P35 has 2 sentences on blade depth:
"Sit at the catch with the blades buried - just the blade and not the
shaft. See where your handle height is and then try to maintain it
through the drive".
Whence this belief that none of the shaft should be in the water?
Whence its corollary - that the top of the blade should run at surface
level & no deeper? Where are the written analytical or experimental
justifications for these popular mantras?
A blade should not wash out, as it then moves through the water rather
than staying with it, stirs it to froth, doesn't move the boat so well &
thus - in the words of Sellar & Yeatman - is a Bad Thing. Indeed, the
final paragraph on that same page correctly identifies the need for
tight, dark puddles. Which is blindingly obvious, but in conflict with
what went before
The physical processes around an immersed oar with a variable depth of
immersion have no reason to flip abruptly as the top of teh blade
submerges. So how & by whom was it decided that, suddenly, it all
changes immediately the blade reaches its flotation depth? What
physical transformation introduces a discontinuity or reversal at that
point by introducing a new & contradictory set of rules?
Yes, the oar shaft, being circular in section, is not best shaped for
boat propulsion - it slips too easily through the water (hence that
flatter bit at the end - the blade). But that means its drag will also
be rather low. Are we so dumb that we must invent fictitious rules
defining precise go/no-go boundaries?
Some simple facts:
1. The performance of the blade certainly improves progressively as it
goes from non-immersion through partial immersion (washing out) to
so-called full immersion (top edge level with water surface). But it
continues to improve as you go yet deeper. There is no sudden cut-off.
2. Immersing part of the shaft in the water is, at the worst, a very
slight source of drag but, when the boat is being rowed hard, at
mid-stroke the blade "turns" in the water not about its centre but
around a point a short way up the shaft from the blade. And the concept
of a point of rotation is anyway meaningless near catch & finish.
3. So a fair (if variable) chunk of the shaft can be immersed before it
can cause _any_ parasitic drag in the water. Until then it actually
contributes, marginally, to overall propulsive efficiency around
mid-stroke, where most energy is otherwise lost.
4. If you do go a tad deeper, to where water is slightly back-watering
over the shaft, that water is still moving but slowly relative to the
immersed shaft so, drag losses being proportional to the cube of
relative velocity between water & shaft, any net losses will remain
trivial for some continued increase in depth.
5. Meanwhile, the deeper you row the blade, the less chance of air
being entrained behind it. That entrained air, by forming a cavity
behind the loaded blade, drastically cuts the essential _tensile_
connection between blade & solid water (it's the back, not the face, of
the blade which transmits the propulsive forces into the water). Thus,
up to a surprisingly great depth, the deeper the blade goes the greater
its efficiency becomes
Since going deeper that the popular prescription continues to increase
blade efficiency, & since it only slowly, if at all, incurs any penalty
from shaft back-watering, a fairly strong case can be made for rowing
deeper than conventional wisdom suggests. And, FWIW, study of blade
depths of the more successful rowers & crews tends to support that case.
Despite the above, which is simple to follow, our sport widely maintains
a collective faith in the spurious concept of a divinely-ordained blade
depth limit.
Apologies if, inadvertently in the above, I just broke any treasured icons.
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)
And you have no comment to make on the cover of this marvelous rag!
Look at the way this younglady is carrying her shell. I took one look at
that cover, photographed it, and sent the photo to Mike Sullivan.
That cover is the sort of thing that would have really thrown me for a loop
had I seen it in my novice days. I probably would have left a post on rsr
asking if this was the way to carry a 1x.
As for Tom Bohrer, the author you quote, I like him a lot. Over the years
his pieces in the Rowing News have helped me immensely. In fact his article
a few months ago on overextending at the catch changed my rowing. But does
this mean he is infallilble? By his own admission, Tom is not the greatest
sculler in the world, although he is still ten times better and faster than
I am.
Just take everything Socratically. Nourish your curiosity. Raise questions.
Learn as much as you can. And be forgiving of the mistakes others make.
"What is the first business of the philosopher? To cast away conceit; for
it is impossible for a man to begin learning what he thinks he knows."
Warmest regards,
Charles
Ps. Our friend sent me photos of his new boat. Talk about "understated!" It
is just magnificent!
You know how Sully & I prefer boats to be carried. But none of us
should fire off every time with every loose screw that rattles around
our empty skulls (or sculls). So I let such things pass ;) Besides,
carrying boats that way helps keep the trade in business.
I would never decry Tom Bohrer's expertise. Nor the value of his
columns. Remember: they who get nothing wrong also get nothing right.
I try hard to get many things right, & I may make more errors than most
in the process.
Anyhow, this ain't about perfection, just about highlighting popular
fallacies - for the dubious benefit of those few in the northern
hemisphere who lack the sense or time to be off on their summer hols.
And why does this particularly irrational fallacy hold such sway within
rowing? Why do we just love to make up daft, untested rules? I tried
calling Socrates, but his secretary tells me he hasn't been back in
since he got to work on hemlock, & I don't think it had anything to do
with woodwork....
Glad you like those photos, taken here just before the boat went into
its box for its trip to Seattle. But when will he get to scull his new
beauty?
While on this boaty digression, those with access to World Rowing
on-line magazine might like to view the article on P32 of:
http://www.worldrowingmagazine.com/worldrowingmagazine/200907/
It's an article on Frans Goebel, with a couple of shots of that still
very fine sculler in his rather beautiful boat.
Actually I thought the more egregious assertion was: "Blades Out
Square--There's no debate here. You are either coming out fully square
or your are not." Now, while on the surface that is a correct
statement, I would certainly debate the effectiveness of waiting to
feather until the blades are completely off the water. This makes for
a needlessly mechanical releases and often upsets the balance & run of
the boat. (I do think square-blade-rowing is an essential drill, but
like all good drills, it exaggerates to teach a lesson.)
Steven M-M
Re: Carl's OP. At the 1999 FISA coaches conference, Canberra, for
some long-forgotten reason we were viewing the ITA LM2X, at the time a
highly regarded crew. A coach from another nation stood and asked
something along the lines of "Aren't their blades deeper than we
usually coach?" and the ITA coach replied along the lines of "Yes,
because it's better for speed," or something very close to that. For
me it was a "lightbulb" moment. I recalled working with beginners,
whose "deep" blade I was trying to get more shallow to match the "just
buried" blade, and thought, Hang on - that deep blade is making them
turn, and the shallow blade is slipping - what if I stop worrying
about the deep blade, and get the shallow blade in the water a bit
deeper, maybe the blade-water connection will be more efficient and
they'll go straight, faster than with the blades skimming with the top
edge at the surface... So - now I look for about 40 cm of shaft under
water (or perhaps more) with a sculling blade at moderate pressure,
and I think about how the really fast guys go in pretty deep...
