Re: sliding riggers

Alexander Lindsay wrote:
"Charles Carroll" <charles_carroll@xxxxxxxxxxx> wrote in message news:7bd37nF21vn93U1@xxxxxxxxxxxxxxxxxxxxx
Carl,

snip

So I will go on to my next concern, which is the idea that one should not try to accelerate the boat. I have found a video of the 1956 Olympic 1x Men's Final in Melbourne. I suspect you have seen it. It is the race where Vyacheslav Ivanov won his first gold medal. He was 18 years old and was "in fourth place at the 1,500 meter mark. With only 500 meters left, he began a devastating sprint, first catching Poland's Teodor Kocerka, then American John B. Kelly, Jr. Finally, with 200 meters to go, he blew past fellow teenager Stuart Mackenzie of Australia who had led the entire race." (Wikipedia) Vkyacheslav's devastating sprint begins about two minutes into the video.

http://www.youtube.com/watch?v=7hhVNRonWf0&eurl=http%3A%2F%2Frow2k%2Ecom%2Fvideo%2Fview%2Ecfm%3Fvid%3D7490&feature=player_embedded

Try as I might I cannot watch this video without thinking that as Vyacheslav rows through these three competitors he is producing "a time rate of change in velocity."

Thus I keep coming back to the same question. If Vyacheslav wasn't accelerating his shell, how could he row through these guys?

So, as you can see, I am still stuck in the same place that I was yesterday. It still seems to me that the question is not whether to "accelerate" the boat, but rather "how" to accelerate it.

So how does Vyacheslav accelerate his boat?

Does it accelerate it by pulling harder? Not from what I see in the video. Quite the contrary, it looks to me that Vyacheslav doesn't actually change anything about his drive. He remains long, the pressure he puts on the pins remains constant, and, perhaps most importantly, he remains relaxed at the catch and continues to stay relaxed through the entire drive.

Then what does Vyacheslav do to accelerate his boat?

To my eye the only thing he does is change the recovery, which he speeds up significantly. Just look at his stroke rate compared to the guys he is rowing through. So how does he get this stroke rate? He looks to me that Vyacheslav produces it in the recovery.

But look at the video, Carl, and tell me what you see. I am always a little afraid to comment on video. I seem to miss so many things that everyone else on rsr sees.

In any event, I want to return to the point I tried to make yesterday. Are we talking about whether Vyacheslav accelerates his boat? I don't think so. It seems to me that acceleration is a given.

So if we are not concerned with whether Vyacheslav accelerates his boat, then what are we concerned with? The only answer I can come up with is "how." What I keep returning to is "how" Vyacheslav accelerates through these three formidable competitors.

Cordially,

Charles


Charles

I am afraid there is a fundamental confusion between acceleration and velocity. To overtake someone you need a higher velocity (i.e to go faster). You don't have to be accelerating.

In outline, what you see on the video is at first all the scullers going at roughly the same mean velocity, with zero mean acceleration.

Then Ivanov accelerates, probably for only two or three strokes, i.e. his velocity increases to be greater than the others. That actually doesn't take much effort: a slight increase in kinetic energy.

Then, because his velocity is greater, he overtakes them. He is not accelerating, he is just going faster.
But that's the remarkable bit, because, by going faster he increases the drag on his boat, and therefore must be working very much harder.

The point Carl is making, I think, is that to win you need to have a higher velocity, not to be accelerating. Accelerating is, by definition, necessary if you want to increase your velocity, as Ivanov did briefly, and as everyone does at the start. But once you have reached your intended velocity, you want as little acceleration as possible as variations in velocity waste energy.

I suspect this would all be much easier to understand if we didn't call the velocity pedal in our cars the "accelerator".

I will leave the shoe analogy to Carl.

Alexander



Charles -

I can't improve on what Alexander has said, but I can flannel on a bit further ;)

In every stroke there are accelerations & compensating decelerations, so that you return to the much same speed at the same point on every stroke. So, no net acceleration there, just the exact cancellation of the integrals over time of the positive & negative accelerations.

When you need to pass the guy with whom you are currently level-pegging, there is only one way: you have to increase your average velocity for a sufficient period to establish the lead you require. That is a minute acceleration imposed on the boat/crew system as a whole, not on any one part of that system which will demand, as Alexander has said, a substantial & _sustained_ increase in your power output.

To put things into perspective:
During every stroke your boat experiences accelerations & decelerations quite close to those imposed on a falling body by Earth's gravity, g - as you see from the loads visibly encountered by coxes. In contrast, to raise boat speed by 1% (say by 5 cm or 2" per second) over the period of a single power stroke demands an acceleration by the system as a whole of ~0.005g. That really is piddlingly minute. However, the price of achieving this increase in mean speed is an increase of ~3% in your power output.

Now you may think that a 1% increase in mean speed is trivial, but over 2k that amounts to 20m, or ~2 1/2 lengths of your single.

Just to complete the circle, if A gains 1 length on B over 5 strokes (say 8 seconds) without B going any slower, that represents a step change in speed of 1m/s. Since that's a good 20% increase in speed, then for those 5 strokes he has to be working at an incredible >70% harder than before his sprint. But even so, if that acceleration was achieved over the period of 1 second, it imposed only 0.1g on the system - & only for that 1 second.

Finally to kill, if I may, your preoccupation with boat accelerations:
If the boat accelerates over time more than you do, you will no longer be sitting on it as it will have moved out to somewhere ahead of you. So the time integral of its accelerations & decelerations has, absolutely has, to match yours - if it accelerates more, it must also decelerate more. Them's the rules!

I used the example of runners' socks & shoes as parallels for the boat & you tried to wriggle out by reference to the barefoot runner. A nice try, but bound to fail, I fear. May I now replace the footwear with the foot itself? Again, the boat moves with the feet, & has no choice in the matter.

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

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