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Rubber sling /(bands) tester

Discussion in 'Underwater Hunting' started by Sam Miller III, Dec 19, 2017.

  1. Sam Miller III

    Sam Miller III Scuba Legend Scuba Legend

    # of Dives: 5,000 - ∞
    Location: CALIFORNIA: Where recreational diving began!
    @Dano --note
    Spear gun Sling/band/rubber power tester
    I am a hold over from the generation that if anything costs more than a dollar we either made it in our garage or trotted over to the Hollywood Riviera and had Charlie Sturgil make it for fifty cents in his garage aka the "Temple of Spearfishing.
    The original spear guns that appeared on the pioneer American market was the homemade CO2 fire extinguisher spear gun developed by fireman Bill Barada, (see Discover Diving; "Magnificent gas gun," Jan/Feb 1993,) Cressi Spring gun introduced by Gus Dela Valle powered by a compressed spring,and Rene Cavalero's popular and ubiquitous rubber powered Champion "Arbalete ( "History of Spear guns" - ADN pt 1 &2 Feb/Mar 1992) ( a few of my now antique 20 year old published articles on spear guns and spear gun history-")

    The Arbalete and many of the early spear guns (Sampson et al) were powered by a solid rubber sling made of "kettle cured rubber," similar to the rubber slings often found on today's European guns. The Arbalete's slings were guaranteed to be grossly underpowered and generally would break at the most inopportune moment.

    In the early 1960s the large out side diameter small inside diameter hole surgical rubber began appearing on the diving scene and was readily adapted for spear fishing
    So it was with the slings, aka bands, aka rubbers.

    We were just slow talking slow walking, slow thinking, hard diving country boys from then a very rural bucolic Orange county Kalifornia. We didn't have the benefit of the modern sling length formula what ever it is ? Double the length, add 27-1/2 divide by 13, add 2 and then you have the correct length ---or something of that nature?

    Nope, a gentleman from San Diego named Jack Prodanovic taught us how to construct a sling testing machine, which most serious spear fishermen made and the local OC dive shops made available to their customers.
    A simple device; a long length of 2X4, generally six foot, a six foot measuring device, (two yard sticks,) a couple of anchoring points on each end, a pair of shackles ,a strong pulley with equally strong non stretchable marine quality line, a some what accurate measuring scale and a short length of strong nylon line.
    The procedure for testing the power in pounds of pull is as follows:
    The slings are attached to the bottom anchoring point, if raw slings they are joined by a short piece of nylon line to form a loop and attached to the anchoring point or if a store bought sling unit, the sling is attached to the bottom anchoring point and the wish bone is attached to the shackle which is attached to the pulley which is attached to the line, which is anchored at the top anchoring point. The machine is activated by pulling on the line which stretches the sling to the appropriate length corresponding with the target notch of the spear shaft. The power is measured in pounds of pull from the scale.
    Experience has indicated some, but not all, slings will tend to lose power aka "creep" when stretched for an extended period. If time allows it is often desirable to leave the stretched sling in a static position to check the sling creep. If sling creep is experienced there are two options, shorten the sling which creates increased loading effort or it is strongly urged just toss in the trash.

    What is the normal sling poundage reading? Around 65 pounds plus or minus for a normal production gun
    My son is one of those Big Mac nourished boys 6-3 -230 pounds ex-high school athlete. Prior to medical school he was a solid mass of muscle, after 12 years of intensive study the muscle has some what lost it turgidity...Never the less the slings on his guns are rated at 120 pounds-- Mine? I am well over twice as old and considerably shorter and weigh less, but discovered the best poundage for me to be +- 90 pounds. We both prefer the antiquated large heavy 3/8 shafts for the majority of our guns and Steve Alexander mechanisms. ( ie Mass X Velocity equals Penetration--M x V=P

    (FYI for those on the central coast ---Number 1 son is now the Diving Medical Officer (DMO) for Calpoly University as well as the Dive Medical Officer for the SLO Search and Rescue team and is on staff at local Marion Hospital in Santa Maria as an ER/ Hyperbaric doctor.--Yes, you will be well taken care of)
    The cost of building a sling tester can be a few dollars or if SS components combined with a high quality accurate scale are used and as I did the cost can escalate faster than Obama's spending of our money.

    There is one available for use or as a pattern to make your own on the Central Coast of Kalifornia..My old antiquated 45 plus year old original sling tester has been donated to Chuck Rawlinson's Depth Perceptions Dive Shop located at 12322 Los Osos Valley Road, San Luis Obispo, (805) 595 36 31.

    Should you like to use it to test the strength of your spear gun slings it is suggested that you first call Chuck at the above number for an appointment, so he will have adequate time to demonstrate the operation and supervise your testing.
    We also staged our slings so they all pulled at the same poundage. If the tabs or the notch was 3 inches apart the slings were shorten 3 inches this combined with a retest on the "Sling Tester" would insure ALL slings pulled with the same poundage. This eliminated one sling pulling at maximum and all the rest at a lessor amount. This is very important if the gun uses multiple slings, with tabs or notches as much as six (6) or more apart from each other.

    It was called "tuning of the slings."-- a long forgotten but certainly very viable process especially with the modern shorter guns.

    Now the spear fisherman's sling tuning has given way to "some thing plus some thing minus some thing equals something," even though it has been proven many many times that all slings are not created equal; they do not have the same elasticity and so many had a tendency to creep further reducing their power, therefore their effectiveness, creating a very weak length in the gun power and possibly effecting the spear gun's accuracy.

    Well! Sun of a gun!
    Last edited: Dec 19, 2017
    northernone and Akimbo like this.
  2. Akimbo

    Akimbo Lift to Freedom Volunteer Staff Member ScubaBoard Supporter

    I think Sam meant to alert Dano of Mako Spearguns, username: @MAKO Spearguns
  3. Sam Miller III

    Sam Miller III Scuba Legend Scuba Legend

    # of Dives: 5,000 - ∞
    Location: CALIFORNIA: Where recreational diving began!
    Yep ! toooo many Danos --but only one Dano @MAKOSpearguns

    Thanks again for your assistance


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