Re: Technical: heels on foot plate?


Steven M-M wrote:
Actually Paul, with Carl's patient explanations, I understand lift. And
clearly anyone who wants to scull/row well needs to understand the
interaction of boat-rower-oars-water-air (is that "the system"?).

So explain again how if the hull is still accelerating after a good
release that the system is no longer accelerating. smm

I think that Mikes example of just sitting and rolling back and forth
on the seat explains that nicely. As you draw yourself toward the
catch, which happens very shortly after the release the hull
accelerates forward relative to our body mass, since the hull + drag is
a fraction of our body mass.

Here is where Mikes exercise gets tricky, since the hull drag is not
fixed, the direction which we move our body mass the most quickly
realtive to the hull, will be the direction the COM of the system
begins to move. i.e. move through the recovery very quickly and then
the "oarless drive" slowly, the system will be moving slowly
sternwards. Do both equally and the system will be stationary.

Perhaps an example from another water sport will serve to help. In the
flat water canoeing events, when the finish is very close you will see
the competitors throw their body backwards at the very last instant in
an attempt to surge their bow across the line first. When they do
this, it is obvious that they "system" cannot be accelerating (there is
no blade in the water) yet the hull obviously jumps forward due to the
exchange of momentum. Now if that were a good way to actually move
their craft, why wouldn't they lay back after each stroke to get that
"extra hull acceleration"? (hint: because it's the system speed which
must be sustained to get to the finish line.)

If we measured "crossing the finish" as is done in running, with the
bow's body breaking the line, system speed would be a lot more
apparent. (Watch the hips of the rowers in side by side boats and you
can see which is moving faster quite easily, regardless of the
"jockeying bow balls" when they are in different phases of the stroke.)
i.e. runners don't extend their hand to break the tape, they throw
their hands rearward quickly in an attempt to surge their body to the
line, even though that is working pretty much with opposite ratio of
masses as we do in rowing it has still become a standard practice.

- Paul Smith

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