the sliding
rigger to break the mould - it would have been fun. But I try to avoid
kidding myself that what didn't present any kind of a breakthrough was a
natural-born winner that was cruelly killed off only by institutional
prejudice & poor technology. That's just another grassy knoll, I'm afraid.
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
Charles Carroll
Once again I find myself am indebted to you. You have such a lovely, clear
way of writing. Immediately upon reading your post I saw my error.
I wrote: "If Vyacheslav wasn't accelerating his shell, how could he row
through these guys?"
What I should have written was: If Vyacheslav "hadn't accelerated" his
shell, how could he have rowed through these guys? The verb tense is
critical.
As you have so gently and lucidly reminded me, "To overtake someone you need
a higher velocity (i.e. to go faster). You don't have to be accelerating."
Thank you again,
Charles
Charles Carroll
> for dear life at the catch while you load up with pressure on the foot
> stretcher, and then make the handles go faster and faster all through
> the stroke until you take the blades out." but I don't use "accelerate
> the boat."
But Walter,
"From the moment the blades touch the water the boat must accelerate."
(Richard Tonks, "Rowing Faster," p. 171)
Cordially,
Charles
Walter Martindale
wrote:
Yup..
I spent the last several months sitting across the partition from Mr.
Tonks. While we say things differently we generally (seem to) agree
on technique... I'm working on my third copy of Rowing Faster - first
one was bought from me by Recep Akici, second one is packed for the
move to Christchurch, and the third one stayed behind at Rowing New
Zealand's office...
I think it is the difference between what a person who rowed for many
years (still does) and coaches gold medal winning crews (what's been
going on at Henley and Munich with them kiwi crews, ennyhoo?) and the
language that he'd use, versus the language that a person in physics/
biomechanics/engineering might use.. Carl's an engineer, I've been
involved in biomechanics - "acceleration" means something to us, and
something different to people who have different backgrounds.
Just because what Dick says may not jive with what an engineer says
doesn't make the crews he coaches go any slower.
Walter
Carl Douglas
Charles -
Nice try! But you're nibbling away at what, I fear, is a non-existent
biscuit ;)
Will you allow words used in a scientific context to have precisely
defined scientific meanings, or would you prefer, as orators do, that
they mean whatever one wants to persuade an audience they might possibly
mean?
At & immediately after the catch the boat (or the ankle bone, if you
wish) does not accelerate forwards. There is almost always a check or
deceleration on the boat, While it continues moving towards the far end
of the course, for that brief period it does so at a temporarily reduced
velocity. It has decelerated. Depending on how the catch is taken, it
may be that nothing except the rower's hands, or bum, do actually
accelerate towards the finish line.
Only after that initial check do we see sometimes quite sharp
accelerations but these are first in various body parts, depending on
stroke technique. That is because the rowing stroke is a form of
lifting yourself by your bootstraps - a trick for levering the body, not
the boat (please note), past a notional (& non-fixed) point in the water
by doing work which transfers kinetic energy into the boat/blades/crew
system but, principally, into the crew. And that's what you see: the
crew go forward towards the bow of the boat. You do not necessarily see
whether the boat is accelerating or not but, because the crew has moved
WRT the boat, you sure as heck know that their bodies have accelerated
more than the boat.
What Mr. Tonks may have said will be how he feels it to be but,
unfortunately, his interpretation is technically quite wrong. He, like
every other rower (& almost all of us is a far lesser rower than him) is
in the business of accelerating (= kinetically energising) his personal
C of G from the instant of the catch. He is not in the first instance
accelerating the boat, except coincidentally & by the bye, & certainly
not at the catch. Rather, he is using the interesting system of pivots
& levers which is the boat, riggers, blades & all the bits of his own
body as a mechanism by which to counter-balance the forces he is
generating such that they will result in a force of reaction between the
water & the blades, without which he could do no useful work.
Like most rowers, Tonks will not see it this way. He will see it to
some degree as he has been coached to see it. And he will naturally
believe it to be so.