WRT the "out square" stuff. Nolte's work from the 80s (described at
the 1992 Barrie Ontario Canadian coaches conference, if I recall
correctly - it was one of those conferences that stuck in my mind
because of the "discussion" between Nolte and Spracklen) and you can
replicate it with frame-by-frame video of elites)) shows that the
bottom edge of the blade is clear of the water while on the square,
and the handle continues towards the bow while the athlete then
feathers the blade, changes direction, and commences the recovery. To
confirm this, get good side-on video of an elite crew/single at race
pace. Advance the video frame-by-frame, and record the position of
the end of the handle each frame - relative to the boat - and also
record events such as
when the bottom edge of the blade touches;
when the blade is fully buried;
when the top edge of the blade is exposed;
when the bottom edge of the blade is clear;
when the blade is squared up;
when the blade is feathered.
You can also record how many frames it takes for each of these events
(burying, releasing, squaring, feathering)...
You'll most likely find that a lot of coaching doesn't match what
elite performers do - who do you listen to - a coach who's telling you
stuff that's been "the wisdom" forever whether or not it is supported
by evidence, or the people who are making boats go fast, sometimes in
spite of their coaching?
The old fashioned way to do this would be to take a piece of overhead
projector film, overlay it on the screen, trace the gunwale and a
couple of reference points such as riggers, and then put a "dot" where
the end of the handle is. Then advance the film, re-index the film
with the boat, and "dot" (digitise) the handle, repeat until the
handle is back where it started. Put a "tick" on the line of dots
indicating all the above events... I've done this, and it (once
again) changed the way I coach.
I no longer have access to Rowing News, but would suggest that as
reported in this thread, Tom Bohrer is wrong about blade depth, and
right about "out square"..
Cheers,
Walter
Walter -
I'd also beg to differ on the blades-out-square aspect (aren't some folk
just plain cussed?). But I have valid reasons (other than natural
cussedness, of course).
Let's first consider whether or not the blade is still loaded as it
rises through & from the water, & whether we want VFM from every inch of
the stroke, or are content with Brownie points for style regardless of
possible loss of content.
If the blade leaves the water square, if not to backwater it must, as
you confirm, be moving astern. Due to its rotation about the pin, the
blade's face-on velocity (angular velocity) WRT the boat is maybe only
~75% of what the boat's speed would otherwise suggest (which makes
finishes a lot easier) but is still substantial. For the sculler, that
reduction in velocity is more meaningful at the handle than for the
sweep rower since the sculler's hands can pass the ribcage diagonally,
whereas the sweep finish brings the hands abruptly to the body - just a
general observation. Anyway, as you say a square finish demands
continuing & useless hand movement to the bow after the blade has
extracted. And it means you have a poor hydrodynamic relationship
between blade & water which tends to prematurely expose the back of the
loaded blade & thus to disconnect it.
So what's wrong with a finish which feathers (partly), before & while it
extracts? I think that you, Walter, accept as I do that as you approach
the finish the blade is once again acting as a foil, working largely by
the generation of lift, due to its action generating a flow from root to
tip that curves along & around its convex back face. And I'm sure that
you'll agree that, while you are extracting the blade, there must also
be a vertical component to that otherwise horizontal flow?
Now if you feather to some degree then, instead of having to keep the
hands moving to the bow, they can move more nearly vertically during the
extraction - just as a part-feathered blade held in the finish position
tends to rise through the water. But also you will now be able to keep
more area of the back of the blade covered during that extraction &, by
the downforce at the hands, to generate useful (propulsive) lift from
this vertical action. And, of course, your blade will be more nearly
feathered as it emerges & more nearly (or actually) stationary as it
clears the water. So, no continuing hand motion into the bow after
extraction, allowing a slightly longer useful draw, & a more effective
last part to your stroke.
Just as we agree that rowing deeper has performance benefits, so I see
real benefit in being prepared to analyse blade fluid dynamics in truly
3D terms (or should I say 4D, it being such a time-dependent action?)
which consider also the fluid dynamics of the vertical motions (catch &
finish, & even through the rest of the stroke) as well as those in the 2
lateral directions. It helps to indicate how hard it may be for some to
see the need for such multi-dimensional thinking if we remember that
many rowers think only in terms of a linear, near 1D, action - which is
why we get that nonsense about needing a hole in the water so we can
extract the blade, & an emphasis on the work done in the midstroke.
Some might think the fluid dynamic significance of these vertical
actions to be of scant importance, but I doubt any rower, let alone the
complete rower, can really afford to spurn minor gains.
I'd welcome your thoughts.
However it raises questions to me:
1) Perhaps this is a complete lack of understanding of hydrodynamics
on my part - when the boat is being driven along it is also lifted out
of the water, and as it decelerates it drops back down again. Whilst
lifted it goes faster partly because the wetted surface area is lower
(main part being that it is the drive phase of course). When the drive
is over the boat drops down as it slows. Surely, if the blades have
been deeper in the water, the shafts will drag the boat downwards as
you extract them? I accept the point that the blades themselves do not
add significant additional drage, but their effect on the hull..? Is
it simply that the additional speed from the depth outweighs the drag?
2) I am always aware that the main discipline discussed here is
sculling and that for one person to change their scull depths can be
done as it is symmetrical. With sweep however this is harder to do (I
know this has been discussed before) but I don't see how to teach
people to achieve a magical unknown optimum depth with people on
either side trying different things. It surely is not going to work?
As far as I can understand it- with sweep at least- we *should* teach
people to row with blades just submerged, but as they gain more
experience that should be progressed into moving the blade deeper.
Particularly with crews used to rowing with each other - possibly
moving the oft seen tape markers to deeper position progressively to
ensure the crew can change together.
I don't receive rowing news so I am not sure of to whom this article
is aimed. It seems to me that for rowing purists, top end athletes
etc, what you are proposing Carl is about right (with the question 1)
still standing) but if you are talking about how to teach people from
beginner to intermediate level, I just don't think it works to take
that purist approach from day one...
If I am wrong on the drag I would be very interested to know - it is
the one thing that has really prevented me from rushing out and
teaching it since I first heard the argument!
James
I'm not theorizing - I'm reporting observations of elite scullers..
Think of "follow through" - when you accelerate the handles to move
the boat past the blades, when the load comes off, you have to follow
through in the direction of movement... Almost like "waving goodbye"
to the puddle. If you try to change directions without this follow
through, you get jerky movements, or unload your blades before you
take them out - frankly I'd rather people were pushing right up to
extraction...
It's what happens. Digitize some elite performers sculling the way
they do, and see what they do... (frame-by-frame - I did this 10 years
ago, - and more recently - ...)
W
Hey Charles,
Can you please tell us which issue it was? I went through a contents of back
issues and can't find anything relevant.
I also may have some questions regarding your post "Feet and Foot Stretcher"
from 13th of July. If you don't mind.
--
Yours Virtually, Zbigniew A.
to e-mail me directly best use zibi(at)netcom,no
Hi James -
I fear that we're into another of those popular fallacies. What you see
as the boat lifting is more a case of the bow lifting because the load
on the blades, acting below the centres of drag & mass, generates a
couple which pitches the boat up at the bow but down at the stern.
Nor would it be a good idea to invest energy ino raising the boat, since
that immediately reduces the energy available to overcome fluid drag. I
know we like to use morally uplifting exhortations about "lifting the
boat", but while this has great psychological value I think its physical
credentials are very questionable.
