Oarshaft Bending
MagnusBurbanks
I attached a thumb-sized video camera to the shaft of one of my
sculls, with the purpose of observing the flex of the shaft from the
frame of reference of the oar rather than that of an outside observer.
The yellow line has been added “post production” and represents the
scull’s resting state. (I challenge anyone watching more than a few
strokes to keep your head straight as you’re watching.)
I would be interested to hear any thoughts on oar stiffness and what
level of stiffness might be optimum.
Here is a perhaps naïve hypothesis: it takes time to bend the shaft,
and more time for it to “unbend”, and that time can be reduced or
largely eliminated with a sufficient level of stiffness. By
eliminating that “wasted” time, can one therefore effectively increase
the stroke rate?
Another consideration is that the shaft is storing a certain amount of
energy as it bends, and that energy is released as it unbends in the
last part of the stroke. For many rowers/scullers, the blade is more
or less out of the water by the time much of that energy is released,
does this make the “finish” a much more important part of the stroke
than many people realise?
Magnus
Charles Carroll
Can you see the stiffness of the oar shaft in the video? I can't. Or
at least I couldn't see it immediately.
Have you looked at RBN No2 Volume 6?
http://biorow.com/RBN_en_2006_files/2006RowBiomNews02.pdf
It discusses an interpretation of the theory of rowing micro-phases,
which Kleshnev names the "Trampoline effect."
Kleshnev writes: "The 'Trampoline effect' can have a number of
consequences," one of which is that "optimal stiffness of the oar
shaft is important and should correspond to the magnitude of the
impact force. Oar shafts that are too soft or too stiff will decrease
the trampoline effect."
Cordially,
Charles
Christopher Anton
>"MagnusBurbanks" <magnus....@googlemail.com> wrote in message
>news:37e4e6f1-44f2-4b49-8a14->776734...@i13g2000yqd.googlegroups.com...
That really is a vomit-inducing video
Anthony
<c.an...@NOSPAM.blueyonder.co.uk> wrote:
> >"MagnusBurbanks" <magnus.burba...@googlemail.com> wrote in message
> >news:37e4e6f1-44f2-4b49-8a14->776734e18__BEGIN_MASK_n#9g02mG7!__...__END_MASK_i?a63jfAD$z...@i13g2000yqd.googlegroups.com...
> >Take a look at this clip on youtube:
> >http://www.youtube.com/watch?v=GxPSGY6Q-k8
>
> That really is a vomit-inducing video
Yes, but interesting how quickly the energy stored in the bent oar is
released - it straightens well before the finish as far as I could
see, although this may not be typical. It might be useful to know how
much pressure was being applied to the oar handle at any given moment
during each stroke, as well as the degree of stiffness built into the
individual oar.
Zbigniew A.
>
> I would be interested to hear any thoughts on oar stiffness and what
> level of stiffness might be optimum.
>
Magnus,
there is certainly a level of flexibility which is optimal; not all flex is
bad.
In early 80s one of the best sculler in the world at that time, Alf Hansen,
has got one of the first ever made pairs of new sculling oars of a new type.
I don't know what their brand is, I don't remember any logo on them; they
are hanging on a wall as an ornament. They are wooden oars; the shaft has
almost square cross-section. Two of the walls -- parallel to a blade -- were
reinforced with layers of carbon.
These oars do not bend at all. Stiff like concrete.
Alf tried them really hard and at the end of the rowing season proclaimed
them "unrowable".
Peter Michael Kolbe when he moved to Norway, he brought a pair of Empacher
sculling oars. They have mostly black shafts with diagonal stripes of yellow
fibers. It was probably one of the first pairs of this type ever made.
They are collecting dust in the attic of our boathouse.
When I inquired P.M.K. about these oars, he said I am free to use them but
he does not recommend them cause they are too stiff. When moving back to
Germany he took his favorite boat with him and left the oars behind.
--
Yours Virtually, Zibi
Bob
> On 27 Sep, 18:40, "Christopher Anton"
>
> <c.an...@NOSPAM.blueyonder.co.uk> wrote:
> > >"MagnusBurbanks" <magnus.burba...@googlemail.com> wrote in message
> > >Take a look at this clip on youtube:
> > >http://www.youtube.com/watch?v=GxPSGY6Q-k8
>
> > That really is a vomit-inducing video
>
> Yes, but interesting how quickly the energy stored in the bent oar is
> released - it straightens well before the finish as far as I could
> see, although this may not be typical. It might be useful to know how
> much pressure was being applied to the oar handle at any given moment
> during each stroke, as well as the degree of stiffness built into the
> individual oar.
Within certain limits, the deflection should be proportional to the
pressure applied to the handle. Regardless of coaching, pressure
usually decreases to zero before the release so that no energy is
wasted.
cheers,
bob
Carl Douglas
Going further, the flex on the oar is, under all normal rowing loads
directly proportional to the load.
Magnus has provided a yellow line by which, at all times, to judge the
precise amount of flex & thus the instantaneous loading on the blade
(subject to assumptions about the location of centre of pressure)
Not only do we see the exact amount of shaft flex at all times, but also
the change in attitude of the blade, which is always bent more out of
line than any part of the oar. Obviously the combined effect of these 2
flexures is to considerably alter the blade alignment from that
generally presumed from measurements of oar angle taken at the oarlock.