Similarly, he will have views on other aspects of his stroke that may
make perfectly good sense to rowers at large but which do not correctly
represent what is really going on, or actually fly in the face of real
evidence.
Thus we coach rowing through a fog of misunderstanding. And one of the
foggier bits, despite all the experimental evidence to the contrary, is
the way we cling insistently to the notion that the stroke is all about
moving & accelerating the boat. It isn't. It's about applying useful
work to overcome fluid friction by what we hope will be the most
efficient means. But it remains foggy because we persist perversely in
kidding each other that it just _must_ be like this, when really that is
& cannot be correct. Thus by limiting our proper understanding of all
the complex process involved, & by preferring naive, faith-based
simplifications over research & real knowledge, we limit our potential
achievement.
Still, 'tis only a game.
Walter Martindale
>
> Still, 'tis only a game.
>
> Cheers -
> Carl
No it's not! Athletes row. Everyone else just plays games.
Walter
Charles Carroll
All Richard Tonks says is that "From the moment the blades touch the water
the boat must accelerate."
It seems to me that it might be simpler if we, like Richard Tonks, focused
on just one thing at a time. Would it be amiss to limit our discussion - if
only for the moment - to what the boat is doing without involving ankle
bones, hands, bum, oars, blades, sliding seats, complicated levers, etc.
etc, etc?
Let's consider just the bow ball as it travels towards the finish line. Let's
assume that all other variables remain constant. The stroke rate remains
constant. The pressure applied against the pins remains constant. The ratio
between the recovery and leg drive remains constant.
Now what happens to the bow ball as it moves towards the finish line? If you
measure the bow ball at different points in the stroke, do you get a
constant velocity? Or does its velocity vary according to where you measure
it? If the latter, then at what point in the stroke is it moving the
fastest? And at what point is it moving the slowest?
Hasn't simple observation yielded answers to these questions? Doesn't the
bow ball reach its highest velocity right after the release? And doesn't it
reach its lowest velocity at the catch?
Now how does a bow ball move from a lower velocity to a higher velocity
without accelerating?
Is it "unscientific" to think that an object moving from a higher velocity
to a lower velocity is decelerating? Is it "unscientific" to think that the
reverse is equally true - if an object is moving from a lower velocity to a
higher velocity it is accelerating? After all, isn't acceleration defined as
the rate of increase in velocity per unit of time?
So why is it incorrect to say that a bow ball during the leg drive is
accelerating? This is really all I am asking.
I cannot believe that we are all that far apart on this idea. It seems to me
that a bow ball decelerates during the recovery and accelerates during the
leg drive. Moreover to produce an average mean velocity per stroke of the
bow ball with respect to the finish line, any acceleration during the leg
drive must compensate for any deceleration during the recovery.
Aren't you saying as much when you write that "In every stroke there are
accelerations & compensating decelerations?"
Or when you write: ". . . you return to much the same speed at the same
point on every stroke." Doesn't the very idea of "returning" to much the
same speed on every stroke presuppose acceleration and deceleration?
Isn't the idea of rowing well to find a rhythm that keeps the amplitude
between these velocities as small as possible, and that allows us to
reproduce the same mean average velocity per stroke for every stroke in a
piece? As you write, "no net acceleration there, just the exact cancellation
of the integrals over time of the positive & negative accelerations."
By the way, what is "net acceleration?" I am not clear on the term at all.
The OED defines acceleration as ". . . in Nat. Phil. the rate of increase in
velocity per unit of time." So by "net acceleration" do you mean the net the
rate of increase in velocity per unit of time? I do not mean to be such a
dunderhead but for the life of me I cannot think of an example.
And another question: why is it of such great consequence to say that Mr.
Tonks "is in the business of accelerating (= kinetically energising) his
personal C of G from the instant of the catch?"
Please understand that I am not disagreeing with what you are saying. I,
too, think it is the rower's business to accelerate his personal C of G.
Nevertheless I wonder if this isn't subordinate to a higher end - namely, to
rowing your bow ball across the finish line ahead of the other guy's. How he
or she manages to accomplish this certainly involves accelerating his C of
G. But doesn't the fact remain that the entelechy of rowing is a bow ball
moving forward?