Now to the consequences of oar shaft immersion: If we suppose that you
did want actual uplift then, slight though it might be, the act of
immersing a bit more shaft will reduce the boat's displacement - on the
Archimedean basis that the mass of water displaced must always balance
the mass of boat, blades & crew, & because there'll be some very slight
uplift from the vertical component of any drag as you lower the shafts
(& blades) into the water. But I'd already noted that there's very
little drag on a short outboard length of a circular section oarshaft &
since at the finish we're not proposing any rapid vertical motion (& the
water at the finish is actually flowing partly _along_ the shaft, just
as it's flowing almost entirely along the blade) you'll get very little
downthrust either.
So, in short, the significant gain in propulsive efficiency from rowing
the deeper blade comes at no significant price - it is all profit. The
deeper blade turns less of your effort into froth & slip, leaving more
for simple propulsive effect. You go faster because you're throwing
less energy away at the end of the blade.
> 2) I am always aware that the main discipline discussed here is
> sculling and that for one person to change their scull depths can be
> done as it is symmetrical. With sweep however this is harder to do (I
> know this has been discussed before) but I don't see how to teach
> people to achieve a magical unknown optimum depth with people on
> either side trying different things. It surely is not going to work?
Good question. Equally, with low-standard crews there's often little
evidence that they row at any set depth, let alone all the same depth.
This is where I'm more with Tom Bohrer: it's a good (or better) idea to
show your rowers the height(s) at which you want them to draw their
hands, then the blades will eventually follow.
The novice has a constellation of coordination problems, plus a
pernicious fear that's too often coached into them that, if they get it
wrong at the finish, they'll catch a crab. Too rarely are they told
that crabs result only when water is allowed to overtake the blade,
either because there's no work on it near the finish, or because the
rower is so keen (through worry) to extract it before the possible crab
that they actually try to push back against the irresistible flow.
First of all, the possibility of crabs should really not be drawn to the
novice rower's attention as that begets fear. Secondly they should be
told that they can & should pull really hard at the finish & the blade
will come out naturally provided they keep the load on the handle.
Once you get that clear, & demonstrate its reality to them e.g. with
single strokes to backstops, they'll be happier stick the blade in & to
row to a solid depth. Until doubts are dead & buried, traces of their
damage remain below the surface of otherwise quite competent strokes.
The other depth problem is that new rowers may try to fix the angle at
which the upper arm projects from the shoulder joint - they tense up
because they're in a boat & this can be one consequence - instead of
learning early to pull with loose arms so the hands can travel in a
straighter line.
All such issues need easing & teasing out of the individuals concerned,
who should not be put under extra pressures until those particular
problems have been resolved.
>
> As far as I can understand it- with sweep at least- we *should* teach
> people to row with blades just submerged, but as they gain more
> experience that should be progressed into moving the blade deeper.
> Particularly with crews used to rowing with each other - possibly
> moving the oft seen tape markers to deeper position progressively to
> ensure the crew can change together.
>
> I don't receive rowing news so I am not sure of to whom this article
> is aimed. It seems to me that for rowing purists, top end athletes
> etc, what you are proposing Carl is about right (with the question 1)
> still standing) but if you are talking about how to teach people from
> beginner to intermediate level, I just don't think it works to take
> that purist approach from day one...
>
> If I am wrong on the drag I would be very interested to know - it is
> the one thing that has really prevented me from rushing out and
> teaching it since I first heard the argument!
>
> James
>
>
If you can get rowers thinking in terms of hand heights (& arm
looseness) rather than bladed depths, until you see they're fully
responsive to that approach, then you'll be able to take them
progressively to being able to row at whatever depth you (& they) want.
Then you can even start to profile the paths their hands take, so as
to control depth variations through the stroke.
We're all fumbling in the gloom towards better ways to do things - hence
these discussions between those of us who really do care. Meanwhile the
shouty types will keep on shouting what their own coaches shouted at
them (& so ad infinitum!).
Walter,
I don't have access to high quality frame-by-frame video, but take a
look at: http://www.invernessrowingclub.co.uk/strokecycles.html There
aren't many good shots of blades but the sculling sequence of Xeno &
Neykova and rowing of the Aussie 2-, Rom 2-, USA 8+, & Ger 8+ give, to
my eye, support for the observation that top scullers and rowers begin
the feather while the bottom 1/2-1/3 of the blade is still covered.
Xeno coaches square out, then feather, but at least in this sequence,
it appears to me he has a more "rounded" release. Do you see "square
out, then feather" in these sequences?
Steven M-M
Thank you! A great answer which has caused me to think of things I had
not considered before- the concept (pardon the pun) of immersing a
blade reducing displacement hadn't occurred to me.
When I was asking the question I had in mind a session when my crew
were testing a boat out prior to borrowing it. The crew were "looming"
in a way that was without question slowing it down. To cut an
otherwise long story short, it turns out that the blades were not at
the right pitch for the gates and it was causing the forced error. In
my mind I had the association: blades too deep = slower. Despite
having read here before that depth could generate speed. What I
suppose I should have thought through was that the pitching was
causing the depth AND an awkward angle which caused the extraction
issues and lowering of speed.
The issue of crabs amuses me - I don't ever dwell on them when
teaching beginners, but I did once have an athlete so prone to them,
also to falling off his seat and a host of weird and wonderful reasons
for catching a crab, that we invested some time teaching him how to
recover from them in case he did so in a race. Oddly I don't think he
crabbed again after that lesson...
I do tend to focus on talking about bring hands in to the right place
rather than the depth of the blade, more by accident that design.
Having said that, visual learners like to have something to look at -
their hands at the finish is not a good option! I wonder then whether
I should start the year with the boat rigged a little high for the
crew (which according to Nolte helps keep shoulder position correct)
and then through the year gradually drop the heights so that hands
stay in the same place and the blades get drawn a little deeper?
Perhaps this is a constant way in which a sweep crew could be changed
together?
Does that make any sense?!
James
Inadequate depth for sweep rowing does seem to be the norm in club
crews, but I'm not sure whether that is just from coaching, or whether
over-gearing has big influence, and when crews aren't rowing that well
together it's physically punishing for anyone who is getting effective
depth.
Rowers do know that rowing shallow & washing out is a real cop-out - a
way of blatantly cheating on your crew-mates. But only to that extent
is it accepted that more depth is better than less.
Once a rower is rowing the blade top flush with the surface, no one can
say they're washing out. It then gets a lot harder for coach to argue
for going still deeper, while a forest of spurious arguments has been
thrown up to defend rowers from having to go deeper - which is probably
why "level with the surface" is the accepted coaching objective. Even
so, you see plenty of washing out with crews going slowly as a result.
As you say, rowing deeper feels a lot harder. That's not because it
makes you pull any harder (only you can decide that) but because it is
more efficient. That means the blade slips less, moves the water less &
the stroke takes a bit longer to complete. There's nothing you can do
to change this - pulling harder makes no difference. But, to add insult
to pain, you then get accused of being late on the extraction!
