Bowmen of Skelmersdale

What Bow Behaviour Needs Controlling?

There is little point in bolting on every stabiliser set-up currently in use by the top 20 archers worldwide. If nothing else, not many people can lift twenty sets of stabilisers.

More to the point, the best stabiliser system is a personal decision.  Every archer has their own preferences and problems, and the best system for the archer is chosen to fit their preferences and solve their problems. As with any other part of archery technique, it pays to start by working out with what you intend to achieve, and why. Since different parts of a stabiliser system can be used to control different types of movement, it’s useful to start by thinking about the different types of movement and what effects they have on the shot and the archer.

Bow movement

Displacement is a mathematician’s word for movement from one place to another in a particular direction, without involving rotation, vibration or anything more exotic. The centre of gravity of the system moves along with the object. For archery, it’s usually convenient to think about three pairs of directions: up and down (vertical movement), backwards and forwards (longitudinal), and left and right (lateral, or sideways). For those with a mathematical turn of mind, those directions are often associated with X-, Y- and Z-axes. Any of these movements can have a direct effect on where the arrow lands; the most serious are vertical and lateral movements. Some movement is inevitable as the arrow moves off, but the movement needs to be consistent from shot to shot. Often, ‘consistent’ will be best achieved by ‘as small as possible’.

Rotation is movement around an axis. There are three axes of rotation important in archery; approximately parallel to the arrow,

approximately down the centre of the riser, and through the grip from left to right. The next few sections cover these in turn.

Rotation around the arrow line

Rotation round the arrow line would appear as clockwise or anticlockwise movement viewed from directly behind the archer.

Though not normally a consequence of the bows natural

mechanics, this movement may, for example, be visible later in the shot as a sharply rotated bow arm returns to rest. It is worth

remembering that rotation about this axis is usually slight both

because there are few forces acting in the relevant directions and because the riser
is hard to move quickly about either horizontal axis.

Rotation around the riser

Often called torque, rotation around the vertical axis is probably the single most important movement stabilisers were intended to reduce. The bow itself is easiest to rotate about its long axis, being long but narrow (more on why later), and the archers hand position can vary enough to add a lot of torque - after all, an off-centre force of 30-40 lb. is hard to resist!. Symptoms of torque include lateral spread of impact on the target, lateral movement of the long rod if fitted, impact of the string on the bracer and reported lateral movement of an extension-mounted sight. Notice that rotating the bow around the riser moves the string sideways; that becomes important during the shot itself.

For practical purposes, a bow wobbling about or rattling is undergoing vibration. The shot  itself puts considerable stress on the bow, and most  of the energy not transmitted to the  arrow  is left in the bow and string  as vibration. Limbs flexing asymmetrically after the shot, a long rod vibrating, or even  a rhythmic wobble as the archer aims, are all  types of vibration.

Forward/backward Roll

Draw a line through the grip from left to right. Rotation around that line, visible as the bow tipping backwards or forwards, is forward or backward roll. Some movement occurs as a direct result of the arrow leaving the bow above the hand position, causing the bow to ‘kick’ upward slightly; that movement is usually compensated in part by careful tillering. Other rolling movements may be caused by a centre of gravity well above or below the hand position (see below), and, after the shot, by the centre of gravity forward or behind the grip. For example, a heavy weight on a long rod will cause forward roll after the shot.

What bow behaviour needs controlling?

Bow  movement

Timing - When is movement important?

Time and Motion

Controlling bow displacement

Weight, Mass and Inertia

Static and Dynamic properties

The misnamed TFC

Controlling bow balance

Centre of Gravity

Finding the centre of gravity

Changing the balance using weight

Weights and Distances

Rods, weights and risers

Controlling bow vibration

Causes of Bow Vibration

Reducing Vibration - Damping

Bow Resonance

Tuned damping - more on TFC’s