Warmest regards,
Charles
Mike De Petris
wrote:
> Hasn't simple observation yielded answers to these questions? Doesn't the
> bow ball reach its highest velocity right after the release? And doesn't it
> reach its lowest velocity at the catch?
No. You are wrong. You didn't observe well.
Carl Douglas
> Carl,
Charles -
Although i do think this is a dead horse, for you I am happy to flog it
a bit longer ;)
>
> All Richard Tonks says is that "From the moment the blades touch the
> water the boat must accelerate."
Then he is wrong.
Please see Walter's very clear graphical depiction of velocities of
boat, sculler & total system:
http://www.rowingnz.com/Resource.aspx?ID=56
This parallels other such data recorded by other researchers, yet rowers
at large ignore it & its significance. For the 1st ~1/4 of the power
stroke the boat's velocity is falling. That is real deceleration. Period.
In contrast, for the 1st 2/3 of the stroke the rower's CofG is
increasing its velocity - it is accelerating. And it is accelerating
more than the total system (which has to be true, since the system's
accelerations will be close to the mass-weighted mean of those of boat &
crew).
>
> It seems to me that it might be simpler if we, like Richard Tonks,
> focused on just one thing at a time. Would it be amiss to limit our
> discussion - if only for the moment - to what the boat is doing without
> involving ankle bones, hands, bum, oars, blades, sliding seats,
> complicated levers, etc. etc, etc?
I would be amiss to do so.
The bowball is rigidly connected to the rest of the boat, so it
accelerates just as the boat does. Your toes are also fixed to the
boat, so they too move in lockstep with the boat. And your ankle bones
are not that much disconnected from the boat, so their accelerations
closely match those of boat, bowball, etc. In short, you cannot
disconnect those items since they are all bound to move in synch. They
therefore represent that one thing of which you speak.
>
> Let's consider just the bow ball as it travels towards the finish line.
> Let's assume that all other variables remain constant. The stroke rate
> remains constant. The pressure applied against the pins remains
> constant. The ratio between the recovery and leg drive remains constant.
>
> Now what happens to the bow ball as it moves towards the finish line? If
> you measure the bow ball at different points in the stroke, do you get a
> constant velocity? Or does its velocity vary according to where you
> measure it? If the latter, then at what point in the stroke is it moving
> the fastest? And at what point is it moving the slowest?
>
> Hasn't simple observation yielded answers to these questions? Doesn't
> the bow ball reach its highest velocity right after the release?
Depends entirely on recovery technique. The body is so much heavier
than the boat that rather slight changes in the tension you apply
through your legs during recovery (which is necessary to overcome fluid
drag on the hull in order to bring frontstops towards you) will have
marked consequences for transient boat velocity. Walter's graph shows a
lull in boat velocity at the finish, followed by a subsequent surge.
This results from one particular style of finish & recovery, whereas
other styles produce other effects including that which you describe.
So there are no absolutes - which is why understanding technique really
is so important, & goes so much further than mere appearances.
And
> doesn't it reach its lowest velocity at the catch?
Clearly not.
>
> Now how does a bow ball move from a lower velocity to a higher velocity
> without accelerating?
>
> Is it "unscientific" to think that an object moving from a higher
> velocity to a lower velocity is decelerating? Is it "unscientific" to
> think that the reverse is equally true - if an object is moving from a
> lower velocity to a higher velocity it is accelerating? After all, isn't
> acceleration defined as the rate of increase in velocity per unit of time?
>
> So why is it incorrect to say that a bow ball during the leg drive is
> accelerating? This is really all I am asking.
Because, as Walter's graphs confirm, if first decelerates & only later
accelerates.
>
> I cannot believe that we are all that far apart on this idea. It seems
> to me that a bow ball decelerates during the recovery and accelerates
> during the leg drive. Moreover to produce an average mean velocity per
> stroke of the bow ball with respect to the finish line, any acceleration
> during the leg drive must compensate for any deceleration during the
> recovery.