Then come the creeping, bogus arguments that a bit of blade slip is
desirable as it's "a kind of gearing". No, it isn't. Slip is a
profound source of lost efficiency, just as wheel spin is a way to
generate heat, waste energy & reduce propulsive efficiency & not another
way to gear down a train or car.
Were there an objective way of measuring each rower's individual
contribution to the moving of the boat, it would soon become clear that
there is a continuing correlation between greater blade depth &
increased boat moving effectiveness, regardless of rower power. Yet
because rowing has wrapped itself in an orthodoxy based on unscientific
myths, it continues more obsessed with style than "how it really works".
That's why film footage so rarely shows the blades: we don't as a
sport understand (or much care) what goes on at that end of the stick,
we kid ourselves it's all sorted, & we have instead persuaded ourselves
that it's what the body does that is all important. So we see no need
to study the interaction between blade & water.
Hi Steven,
Well, I've had a look at a few of these and yes, the blades do seem to
still be a little in the water when they start to feather. It also
looks like some of their handles are continuing towards the bow during
the feathering, but it's not the best video.
They're definitely square until most of the way out. Are they cutting
off propulsion by stopping the push and feathering before completely
out? I realise that they're champions, but could they have been
faster? I've seen video of some pretty good athletes completely clear
of the water before feathering, too...
When coaching, I ask people what's the most important part of the
stroke, and while they're thinking, I say "All of it."
Rgds,
Walter
My guess is theat at lot of this is individual experimentatioin and
finding out what depth, and what power applicaion is best for each
person's innate gearing, strength, as well as rigging. Just my humble
opinion from a frequent lurker.
Steve Giddings
> ...
>
> read more �- Hide quoted text -
>
> - Show quoted text -
Zbigniew,
Delighted to. It is The Rowing News, Volume 16 Number 7, September 2009.
Also I just sent you a private email.
Cordially,
Charles
Superimpose a Macon blade onto a Hatchet & you'll find the differences
are not quite as you describe. The hatchet shape is created by
stretching the outer part of the upper edge up towards the waterline &
the inner part of the lower edge downwards. (On the surface of the
earliest Hatchets you could actually see how the Macon shape was
extended into the Hatchet in just this way). Thus the Macon blade runs
diagonally through the Hatchet, with its upper edge almost everywhere
running _deeper_ than that of the Hatchet.
This greater submergence of most of the top edge on Macons may well
explain why the originally-claimed astounding difference in performance
with Hatchets was not seen in practice.
Which brings me to your reference to that curved top lip. If blades
worked by pushing water, as is so commonly but wrongly believed, then a
lip might help. In reality, however, the blade locks into the water not
by pressure on its concave face but by tension within the water covering
its convex back. As I noted in an earlier posting, shallower immersion
(e.g. top just below water surface, or higher) allows the fall in
pressure in the water behind the blade (due to that tension) to
precipitate a rapid fall in water level behind the blade. This
sufficiently reduces the immersed area & increases aeration of the back
of the blade that the tensile connection is first weakened & then
disrupted - breaking the essential blade/water connection. A similar
phenomenon is well understood in sailing, where entrainment of air down
the low-pressure face of a rudder, or even a keel or dagger-board, can
cause sudden loss of control.
Which returns us to the original argument that, contrary to Tom Bohrer's
advice in the latest Rowing News, for the best results you should row
the blade significantly _deeper_ than the "flush with the surface"
target of conventional wisdom. And you should do this regardless of
your innate gearing, strength or rigging, since the objective (if you
wish to move fast) should always be to row an efficient stroke, not to
row a less efficient stroke because it's easier that way.
Sure, a more efficient stroke takes longer to pull through as it slips
less but, by slipping less, it throws away less of the energy you invest
in each stroke. Throwing invested energy away is no way to get the best
out of your rowing, or anything else & is certainly not a cunning type
of gearing. As pulling harder on a deeper, thus more efficient, stroke
won't reduce the time it takes to complete, you may also need to adapt
your stroke/recovery rhythm, & maybe even your stroke length at first,
to the new realities of the deeper stroke.
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
There's not much boat lifting effect (the bow lifts, the stern doesn't
dip quite as much), for one thing. Then - well, if you were dragging
the boat down, you'd be doing it by pushing down with your hands on
the sculls to extract them. Think about how the finish feels - you
don't even notice that you're tapping down, normally. Certainly
there's not any significant force; and since there is already the
significant force of your body weight pushing the boat down, whatever
little extra your hands provide will be not worth worrying about.
> 2) I am always aware that the main discipline discussed here is
> sculling and that for one person to change their scull depths can be
> done as it is symmetrical. With sweep however this is harder to do (I
> know this has been discussed before) but I don't see how to teach
> people to achieve a magical unknown optimum depth with people on
> either side trying different things. It surely is not going to work?
On that theory, why not just stay out of sweep until everyone can row
the same way on both sides..? All that will happen is that the balance
will be slightly upset (and it will be a small effect) until both
sides compensate to sit the boat again, or to row better. So, why not
simply coach the less effective people to row better instead of asking
the people who are already rowing better to do the wrong thing?
Pete
Pete,
I think perhaps there are two conversations or sets of uses going on
at once and one assumed statement:- Carl is talking about the ideal to
which we all aspire. He knows from what I have said before that I deal
with complete beginners - there is no need to consider those of
different standards - there are none, they are all completely new to a
boat never mind the fine art of establishing the optimum blade depth.
My first question was for the assumption of that ideal - however I am
a cox by origin (though competent with a blade) so sometimes I do miss
how things feel.
The latter part was to do with those beginners. I defy anyone to tell
a group of people with a blade in their hands for the first time to go
out and put the blade in the water to an unspecified depth with no
visual references or experiences against which to compare. No matter
how hard they try they will not get it right or consistent across the
crew. They need a visual reference to compare to until they have
learned the basics and the feel, then they can be coached into
changing what they now perceive as the correct feel/depth.
I think I am to take it from "then why not stay out of sweep..." that
you mean to teach everyone to scull first? Oh for that little luxury!!
I moved clubs at the start of last academic year to try and assist a
club with 1 pair/double and one 4+. Trying to send people out sculling
to get the finer points right in a scull was unlikely in the
extreme...! [If anyone has any sculls in their clubs they don't need I
would be VERY grateful, we may be able to find some small funds!]
Apologies for assuming everyone would know something of what I am
involved in!
James
(snip)
> Sure, a more efficient stroke takes longer to pull through as it slips
> less but, by slipping less, it throws away less of the energy you invest
> in each stroke. Throwing invested energy away is no way to get the best
> out of your rowing, or anything else & is certainly not a cunning type
> of gearing. As pulling harder on a deeper, thus more efficient, stroke
> won't reduce the time it takes to complete, you may also need to adapt
> your stroke/recovery rhythm, & maybe even your stroke length at first,
> to the new realities of the deeper stroke.
>
> Cheers -
> Carl
And - just for the sake of really flogging the horse - the less the
blade slips, the more the boat moves, yes?
8-)
Walter
No, the intention was that you are never, however you do things, going
to coach a boat where everyone does the same thing on both sides,
whether that's the right or the wrong thing. And even if you did, when
you tell them to change something then they will not do it all
together and your boat will do different things on different sides.
