Scull (or for that matter oar) length
stan
applies to the handle is limited by the rower that a more efficent
impulse to the boat can be gained by shortening the drive phase by
rowing with a shorter outboard.
Another coach I know posed the question that does the gearing want to
be as light as possible without tearing the water?
The Rowing illustrated board seems populated by numerous people
esposing the tight span or stretcher 1cm forward with C2 fat smoothies
set as short as they will go. Arguing that the hydrodyamics are
better.
This is quite departure from the norm which as can be seen in the
various threads about bow verticalness or Singles at HRR is not normal
for the rowing community.
What do the wise people of RSR think?
Carl Douglas
> Volker Nolte's most recent paper suggests that as the force the rower
> applies to the handle is limited by the rower that a more efficent
> impulse to the boat can be gained by shortening the drive phase by
> rowing with a shorter outboard.
I hate to argue against Volker Nolte, but here I must.
In simple terms the force on the blades doesn't, of itself, matter a
damn. What matters for propulsion is the product of force x stroke
length. In the real world you can, for better accuracy, multiply that
by the propulsive efficiency. If you reduce outboard length, then the
force rises but the immersed stroke length falls in exact proportion so,
unless there are consequent improvements in rower power output due to
the resulting shorter stroke duration, there is no gain. However, the
increased blade loading will increase the mid-stroke stall, & that will
reduce the propulsive efficiency.
Looking at it from another angle:
This discussion is fundamentally about gearing. For any athlete there
is an optimum speed of action & you gear your action to facilitate that.
If the stroke duration is reduced, as indicated above, then the speed
of action must increase _without_ any decrease in the load at the hands
- you work harder for a shorter period in each stroke. It may be that
this will benefit the rower by moving their action to a more effective
speed, or it may be counter-productive. But that is an argument not
apparently addressed if Nolte's original argument which, as you state,
was about "more efficient impulses".
Actually, I'm unsure what can be meant by that last term. It is not the
impulse which is efficient but the product of impulse (= force at the
blade) & apparent linear movement of the blade (less any slip) that
moves the boat. And that takes us back to my first paragraph.
>
> Another coach I know posed the question that does the gearing want to
> be as light as possible without tearing the water?
There can be no stroke "without tearing water" & no point at which this
tearing first matters. There are strokes which tear water more or less
(according to how heavily the blade is loaded & a string of other
factors) but none that tear it not at all. This "tearing" is the
shearing of water, which occurs most around mid-stroke & most with the
higher loadings. It can be reduced, & usefully so, by rowing deeper,
because you get less shear & slip (or skid) when water extends beyond &
above the blade - top, bottom & sides - than when the top edge is
exposed or near the surface such that the pressure drop behind the blade
allows the water there to separate from the back of the blade.
>
> The Rowing illustrated board seems populated by numerous people
> esposing the tight span or stretcher 1cm forward with C2 fat smoothies
> set as short as they will go. Arguing that the hydrodyamics are
> better.
Well, they would, wouldn't they? In certain audiences uttering the word
"hydrodynamics" suggests to others that you know what you are burbling
on about. But it doesn't always make it true.
>
> This is quite departure from the norm which as can be seen in the
> various threads about bow verticalness or Singles at HRR is not normal
> for the rowing community.
The norm is not normal?? I think I'm confused there....
>
> What do the wise people of RSR think?
That presupposes any of RSR's contributors & readers are wise. The best
any of us can claim is that we try to think harder.
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 Hunt
This is similar to a topic I was considering: my coach has rigged my
single with blades 288/89 and span 158cm (a span smaller than usual,
and blades with shorter outboard, longer inboard, compared to what the
FISA rigging survey shows as average for LWT 1x, and than what most
lightweights I know use). From what I can see, while the load on the
blade is reduced and angular velocity of the blade is increased,
distance through water (or angle that is rowed through) is increased,
meaning you can row the same rating for same power? Would these larger
angles be more efficient at all? (If talking about the mid-stroke
stall which I however know little about I would presume this setup is
more efficient since the angle range where stall happens is passed
more quickly for a given rating, however due to the angles at catch/
finish the components of sideways force through the blade will also be
larger, i.e. propulsion forces lower when at an angle.)
Carl Douglas
That's a fairly large overlap?
From what I can see, while the load on the
> blade is reduced and angular velocity of the blade is increased,
> distance through water (or angle that is rowed through) is increased,
> meaning you can row the same rating for same power?