While what Bob says about unloading by the finish may often be true, the
rattle or clonk heard at the finish in many crews suggests that the
blade still contains unreleased strain energy at extraction which
releases itself uselessly during the feather.
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)
Bob
> On 27/09/2010 23:49, Bob wrote:
>
>
>
> > On Sep 27, 3:28 pm, Anthony<anthonyjones...@hotmail.com> wrote:
> >> On 27 Sep, 18:40, "Christopher Anton"
>
> >> <c.an...@NOSPAM.blueyonder.co.uk> wrote:
> >>>> "MagnusBurbanks"<magnus.burba...@googlemail.com> wrote in message
> URLs: www.carldouglas.co.uk(boats) &www.aerowing.co.uk(riggers)
Exactly, Carl,
but I've seen crews (or at least individuals) who make a release
with little or no pressure and still effect the "clonk" by giving a
sharp jerk to the blade after release. You see sweep crews do this a a
low paddling rate, but they still have the "clonk". It seems that
they're clearly releasing early. It's just another stylistic effect
which wastes energy. It's not as common among scullers,
cheers,
Bob
Sarah A Harbour
>
> - Show quoted text -
I hate clonky finishes. One of the first coaches I ever had at college
told us off for having noisy finishes, and since then I've always
tried to time the finish so as not to make a clonk.
Much to my annoyance though, another coach a few more years down my
rowing career exclaimed how good it was now we had a new Filippi that
meant you could hear the finish. Er, no. A stiff boat is a good thing,
but you shouldn't need to hear the finish to know you're in a stiff
boat. Grumble grumble...
Sarah
Richard du P
>
> [big snip] ............. another coach a few more years down my
> rowing career exclaimed how good it was now we had a new Filippi that
> meant you could hear the finish. Er, no. A stiff boat is a good thing,
> but you shouldn't need to hear the finish to know you're in a stiff
> boat. Grumble grumble...
>
> Sarah
I'd understood the best thing about having a new Filippi to be that
you don't get sneered at by the club next door that has a new Filippi.
This closely parallels the discussions that my relations by blood and
by marriage have about handbags.
Richard du P
Carl Douglas
And what, pray, has Dame Edith Evans (or Oscar Wilde) got to do with, or
to say about, rowing, Richard?
--
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
Andy McKenzie
> On 28/09/2010 22:47, Richard du P wrote:
>
>
>
>
>
> > On Sep 28, 8:29 pm, Sarah A Harbour<sarahaharb...@gmail.com> wrote:
>
> >> [big snip] ............. another coach a few more years down my
> >> rowing career exclaimed how good it was now we had a new Filippi that
> >> meant you could hear the finish. Er, no. A stiff boat is a good thing,
> >> but you shouldn't need to hear the finish to know you're in a stiff
> >> boat. Grumble grumble...
>
> >> Sarah
>
> > I'd understood the best thing about having a new Filippi to be that
> > you don't get sneered at by the club next door that has a new Filippi.
>
> > This closely parallels the discussions that my relations by blood and
> > by marriage have about handbags.
>
> > Richard du P
>
> And what, pray, has Dame Edith Evans (or Oscar Wilde) got to do with, or
> to say about, rowing, Richard?
>
> --
> 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 -
"‘We went down to the horrid regatta on Thursday last.’ Letter of 5
September 1868 to his mother, the earliest letter of Wilde's to
survive. Merlin Holland & Rupert Hart-Davis: The Complete Letters of
Oscar Wilde (2000) p. 4.'
(Although to be fair I think it was a sailing regatta.)
Well you did ask!
Andy
Charles Carroll
I seem to remember Oscar Wilde's being talked into trying rowing while
he was at Magdalen. While he admired the physiques and manly beauty
and fellowship of rowing men, he hated the exertion and sweatiness of
the sport itself. I forget how many times he was in a boat. Maybe just
once?
"In October 1874 Oscar arrived at Oxford after Magdalen College
offered him a scholarship. Oxford was "the most beautiful thing in
England," and his time there was "the most flower-like time in my
life." An English accent was cultivated, cricket was watched, and a
stint on the college rowing team ended with a steadfast refusal to
continue exertion to the point of exhaustion. Rowing seemed to bring
an end to any interest in exercise: "I am afraid I play no outdoor
games at all. Except dominoes. I have sometimes played dominoes
outside French cafes." Study continued, usually late at night, so that
days could be spent in a more casual manner. In early 1877 Oscar
travelled in Europe, visiting Greece, Genoa, Brindisi and Rome. He
called the grave of Keats "the holiest place in Rome." This irritated
his catholic friend Hunter Blair, who perhaps was already suspicious
of Oscar's interest in Catholicism: it was the colourful ritual that
seemed to be the real attraction. Nevertheless even Oscar's
refreshingly superficial interest in Catholicism had already put the
university authorities on their guard. Anti-catholic feeling was still
strong in Oxford; so when Oscar found that his trip to Europe had made
him two days late for the beginning of Easter term, he was suspended
from the university - or "rusticated" - for two terms. Visiting Greece
whilst on a Classics course was not a valid excuse. The harsh
punishment stood. "I was sent down from Oxford for being the first
undergraduate to visit Olympia." Already Oscar Wilde seemed to be the
victim of stupidity dressed up as rectitude."
http://www.infobritain.co.uk/oscar_wilde_biography_and_visits.htm
Cordially,
Charles
Carl Douglas
The bit about Wilde's visit to Olympia leading to rustication reminds me
of when I was hauled before a certain club's committee for refusing,
when burdened with sticky things in hand, to immediately cease repairing
a club boat - just because one of the elders among the club's old farts
wanted to lock up & go home. "Don't worry," I'd said, "You lock up and
I'll go back in through the Gent's window" (which is what I then did).