So, why not simply coach them to do the right thing? I assume you
aren't coaching your beginners to row the whole outing watching their
blades from the catch to the finish, so they can't see where their
blades are until near the finish most of the time anyway. The blade
height will surely change through the stroke, so they'll have no idea
whether they really have their blades in the position you coach except
near the finish. Fine, you can worry about how telling them to row at
some loosely specified depth may make them inconsistent and the boat
unbalanced - but why? They are inconsistent anyway, the boat is
unbalanced already, your coaching will be pretty similar whether
you're coaching blades at the surface or a bit lower: '3, too deep at
the catch.. better... 4, deeper, ..'. If you're really set on the
idea of a visual reference (which they cannot see for most of the
stroke except by looking round and rowing with a different body
position to normal...), put red tape a little way up the oarshaft and
tell them to cover up to the tape.
Pete
So, to my thinking, the question becomes, how much deeper is enough,
and does the increased efficiency outweigh the negative impact of the
greater time and/or energy required for the vertical movements at the
entry and the extraction, which do not effect forward motion, and also
may impact the timing of the catch and the finish? Is this blade
specific? Is it predictable? Is it dependent on the amount of force
applied to the blade?
Steve Giddings
There can be no hard & fast answers, but first I should say that I think
you will spend no significant extra time or effort in entry or
extraction. We are not talking about immediate deep burial, just a
well-buried catch followed by progressive deepening through the
mid-stroke, and then a gradual reduction in depth (but still properly
buried) towards the finish. Let me explain further:
The tendency for the water to recede from & expose the convex back of
the blade at any depth of immersion is amplified by several factors:
1. Load - the greater the load, the deeper you need to be to ensure the
blade is completely embedded within the water & not aerating. At the
catch, & shortly thereafter, the load is not very high. We think it is.
We are told it should be. It would be good if it was. But the
reality is that the load takes time to build. However, in the
mid-stroke the load is high, which is where depth becomes most important.
2. Flow direction - if the flow past the blade is relatively swift & is
parallel with its back surface, then the low-pressure region is being
continually re-filled with new, smooth, previously undisturbed water.
The flow is along the blade near the catch & finish, which thus reduces
the tendency for the water level behind it to drop & the blade to
aerate. In the mid-stroke the flow is from face to back, under the
blade, around its ends &, but only if it is "properly" buried, over its
top edge. But if the blade is near the surface, this water going behind
the blade is very frothy & can't in any case adequately replenish the
cavity growing there.
3. Duration. The longer the blade spends with water coming face-on,
the more likely that an air-filled or aerated cavity will form behind it
- which describes the mid-stroke to late mid-stroke situation & is a
special case of 2 above.
The deeper you row, the more efficient the blade becomes, but clearly as
you go deeper the process must be subject to a law of diminishing
returns since at no depth will you get 100% propulsive efficiency. So,
while it is easy to explain & justify the need to row deeper when most
of us row evidently too shallow, & while one can further expand on where
in the stroke to row deepest, it is not possible (without detailed
experiment on a variety of stroke force profiles, & a knowledge of each
rower's stroke force profile) to give precise rules on exactly how deep
to go & in what progression through the stroke.
We are here setting out the hydrodynamic reasons why rowing deeper than
flush with the surface must enhance stroke efficiency. Indeed, the
simple fact that if you row deeper it feels harder & takes longer is a
strong indicator that it must be more efficient. Now it is up to
individuals & coaches, if they wish to, to run with this ball & see
where it takes them. It's a journey of exploration, not a predetermined
bus ride. Rowers so often want precise rules spelled out to them (even
though they will probably break or adapt these!) before doing something,
but this is a case where the initial benefit is very clear & the point
where new sources of lost efficiency may start to take the shine off the
process have yet to be established & may differ for each person.
As an aside: had you considered how the traditional lugging oar works -
you know, the whaler or longboat oar which has a long straight blade
which is an elongated diamond shape in its cross-section? With this oar
you don't stick it in at the catch & pull horizontally through, 'cos
that is very inefficient, with lots of slip & turbulence. Instead a
dipping stroke is used, the blade being driven & cutting downwards,
edge-first, at a steepish angle & then being being drawn back to the
surface again at an opposite, steepish angle. Used thus, this kind of
oar is really rather efficient. It acts as a hydrofoil or under-water
wing on both paths - due to its diamond or lozenge cross-sectional
shape, which is a reasonably efficient foil in either direction. Its
vertically angled motion through the water generates lots of lift in the
boat's forward direction & relatively little drag, & it lends itself
well to use in a relatively slow & heavy craft. Only as the boat speed
increases towards that of rowing shells, giving insufficient time for
performing this largely vertical action, do we need to use the long
stroke & the conventional scull-shaped rowing oars. But that doesn't
mean we should completely flatten out our stroke action, nor that we
should row right at the very surface.
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
Yours, Magnus
Those are excellent points, Pete.
I would add that in a crew the effect of unequal blade depths on balance
tends to be less than in a single or pair, there being a fair chance of
a deep one cancelling a shallow one. The real pig is when all of one
side rows shallow, or finishes low, & most of us have been in one of
those in the past.
The novice rower has many problems to overcome &, sadly, they get
inflicted not just on that person but on the rest of the crew. So the
task of coaching novices, which can be the most rewarding of all
coaching tasks, does need the patience of Job on both sides of the bank,
plus a few wise words to increase relaxation, some simple drills to
establish better confidence & reduce the human tendency to over-correct,
& lots of little bits of individual encouragement.
I'd prefer not to put tape markers on the shaft as they give the false
notion that you must go straight down to that mark & stay there. Better
to accept a degree of instability & irregularity & progressively to
nudge each rower towards your own objective, thus wearing away their
overall instability & giving the whole crew a steadily improving
experience. No one rower's changes can have much effect on the boat,
which makes it that harder for them to learn those changes. So it is
best if everyone can be helped to make their own most important
improvements, which will not be the same as the next person's, which is
why instruction should be individual & low key whenever possible - &
limited to only 1 topic per person per outing. In that way the crew
will feel itself improving together, as the different bumps are ironed
out simultaneously, & each member will have the feeling that it had a
lot to do with changes they themselves made.
Obviously that kind of subtlety is less showy than megaphone
dictatorship, but worth a try.
The less the blade slips, the more efficient the stroke!
The less the blade slips, the less energy you throw away!
The less the blade slips, the longer the pull through!
The less the blade slips, the more the boat moves!
Does this remind you of Bourne's famous passage?
"The oarsman should have a clear conception of what is required of him . . .
He should understand, and be quite sure that he does understand, that he is
not so much required to set water in motion and shovel it along past the
side of the boat, as to stick the blade of his oar as firmly as he can into
a given spot in the water and to lift the boat as far and as quickly as
possible past that spot. His attention must be concentrated on moving the
boat, not stirring up water."
I never tire of that passage, although sometimes I find myself wishing that
Bourne had not tried so hard to be poetic. If only Bourne had refrained from
using the word "lift!" Maybe then he would have written the perfect
description of moving a boat with an oar.