The long inboard would give you a smaller stroke angle, & might further
shorten the length at the finish by the hands being unable to pass/go
too near the ribs.
The narrow span would, otherwise, increase the available stroke angle.
Would these larger
> angles be more efficient at all? (If talking about the mid-stroke
> stall which I however know little about I would presume this setup is
> more efficient since the angle range where stall happens is passed
> more quickly for a given rating, however due to the angles at catch/
> finish the components of sideways force through the blade will also be
> larger, i.e. propulsion forces lower when at an angle.)
The side-forces are not indicators of inefficiency, contrary to what is
so popularly believed. Treat them as byproducts of what, at catch &
finish, is a very efficient process for boat moving, just there are huge
forces locked up in a gearbox which go nowhere & thus cause no losses
either. The side-forces are balanced across the boat & thus do not move
the boat. Nor do they to any noticeable degree move water sideways, so
again they incur minimal losses. They are the same as the lift forces
on the wings which keep a plane in the air - power is consumed to
overcome air friction to move the plane & its wings forward through the
air, but the lift forces are a byproduct which, as a first
approximation, do no work. As long as the plane keeps moving at the
right speed, the lift forces on the wings keep it up there very efficiently.
The ideal for an oarblade is that it does _no_ work in the water. If
water was solid & your oar could hook frictionlessly into it, then all
the work you do would go to propelling the boat. In reality, there is
fluid friction between oar & water but, much worse, there is midstroke
stall, which allows the blade to slip or skid through the water. When
you are at the catch, although it may take a moment to realise it, the
water is moving along the blade from tip to root. That is just like air
flowing over a wing, & the shape of the blade, & its loading, lead that
flow to generate lift forces across the convex back of the blade which
exactly counter that loading.
For there to be this efficiently generated lift, you must have flow
along the blade. As you near the midstroke, the longitudinal flow falls
& ceases. The process which generated lift are thus gone, so the blade
"falls" face first sternwards through the water. That slip, skid or
fall creates large amounts of turbulence - chaotically spinning &
undulating packets of water - which absorbs lots of energy. The energy
thus absorbed can be measured by the force on the blade multiplied by
the amount of that slip towards the stern. All that lost energy ends up
as your puddle and is unavailable for boat moving. And that's the
mid-stroke stall. You really don't want it, & going through that phase
faster will only increase the total energy loss.
I hope that explains more than it confuses. And I hope it will start to
help you to understand a) that there is nothing wrong or inefficient
about sideforces & b) that pulling hardest in mid-stroke "becasue the
forces are all in the right direction" is neither rational nor the best
idea?
IPS
> URLs: www.carldouglas.co.uk(boats) &www.aerowing.co.uk(riggers)
Then what should we do in order to get through that mid-stroke phase
as efficiently as possible? Keeping the blades buried is a given. You
suggest that trying to move quicker through mid-drive results in more
wasted energy, yet actively slowing through there seems to be counter
intuitive.
zeke_hoskin
Take a pair that tends to pull to a particular side. Lengthen the oar,
both outboard and inboard, for the "weaker" rower, preserving that
rower's optimum gearing. Result: same force, more turning moment, pair
goes straight. Drawback: shorter arc, therefore higher proportion of
stroke in stall regime. Probably requires longer rigger on that side,
one more setup hassle.
I put "weaker" is in quotes because it may be the case that the rower
in stroke position is slightly stronger, but that the bow rower exerts
more torque about the fin.
Carl Douglas
Good thoughts, which raise further questions & answers.
The boat does not turn about the fin. How & about where it turns
depends on the position of its centre of its resistance to any sideways
movement, which itself depends on its forward speed, fore-aft trim, hull
shape, fin form & location, etc. The boat will also turn differently
under rudder control than under oar control. And, in any case, the boat
when moving turns about a point way off to one side of its path, since
that path describes an arc through the water.
As regards balancing a pair's steering: this is done in good pairs by
adjusting stroke lengths & force profiles, just as a sculler does it.
In that way a pair with fairly mis-matched physiques can still go very
straight, but it demands that its crew row sympathetically. Taking that
a stage further, IMHO it helps in discussing the handling of a pair to
see it as a 2-person 1x - if that makes sense to anyone.
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
Carl Douglas
<snippage>
>
> Then what should we do in order to get through that mid-stroke phase
> as efficiently as possible? Keeping the blades buried is a given. You
> suggest that trying to move quicker through mid-drive results in more
> wasted energy, yet actively slowing through there seems to be counter
> intuitive.