Apparently that was insubordination & impertinence (on my part), not
crass stupidity on his.
So, did Wilde get to meet Newman, himself so recently & quaintly parted
(as dust) from joint interment with his long-time male companion so he
could be beatified by our recent German visitor with the nice red shoes?
Their times at Oxford clearly overlapped.
But have we strayed too far off topic, even for RSR?
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
I had no idea that Newman had a male companion. That's something I
will have to look up. I have a close friend who has made Newman one
of his subjects. He has long admired Newman and has read everything
Newman has written several times over, and has himself written about
Newman and Newman's ideas many times. I'll ask.
About letting yourself out through the Gent's window, it is funny how
such things work out. Amazing the little things people pick on when
they want an excuse to oust you from "the club!"
In the seventh grade (I was 12 and 13 years old) I had a wonderful
teacher who is responsible for my love of Shakespeare. The BBC had
produced a series of plays called "An Age of Kings," which Georgetown
University put on their private television station. It was just simply
the series of Shakespeare's plays that cover the War of the Roses
(Richard II through Henry V). He assigned these plays as homework, and
afterwards we read them together in class. This teacher had the knack
of making the plays come to life. But he also had a knack of
irritating the people who ran things. In the end the local School
Board found an excuse to dismiss him. On what grounds, you may ask? On
the grounds that he had "departed from the curriculum!" Can you
imagine?
Now wait until you hear what the problem was. "The Age of Kings" was
broadcast on Sunday Evenings at the same time as a popular television
show, "Bonanza." One of my classmates father's was incensed that his
son was forced to miss "Bonanza" in order to complete his homework.
The man also happened to be on the School Board.
But this is quite a departure from the flexiblity of oar shafts. I
apologize.
Cordially,
Charles
Richard du P
wrote:
> Carl,
>
> I had no idea that Newman had a male companion.
................... massive snip .........
>
> Now wait until you hear what the problem was. "The Age of Kings" was
> broadcast on Sunday Evenings at the same time as a popular television
> show, "Bonanza." One of my classmates father's was incensed that his
> son was forced to miss "Bonanza" in order to complete his homework.
> The man also happened to be on the School Board.
>
> But this is quite a departure from the flexiblity of oar shafts. I
> apologize.
>
> Cordially,
>
> Charles
Charles
In respect of Newman's burial, and sexuality, I fear you will find at
least two mutually contradictory strands of belief - something of a
"tug of love" between the present-day hierarchy of his church, and
campaigning sexual politicians. Quite a little storm when the former
group removed Newman's remains - such as they could distinguish - from
the grave he shared with ?Ambrose St John.
The "Bonanza" difficulty on the other hand, might strike an odd chord
with Newman. I THINK I've heard that when he was still an Anglican,
and Rector of St Mary's, the University Church, his sermons so upset
the Presidents, Masters, Rectors, Principals, Dean &c of sundry Oxford
Colleges that they changed the time of [then compulsory] dining in
college, so that undergraduates would be unable to hear Newman at
Evensong.
Nothing to add about oar shafts.
Richard du P
MagnusBurbanks
Zibi’s comments about Alf Hansen and P-M Kolbe each regarding
extremely stiff sculls as “unrowable” are fascinating, I hadn’t heard
of this before. It suggests that oar stiffness is a critical factor in
the dynamics of rowing, and any CFD simulation which ignores it (and
the resulting change in attitude of the blade) is attempting to draw
useful lessons and results from the modelling of an effectively
unrowable situation.
If there is anyone reading this with the inclination and capacity to
perform the CFD including this element (Stephen Schaffran springs to
mind?), the results would be fascinating, and in particular using
stiffness as a main variable for comparison.
Cheers, Magnus
Charles Carroll
What did I miss?
I thought Valery Kleshnev had a lot to say about the subject of oar
flexibility in RBN No. 2 Volume 6, in which he addresses the question
of “Trampoline effect,” which occurs at the catch and in the first
half of the drive.”
The “Trampoline effect” works as follows:
1. At the catch (end of R3 and D1 micro-phases), the rower approaches
fast towards the stretcher and creates an impact push on the stretcher
at the moment of the blade immersion.
“2. This impact force is transferred though the rigger and pin to the
oar sleeve and bends the oar (D2 micro-phase). The oar shaft
accumulates elastic energy, which could amount to 25% of the total
power at the catch (RBN 2001/05)
“3. In the D3 micro-phase, the oar shaft springs back, i.e. the oar
works as a trampoline. The recoil force goes back though the pin and
rigger and creates a high positive boat acceleration called the “first
peak”.
“4. Rowers use the accelerating stretcher as a support for effective
acceleration of their CM during the D4 micro-phase.
“The “Trampoline effect” theory can have a number of consequences.
Here are some of them:
“1. Fast approach to the stretcher before the catch is beneficial.
This contradicts some theories, which propose a slower approach to the
catch.
“2. Good timing is really important. Each rower has to feel the moment
when he/she: a) kicks “the trampoline” and bends it; b) applies the
handle force to support “the trampoline” from the other side; c) picks
up the recoil force and uses the legs to accelerate the body CM.
