Exvaulter, I’m sorry, but that’s not it. Your description of the tuck defies a law of physics.
I agree that the tuck and shoot is inferior, but not for the reason that you’ve stated.
The most correct part of what you said is:
exvaulter wrote: But if you, by tucking in and then straighten out have let the pole recoil before you turn and then you MAY may reach a good height, but then you will fall down on the bar because you lack the momentum from the pole.
That part is correct – you imply that you have [improperly] let the pole get ahead of you. So I know you understand the physics of it. You just haven’t explained it correctly.
Let’s break this down …
exvaulter wrote: 1) When you tuck your legs in sharply then your centre of gravity is relatively low (relative to your grip on the pole).
Relative to your hand grips – true.
exvaulter wrote: 2) Then, when you straighten up your body into a nearly vertical position the center of gravity suddenly rises, maybe around 1 foot.
OK, as you say, relative to your hand grips (not relative to the box, as that will depend on the coil/recoil of the pole AS WELL AS to the position of your CoG relative to your hand grips). So far, so good.
exvaulter wrote: 3) When the CoG rises the pole will recoil as a reaction.
Not true! Every action has an equal and opposite reaction. So if your CoG is going UP, then there’s a DOWNWARDS force on the pole. In reaction to ONLY this force, the pole doesn’t tend to RECOIL – it tends to COIL - the opposite of what you’re stipulating!
I say “tends to” in order to distinguish the direction of the force from what actually happens. What actually happens will depend on the relative flex of the pole to the amount of force exerted in the extension, as well as the state of coil/recoil that the pole is already. You have to sum the forces in each direction to determine the NET force. The net force is what will cause the pole to actually coil more or recoil more.
If you consider where the pole is in its coil/recoil sequence when the vaulter extends (i.e. shoots out of his tuck), you are likely incorrect in saying WHY the pole will recoil. As you extend, it will recoil, but not (as you say) because of the force of the rise in the CoG, but because of the return of the pole’s potential energy back to kinetic energy – energy that was injected during the bottom half of the vault.
exvaulter wrote: 4) And if the pole recoils at that moment (too early), then you will get no help from it to lift you over the bar.
This part is true, if you replace “get no help” with “not get as much help”.
Tuck/shooters typically let the pole get ahead of them during the bottom half of their vault. That’s the reason they tuck – to catch up to the pole’s imminent recoil. I say “imminent” because they start tucking during the last part of the coil phase of the pole (near where the CoG passes the chord), so that by the time they’re finished the tuck, they’re ready to “shoot” in time with the recoil. But typically, they’re either tucking too early, or shooting too late (for optimal energy conservation).
If they’re shooting early enough (i.e. exactly in unison with the recoil of the pole), then they would have had to tuck during the coil of the pole – at a time when they could have driven more energy into the pole (with a long trail leg, right through the whip and then some). As soon as they tuck, they’re not loading the pole (optimally) anymore.
IMHO, there’s also leakage involved in a tuck. In the continuous chain method (a part of the Petrov model), the entire body is somewhat rigid – not relaxed. That minimizes leakage. Not so with a tuck.
Furthermore, the “shoot” of a tuck/shooter is usually too quick. If it’s not done in full unison with the entire recoil of the pole, then it’s less efficient. This deficiency is much more pronounced with young vaulters than with elilte vaulters, but even with the very best tuck/shooters, it's not a single continuous and harmonious action - free of leakage.
Having said that, there is one advantage that I believe tuck/shooters have over followers of the Petrov model (and in particular, their continuous, harmonious swing from the Whip to the Extend). The tuck/shooters’ advantage is that they can time their “steer” much better. All they need to do is vary the amount of time that they pause in the tuck. Then they shoot when they feel the pole has rolled sufficiently to vertical. Some can also see the bar then, and aim their shoot accordingly.
Petrov model vaulters (myself included) can’t do this as easily. Since we’re doing a “continuous chain”, we have to keep that motion going. There’s no point in the flow at which you can pause if you’re too far behind the pole. Conversely, there’s no point in the flow in which you can speed things up (i.e. there’s no opposite to “pause”) if you’re ahead of the pole. By definition, a “continuous chain” is just that – there’s not as much opportunity to speed it up or slow it down. Thus, you can’t time the “steer” as easily.
As always, my assertions about my technique (a variant of the Petrov model) are based on personal first-hand experience, but my theories on tuck/shooters aren’t – I’ve never tried that technique. They’re based only on observation and physics.
Kirk