Speargun Modding :
(created: October 2006, last updated 30/03/2008)

Here explain some changes taking as an example the Sporasub Stealth speargun .

Sporasub Stealth

(overview of the main changes and their impact around the power, precision and mimicry )

Work tools:
The tools i use for my works

The Head:

A classic modification consist in a conic enlargement of everyone of the four oles in the head.
This promote the water expulsion from the rod

Shaft , scorrisagola(?) , inox ring and codolo(?):
You can see two levels modifications:

Level One ( simple mod) :

It consist in:
A) cutting the codolo borders creating a conic surface . The same on inox ring .
This make soft the impact of the codolo on the inner borders of head
reducing consumption and noise.

B) making 2 tiny (1 diameter millimiters ) for the nylon rope and reducing the unused parts
of the scorrisagola making it very
hydrodynamic .

Level Two (complex mod):

Make a 2mm hole on the top of the shaft used for tieing the corde to the shaft himself.
After you must create a sliding eyelet ( i have used two sleeves)
but it must stop before the enf of the shaft .
Because? Simple : this eyelet transfer the negative force traction of the corde perfectly on the
axis of the shaft and it dont
deviate from the shooting path .
Your shaft is now extremely hydrodinamic .

Using this system there are a negative thing:
there is a excess of cord thath you cant put on the cord release near the trigger.
I resolved the problem using a rubber ring on the tank near the head of the speargun.
(see the figure below number 3 )


The cyrano and stealt speargun pistons have a strange o-ring .
It's too big for the 11mm internal diameter of the cane so that the piston move width
a great resistance that required 5 kg appoximatively .
Using a smallest o-ring or reducing the original one the piston now require only 1 kg to move
into the 11mm cane incresing performances .

Power Regulator:
The power regulator block divide the speargun tank into 2 parts , a smallest one near the handle
and a greater one near the head . The pressurized air pass from the grater one to the smallest one between a very small
hole ( oval hole 6mm x 4mm ) thet generate a air resistance reducing performances.
So that if you want the maximu power you must eliminate the power regulator block
(the white plastic cilinder you see below)

Lubricant :
Oils with a greater viscosity may decrease the velocity of the piston.
The best for me is an 10w fork oil that have a good grade of lubrication but at the same is quite fluid .
N.B. Motorbyke fork oils have a protective additives that protect orings and alluminium .
Dont use brake olils because it's corrosive !
Remember: you must fill the speargun whidt 15ml - 30 ml of oil depending on the speargun lenght.

Piston System release:

The piston system release is composed by:
-trigger (grilletto)
-adjustement srew (vite)
-connection pivot ( perno 1,5mm)
-catch hook ( dente di sgancio)
-spring (molla)

The modification consist in :
A) reduction of the friction using a polyshing paste on every contact point between every
piston system release components

B) Reduction of the trigger hardness following two way : if your speargun use a 3mm connection pivot you must change it
whidt a 1,5mm one . For second you should change the spring whidt a softer one .
If you have same problems to find the right spring i suggest you to use the one present on the “power regulator”.
n.b. This spring is good but is a little longer , so that you must cut some spire after mount it on the catch hook.

Here some tests of the trigger load required to unlock the piston:
(see the video below to undestand how i have executed the test)

Trigger load test at 0 bar speargun :
**Stealth 850 ( original ) : 1kg
**Mares Stealth 850 ( original 1,5mm pivot and using the power regulator spring without 4 spires) : 0,5 kg

Trigger load test at 20 bar speargun :
**Stealth 850 ( original) : 1,3 kg
**Cressi SL star 70 (this speargun have a 3mm pivot and have the original spring but without 1,5 spires) : 1,5 kg
**Mares Cyrano 700 :(original 1,5mm pivot and power regulator spring without 2 spire) : 0,8 kg
Miniministen : (original pivot 3mm and original spring ) : 2 kg

Trigger load test at various speargun pressions :
(every speargun have the same modify listed on the previous test)
*Cyrano 700@26 bar di precarica : 1 kg
*Stealth 850@26 bar di precarica : 1,4kg
*Stealth 850@28 bar di precarica: 1,5 kg

*Stealth 850@28 bar di precarica ( molla variatore ) : 1kg

(see the video below to undestand how i have executed the test)


Cord release system (line release system):

It is composed by two elements:
1.the trigger
2.the hook

The cord (line) generates a quite pressure on the hook , and it make an annoyng friction on the trigger.
To reduce it the better way i know is cut a little the trigger as shown in pictures below.
n.b: cutting the hook ist a good idea.

In case you want heavy anticipate the trigger release using the trigger adjustement screw ...:
...remember that the trigger must be cut more because if you dont it the hook could not release the cord(line)!
In the picture below in yellow color you must see the trigger i have cut and now it work perfectly.

The handle:
The handle is very important because a good handle give feeling and , more important, can reduce
the recoil and the shot become more precise .

There are many way to create an anatomic handle, using wood, using “utileplast” ( plastic tini balls that become tender at 60°c
assuming every shape you want) or.. using sintetic cork ( rectangular size of cork that i have modified
cutting it whith paper glass.. see the picture below)

The floating:

The air pressure spearguns unfortunately are negatives in water ( dont float).
This generate an annoing tiredness on wrist .
To avoid it i use sintetic cork as show in picture below

The shaft:
This is an idea to transform a thread shaft into a taithian shaft like .
The thread remain and you can quickly mount a fiocina( ? ) on it
( fiocina image)

Here some mimicry examples ...

using an adesive paper

and spry syntetics colors

speargun spearfishing mares sporasub cressi cressisub omersub sea fish