“3. In crew boats, all rowers have one common trampoline because their
stretchers are connected through the shell. Therefore, one rower can
create the trampoline effect for other rowers in the crew. This
happens quite often in pairs, where the stroke rower increases force
much more quickly than the bow rower.
“4. Optimal stiffness of the oar shaft is important and should
correspond to the magnitude of the impact force. Oar shafts that are
too soft or too stiff will decrease the trampoline effect.
“5. Rowing on ergometers does not allow experiencing the trampoline
effect.”
Doesn’t #4, “Optimal stiffness of the oar shaft,” address your
question? Isn’t there a method by which we could measure how much
force we were capable of exerting on an oar? If so, then why wouldn’t
it be a simple matter of measuring this force, and then purchasing an
oar with a corresponding stiffness?
Cordially,
Charles
Charles Carroll
As oar shafts are shortened don’t they become harder to bend?
If so, does this mean that those of us who have been experimenting
with shortened oar shafts may be losing some of the Trampoline effect?
mruscoe
> Magnus,
>
> What did I miss?
>
> I thought Valery Kleshnev had a lot to say about the subject of oar
> flexibility in RBN No. 2 Volume 6, in which he addresses the question
> of “Trampoline effect,” which occurs at the catch and in the first
> half of the drive.”
>
> The “Trampoline effect” works as follows:
>
> 1. At the catch (end of R3 and D1 micro-phases), the rower approaches
> fast towards the stretcher and creates an impact push on the stretcher
> at the moment of the blade immersion.
>
> “2. This impact force is transferred though the rigger and pin to the
> oar sleeve and bends the oar (D2 micro-phase). The oar shaft
> accumulates elastic energy, which could amount to 25% of the total
> power at the catch (RBN 2001/05)
>
> “3. In the D3 micro-phase, the oar shaft springs back, i.e. the oar
> works as a trampoline. The recoil force goes back though the pin and
> rigger and creates a high positive boat acceleration called the “first
> peak”.
>
> “4. Rowers use the accelerating stretcher as a support for effective
> acceleration of their CM during the D4 micro-phase.
>
I'm puzzled by the explanation of the "trampoline effect".
"In the D3 micro-phase, the oar shaft springs back" - I haven't seen any
evidence from biomechanics measurements or video that the oar unbends at
that point in the stroke. To recover the strain energy in the oar
requires a reduction in the bend of the oar, and hence a reduction of
the force that is maintaining that bend, and I don't know that there is
anything to suggest that happens at that point in the stroke.
A Browne
Carl has gone over this ground in the past: the oar can be bent as long
as the force on the handle and the resistance at the blade are great
enough to bend the oar. The oar will un-bend when either force lessens,
e.g. when the blade slips in the mid-stroke.
On the subject of Hansen and Kolbe disliking stiff looms, there needs to
be consideration that these guys had reached the top of their craft
using wooden oars with relatively springy and heavy shafts. The change
in rowing style required to accommodate the significantly lighter and
stiffer early carbon-fibre looms has little relevance, I would suggest,
to any discussion of stiffness options available in today's oars.
Regards,
Alistair
MagnusBurbanks
Quite. I too would take issue with "trampolining".
You can see from the video in the original post that there is no
apparent effect at the start of my stroke at least. The deflection of
the oar increases smoothly and progressively as force is applied to
the handle from the beginning of the stroke, and the deflection
correspondingly smoothly reduces as the load comes off towards the
end. To that extent the oar is behaving as a strain gauge.
M
MagnusBurbanks
> be consideration that these guys had reached the top of their craft
> using wooden oars with relatively springy and heavy shafts. The change
> in rowing style required to accommodate the significantly lighter and
> stiffer early carbon-fibre looms has little relevance, I would suggest,
> to any discussion of stiffness options available in today's oars.
Good point. But, I myself learnt to scull and did all my early racing
using wooden oars in the late 80s/early 90s. Alongside the vast
majority of rowers and scullers, I changed to using carbon fibre oars
in one outing, and, like many people, I loved them immediately. All my
significant wins subsequently came using carbon oars. Kolbe and
Hansen, as mentioned, were scullers at the extreme top of their game.
If I can adapt so quickly I think their reaction should not be
dismissed lightly.
In addition, I am not (yet) convinced that my Concepts are
significantly, if even, stiffer than the 1980s wooden ones. (Of course
they are lighter, but that’s not what we’re discussing here). I still
possess a pair of 1990 Stampfli wooden sculls hanging in my boathouse,
I will compare stiffness with my Concepts this weekend and revert.
M
Walter Martindale
wrote:
To do that you need to fix the blades in a jig and apply known weights
to either the handle or the blade, and measure deflection as load
increases. e.g., apply loads starting at 2.5 kg and going up in (say)
2 or 2.5 kg (convenient weights found in a weight room, when combined
with 5, 10 and 15 (say) kg weights you can make 2.5 kg steps all the
way up to 32.5 kg without referring to a 20 kg plate, and not (I hope)
overload your oars) steps, measure the deflection each loading. You
can check for linearity by plotting the deflection in mm against the
load in kg, but hysteresis might be a stretch without a previously
calibrated load cell.... I suppose you might be able to do other
tests to see how quickly the blade will spring back after unloading
(how high will a 5 kg weight be thrown when you apply a force of 200 N
to the handle, if the 5 kg weight is balanced on the spoon, for
example). People with engineering/lab equipment could do lots of
studies without actually destroying the blades..