The speed at which you transit the mid-stroke phase is dpendent first on
boat speed & then by how much stall you induce. A more pronounced stall
will still only slightly reduce transit time & the bigger the stall the
bigger the losses. So there is no money on "getting quicker through the
stall phase" as in reality that is a misapplication of effort.
The way to see this is to view the stroke as an investment of your
effort. You have to distribute 100% of your capital between catch &
finish, but as a physical being you are to a degree limited in how much
you can skew or re-shape that distribution without impairing your
ability to offload your available effort (force x distance) into each
individual stroke. To invest nothing in the midstroke involves a very
artificial action, & you'll still move at no less than boat speed
through that region. Of course you can reconnect to the final phase of
the stroke after a complete unloading but, since you can only pull so
hard at any given part of the rest of the stroke, that reduction in the
work duration by over-lighten the middle will leave you too much to do
at either end. Exaggeration is never good policy, but small
modifications can be.
This is something I've discussed before. To improve your return on
investment, moderately re-shape your force profile to fill out the ends
a bit more at the slight expense of the middle, In that way you do at
least get a bit more invested into the more efficient parts of the
stroke. But there will be clear limits to how far you can take it. So
what I'd say is that it'll pay to think about a more rapid connection at
the catch (e.g. Ivanov) & a better drawn finish. (In your case, Ian, I
am sure, you have a lot of that already ;) . Or you used to, IIRC.)
Another thing you can do is take the midstroke a bit deeper. That
reduces air entrainment behind your blade & even without air entrainment
is would still increase its drag coefficient when stalled. Where all
you've got to resist slip is pure drag, then you really do want to do
whatever increases that drag, & going deeper does just that. And you
see that by the less evident & greyer puddles, & by the fact that the
stroke seems heavier. Both are good indicators of less slip. Since
energy loss = slip distance x load on blade, that confirms a gain in
efficiency & a better RoI.
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
Walter Martindale
> URLs: www.carldouglas.co.uk(boats) &www.aerowing.co.uk(riggers)
My take on this is from observing people rowing with heavier and
lighter rigs, longer and shorter strokes, and higher and lower stroke
rates. Unfortunately it's all "eye" stuff and not supported by any
hard data.
People who win at racing have higher stroke rates.
People who win at racing have longer arcs in their strokes.
If someone has a heavier rig and is going 10 m/stroke but at 32,
that's about 320 m/minute.
If someone has a slightly lighter rig and is going 9.5 m/stroke but at
36, that's about 34 m/minute.
2 m/minute over a 4 minute masters singles race is a 4 metre
advantage. There are a LOT of assumptions that I'm not going to
bother with, but the good old "all else being equal" I'd go for a
higher stroke rate, as long as the stroke has a "live" look to it and
the "ratio" is good - what's "good" ratio? Hard to say - at
international race pace, there is more time spent in the water than in
the air, but it still looks controlled. Row the same stroke rate at
"club" or "novice" level and it looks like - well - club or novice
level...
Oh well - there has to be a balance between the art and the science of
all this stuff - the art has to be based on the science, but in a way
that gets people going fast and not overthinking it all the time.
W
Carl Douglas
Little to disagree with, Walter - except your maths. (Wouldn't
2m/minute for 4 minutes gain you 8m, or are things done differently in
the Antipodes? ;) )
But I don't think that, on all levels of this sport, we should fall back
on plausible assumptions. For most of us those assumptions might be
valid or make no useful difference. At the elite level, however, you
race for very high stakes on large investments. You don't design
commercial or military aircraft, or program their systems, except on
verified science & verifiable data. You design & match the parts on
racing cars with only the best available science & correlations,
evaluating performance with data you can generate & validate. And in
each case, while you allow for the human factors of flair & insight in
the pilot/driver, you very soon change human responses which prove
counter-productive, or those humans whose responses are inappropriate.
So, when discussing fundamentals of how to row fast (& there may be more
ways than one to go fast), we need to avoid touchy-feely stuff like the
plague. Too often discussions of rowing science collapse into the
apology that, "well, rowing's an art as well, so you can't get a grip on
everything". I think that's an unnecessary cop-out. You wouldn't have
flown from Canada to NZ had such attitudes prevailed in aviation, & I
think rowing is no less susceptible to in-depth analysis. But first we
have to clear the air of preconceptions that keep drifting in & clogging
up the thinking.