>
> Aren't you saying as much when you write that "In every stroke there are
> accelerations & compensating decelerations?"
Yes.
>
> Or when you write: ". . . you return to much the same speed at the same
> point on every stroke." Doesn't the very idea of "returning" to much the
> same speed on every stroke presuppose acceleration and deceleration?
>
Yes.
> Isn't the idea of rowing well to find a rhythm that keeps the amplitude
> between these velocities as small as possible, and that allows us to
> reproduce the same mean average velocity per stroke for every stroke in
> a piece? As you write, "no net acceleration there, just the exact
> cancellation of the integrals over time of the positive & negative
> accelerations."
>
> By the way, what is "net acceleration?" I am not clear on the term at
> all. The OED defines acceleration as ". . . in Nat. Phil. the rate of
> increase in velocity per unit of time." So by "net acceleration" do you
> mean the net the rate of increase in velocity per unit of time? I do not
> mean to be such a dunderhead but for the life of me I cannot think of an
> example.
Nt acceleration occurs when you increase your mean velocity, as when
going from cruising pace A to sprint pace B.
>
> And another question: why is it of such great consequence to say that
> Mr. Tonks "is in the business of accelerating (= kinetically energising)
> his personal C of G from the instant of the catch?"
Because that's the correct description of what's happening. If your
mental model is fundamentally false, the lessons you hope to learn from
it will lead to a dead end. If I believe that the chisel's handle does
the cutting, so I hold it by the blade, I'm going to find, suddenly &
painfully, that my model is wrong
The rowing stroke is an intermittent application of power to overcome a
continuing if varying fluid resistance. The only way it can work even
half usefully is for surplus energy to be stored, during the power
application, in the increased speed of progression of the heaviest
component (the body) in the system's general direction of motion - you
increase its kinetic energy.
>
> Please understand that I am not disagreeing with what you are saying. I,
> too, think it is the rower's business to accelerate his personal C of G.
> Nevertheless I wonder if this isn't subordinate to a higher end -
> namely, to rowing your bow ball across the finish line ahead of the
> other guy's. How he or she manages to accomplish this certainly involves
> accelerating his C of G. But doesn't the fact remain that the entelechy
> of rowing is a bow ball moving forward?
Unfortunately any close consideration of the bow ball amounts
ergonomically & in every other relevant sense to putting cart before
horse, or counting angels on the head of a pin. Nothing you can do in
considering the bowball, beyond ensuring that what you do does not
needlessly increase the cyclic fluctuations in its velocity (which is
also the boat's velocity, & that of your toes, etc.) offers useful
insights or models through which to improve your rowing
>
> Warmest regards,
>
> Charles
And mine to you -
Charles Carroll
>> bow ball reach its highest velocity right after the release? And doesn't
>> it
>> reach its lowest velocity at the catch?
> No. You are wrong. You didn't observe well.
Mike,
You are right to say that I didn't observe well. I have just looked at the
Graph Walter Martindale includes in his paper on "Velocities in Sculling."
If I am reading the graph correctly, the boat continuesw to decelerate about
one-fifth of the way through the leg drive, at which point it reaches its
lowest velocity. No surprise there, I guess.
But what is surprising, leastwise for me, is that for the first one-fifth of
the leg drive the sculler is accelerating while the boat is decelerating.
Walter writes, "The sculler shares her momentum with the boat." Evidently
this shared momentum is not instantaneous. Why?
Now, as for when the boat reaches its highest velocity, Walter's graph shows
that it occurs during the recovery, actually a little less than half way
through the recovery. So I was quite slapdash in my choice of words. Halfway
is certainly not "right after." I apologize.
Cordially,
Charles
Mike De Petris
wrote:
> You are right to say that I didn't observe well. I have just looked at the
> Graph Walter Martindale includes in his paper on "Velocities in Sculling."
>
> If I am reading the graph correctly, the boat continuesw to decelerate about
> one-fifth of the way through the leg drive, at which point it reaches its
> lowest velocity. No surprise there, I guess.