After that you can take them out on the water and see if you can
actually feel any difference. To be a little more thorough, have
someone else do the load-measure experiment and not report the
findings to you until after you've reported what you feel...
W
MagnusBurbanks
jigging, noting and plotting weight and deflection. Interesting
suggestion to avoid contaminating my "feel" by knowing the stiffness
result ... I'll have to see. I might have trouble persuading a
suitable helper. I had intended to leave any "feel" comparisons until
another time, I haven't used wooden blades since 1989. Alternatively I
may simply take both out and note my experiences before I do the
measuring.
I'll report back, and hopefully I'll avoid damage/destruction.
M
Walter Martindale
wrote:
That's the double-blind thing - almost. If it were possible for
whomever was doing the measuring and loading to not know which model
he or she was testing you would be closer to a double blind study.
It might be interesting to test the port-starboard differences between
the blades, too - and see if the wooden sculls are more or less
variable (ok, it's a small sample) than the carbon sculls...
W
Carl Douglas
This is all very simple stuff, chaps! Didn't we all do Hooke's Law
experiments when at school.
When talking of rebound rate, take care. If a blade is rebounding in
air, you have to make allowance for air-damping. And rebound rate is
determined by oar mass distribution - which may be relatively irrelevant
when an oar is unbending under typical rates of load reduction. If a
loaded blade is rebounding/unloading during the stroke (the infamous
so-called trampoline effect - no Charles, it really doesn't exist) in
moving water, then I doubt that shaft hysteresis need be considered &,
unless it is to be pushed by an external force in the reverse direction,
the water will do almost no damping or forcing. To the extent that
water damping or forcing can occur under rapid loading & unloading,
that'll arise from transient responses in the surrounding static
pressure field & associated changes in water levels around the blade
(water bounces when loads change).
I don't think modern carbon oars & sculls are that much stiffer than
wooden ones, & I doubt modern carbon oars are as stiff as the original
wood/carbon composite oars used by some GBR crews in '76. In both
cases, there was one particular advantage for the carbon & carbon/wood
shafts - lower wind resistance due to reduced cross-section (& to
smoother section with the tubular carbon shafts).
Finally:
Remember that you have to learn how best to use novel equipment which
may offer performance benefits. If your at the top of the tree, you
have little incentive to complicate life by changing kit, & if those
around give you excuses to not change, the validity of their arguments
will seem compelling. If, OTOH, your support team makes seemingly
compelling but actually bogus arguments for change, then you may change,
& hopefully lose nothing. But if someone goes past you when using the
equipment you have rejected will you make the change. And even then the
reason for their enhanced form may lie elsewhere.
Only meticulous testing & experiment based on sound theory can take
things forward. Not too common in rowing, I fear.
Charles Carroll
You might imagine my delight when I found that newspaper description
of Steve Fairbairn describing him as "the Socrates of the towpath." I
wonder if in a similar vein you might not be described as "the
Socrates of r.s.r."
You may recall that Socrates famously described himself as a midwife
helping give birth of new ideas. Socrates' particular specialty, of
course, was helping would-be parents recognize whether their precious,
much cherished infants were merely gas or actually healthy infants who
could grow up to become true adults.
Steve Fairbairn investigated many cherished notions about rowing, and
those that proved to be gas he lumped under a general category, which
he named "Orthodoxy." From what I am able to tell, you are a little
more sophisticated. You have two categories into which you lump
gaseous ideas: rowing myths and pseudo-science.
This is not a complaint. Over the years, as you well know, I have
sought your opinion on the merit of many ideas. I always feel indebted
to you when expose some silly notion for the gas that it is.
So I am happy to concede that the notion of a "trampoline effect" is
just a lot of gas. It is a difficult notion to understand anyway. As
Mark Ruscoe asks, where is the evidence that in the D3 micro-phase the
oar shaft springs back?
But in dismissing "the trampoline effect" I am left with a few
questions.
For example, Dr. Kleshnev posits the idea of "the trampoline effect"
as a hypothesis. It is intended to explain why "a high positive boat
acceleration called the 'first peak' occurs in the D3 micro-phase of
the drive (RBN No. 2 Volume 6). Kleshnev says that "[first peak] can
be found in all crews with a fast increase of the force at catch," but
"was not found in crews with the force emphasis at the second half of
the drive." (RBN No. 11 Volume 3)
So what causes a high positive boat acceleration in the D3 micro-phase
of the drive? And why do you have a slight deceleration afterwards?
And why is first peak found in all crews with a fast increase of force
at the catch?
And why is it missing in crews with the force emphasis at the second
half of the drive?
Cordially,
Charles
Tinus
wrote:
> So what causes a high positive boat acceleration in the D3 micro-phase
> of the drive? And why do you have a slight deceleration afterwards?
>
> And why is first peak found in all crews with a fast increase of force
> at the catch?
>
> And why is it missing in crews with the force emphasis at the second
> half of the drive?
You may have to realize that relation between handle speed and rower
speed is not linear. The D3 micro-phase simply means that there is a
negative acceleration of the rower relative to the boat. This does not
have to mean that the handle has negative acceleration.
