Re: sliding riggers

On Jul 6, 11:16 am, Carl Douglas <c...@xxxxxxxxxxxxxxxxx> wrote:
ATP* wrote:
"Carl Douglas" <c...@xxxxxxxxxxxxxxxxx> wrote in message
news:7bbpg4F22ft3eU1@xxxxxxxxxxxxxxxxxxxxx
Charles Carroll wrote:
. . . the fact that rowers across the world are daily urged in all
seriousness to "accelerate the boat" each stroke confirms that blind
ignorance of the inertial dynamics of rowing is widespread.
Carl,

Is it possible to maintain constant boat velocity during each stroke?

If it isn't, then doesn't this presuppose that during a stroke cycle a
shell going to reach a maximum velocity, then regress to a minimum
velocity?

And if so, then how can we not conclude that the function of the drive is
to bring the shell from minimum velocity back up to maximum velocity,
that is, to produce "a time rate of change in velocity?"

It seems to me that the question is not whether we are trying to
accelerate the boat, but rather how we are trying to accelerate the boat.

How do we take the catch? How do we drive? "Thrust-stroke?" Or "solid
stroke with hard beginning?" Schubschlag? Or Kernschlag? Hasn't this been
discussed and argued for decades and decades?

Cordially,

Charles
Charles -

The boat is the junior partner in the team dynamics.

The boat is just a piece of lightweight kit, albeit the largest & most
important bit of it (or you'd be swimming).  It moves always at about the
same speed as the balls of your feet.  So, do you think about accelerating
the balls of your feet towards the finish line during the stroke?  I think
not.

Acceleration is a much over-worked & misused term in rowing.  It sounds so
important of itself that folk think it must mean something vital.
Acceleration (& its mirror, deceleration) are names we give to rates of
change of velocity.  When launching a space probe, acceleration _is_ vital
as without it you will not reach the velocity either to achieve earth
orbit, or to escape that orbit.  When driving a race car, acceleration is
also vital, if we may ignore a host of other factors, since it determines
who gets ahead before the first corner, who can pass whom & who may
out-brake whom (deceleration).  In rowing it only matters for about the
first 7 strokes - the time it takes to reach cruising speed.  Thereafter
you will go no faster & will hope also to go no slower.

Sure, the boat's speed does vary about its mean cruising speed throughout
every stroke.  But that's a reflection of teh fact that its mass is so
much less than that of the crew.  The velocity of the combined system's C
of G varies by much less - because boat is more like the shoes of the
runner or the boots of a skater.  Like them it serves to support you above
your chosen medium (land, ice or water) &, like them (& so unlike the race
car), it is a lightweight sub-component, securely attached to your feet,
with no choice but to go where your feet go & thus to come along for the
ride.

Which pinpoints one of the sadly ignorant ways in which rowing's dynamics
are misunderstood & mis-taught.  Were your boat a 1 tonne mass, & just
suppose it incurred no more fluid drag than your single with you sat upon
it (which could not be true), you'd then be spending a lot of the time &
effort in each outing in just accelerating it gradually up to race pace -
because at that speed it'd be storing >71 times as much kinetic energy as
is averagely stored in your 14kg boat at the same speed.  (Since the
combined mass of you + boat in this thought experiment would be almost 13
x greater than normal, it would take you
90 strokes to hit race pace).  And, being so much heavier, the boat
would scarcely fluctuate in speed through each stroke.  Crazy?

Yet that's exactly how all those folk who talk about needing to
"accelerate the boat each stroke" would seem, if logic intruded upon their
analyses, to view the relationship between boat & crew - as if the boat
was where all the mass was concentrated & the mass of the crew was
immaterial.  As I've said elsewhere, who cares about accelerating the
running shoe?  Or the skate, or even the rower's socks?  So who, after
those first few strokes, should care about accelerating the boat? Firstly,
the boat is not the major mass component in the system, you are.
Secondly, after the catch it is an inescapable fact that you will
accelerate _more_ than the boat, otherwise you would not be moving away
from the stretcher.

So, if it ain't going to be possible to accelerate either you or the boat
to beyond a certain mean velocity, you need then to concentrate on
_reducing_ both the accelerations & decelerations in the boat's velocity
(&, of course, in yours) about that mean.

