How to use the Speargun Simulator:
| Input | Instructions |
|---|---|
| Stock weight | Input the weight of the speargun without bands or spear (these are calculated by the simulator separately). The weight must be in kilograms and can have a decimal point with up to three numbers after (accurate to within 1 gram). Example: 1.759 |
Pull length |
This is the distance that you pull the dyneema/rubber back along the top of the speargun, measured in meters. For conventional spearguns, such as this Riffe Marauder: 
This is the distance from the rearmost fin/notch to the band hole. For inverted or roller spearguns, such as this MVD Predator: 
Pull length is the distance from the rearmost fin/notch to the front roller axle. The pull length must be in meters and can have a decimal point with up to two numbers after (accurate to within 1 centimeter). |
| Mid handle? | Does the speargun have a mid handle like this? If so, select "Yes" 
If it has a handle at the butt like below, select "No" 
This option only affects the room available under the speargun for inverted and roller bands; it doesn't affect conventional bands. |
| Spear diameter | Select the appropriate diameter from the drop down options. This diameter is used to calculate the spear weight, among other things. |
| Spear length | Enter the spear length in meters. It can have a decimal point with up to two number after (accurate to within 1 centimeter) It is measured from the end to the tip, like below: 
The spear has to be longer than the pull length. How much longer is called the "overhang".
|
| Conventional band diameter | Select the diameter of the conventional bands (14, 16, 18 or 19mm). This determines how hard they are to load, and how much energy they store. Conventional bands are bands that aren't roller or inverted. They can be sling bands designed to thread through the stock like this: 
Or split bands designed to screw into the stock like this: 
|
| Conventional band quantity | How many conventional bands? (up to max 6). Each 'band' is considered either a sling or pair of splits. Leave this as zero if you don't want any conventional bands. |
| Roller band diameter | Select the diameter of the roller bands (14, 16, 18 or 19mm). The diameter determines how hard they are to load, and how much energy they store. |
| Roller band quantity | The quantity of roller bands. This single roller Salvimar Hero is considered to have 1 roller band. 
Whereas this Neptonics double roller is considered to have 2 roller bands.
Leave this as zero if you don't want any roller bands.
|
| Inverted primary band diameter | An inverted 'primary' band is always connected to the pulley and stock on an inverted speargun. For example, the top band on this MVD Predator is the primary band as the top cable cannot be loaded onto the spear without the primary band being stretched. 
The two bottom bands can be detached, making the initial cable pull easier. These are considered secondary bands. |
| Primary bands doubled? | Doubling the primary band means attaching two bands of the same diameter in parallel where neither can be disconnected when pulling the top cable, like this: 
An inverted pulley doubles the pull force whilst halving the travel distance, so doubling the primary rubber in an inverted speargun keeps the pull force in line with a conventional or rollergun equivalent.
It is recommended to double the primary rubber, unless you're using a larger diameter primary rubber (19mm or more). |
| Inverted secondary band diameter | An inverted 'secondary' band is a band that is not connected when loading the top cable of an inverted speargun, for example: 
Secondary bands are like loading conventional bands, but upside down. Use the same diameter you would for a conventional band. They are not demultiplied when loading (like primary bands) and should not be doubled. |
| Inverted secondary band quantity | The number of secondary bands. No more than two per primary band is advised as this can tend to overload the pulleys and rollers. Leave this as zero if you don't want inverted secondary bands. |