Just an example of how it could work:
At the catch more body displacement must be moved for the same amount
of handle displacement. This causes an effect of decreasing body speed
for the same handle speed. The reason why the D3 phase goes into the
D4 phase is because at the perpendicular for the same boat speed a
higher handle speed is needed increasing handle speed requires more
body speed. And then the D4 phase ends again because at the end less
body mass is moved and less body impuls is needed for the same handle
speed.
Difference between sweep rowing and sculling may also fit in above
theory. Scullers are able to use more arms at the catch and have less
pronounced D2,D3 phase.
Tinus
> You may have to realize that relation between handle speed and rower
> speed is not linear.
Should read:
You may have to realize that relation between handle speed and rower
impulse is not constant.
Carl Douglas
I'm a bit preoccupied right now, Charles, but see that Tinus has given
you answers which should be helpful.
As for Socrates? No, intellectually. Who came anywhere close to that
man's wisdom? And, no, I don't fancy taking hemlock (the poison).
Hemlock (the timber) has many more valuable uses, however.
MagnusBurbanks
Although I didn't manage to actually use the wooden blades, I did do
the weight/deflection exercise.
The Stampflis are only slightly less stiff than the Concepts up to a
point, and beyond that point, more markedly so.
At a distance of 149cm from the button, I suspended 5, 10 and 15kg
weights. A vertical scale was placed just alongside the sculls where
the weights were suspended. The resulting measured deflections for 5,
10 and 15kg were:
Concept 3.0 / 5.9 / 9.0 cm
Stampfli 3.3 / 6.5 / 11.0 cm
or as successive deviations:
Concept 3.0 / 2.9 / 3.1 cm
Stampfli 3.3 / 3.2 / 4.5 (!!!) cm
Thus up to a moment of 146Nm (i.e. 10kg suspended 1.49metres from the
support), the Concept deflects 10% more than the Stampfli, which in
layman's terms equates to "slightly stiffer".
However, the Stampfli became markedly more flexible somewhere between
10 & 15kg, or 146-220Nm moment. Are these likely loads for a sculler?
Off the top of my head I don't know.
The sculls used were Concept Low-i Med Stiffness, which I believe the
vast majority of poeple order, and a pair of wooden Stampfli sculls
from 1989.
For a jig I used a set of steel trestles weighted to the ground with
heavy weights.
Cheers, Magnus
PS I will get someone else, a very talented sculler, to actually use
both sets and repoprt back on how they feel now I have been
contaminated.
MagnusBurbanks
wrote:
Interestingly, if I recall correctly the PhD paper recently posted up
(on CFD of an oarblade) also showed the initial peak.
Magnus
Tinus
> (on CFD of an oarblade) also showed the initial peak.
>
> Magnus
It can not be the PhD paper by Anna Coppel. She models a simplified
motion of the rower movement without a D3 microphase dip
5.4) x = -a cos(t/T)
She does have a peak dip peak pattern in the blade lift force (fig
5.6) but that's a different story.
Charles Carroll
> man's wisdom?
Carl,
Did Socrates possess wisdom?
I suspect that Socrates would answer no. Those he most esteemed were
philosophers, the lovers of wisdom, anyone who would relieve himself
of the burden of ignorance.
The possession of wisdom, on the other hand, Socrates equated with
ignorance.
"And herein lies the evil of ignorance, that he who is neither
good nor wise
is nevertheless perfectly satisfied with himself; for he feels
no desire
for that of which he feels no want."
When you think you have arrived at your destination and made yourself
wise, it is then that you most need to examine your thoughts yet one
more time. Socrates went to great lengths to make us understand that
inherent in the love of wisdom is the want of wisdom. For Socrates the
end was not the destination, but the road getting there.
Warmest regards,
Charles
Carl Douglas
>> As for Socrates? Who came anywhere close to that
>> man's wisdom?
>
> Carl,
>
> Did Socrates possess wisdom?
>
> I suspect that Socrates would answer no. Those he most esteemed were
> philosophers, the lovers of wisdom, anyone who would relieve himself
> of the burden of ignorance.
And that's the point. The more we know, the better we see the huge
extent of our ignorance. Socrates was a wise man, for he had the wisdom
to see how little he knew. I search of greater wisdom he asked
inconvenient questions which exposed the ignorance of the well-placed
self-important people. And he saw always the bigger picture. This was
bound to end in tears for his followers and friends but not, because of
his philosophical view, for Socrates himself.
Mind you, I don't suppose Socrates did a lot of rowing. So might we
have wandered off topic?
>
> The possession of wisdom, on the other hand, Socrates equated with
> ignorance.
>
> "And herein lies the evil of ignorance, that he who is neither
> good nor wise
> is nevertheless perfectly satisfied with himself; for he feels
> no desire
> for that of which he feels no want."
>
> When you think you have arrived at your destination and made yourself
> wise, it is then that you most need to examine your thoughts yet one
> more time. Socrates went to great lengths to make us understand that
> inherent in the love of wisdom is the want of wisdom. For Socrates the
> end was not the destination, but the road getting there.
>
> Warmest regards,
>
> Charles
>
>
You could say that there is little that is Socratic in wanting to know
more & more about what makes rowing tick. But you know the guy better
than I do ;) BTW, did Socrates know about the Buddha? One can imagine
a most interesting philosophical examination by the former of the latter.
tjhc*
Following the discussion above I've been reading up on Dr. Kleshnev's
microphases and I've got a question I'd like help with. On page 13 of
this publication, http://www.biorow.com/Papers_files/2006%20Rowing%20Biomechanics.pdf,
Dr. Kleshnev shows some data plotted from a session with a single
sculler. I'm particularly interested by the top graph which shows the
force at the stretcher and the force at the gate through the stroke
cycle.