>
> But what is surprising, leastwise for me, is that for the first one-fifth of
> the leg drive the sculler is accelerating while the boat is decelerating.
> Walter writes, "The sculler shares her momentum with the boat." Evidently
> this shared momentum is not instantaneous. Why?
>
> Now, as for when the boat reaches its highest velocity, Walter's graph shows
> that it occurs during the recovery, actually a little less than half way
> through the recovery. So I was quite slapdash in my choice of words. Halfway
> is certainly not "right after." I apologize.
You've hot the light now, and as a wise and polite rower, you will no
doubt be able to share with us all your toughts about how to scull and
how to practice in the most effective way.
So many variables come to play that it's still a lot a mix of instict,
sensitivity, being smart, open mind and last but not least
perseverant.
So what will be the best draw/recovery ratio for a given rate? And how
will it change at different average speed? And what about when in a
strongwind? And tailwind? And waves? And the ratio is not enough! Fast
hands away and slow seat? Or stay at the finish? And how much to lean
back? And which leverage to use?
Rowing is magic.
Charles Carroll
How does one argue with Walter's paper?
So it is time to admit it. I am wrong. No matter how hard I try, I now see
that I am never going to raise Lazarus from the grave. Lazarus is the name
of your dead horse, is it not?
I copied Walter's graph from his paper, opened it in Word, then changed the
page to landscape and enlarged the graph as much as I could. When I finally
found the time to really look at the graph, I was amazed. Stunned is
probably more like it. I do not think I could have been much more mistaken.
Mike De Petris is right. I did not observe very well. Mea culpa, mea culpa,
mea maxima culpa!
Carl, I do not know how to thank you for your generosity and time, and
especially for your patience.
I think the biggest thing I misconstrued was the first ~1/4 of the leg
drive. I just assumed that if the sculler was accelerating, the boat also
had to be accelerating. But according to Walter's graph the sculler
accelerates while the boat decelerates.
Another surprise was right before the catch. This is the only time when
sculler, boat and Total System intersect - i.e. move at the same velocity. I
had thought they also moved at the same velocity at the finish, but
according to Walter's graph they don't. The sculler at the finish is moving
faster than both the boat and the Total System.
Arrrrrgh!
Am I ever going to understand what it is I do when I scull?
Warmest regards,
Charles
ben
wrote:
It's funny how this topic comes up periodically. I was just looking
through the old threads and the debate basically boils down to Volker
Nolte's thesis on the sliding rigger versus the observation that times
didn't really get faster while it was used or slow down when it was
outlawed. I was coached by Volker for a few years and we used to ask
him about it all the time. He obviously very much a believed that it
was theoretically faster (basically for the reasons Magnus pointed
out) and had all kinds of stories about racing with the sliding
rigger. He raced a two day races one day with the slider and the next
day with the conventional rigger and from what I recall, in his mind
it was not really even a debatable point from a scientific or
anecdotal point of view that the sliding rigger was faster --
particularly if it had been further developed with better technology
and the technique and ideal rigging rations perfected. Although
biased to a certain degree, he is a scientist above all and was very
objectively confident that the numbers were very clear. It's hard to
argue that anyone was more familiar with it than he was. The biggest
problem apparently were the ass blisters you got from some of the
early models. He also said it was very easy to row at very high
rates, which might have been something that was not properly
exploited. As for the times -- obviously it would have been noticed
if the boats were 50% faster but given the short time period over
which they were used at a high level and the vagaries of times
achieved in a weather dependent sport, a small but real difference of
something like say a boat length would be impossible to prove or
disprove based on the observation of a couple of years international
racing times.
Walter Martindale
wrote:
The "total system" is the average of the velocities of the sculler and
the boat. The boat and the sculler do indeed have the same velocity
at two different points in the stroke, and I think I mentioned that
the data (while taken from real film of a real sculler) were from a
very small image, lending to the "bumpiness" of the velocity curves
and some possible inaccuracies in the ACTUAL velocities. The shapes
of the curves, generally, jive with information derived from scullers/
rowers/boats with more modern methods but the big message of my
article is that the boat and the crew are connected, they interact,
and they exchange energy/momentum during. That the "total system"
doesn't intersect the other two curves at the finish may be thanks to
how the numbers were obtained. The boat and the sculler are at exactly
the same velocity at two different points during the stroke.