Rowing at club level will always reflect (if not always very accurately)
what happens at elite level. I remain disappointed by the poor 2nd
place given to the science of boat propulsion within elite rwing.
IMHO, of course!
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
Walter Martindale
Well of course your arithmetic is right - what you get when writing
with wine coursing through the system..
I do understand the need for the scientific investigation of our sport
so that the people pushing on the foot stretchers can have the best
equipment and the best technical model. However, I also understand
the need for those "in the know" to be able to get 'the message'
across to the people at the 'coal face' - if you will.
As a person who has facilitated coaching courses for quite a while, I
count myself a failure if, at the end of the "biomechanics" section,
the car salesman, the auto mechanic, the share-milker, and the legal
secretary are sitting there scratching their heads or merely shut off
hoping that I'll stop soon.
When they start nodding and "oh, I get it" when I've been chasing
velocity curves around, explaining things in terms they get (you won't
hear me say 'moment arm' too frequently in a coaching course), but
based on the science of the sport. THEY can then turn around and
teach/guide/coach/facilitate the group of 15-year-olds to learn to row
with good principles, and then those 15 year olds don't have to un-
learn a bunch of meaningless twaddle when they're trying to make it to
higher levels.
At the elite level in rowing, you're still dealing with a hooman been
sitting in a boat, responding to and blending with the movements of
the rest of the crew, the waves, the blades, the wind, and finally
racing other crews - THEY have to be able to "do" without thinking,
and it's the coach's job to help them learn how to "do" without
necessarily understanding why, or what they're doing - they need to be
able to do... Can Beckham explain the physics behind exactly where,
how hard, and in what direction he kicked when he was in his prime?
Or was it something he learned through countless hours of training?
How many rowers get deeply involved in trying to explain every nuance
of their technique, instead of having a gut-level "feel" based
understanding of how to do it? It's the coach's job to have them
learn that "feel", and it's the coach-educator-researcher's job to
help the coach understand how to train this into the athlete.
At least, that's what the folks at SPARC in NZ and the Coaches of
Canada seem to be saying, unless I'm hearing them with biased ears
which is another possibility..
Walter
Charles Carroll
> - you work harder for a shorter period in each stroke.
What if you looked at stroke duration from a slightly different perspective?
Instead of working harder for a shorter period in each stroke, you simply raised the rate?
This has been a question in my mind for the last month or so, ever since I read the following:
"[.] shorter drive time and lower rhythm (ratio of the drive time to the total cycle time) could cause decreasing of boat speed fluctuations and eliminate some energy losses (1). For example, shortening of the drive time from 1.0 down to 0.9 sec would reduce variation of boat speed by 3% and increase its average value by about 1%." (RBN July 2001)
Cordially,
Charles
Carl Douglas
I couldn't disagree, Charles. A higher rate allows you (provided you
coordinate it as Ivanov did) to reduce not just speed fluctuation but
also to lower the force you must apply to maintain the same work rate.
I have always advocated that when you need to sprint you do that by
raising the rate, not hardening on. When you're told to "raise the rate
through the water", that is both impossible & counter-productive. It's
impossible, 'cos the tiny increase in boat speed does not allow any
significantly faster blade movement in the water except through
increasing stall (usually a direct result of rowing shallow to match the
unrealistic demand), & it makes no sense since to raise rate & pressure
is a 2-way hit that bids fair to cause premature fatigue. Instead, you
rely on your muscles ability to do disproportionately more reps at only
slightly lower loadings - so you reduce pressure but by less than you
increase rate, the stroke feels easier & more lively & the actual
work-rate increases without it suddenly feeling impossibly heavy.
Carl Douglas
No disagreement. When you're coaching, which we're _not_ doing here,
you engage with the mind & body of your student. Every student has a
different way to see & to learn, so you keep re-packaging your advice in
garments of varying rationality - & when you find one that does the
trick, that's all you need & you don't need to confuse them with the facts.
That's fine when coaching. But when we're discussing the science, then
we should keep that science clean & not fog the understanding of
onlookers by suggesting it is impossible because rowing is partly art,
or that the science may be fine but is not relevant to real rowing.
What is highly relevant, in discussing the science, is at times to
examine how to get the message across in a productive form to the great
majority who have no wish to engage with that science. Which is back to
the art (which is really a science) of education - how to get into their
grey matter the real feelings of the actions you want 'em to perform.
After all, it is just as useless to say "do this" to someone who has no
idea what "this" feels like when done properly.
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
Xeno Muller, www.gorow.com
suddenly get faster.