During R3, the oarsman is still moving towards the stern and starts
pushing on the stretcher to slow their approach to the catch, the
force on the gate increases as the oarsman also applies a force to the
handle to slow the rotational velocity of the blades. D1 shows the
legs starting to push the stretcher while the spoon is in the process
of being buried. As the blade locks on during D2, the force at the
gate quickly rises to match that at the stretcher (the lag presumably
being linked to the loom flexing and the spoon slipping before it
grips) and the two remain similar through D3 and D4.
As the blade passes the perpendicular, the force at the stretcher
drops off faster than the force at the gate. This is the bit that I'm
stuck with. Where does the force at the gate come from if not through
the stretcher?!
One of the plots lower down shows that this is the point where the
legs start to lose their advantage, so the trunk starts to swing in
order to maintain the connection, even so, the work's still got to go
through the stretcher! Doesn't it?!
Help, Rec.Sport.Rowing!
Tom
Dave Sill
> As
> the blade locks on during D2, the force at the gate quickly rises to
> match that at the stretcher (the lag presumably being linked to the loom
> flexing and the spoon slipping before it grips) and the two remain
> similar through D3 and D4.
>
> As the blade passes the perpendicular, the force at the stretcher drops
> off faster than the force at the gate. This is the bit that I'm stuck
> with. Where does the force at the gate come from if not through the
> stretcher?!
From the loom unflexing?
-Dave
Alexander Lindsay
"tjhc*" <tjhco...@googlemail.com> wrote in message
news:d375cc07-5ecc-4dfe...@a36g2000yqc.googlegroups.com...
> Dear All,
>
> Following the discussion above I've been reading up on Dr. Kleshnev's
> microphases and I've got a question I'd like help with. On page 13 of
> this publication,
> http://www.biorow.com/Papers_files/2006%20Rowing%20Biomechanics.pdf,
> Dr. Kleshnev shows some data plotted from a session with a single
> sculler. I'm particularly interested by the top graph which shows the
> force at the stretcher and the force at the gate through the stroke
> cycle.
>
> During R3, the oarsman is still moving towards the stern and starts
> pushing on the stretcher to slow their approach to the catch, the
> force on the gate increases as the oarsman also applies a force to the
> handle to slow the rotational velocity of the blades. D1 shows the
> legs starting to push the stretcher while the spoon is in the process
> of being buried. As the blade locks on during D2, the force at the
> gate quickly rises to match that at the stretcher (the lag presumably
> being linked to the loom flexing and the spoon slipping before it
> grips) and the two remain similar through D3 and D4.
>
> As the blade passes the perpendicular, the force at the stretcher
> drops off faster than the force at the gate. This is the bit that I'm
> stuck with. Where does the force at the gate come from if not through
> the stretcher?!
>
Deceleration of the body?
> One of the plots lower down shows that this is the point where the
> legs start to lose their advantage, so the trunk starts to swing in
> order to maintain the connection, even so, the work's still got to go
> through the stretcher! Doesn't it?!
>
No. If the body is decelerating, i.e. its CG is moving towards the bows
more slowly, the force on the stretcher must be less than that on the
handle. And vice-versa.
Alexander Lindsay
> Help, Rec.Sport.Rowing!
>
> Tom
Carl Douglas
Further:
The first part of the stroke tends to be about accelerating the body.
During the second part, the boat catches up with the body.
StephenA
wrote:
Hi,
I tested 4 of Concept 2 blades in the gym, one standard and the
others shortened by chopping the loom short. All blades deflected
linearly with force up to 40 kg or 394 N (force of an elite
heavyweight sculler). What was more interesting for me at the time
was that for the standard blades the cant angle of the spoons
deflected by up to 10 degrees to -9 from its initial +1 (the shorter
stiffer blades went to 6 deegres). This means that as the spoon bends
back the angle of attack of the water on the leading edge is increased
causing the stall to happen earlier in the sweep than the CFD models
calculate. So the lift /drag ratio of the blade is different with
drag dominating earlier than calculated and blade efficiency (Kleshnev
definition) dropping sooner than otherwise. Whether this is a good or
a bad thing I don't know but probably bad as overall blade efficiency
is reduced. Once the oar has passed peak handle force (usually just
before the orthogonal) the loom will start to unbend and at the finish
when handle force is zero it will be straight again in my view and
will not be bent back or have flicked forward significantly if finish
is good.
On another note Macrossan recently pointed out that once the blade
passes the orthogonal the spoon is for the first time working in
turbulent water created by the first half of the stroke so it is
unlikely for any laminar flow to be established in the reverse
direction towards the finish. So the second half hydrodynamics is
more complicated than the simple analysis using oar angular and boat
linear velocity would suggest and is probably much more drag
dominated. A question is why is it worth finishing at 40 – 43 degrees
at the finish (in sculling)?
Stephen
Carl Douglas
> On Oct 4, 3:57 pm, MagnusBurbanks<magnus.burba...@googlemail.com>
> wrote:
>> OK the results of comparing stiffness wooden vs Concept...
>>
>> Although I didn't manage to actually use the wooden blades, I did do
>> the weight/deflection exercise.