I never said that understanding the inertial interplays in rowing would be
straightforward.  But that does not excuse the widespread, & sometimes
aggressively defended, misunderstandings of the dynamics of the rowing
stroke.  Applying a bit of simple science might help clear the air,
leading to better insights &, perhaps, to better rowing & reduced injury.

Cheers -
Carl

--
The idea that the rower shoots the shell out from under him and that the
effect enhances the overall progress of the system is certainly
wrong-headed. However, it does seem that all other things being equal, a
shell equipped with a sliding rigger would be ever so slightly more
efficient if only due to the fact that the rower's torso is staying in the
same place relative to the hull.

But only if that situation carried real advantage with it.  We can posit
all manner of things which, because they have a pleasing aspect, we
think ought to be "right" (e.g. not looming), but unless we analyse them
and can quantify whatever benefits we suppose they may bring, they are
worth no more than any other such notion.

In an activity such as rowing, in which load is intermittently applied,
it may actually make more sense to operate an energy storage & return
system involving a sliding mass.  In rowing, that sliding mass happens
to be you.

AFAIK, there is no statistical evidence to suggest that the sliding
rigger made for faster times in international competition.  It'd be
pleasing to some of us if it did, but we must work with the evidence,
not our wishes.

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: c...@xxxxxxxxxxxxxxxxx  Tel: +44(0)1932-570946  Fax: -563682
URLs:  www.carldouglas.co.uk(boats) &www.aerowing.co.uk(riggers)- Hide quoted text -

- Show quoted text -

To quote Carl:

“AFAIK, there is no statistical evidence to suggest that the sliding
rigger made for faster times in international competition. It'd be
pleasing to some of us if it did, but we must work with the evidence,
not our wishes.”

There may not be any data around about sliding rigger systems, but my
guess is that it’s mostly because at the time FISA outlawed them, the
internet did not exist. There are good theoretical reasons to suggest
that sliding rigger systems make for faster scullers, though.

Carl again:

“The boat is 1/5 of your weight, so it, not you, is already the most
accelerated/decelerated item. And the more that you cause its velocity
to fluctuate by your efforts to accelerate it, the less & less
efficiently it moves.”

Correspondingly, the *less* you cause the boat’s velocity to
fluctuate, the *more* efficiently it moves. With a sliding rigger
racing shell, the sliding rigger will weigh an order of magnitude less
than the boat, because ~90% of the system’s mass comprises the boat
which now includes the rower. So the acceleration/deceleration
resulting from momentum transfer from the sliding rigger to the boat
will be small. Thus, using Carl’s own line of reasoning, one should
expect the sliding rigger system to be more efficient.

Magnus
.

Relevant Pages

  • Re: sliding riggers
    ... Is it possible to maintain constant boat velocity during each stroke? ... accelerate the boat, but rather how we are trying to accelerate the boat. ...
    (rec.sport.rowing)
  • Re: sliding riggers
    ... seriousness to "accelerate the boat" each stroke confirms that blind ignorance of the inertial dynamics of rowing is widespread. ... It seems to me that the question is not whether we are trying to accelerate the boat, but rather how we are trying to accelerate the boat. ... Acceleration is a much over-worked & misused term in rowing. ...
    (rec.sport.rowing)
  • Re: sliding riggers
    ... seriousness to "accelerate the boat" each stroke confirms that blind ignorance of the inertial dynamics of rowing is widespread. ... If it isn't, then doesn't this presuppose that during a stroke cycle a shell going to reach a maximum velocity, then regress to a minimum velocity? ... It seems to me that the question is not whether we are trying to accelerate the boat, but rather how we are trying to accelerate the boat. ...
    (rec.sport.rowing)
  • Re: sliding riggers
    ... Is it possible to maintain constant boat velocity during each stroke? ... accelerate the boat, but rather how we are trying to accelerate the boat. ... There may not be any data around about sliding rigger systems, ...
    (rec.sport.rowing)
  • Re: sliding riggers
    ... Please see Walter's very clear graphical depiction of velocities of boat, ... for the 1st 2/3 of the stroke the rower's CofG is increasing its velocity - it is accelerating. ... Moreover to produce an average mean velocity per stroke of the bow ball with respect to the finish line, any acceleration during the leg drive must compensate for any deceleration during the recovery. ...
    (rec.sport.rowing)
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