Cordially,
Charles
Ps And that's really flogging a dead horse, no?
I didn't think of this until after I had sent the first reply, but I have
what may be a really good example of how a more efficient stroke with a
longer pull through results in moving a shell faster through the water.
My friend, David Lay, just purchased an ancient Van Dusen. For the last
month he has been making some minor modifications to it. But the one thing
he hasn't been able to do is change the spread.
For several years David has been sculling with a 158 cm spread, but the Van
Dusen came with a 161 cm spread. The Van Dusen has flat plates that are
attached to the riggers and into which the oarlocks are bolted. To change
the spread you have to unscrew the plates and moved them in or out.
Unfortunately the screws holding the plates to the riggers are frozen. David
has not found a way to loosen them.
For this reason David has adapted to a 161 cm spread and lengthened his oars
accordingly. In conventional thinking isn't this new gearing suited to a
bigger, younger man? But it is what David had to work with, so he had no
choice but to accommodate himself to it.
We were discussing the results yesterday morning. He had just come back from
a row around Angel Island. Was he ever surprised! For the first half, while
the water was flat, he had rowed his best time ever. A significant personal
best!
David attributes this to the slightly larger spread and longer oars, which
force him to have a longer pull through. The longer the pull through, the
longer the blades are in the water, the more you move the boat
To accommodate the longer pull through David said he had to lower his rate.
But this obviously didn't slow him down. When he goes around the island his
rate has been normally 28 to 30. Yesterday morning his rate was 24 to 26.
Interesting?
Cordially,
Charles
Hi Charles,
I have a copy of Bourne, somewhere, but it's been quite a while since
I opened it.
Horse well killed.
W
Sounds like dipping the rigger plates into an industrial ultrasound
cleaner with a good detergent, after soaking for a few days in a
penetrating solvent might be called for.
Or talk to Carl about new riggers.
However, I believe that the speed depends to a great extent on the arc
length described by the blade, and the blade movement during the first
part of the stroke while it is travelling end-on through the water.
(boat speed depends on a lot of other factors, too - just as elite
level target pistol shooting requires that the shooter be knee-deep in
brass spent during deliberate practice, elite rowing boat speed
depends on having a heck of a lot of water flow past the fin - also in
deliberate practice...) Yes, moving the boat farther per stroke will
(well, should) make it faster. At some stage, if racing, the stroke
rate needs to go up so that there can be more time spent in the water
propelling the boat, and less time out of the water recovering. If
that increased time in the water is done slowly, you get the "oh my
gosh that's heavy" drive and the "flaming slides" recovery. By having
a long arc with a short overall blade, you can get lots of good blade
action in the water, a fast, dynamic drive, and a controlled
recovery. All the bilge about whether the bottom edge is free of the
water before feathering or not is probably an irrelevant distraction,
but I don't have the research to back that up.
I have a friend who says that years ago he found a way of taking care of
frozen screws. He thought it up when he was the "go to guy" at the Rad Lab
(Lawrence Hall of Radiation at UC Berkeley). Actually he was hunting heavy
elements at the time, but he was also very good with his hands and blessed
with loads of imagination and common sense.
He says to get one of those small, hand held torches sold in Gourmet Stores,
the ones used to caramelize sugar on top of a Cr�me Br�l�e. Their flames are
tiny and can be adjusted to be white hot and as narrow as a sewing needle,
and are very good at oxidizing rust and breaking bonds. He claims it worked
for him every time.
Of course dipping the rigger plates into an industrial ultrasound cleaner
with a good detergent, and soaking for a few days in a penetrating solvent
also works. But it is messy and takes longer.
Cordially,
Charles
Means of separation for corroded mild steel include immersing in
Phosphoric acid solution (some swear by Coca Cola, which tells you why
it's best avoided!).
If forces are applied the change of position of the blade in the water
is partly determined by the direction of the force on the blade (or
alternatively the angle of the blade) and the direction of the force
on the handle (or alternatively the height of the handle influencing
this direction). During the stroke there is some balance between these
forces resulting in the blade traveling in horizontal direction
relative to the water surface and little vertical motion.
If one desires a rower to move the blade deeper trough the water in
the middle of the stroke, then one can instruct the rower to do so.
But, is it also good idea to just alter the angle of the pin a degree
towards the bow side and have the rower maintain the notion of
applying the force in the direction of the stretched arms instead of
trying to actively move the arms up or down.
May I gently question your remark about moving the blade through the
water easily, Tinus, although I am sure I partly misinterpret what you
say? The objective in rowing should be to minimise the face-first blade
movement through the water, since that's what generates your losses.
And moving it easily confirms that losses are being made.
Oar makers may or may not mean their blades to float at what is
popularly thought to be the "right" level, but none of them writes to
RSR so we can't say. I would not blame them for working to get that
result, since you'll sell most by supplying what the market thinks it wants.
However, it takes little effort to row a little deeper for part of the
stroke. We do hear arguments that better rowers need less pitch on
their blades, which might be a skewed or accidental reflection of your
point that less pitch will help achieve a deeper stroke.
How the blade depth varies through the stroke can be strongly influenced
by small variations or irregularities in blade shape. I recall an
"interesting" outing when a 2x I was coaching went out with a set of new
blades which had been made by the husband of one member. (I'll give the
short version here). Her partner stopped sculling after a few strokes,
saying she found one blade's depth impossible to control. There was a
bit of an argument on the water. They came back in. They swapped
blades. They came back in, having agreed that that 1 blade was
unrowable. Yet at first sight the 4 blades were identical. Only on
closer inspection could we see that the offending blade had a small
local difference in shape, a warp, from the other 3.
I don't think that changing depths through the stroke is an exercise in
actively moving hands up & down. That sounds like a set of separate
motions which is not how the body or a well-made machine really works.
What we should seek is that the hand path develops into the well-learned
smooth but vertically (slightly) curved line that will achieve the
desired outcome. Thousands of kilometres of good practice is all that
should need....
I meant moving easily as in easy coordination. For a rower it is easy
if the arms are used passively in the early phase of the drive and let
the tension in the arms be the force to move the handles. In that
case, if the arms work as if they are pieces of strings, the force on
the handles is parallel to the arms. It is difficult to apply and
control forces in perpendicular direction. So, it would be a good
thing if blade depth would be controlled "automatically" by geometry
of the blade.
> We do hear arguments that better rowers need less pitch on
> their blades, which might be a skewed or accidental reflection of your
> point that less pitch will help achieve a deeper stroke.
> How the blade depth varies through the stroke can be strongly influenced
> by small variations or irregularities in blade shape.
I wondered if this idea of moving the blade moving deeper trough the
water is an issue of changing a rowers technique or an issue of
changing rigging and blade shapes. It seems to me (assuming the forcec
on the handles to be "simple") as if the changes need to be made by
adjusting the boat+oars instead of adjusting the rower (besides a need
for the rower to have better skills in balance because moving the
blades at the surface allows for better control of balance by using
the blades as if they are training wheels). It would also be nice if
there would be an oar designed to reduce the drag of the oar shaft in
the water.
