Posts by grossetti

  • Roller spearguns

    You could measure the recoil, it is a force in the opposite direction. If you had a scale that worked under water and you put it against your chest and put the hit of the gun against it and film the "weight" that pops up and compare that

  • Retractable Shark Spike


    Thanks Dan, I hadn't understood you had one. It's more for a wooden gun though, I think.


    Having a removable one is nice, so you can move it to the gun you want to use or not put it at all if it is not needed (for people who air travel to hunt every gram of weight counts!)

  • Retractable Shark Spike

    Quote from Treebilly3

    The spring could fit behind the spike the latch threaded to fit in the spike to make assembly easy.
    Sounds like you'd be making a spring assisted gate latch with a sharp point.


    It would be safer with the spring in front, that way it cannot engage accidentally.

  • Retractable Shark Spike

    Quote from Linghunt

    As an assembly that gets mounted like the flashlight would be more practical to most out there is my thought.


    The Retract safe position: I would have it inside the housing completely.


    Hi John, yes, I was thinking that, my drawings are not very good, that is why I am not an artist :)


    Quote from Linghunt

    The side slot I would do straight vs an angle, then add a notch on the end to hold it in place. ( be easier to make)


    Thinking of a bolt on a typical rifle out there.


    My thoughts exactly.

  • Retractable Shark Spike

    A retractable ball point pen like mechanism could work too, not sure if pushing from behind is easier than pushing a lever from the side though, with gloves and the stress and all.

  • Retractable Shark Spike

    Hi all,


    I asked Dan why his current speargun models don't have shark spikes anymore and he explained that it can be dangerous, if you are handling a strong fish by the shooting line and the fish darts off, the line may slip through your hands and the gun can stab you from behind (Dan, correct me if I warp your explanation).


    I like the idea of a shark point for hunting in shark territory but he does have a point. I was wondering how hard it would be to make a retractable one, I was thinking a bit like those one shot rifle loaders or a sliding bolt lock. If you have space in the front part of your tube and you make cap with a hole the diameter of the spike and you attache a spring to the inner par of the cap in such a way that the spike runs through it (like a ball point pen works, the kind you click the back of to open/close). The spike would have a bar attached to it at 90° and the side of the gun is milled to allow you to move it back and forth. Close to the front it would be milled down with an angle so you can lock it into position. The barrel would need to be reinforced so that it doesn't warp from the strain of the bands. Here is a crappy drawing to illustrate:


    I guess there needs to be a lot of reinforcing to do, maybe it could be done as an attachment below the barrel so you don't have to mill the barrel, a bit like some people attach a flashlight: .


    Or something like that. Any ideas?

  • Roller spearguns


    So what you are saying is that a conventional gun twice the length of Dan's gun's and that is using the using the roller's bands (turning into a euro gun) would be just as powerful as Dan's half as long double band gun?

  • Roller spearguns

    Quote from Wishihadgills

    You did the extra work of looking up real values of the bands which I applaud. I was working off the assumption the bands would be the same and was just doing a rough analysis to prove a point.


    Thanks, I was surprised on how hard it is to find the data linked to the elasticity/force of the band, even from makers (which are not easy to find either). The chart mentioned above is one of the best I found.


    I think your analysis got idea through quite well I think. Now all we need is the real world test which Makoa said should happen in the up coming months.


    Quote from Wishihadgills

    The only thing a roller gun has done is to change the location of where the relaxed band is located.


    Imagine for a second you had a 100 cm long gun. When the band is relaxed the wishbone is roughly 75 cm form the muzzle. Put an imaginary hinge right where the wishbone is and bend the tip under the gun. Put a roller at the new tip for the band to go around and now you have the idea of a roller. Same bands same everything but now the gun is only 75 cm from mech to tip. Not magic just a clever use of physics.


    Yes, that is what I had tried to explain a couple of posts back, you probably explained it better as nobody understood me I think.

  • Roller spearguns

    Super Makoa, eager to see it!


    I just wanted to say that for our application the constant k can be any number greater than 0 since we are not needing to use the results but just comparing the results.

  • Roller spearguns

    I think I should have calculated k like k = 267/1 = 267, this supposes a 1m piece streached 100%, then k (Newtons/m) is a constant so that gives:


    dual band gun: PEe = 1/2*(4*267)*0.756^2 = 305.2 J
    single euro gun: PEe = 1/2*(2*267)*0.756^2 = 152.6 J
    roller gun: PEe = 1/2*(2*267)*1.53^2 = 625 J
    triple band gun: PEe = 1/2*(6*267)*0.756^2 = 457.8 J

  • Roller spearguns

    I went at it a bit diferently from Wishihadgills, but I end up with the same type of results:


    Using the chat taken here (Speargun Band Force Calculator - Spearboard.com - The World's Largest Spearfishing Diving Boating Social Media Forum), for a 16mm tube you get about 267 Newtons of force for 300% stretch


    Hookes law states that F=kX where:


    K = force in N
    X = streach distance in m
    k = a constante defined for each spring


    For parallel springs you have k = k1 + k2 + k3 + ...


    we are mising k so k=F/X


    The Engery is PEe = 1/2kX^2, PEe is in Joules


    I used Spearit Knowledge Base How to Calculate Speargun Band Length to calculate a band of length 51cm for a distance of 1m from the attachement to the 1st sharkfin, this gives us 25.5 for each side of the gun (either for a euro or once bent in two). This means X = 0.756 so k = 267/0.756 = 353.2; For a roller, the bands are twice as long, X = 153 so k = 267/1.53 = 174.5


    That gives us:


    dual band gun: PEe = 1/2*(4*353.2)*0.756^2 = 403.7 J
    single euro gun: PEe = 1/2*(2*353.2)*0.756^2 = 201.86 J
    roller gun: PEe = 1/2*(2*174.5)*1.53^2 = 408.5 J
    triple band gun: PEe = 1/2*(6*353.2)*0.756^2 = 605.6 J


    So technically, the roller is more powerful than the dual band gun but not more than the triple band gun


    Ref:
    PhysicsLAB: Springs: Hooke's Law

  • Roller spearguns

    A single pulley merely changes the direction of the force, nothing more, 50 lbs force on one side transfers 50 lbs on the other side.


