Notes on boat-check from Bill Tytus
Of all the things to worry about these days, boat-check may not top your worry list. But you can't have rowed very long if you if you have not been told you should be concerned. Perhaps these notes will relieve at least a small part of your worry burden.
Newtonian Physics and Rowing
Considering the system of you, your boat and oars, note that your mass (same as your weight on the surface of Earth) is in the neighborhood of six times greater than all the other parts, which is why (only) from a Newtonian point of view you are six times more important than anything else.
Because of rowing's cyclical nature, and the many changes of the direction of motion through the stroke, many accelerations and decelerations of you and the parts of your system occur. These many accelerations require many forces. (Newton's 1st law)
Newton's second law states that a force is equal to the mass of the forced object multiplied by its acceleration.
Acceleration over time increases velocity. (our primary objective)
- the same acceleration, over more time = more speed
- more acceleration, over the same time = more speed
The obvious conclusion, as you already know, is more force (acceleration), applied sooner, over a longer drive, will generate more boat speed. As you think this through, don't focus on the boat. Instead, think about accelerating your body, it being the most massive part of the system. (once you get that body moving it drags the rest of the system along with it).
So how do we accelerate our body??
The only way, in a rowing boat, to accelerate your mass towards the finish line is to push off the stretcher. It's the same as accelerating your mass towards the sky by jumping off the ground.
BUT ....
Many of these accelerations (at least half) are in opposite directions and cancel each other out. (try rowing through several cycles with your blades flat and see how far you get).
And worse, that mighty leap off the stretcher that should accelerate you to the finish line actually moves you only a little bit, while moving your boat much further, back toward the start line. (Newton's 3rd law)
That is what we call boat-check.
Try this:
Take with you on your next outing, something small that floats (wine corks are perfect). Find a calm spot, stop your boat, and put your floater in the water next to you. Then, while keeping your blades flat, watch your floater as you drive (jump) off your stretcher. What happens? Big boat-check?
Do it again, but this time make a catch. (like the "catch drill plus legs")
Perhaps the boat still checks a little?
Can you eliminate the check entirely?
When you make a catch, you mechanically transfer your leg drive force to the water, which is vastly more massive than you and your little boat. The force, action and reaction are exactly the same, except now you are the smaller mass, and thus you now move the farthest.
BUT ...
Making a catch is a fairly complex process which takes a certain amount of time. We can define the "catch" part of the stroke as beginning when the oar blade stops moving toward the bow of the boat, and ending when it is actually pushing water.
Here then are all the events that must occur between the beginning and the end of the catch.
The blade is still in the air. It must start moving down toward the water. If the boat is moving forward, then, relative to the boat, the water is moving, from bow to stern. If the blade goes straight down it will back against the water, stopping the boat. So the blade must also start moving sternward to match the water.
The blade enters the water, still moving down and sternward. It can start pushing water as soon as it first touches the water, but it will be most effective only when fully buried, pushing against the greatest possible mass of water.
Water is not solid. it is a fluid, and therefor the blade must further move, or slip relative to the water in order to develop a force.
All these events take time. If accomplished quickly, the time can be compressed but not eliminated. Also, the only force that can move the blade sternward is the equal and opposite force that the rower applies to the stretcher. (Newton's 3rd law again)
Whatever time it takes you to make the catch is time you are pushing your boat back, not the water.
And that is boat-check.
References
A good website should you want to bone up on newtonian physics
Here's what Kleshnev has to say:
Kaccel-23390.pdf
Take a look at the Kleshnev newsletter 2004RowBiomNews02. Note particularity the graphs on the right hand side of the page which are graphs of two rowers. At the top is their boat velocity and acceleration and below is the velocity and acceleration of the rowers center of mass. Note how different these two graphs are, note how much smoother ("less fluctuations") of the center of mass graphs. You can suss out the points he is making but I include this because here is empirical data that says a quicker catch ("application of force") is faster even compared to a slower catcher who pulls harder.
Also included is an info-graphic that demonstrates the same thing, comparing Olympic caliper to National caliper rowers and concludes that the best rowing crews have the highest magnitude of negative acceleration at the catch and the highest early force peak. This is exactly what is meant by checking the boat. (In case you were wondering) When you leap off of the ground you actually move the earth a distance based on the proportion of your mass to that of the earth. Similarly, every stroke you take either retards or speeds up the Earth's rotation, depending on which direction you are pointing.
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