I think it would be wrong to trust in string theory here ;)
I measured some forces before responding:
1. Downforce on the hand of a relaxed arm = 1.05kgf
2. Downforce at handle to balance a sculling oar in air= 0.68kgf
And, not measured:
3. Downforce to slightly cover blade in water, say = -0.2 kgf
(negative, so it takes positive uplift)
So to amply cover the static blade I'd have to provide a positive uplift
of ~1.2kgf, while to keep it on the feather needs ~0.4kgf.
That's the statics done. but how about the dynamic effects? Is your
arm pulling level from the shoulder of is the hand lower than that, in
which case what vertical force component is generated thereby to bury
the blade & how does it vary through the stroke? What's the dynamic
uplift generated by the blade's pitch in its varying hydrodynamic
situations?
And how, then, about the varying, but significant, effects of head &
tail winds on the oar during recovery?
I'd suggest to you that we have evolved to be inherently very good at
ensuring that our hands, regardless of the vertical & lateral forces
imposed on them, follow whatever path we choose. And we're even better
at this after a bit of practice.
>
>> We do hear arguments that better rowers need less pitch on
>> their blades, which might be a skewed or accidental reflection of your
>> point that less pitch will help achieve a deeper stroke.
>
>> How the blade depth varies through the stroke can be strongly influenced
>> by small variations or irregularities in blade shape.
>
> I wondered if this idea of moving the blade moving deeper trough the
> water is an issue of changing a rowers technique or an issue of
> changing rigging and blade shapes. It seems to me (assuming the forcec
> on the handles to be "simple") as if the changes need to be made by
> adjusting the boat+oars instead of adjusting the rower (besides a need
> for the rower to have better skills in balance because moving the
> blades at the surface allows for better control of balance by using
> the blades as if they are training wheels). It would also be nice if
> there would be an oar designed to reduce the drag of the oar shaft in
> the water.
>
So, as indicated above, I think we're well able to make the blade take
whatever path we choose within the water.
Rowers are so good at imagining that they, poor dears, have such limited
control over what they do. To me that's deeply embarrassing -
especially when we see the splendid bodily skills & coordination
routinely demanded & displayed in so many other sports & games. From
the way rowers talk, many would long ago have determined that
ice-dancing was impossible & that no one could, with a flattened stick,
ever hope to accurately hit a ball travelling at IRO 200km/hr. In
reality, the rowing action is so incredibly simple, if subtle, & we get
to repeat it so often, that learning it should present no problems. And
the balance problems we encounter are also trivial compared with those
for gymnasts or K1 paddlers.
I was recently sent some images by Jim Dwyer which, among other things,
neatly confirm, as I've said already, that the shaft does not backwater
during the stroke - even when substantially immersed. That notion which
infests our sport - that "looming" causes backwatering which, suddenly &
mysteriously, imposes deleterious amounts of drag - is, in short, total
hogwash. So perhaps we should not try to solve a non-existent problem
in oarshaft design, but rather we might look at flattening out the loom
so it presents a larger face area to the water during the stroke.
Any comments on the analyses I sent you in my reply, Jim?
In fact, we could even go back to longer, thinner blades ;) That way
we'd get deeper immersion of that upper edge & perhaps a higher total
drag during the mid-stroke stall phase. As I've noted on RSR at other
times, I have a deliberately unmatched pair of sculls: one blade has had
a strip about 25mm deep by 150mm long cut from its upper edge, from the
tip towards the root, so it's quite a lot smaller than its partner but
has its upper edge (over that distance) markedly deeper. Despite the
big area difference, you can use (& many have) those blades without
noticing even the slightest difference in feel or performance between
them. The conclusion has to be that any loss in performance due to the
reduced area is neatly counteracted by an improvement due to the reduced
scope for air entrainment.
As I've said before, we should open our blinkered eyes, make more
experiments, use the evidence everywhere before us, actually study what
we warble on about, take more simple measurements (as above) & be deeply
sceptical of all those popular but unproven coaching mantras & the
authoritative pronouncements of bar-room experts.
Some might call that iconoclasm. Such folk are appalled when I suggest
that rowing ignorantly misinforms its participants about the mechanics
of the stroke. They cling for safety to the bogus "certainties" rammed
down their throats as they learned the sport. Meanwhile, those with
open minds go & do more digging, study, thinking & experiment. Thus it
cost me 10 minutes to supposedly "wreck" a pair of sculls, but I learned
so much & they still work just as well as ever. Even if they had
actually been wrecked, wouldn't the lesson learned have been worth the cost?
I am not talking about the recovery but the start of the drive when
arms act to channel the force from the trunk to the handles. Of course
in other parts the handle position is more directly determined by the
vertical forces actively applied by the arms. Just imagine the catch
and the release. Still there are varying effects which do effect the
drive. But, these effects can make rowing feel very awkward. I am used
to row on a river with a lot of current and this doesn't really make
the stroke feel better.
> I'd suggest to you that we have evolved to be inherently very good at
> ensuring that our hands, regardless of the vertical & lateral forces
> imposed on them, follow whatever path we choose. And we're even better
> at this after a bit of practice.
The rower having a certain idea about the path the hands should follow
does not oppose the idea that during the first part of the drive the
arms are used like pieces of string. The way the rower feels the
motion could be a composite of both the rower feeling to move the
hands along a certain path and the rower feeling a balance in the
vertical forces with little effort needed from angular movement/forces
of the arms.
You posted an example yourself in which the rowing didn't feel nice
because a blade wasn't shaped well. If rowers would only feel and
control the path of the handle/hands and not the vertical forces then
this experience with a wrongly shaped blade wouldn't have been felt as
a problem. This example shows that rowers must be feeling the amount
of effort needed to move the blade horizontally or a certain path.
Rowers are very good at feeling the force from the handle. I suggest
that it is best if this effort is as low as possible. On an erg it can
be seen very well. In the first part of the stroke, forces tangent to
the arms are zero and the position of the handle is determined by the
tension in the arms (at least for those who don't flex the arms at the
start). Only in the recovery and the last part of the stroke do rowers
actively control the path of the handle. Also, the harder a rower
pulls the higher the hands are moved.
So, if we want to change the path along which we want a rower to move
the blade (and consequently the path of the handle) should we alter
the rigging and the oar such that this path becomes a path of least
resistance? As in no angular forces needed from the arms but only
tension. You are right that the rower must also reconsider the path
along which the handles move if the blade is to be moved along a
different path.
> In fact, we could even go back to longer, thinner blades ;) That way
> we'd get deeper immersion of that upper edge & perhaps a higher total
> drag during the mid-stroke stall phase.
A longer blade has a fulcrum further away from the blade tip which
increases the amount of slip. That wouldn't be a problem if the blade
wasn't rotating. But since an oar has to rotate in order to apply
force the optimum length of the blade can't be increased much. My idea
about this rowing style in which the blade is immersed more deeply is
that it moves the fulcrum away from the tip which will decrease the
positive effect of the increased drag of the blade. The deeper
immersion should be realised without increasing the length of the
blade. (It is also debatable whether the better rowers which immerse
the blades more deeply are really rowing more efficiently or just need
the extra drag because they are so strong).
