March '24 - Tail Up or Down?

For the tip to stick, the shuriken has to be somewhat horizontal when it hits the target. But which is best as the ideal - perfectly horizontal, tail slightly up or tail slightly down? Let's explore some different ways of looking at it.

No matter how fast the throw, the shuriken falls under gravity, traveling in an arc. A higher speed gives a flatter arc for a defined distance but it is always released traveling at a small upward angle and spends roughly the second half of the journey falling back down.

As the shuriken hits the target it is moving forward on a slight downward arc. To drive the point in most effectively the centre of mass needs to be lined up with the tip. An analogy is how hitting a nail with the hammer moving in line with the nail gives the most effective transfer of force. Standard MSR shuriken have a centre of mass near the middle along the length. So ideally, lining up the length of the shuriken with its angle of forward velocity will get the weight directly behind the tip to give the maximum transfer of force. A slower throw will travel in a bigger arc, while a faster throw will travel in a flatter arc. But at any speed the fall from gravity means the velocity always has some down component, so rotationally the tip also needs to be slightly down, or the tail or slightly up as it hits the target.

The next component to consider is that the shuriken is spinning as it travels to the target. Jiki Daho - direct striking method or commonly called a no spin throw, is not really no spin but more like a quarter spin. The shuriken leaves the hand quite vertical (in fact laying back a bit) and is around horizontal when it hits the target. Again the centre of mass for a standard MSR shuriken is around the middle. So as it moves through the air there is a slow spin end to end around the middle and of course controlling this slow spin is a key skill we develop in learning to throw.

For the segment of time when the tail is below the tip, this rotational inertia is moving the tip forward at a slightly faster velocity than the centre of mass. It is also rotating to drive the tip in when it hits the target. If it rotates past horizontal, the tail gets to be above the tip. Then the rotational inertia is moving the tip backwards compared to the centre of mass, resulting in a slightly slower tip velocity. It also rotates in the direction of retracting the tip at the surface of the target. So for the rotational movement, tail slightly down give slightly faster tip speed and works to drive it into the target slightly better.

In reality the shuriken is both traveling in an arc and rotating as it moves through space between the point of release and the target. With the above conflicting theories, does slightly tail up or slightly down dominate for a better throw?

In Danny Fletcher's book "Japanese Throwing Weapons" he says that ideally the tail should be pointing down a little bit because then the rotational energy helps to drive the point in deeper, as I described above. There are technical aspects taught in the MSR method of throwing that assist with a straighter trajectory and a flatter arc, making the tail slightly down the ideal to aim for. Interestingly I've had it explained to me by someone from another school and style that the falling arc behaviour is dominant and tail slightly up is their ideal. So it all depends on the throwing style and methods of the school.

Anyone that throws shuriken knows anywhere a bit either side of horizontal is generally very effective. Even at a high level of skill there is variation in this due to how fine you have to control the speed of spin to get even in this range. But it is also worth knowing what ideal looks like and why, so we can work towards it over a lifetime of training.

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