Single vs. Multi Band Setups

Although this subject can be debated extensively there are a few bits of fact that cannot be overlooked. In the following guide we are going to touch base on the key factors that differentiate single band setups from multi band setups. This basic review should give you the knowledge necessary to make and educated choice when you are trying to determine which is best for you and why.

We’ll start off with a simple and broad summary for those of you that just want a basic answer without all of the science. As a general rule of thumb you can follow these two definitions when determining which setup suits you best.

• Single band = great accuracy and penetrating power at shorter range.
  • Single band guns are best suited for reef hunting or close quarter hunting.

• Multi band = greater penetrating power at longer ranges with slightly reduced accuracy.

  • Multi band guns are better suited for longer range, larger specie, hunting such as blue water hunting.

Now, on to the physics behind these answers…

The Science

Spearguns follow a relatively simple application of basic physics. Essentially we are accelerating an object (spear shaft) towards another object (prey) of which the accelerated object (spear shaft) must maintain enough kinetic energy to overtake (penetrate).

Kinetic energy of rigid bodies is calculated as follows:

Loosely translated to Energy = ½ mass x velocity²

As you can see the velocity has the greatest impact on kinetic energy as it affects the output exponentially.

So to put this in the context of spearguns:

½ mass (our speargun shaft), times velocity (the maximum recoil speed our power band, or bands, can achieve), directly correlate with the power and/or effectiveness of our speargun.

As stated above, velocity has the greatest impact on the amount of kinetic energy achieved and the guns band is what accelerates the mass to this velocity. So, at first glance, the more band power, the greater the energy. Well of course there are many more variables (as in many THOUSANDS more) that impact the energy of your spearshaft. We are not going to cover any of them in greater detail, but here are just a few with great impact: the medium through which it is fired (water), drag, tracking ability, shaft whip, recoil energy, etc.

A band or multiple bands accelerate the speargun shaft within the acceleration zone of the band. You can very roughly calculate the acceleration zone as .33x band stretch. So a speargun with a band stretch of three feet would only accelerate the shaft for the first foot of recoil and the bands would only follow the shaft the remainder of the way. The property of the rubber results in less recoil energy as the stretch is reduced, ie: the less stretch on the rubber, the slower the recoil and the more stretch on the rubber, the faster the recoil. This can be verified by the fact that the shaft leaves the speargun before the bands are fully recoiled; the shaft’s velocity matches that of the bands at their greatest stretch while the bands are slowing as the stretch is reduced.

Now that we have covered the basic physics behind spearguns, we can better understand the logic behind “single band” and “multi band” setups.

A single band gun uses one larger band to accelerate a thin shaft of less mass. The logic is that the lesser mass of the thin shaft should accelerate to a greater velocity. Remember the equation E_k = ½ mv², which also reminds us that less mass results in less energy. Essentially the thinking is that the lesser mass can take advantage of the additional velocity to produce the energy required at impact for penetration. This is true, but the decreased mass of the spear shaft results in less momentum available to counter the opposing drag. Therefore the velocity of the shaft drops off rapidly which reduces the range of the gun.

In contrast, a multi band speargun utilizes multiple smaller bands to accelerate a thicker shaft of greater mass. The logic here is that the greater amount of band power will result in increased acceleration throughout the acceleration zone in order to achieve an increase in energy. The increased mass of the shaft generates greater momentum which results in greater opposition to drag. This allows the spear shaft to sustain its energy over a greater distance, which in turn increases the effective range of the gun. Another factor to consider is that multi band guns are commonly much longer guns which increases band stretch thus increasing the effective stretch (acceleration) zone.

All of the above conspires to beg the question, “Why not add more and more bands to a thin shaft?” The problem with this lies in the thousands of variables that we have not covered in this discussion. Most impacting in this case would be shaft whip which results in an adverse impact on accuracy as well as an incredible increase in drag.

Again, this discussion only touches on the immense number of variables that impact the range and effectiveness of spearguns. The fact that they are being fired into the very unforgiving medium of water only complicates matters even more. A fully accurate discussion would require a degree in fluid dynamics among others!

Hopefully this guide has given you a general understanding of the physics behind the decision of single band vs. multi band setups.