Your idea about cutting away the upper edge of the blade is
interesting. If it would be done without reducing the blade area, by
adding the area back at the lower edge, then we might have a super
blade. It does require more vertical space though and the torque/twist
along the axis parallel to the oar shaft would increase. Do you really
believe(/know) these kinds of experiments are not performed?
There is no edit function here isn't there? tangent should have been
perpendicular.
I used the reference to the recovery only to illustrate how well we can
cope with all forces that rowing imposes on our arms.
Of course
> in other parts the handle position is more directly determined by the
> vertical forces actively applied by the arms. Just imagine the catch
> and the release. Still there are varying effects which do effect the
> drive. But, these effects can make rowing feel very awkward. I am used
> to row on a river with a lot of current and this doesn't really make
> the stroke feel better.
>
>> I'd suggest to you that we have evolved to be inherently very good at
>> ensuring that our hands, regardless of the vertical & lateral forces
>> imposed on them, follow whatever path we choose. And we're even better
>> at this after a bit of practice.
>
> The rower having a certain idea about the path the hands should follow
> does not oppose the idea that during the first part of the drive the
> arms are used like pieces of string. The way the rower feels the
> motion could be a composite of both the rower feeling to move the
> hands along a certain path and the rower feeling a balance in the
> vertical forces with little effort needed from angular movement/forces
> of the arms.
I am, as you'll have seen, slightly unsympathetic to the view that
rowing is already so perfect that all we do has to feel right to be
right. Rowing is a compromise, an activity for which we were not
designed & for which our equipment is probably imperfectly designed. So
we must be prepared for forces we'd prefer not to have to handle, &
learn to handle them well.
>
> You posted an example yourself in which the rowing didn't feel nice
> because a blade wasn't shaped well.
It was not that it didn't feel right but that a quite subtle error in
shape made that 1 blade respond so differently from its companion,
generating a significantly different profile of vertical forces, that it
made it impossible for its user to row as well as required or to
contribute to the smooth balance of the 2x. You can drive a car with a
flat tyre, but not as fast or as safely as with all tyres working properly.
If rowers would only feel and
> control the path of the handle/hands and not the vertical forces then
> this experience with a wrongly shaped blade wouldn't have been felt as
> a problem. This example shows that rowers must be feeling the amount
> of effort needed to move the blade horizontally or a certain path.
It was not the feeling that mattered; it was the actual imbalance of
vertical forces out at the end of the blades. Except by leaning over,
there was no way to correct that, but leaning as required prevent the
user from working fully or well. So you are drawing inappropriate
conclusions from my example.
> Rowers are very good at feeling the force from the handle. I suggest
> that it is best if this effort is as low as possible. On an erg it can
> be seen very well. In the first part of the stroke, forces tangent to
> the arms are zero and the position of the handle is determined by the
> tension in the arms (at least for those who don't flex the arms at the
> start). Only in the recovery and the last part of the stroke do rowers
> actively control the path of the handle. Also, the harder a rower
> pulls the higher the hands are moved.
>
> So, if we want to change the path along which we want a rower to move
> the blade (and consequently the path of the handle) should we alter
> the rigging and the oar such that this path becomes a path of least
> resistance? As in no angular forces needed from the arms but only
> tension. You are right that the rower must also reconsider the path
> along which the handles move if the blade is to be moved along a
> different path.
As I say, it would be nice if the blades could be forced to follow a
set, hopefully optimal, path. To do that would require additional
machinery which would not go well in this sport. So, if you want to get
the best from yourself you may have to learn to profile stroke depth,
regardless of the (I think minor) vertical forces that requires. I've
indicated how very slight those forces will be, which leaves no grounds
not to apply them. But you are free to row as you wish, even if that
limits your potential performance.
>
>> In fact, we could even go back to longer, thinner blades ;) That way
>> we'd get deeper immersion of that upper edge & perhaps a higher total
>> drag during the mid-stroke stall phase.
>
> A longer blade has a fulcrum further away from the blade tip which
> increases the amount of slip. That wouldn't be a problem if the blade
> wasn't rotating. But since an oar has to rotate in order to apply
> force the optimum length of the blade can't be increased much. My idea
> about this rowing style in which the blade is immersed more deeply is
> that it moves the fulcrum away from the tip which will decrease the
> positive effect of the increased drag of the blade. The deeper
> immersion should be realised without increasing the length of the
> blade. (It is also debatable whether the better rowers which immerse
> the blades more deeply are really rowing more efficiently or just need
> the extra drag because they are so strong).
I didn't say you should, just that you might. You seem not to have
understood that the supposed fulcrum is already inboard of the inner end
of the blade, as I did say. And that fully explains why the shaft of
the oar does not backwater, even if buried for some distance. I can
tell you this, but you are still free to ignore what I tell you, or to
disbelieve not just me but the evidence of most of the solid strokes
that are ever rowed. And by doing so you can generate unsound notions
which try to put the centre of rotation in the water out at the tip
during the mid-stroke stall phase. That would, of course, result in
nearly all of the blade backwatering.......
>
> Your idea about cutting away the upper edge of the blade is
> interesting. If it would be done without reducing the blade area, by
> adding the area back at the lower edge, then we might have a super
> blade. It does require more vertical space though and the torque/twist
> along the axis parallel to the oar shaft would increase. Do you really
> believe(/know) these kinds of experiments are not performed?
If you cut from the top edge & add the same amount to the bottom, how is
that in any way different from rowing the original blade deeper buy that
same amount?
The top part of the blade has so little tension behind it that it makes
no meaningful contribution to the torque generated.
And, no, I have never found anyone who has made, or tried to make, even
so simple experiment as that which I have described. I have met only
with incredulity that I would even think it OK to row with such
seemingly mismatched blades - which tells us plenty about how little is
understood about the way a blade interacts with the water & with its
free surface.
perhaps there could be an alternate way of looking at this. Washing
out of being locked deep are aspects of the overall gearing giving a
load on the individual. Providing the sculler or crew is consistant in
what happens with the blade throughout the stroke and the gearing is
appropriate is there necessarily any real difference in how this is
achieved? Im not talking about chucking the finish away having been
locked up early in the stroke but some people get away very well with
an element of froth to their stroke...
Donal
I missed this one first time around - sorry.
We are here discussing the mid-stroke stall zone, so it is fair to talk
in terms of drag & slip
Extra drag is what we all need. Extra drag is what reduces slip, for
all of us. Sure, the stronger guy will get more slip when using the
same size of blade. And I agree that by going deeper will reduce that
slip. But all of us will reduce slip by going deeper. If you are
racing someone stronger than you are, then you have less power & less to
throw away, so you have more need of reducing slip than he does.
Remember that drag, like lift & slip, is something which develops in
direct response to whatever load you apply to the blade & how you use
that blade (including how deep you row it. It is only there in response
to the loading you apply, not something that the water imposes on the
blade regardless of how you pull, & the water never imposes a loading on
the blade except in a direct & exactly equal reaction to the load you
apply to the blade.