People who "think" themselves going towards the stern during the
recovery tend to have timing and smoothness problems at the catch, and
believe that they have to keep their knees locked straight until very
late in the recovery. People who "think" the boat coming forward (in
boat terms, not wrt the way the rower is facing) under them tend to
have smoother recovery movements, and allow their knees to be softer
during the early part of the recovery, and probably allow their boats
to run more smoothly under them. The sculler from whom the graphs in
my article are derived was trained to keep her knees straight, which I
think may be responsible for the big wobble in the boat's velocity
just after the release. The film is long gone, and I can't review
it. I've recently re-crunched my numbers, and generated a few more
plots with some other athletes from my thesis data, but as I presented
these to an RNZ coaches training session, they stay IP of RNZ for the
next little while.
Walter
Mike De Petris
> these to an RNZ coaches training session, they stay IP of RNZ for the
> next little while.
can you please exlain "they stay IP of RNZ" Walter?
IP is not for Internet Protocol I guess.
David McC
Intellectual property of Rowing New Zealand
Taniwha
Walter Martindale
Dave got it right....
Intellectual Property...
Walter Martindale
There's actually a bunch of stuff that's been developed by RNZ that,
while I no longer work there, I'm not allowed to disclose. It would
essentially be professional suicide to go on this forum and blab on
about the studies that are ongoing with the training programmes,
biomechanics, and other areas. I imagine that most international
rowing programmes have similar strictures on publication/disclosure of
their research, with publication bans on some of the research
extending until the end of the current Olympiad.
Walter
Carl Douglas
In view of the splendid performances we're seeing, one might be tempted
to suppose that, among other things, NZ are doing good research &/or
analysis on some aspects of the stroke? No, I don't expect you to
answer that, Walter!
BTW, do others share my frustration that video footage nearly always
concentrates on the region from oarlock to oarlock (ish) & from knees to
head? I really don't want to see what faces they're pulling (the
snot-shot).
I really do want to see how the blades are being used in the water, how
the boat is behaving & how the who body is working. And, please, no
more garbage about lifting the bows - no, the objective is not to lift
the bows, bows don't necessarily lift & if they do that is not a sure
indicator of speed. I don't want someone trying to excite me with their
hackneyed phrases. Nor should anyone be trying to "excite" the
non-rowing viewer who has tripped over our strange sport while channel
hopping. They & I want a knowledgeable & clear analysis of what is
happening & why the guys in lane 3 might be doing what they are doing.
It is teh sound of real knowledge, clear explanations & insight that
gets folk intrigued.
In the W2x in Munich, the UK commentary went bananas over GER, tried to
kid us that GBR still had a hope of getting back when really that looked
improbable & they looked distinctly uncoordinated, & then barely saw the
Poles, who came so sweetly from nowhere in the last 500 to win in a way
which seemed barely to disturb the waters while GER were clearly
struggling & losing composure.
Cheers -
Walter Martindale
> URLs: www.carldouglas.co.uk(boats) &www.aerowing.co.uk(riggers)
Would be nice, wouldn't it...
The skills, (bladework, neuromuscular, physiological) that contribute
to a winning performance often go back to the top few inches of the
athlete - the portion between sella turcica (sp?) and the saggital
suture...
W
Charles Carroll
I cannot thank you enough for "Control of Momentum in 2007." It is no
exaggeration to say that this paper has changed my sculling significantly.
Looking back to my earlier posts in this thread, I do not see how I could
have made it clearer that my understanding of how the boat and crew are
connected, how they interact, and how they exchange energy/momentum during a
stroke cycle is horribly murky and altogether entirely mistaken.