>> The Stampflis are only slightly less stiff than the Concepts up to a
>> point, and beyond that point, more markedly so.
>> At a distance of 149cm from the button, I suspended 5, 10 and 15kg
>> weights. A vertical scale was placed just alongside the sculls where
>> the weights were suspended. The resulting measured deflections for 5,
>> 10 and 15kg were:
>> Concept 3.0 / 5.9 / 9.0 cm
>> Stampfli 3.3 / 6.5 / 11.0 cm
>> or as successive deviations:
>> Concept 3.0 / 2.9 / 3.1 cm
>> Stampfli 3.3 / 3.2 / 4.5 (!!!) cm
>> Thus up to a moment of 146Nm (i.e. 10kg suspended 1.49metres from the
>> support), the Concept deflects 10% more than the Stampfli, which in
>> layman's terms equates to "slightly stiffer".
>> However, the Stampfli became markedly more flexible somewhere between
The flexural linearity you measured, Stephen, corresponds with my own
past findings. Unless there's a structural failure I would not expect
significant non-linearity.
I have previously noted on RSR that oar flexure must affect blade
alignment during the stroke, that loading must thus influence angle of
attack & that this discredits the unstated but factual presumption that
one oar pretty much suits rowers of all strengths & sizes. Similarly,
it is not remotely understood that changing oar flexibility must also
have significant consequences for AoA as well as for the obvious (but
probably more easily accommodated) impact loads at catch.
Stephen refers to angular deflections of the blade's principal axis
amounting to 10 degrees, & indeed you can easily see similar deflections
in many rowing photos. However, I don't think one can automatically
assume such deflections are undesirable, there being no grounds to
presume that the non-deflected blade alignments are relevant or optimal
since oars are never used unloaded. The real problem is that we simply
haven't a clue what alignment (& which physical characteristics meant to
minimise changes in that alignment) should be most desirable.
So we're pretty clueless, aren't we?
The alignment of blade WRT oar shaft also matters during recovery: if
the blade is angled in what is the upward direction WRT shaft when
feathered, will it behave as well when bouncing off the water during
recovery &, if angled the other way, mightn't that give problems of
clearance, etc.? All this suggests that blade alignments & forms have
evolved largely as a non-analysed working compromises. Such compromises
may be fine for the mediocre bulk of us rowers, but may adversely affect
the highest performers
However, I don't buy Stephen's comments on how turbulence may affect the
latter part of the stroke. Most foils do have to work in turbulent
flows - even if the turbulence is mainly a self-generated, Reynolds
number-related outcome - & laminar flow foils are rather specialist &
sensitive beasts which seem to bear no good relationship to oarblade
designs. Thus the front wings on F1 cars still generate high (if
impaired) lift forces when running in the immediate wake of a car barely
half a metre in front.
Charles Carroll
I wrote to Valery Kleshnev about the “Trampoline effect.” While I do
not think his reply will offer any surprises, I thought in might be
interesting in light of the discussion.
I wrote:
In a rec.sport.rowing Newsgroup thread, titled “Oarshaft Bending,” I
introduced the idea of the “Trampoline effect,” which you discussed in
RBN No. 2 Volume 6.
As you can see, I quoted you extensively.
In response Mark Ruscoe replied with the following:
“I'm puzzled by the explanation of the "trampoline effect".
"In the D3 micro-phase, the oar shaft springs back" - I haven't seen
any evidence from biomechanics measurements or video that the oar
unbends at that point in the stroke. To recover the strain energy in
the oar requires a reduction in the bend of the oar, and hence a
reduction of the force that is maintaining that bend, and I don't know
that there is anything to suggest that happens at that point in the
stroke.”
In yet another reply Carl Douglas writes: “the infamous so-called
trampoline effect … really doesn't exist.”
I have two questions:
1) What initially caused you to write "In the D3 micro-phase, the oar
shaft springs back?"
2) And have you since changed your mind about this?
I realize that it has been over four years since RBN No. 2 Volume 6
was published. While I don’t think anyone wants to hold you to what
you wrote four years ago, I am curious about the “Trampoline effect.”
It seems to me that it might be observed in the beginning phases of
the drive, both in the “push” and the “pull.” Perhaps it could be
measured in the change of forces on the stretcher and oar handle.
Anything you can say to elaborate on this matter would be much
appreciated.
________________
Dr. Kleshnev’s reply follows:
Dear Charles,
Thanks for your support and informative message.
Of course, rowing is not a trampoline jumping and I’m not so excited
about this concept as four year ago.
Definitely, the oar cannot recoil, when the force increases at catch.
It can do it at finish, when force decreases, so some sort of
“trampolining” in rowing still exists. Therefore, it is important to
maintain pressure on the stretcher as long as possible at the finish.
At catch, the “trampoline” concept helps to understand better the main
idea: earlier acceleration of the point of support (the boat and
stretcher) makes acceleration of the athlete’s CM more effective.
Obviously, mechanics is different: spring board recoils itself, but a
rower has to provide this acceleration by means of fast increase of
the handle-gate forces.
Later (RBN 2008/07) I’ve found that the boat acceleration during D3-D4
micro phases could also be explained by other factor: change of the
leverage of the stretcher force, when a rower shifts it from toes to
heels.
I still think that “trampoline” effect makes sense in rowing, though
it should not be understood so directly.
You can quote this on the forum if you like.
Best regards
Valery