    I agree the anchorage is in a different place on a roller, but if you make the barrel longer, keep the roller head, tie two strong lines (one for each side) to the bottom anchorage system and the other side of the lines to the ends of the rubbers, in such a way that the line wraps around the pulley and the rubber's en sits just after it. You still have the same power transferred to the spear as before, nothing has changed in that perspective.


    I over simplified it in reality because as mentioned in my previous post on a roller not all of the rubber's force is transferred to the spear, but you should get the idea.


    I'm always answering from my mobile so I can't draw it for you.


    I would like to remind you that to make a speargun more powerful (I'm simplifying it a bit) you must either tweak the rubber (get a thicker one or shorten it, use a smaller ID, etc), use a longer tube or add rubbers in parallel. The roller is a variant of the longer tube with a tweak (wrap the rubber around so you don't have to have a longer tube). I don't see why this is so difficult to understand, it is not magic.

  • Roller spearguns

    Quote from Dan

    For grossetti and others who may be having difficulty visualizing why a "single" band roller is the same as a two band conventional speargun, I made this animation highlighting the bands with a red line. Clearer than this I really can't make it so I'll just sit back at this point.


    Thanks Dan, I think we may not have the definition of what makes makes up a single or double banded speargun. From your image I take it that for you the fact that the roller has one rubber on one side and another on the other side that makes it equivalent to a double. If that case, a single band euro gun is also a double, as it has one rubber on one side and another on the other side. If you look at a roller gun, it is just a standard single euro with longer rubbers. Since they are longer but the body of the gun is not, they are wrapped around using a pulley (to reduce friction). If you were to elongate the body of the speargun, your roller gun would effectively be a simple (albeit long) euro gun.


    For me a double sling refers to the number attache points (wishbones) on the spear (e.g. in parallel).


    I would also like to point out that a dual band or even single band (using my definition) speargun has each of it's pairs of rubbers supply 100% of their energy, in a roller gun this is not the case, the band still has stored energy after the shot (i.e. it is still stretched). So you cannot even say since it is 2x longer it is like having two bands.


    That is why I believe the comparison is wrong. In your setup the dual band will be more powerful, I believe, simply because you are comparing different things.


    The only way to be sure is to calculate the physics of it anyways, I will try to find some time to do it.

  • Roller spearguns

    I agree with wishihadgills, that is the idea behind a roller. I think comparing two spearguns,one roller and one single band is a better comparison. If they are of the same length, same spear, band thickness, etc the roller should theoretically be better, if you shorten the roller by the relaxed normal speargun's band's length then they should be equal. Comparing a multi band speargun of the same length with the same band thickness is not a good/fair comparison.


    I have a roller, two multi bands (one with 2 and one with 3) and 3 single band guns, unfortunately none could be correctly compared to each other. I can say though that the roller has less recoil, the roller and the multi band guns are equally a pain to load when in a hurry. They can both be fully loaded half loaded depending on the distance of the fish. Also, my multi band guns have thinner bands then the euro (single band) and than my roller (if not they would be horrible to load). I believe each type has its pros and cons, neither can be declared better. I enjoy them all, in different situations.


    It's like comparing a Hummer and a Lamborghini, both powerful cars just not in the same way. On a racetrack I would use the Lambo but on the sand the Hummer, the other way around would suck :)

  • Aries f10

    Quote from Mahmoud

    Hi All
    please i wanna to get new watch, i think about Aries 10, but i heard that it is hard to listen to its depth alarm if you wore a hood , and the Suunto d4i has a clear sound but its battery is not user changeable
    i look for a watch that sound is clear, user changeable battery, and show the last max depth as soon as you end you dive with no need to press any button
    thanks, for your help


    I wanted exactly what you want, I decided to go for the F10v2 at the end.


    So, with a 5mm hood I hear nothing when the alarm goes off, I had to dive down and put the watch agaunst my head to hear the faintest sound. I was dissapointed because I wanted the alarns as a safety feature. The red led is so faint that it is useless IMO, you might as well look at your screen. I then turned off the useless sound alarm (which also turns off the red led) and decided to rely on the screen which is supposed to have the backlight turn on when an alarm goes off, regardless of the audible alarm setting. I never noticed it lighting up so either the Aeris person I had on the phone lied (and the user manual) or unless you are in the dark the environment lighting is too strong and thus not visible.


    I don't think that the Sunnto is much better in that regard, but the button navigation is supposed to be much easier. I always have to re-read the manual before a dive (I don't get to go often). I did see a guy that posted a video (youtube) on how to change the battery yourself in the Sunnto though, he said it wasn't pressurized in reality, so that may work for you if you are willing to risk it.


    Personally as a spearfisherman I am waiting for a rechargeable watch that vibrates when an alarm goes off.


    I hope that helps.