While I still cannot claim to have found a perfect understanding of how the
boat and crew are connected, I think I may have begun to appreciate a little
better the importance of this connection and how understanding it may
improve my sculling.
And indeed it has. The proof is in the last two times that I have gone out.
Each time I have found myself thinking that I have never sculled so well nor
has sculling ever seemed so enjoyable. I owe this to you.
Let me try to explain. Thinking about the changing velocities of the sculler
and boat, and how they exchange energy/momentum during the stroke cycle, I
decided on an experiment. At the finish while I slowly moved my hands away
and over the knees, I also pivoted forward. I used a kind of blended or
concurrent movement. As a result I established most of the forward angle
simultaneously with the hands crossing over.
At this point, as the hands crossed over the knees, I stopped. A dead stop!
Or at least it felt like a dead stop.
Usually, in an effort to get long at the catch, I come forward- i.e. move
myself through the pins to the stern.
Instead, this time the only movement I made towards the stern was a slight
forward movement with my hands as I attempted to spread the oar handles as
wide apart as I could. Otherwise I tried to pull the stern to me. I used the
legs and feet, especially the heels, to draw the shell underneath me.
I can still hear Gordon Hamilton's voice during my last lesson with him.
"Don't try to get long by moving into the stern. Get long by spreading apart
the oar handles."
I must tell you, Walter, that this not coming forward was very
disconcerting. No! "Disconcerting" isn't the right word. Weird might be a
better choice. And bizarre better yet!
I could not help thinking that if anyone was watching they are going to
think I am an idiot. What they would see is a remarkably slow sculler doing
nothing for the second half of the recovery.
"This is ridiculous," I thought to myself. "I'm stopped. I am not going
anywhere. All I am doing is making myself slower and slower."
But it wasn't true. I was actually moving. The stern was coming to me. I was
moving the shell underneath me while all the while the shell and I were
moving forward.
After a number of strokes like this, I thought, "This feels pretty good."
I didn't mean "feels pretty good" in the sense of "feel good" sculling. I
meant "feels pretty good" in the sense that the shell was flying. I was in a
section of the Sausalito Channel that I have rowed at least a thousand
times. I have all the markers memorized. And they were whizzing by.
I looked at my watch. It said I was going faster than I ever have. I wasn't
even trying. I was rowing only at half pressure or less. The sculling felt
effortless. Yet trying not to move to the stern made it feel as if I wasn't
moving at all, or that at best I was moving very slowly and not working hard
enough. To myself it seemed that I was going slow. But, as we all know,
appearances can be deceptive. The watch said I was moving much faster than I
usually move.
And this brings me to Steve Fairbairn. You close your paper by quoting from
Fairbairn's famous passage in "Rowing Notes," (1904), "It is important to
come slowly forward because . . ." Then you list Steve's five reasons that
support this premise.
Let me add Fairbairn's closing paragraph, which follows these five reasons.
"I have used the terms 'slow' and 'slowly forward'; this is what it appears.
But it should be 'evenly' and 'steadily forward', for the oarsman coming
(what is called) slowly forward, comes forward further and faster than the
oarsman rushing (i.e. trying to get) forward. The oarsman does not really
travel in the direction of the stern of the boat at all, for the boat is
travelling (after the first few strokes) in the opposite direction faster
than the oarsman's body is coming forward, so what he should do is to try
and stay where he is. To do this he must utilize the run of the boat as much
as possible to bring him forward. That is, press the feet into the stretcher
and let the boat run out from under him. The old professional says, 'Hook
the boat up to you with the straps.' He has learnt how to do this after many
years. To try to teach a young oar to hook a heavy boat up would make him
jerk toes and heels off the stretcher and bucket worse than ever. The old
'pro' sticks his heels firmly into the stretcher as he hooks at his straps
with his toes; the young oar should be sure he is pressing his heels, at any
rate, into the stretcher on the forward swing. The forward swing cannot be
too quietly easy and the hands must hold the oar as lightly as possible.
Usually the crew that does the least work on the forward swing wins."
Thanks again, Walter. I have found your paper invaluable.
Warmest regards,
Charles