Band rubber speed?

I found .5 as the drag coefficient for a cone (found online) which is the shape of the spear tip (minus the flopper but I doubt you could find that info). And the italic p is rho = the density of the fluid. For water I used one although salt water would be a little denser. The graph would probably look similar to 1/x the lighter shaft starting at a higher velocity but initially decelerating at a faster rate. The heavier shaft having a lower initial velocity and not decelerating as fast. The drag wont stop them completely because as the velocity approaches 0 so does the force of drag. So the graphs of both shafts should approach zero and the farther from the initial point the closer the graphs should get.

one thought.
in a theoretical model you can add mass to a lighter shaft by making it longer right? so what if they were of equal mass? if you dont consider cavitation and other factors like accuracy, would the thinner spear move faster and hit harder? clearly a spearo could not use a shaft that was 4 ft longer but that makes the comparison interesting.

By making it longer you would be able to add mass but then you would sacrifice speed and pull even again. The comparison of shaft diameter is only effective if that is the only variable. Just like in any science experiment it becomes a lot harder to measure multiple variables at once. By keeping everything the same (bands, gun, shaft length, etc you can calculate the effect of a change in mass.

I guess the real trade off here is mass vs recoil and velocity. In water a much heavier object will continue to move longer but will be much slower. A fast moving spear will get to the fish much faster. A really heavy fast moving spear creates a lot of recoil.

I think what Jeff was looking for was simply what are the theoretical thresholds of band speed, and adding more bands vs a heavier shaft. Simply put how many bands do you really need and at what point does that number become ineffective or a waste and would it be more effective to increase shaft diameter or add more bands?

A practical example of what's going on is this:

Throw a baseball with all your strenght and then do the same with a paper ball. The initial speed will be the same, but after just a couple feet, there will be a noticeable loss of energy due to the mass difference.

Quote from Tin Man

Exactly. Simply put, is there a point where a smaller shaft no longer goes faster, or where adding bands no longer produces more speed.

I do think there is. I think you can only add so many bands to a certain size shaft and weight. The ideal spear setup for max power and speed in my opinion is a short fat spear if your gun can handle it,of course. Short fat spears will bend less when propelled through the water so much of the energy is not lost. There are pros and cons though. The less overhang you have, the harder it is to aim. People will say just use enclosed tracks and put extra bands. Well, enclosed track guns also slow down the shaft. I think short thin band setups are also very good because the shaft will stay propelled longer on the rail even though you might lose a little bit of power stretching them so much.

Just my opinion.

Quote from Marco

A practical example of what's going on is this:

Throw a baseball with all your strenght and then do the same with a paper ball. The initial speed will be the same, but after just a couple feet, there will be a noticeable loss of energy due to the mass difference.

this practically is the only thing i understood, thanks marco.

thanks jeff for a very interesting thread, i can't contribute anything more than what others already said but i will try to sum up what i think i know on the subject.

adding more bands does not increase shaft speed but it does increase the distance the shaft will travel and the punch it will deliver when it reaches it's destination. there are limitation here but suffice it to say that the thicker the shaft the better the more bands option works as most have already said.

to get the maximum velocity from the shaft i think you need to decrease it's drag somehow. europeans because they tend to shoot smaller and more skittish fish have come up with all sorts of things. as most of you already know, salvimar has introduced a new flopper that hugs the shaft so the flopper does not add any more area to the shaft. others have added a cone on front of the flopper to streamline things. flopper size is also important and again salvimar and others have done what they could to decrease it's area. also, some euro shafts have placed the smaller shark-fins in a "trough" to decrease resistance, of course notched shafts have no such need. abellan guns use salvi shafts that have a "shoulder" on either side of the line attachment hole in the back of the shaft to better streamline the line. of course the line itself introduces drag so the thinner the line the better and i think it also makes sense to attach it in the back of the shaft instead of a shark-fin. finally, demka has published a study on it's website about the effect the shape of the end of the band and the wishbone have on the speed of the band as it collapses back to it original length. they consistently saw about a 10% increase in the speed if the ends of the bands are cone shaped. this last part may be the only way to increase shaft speed.

any of these changes will have a minimum effect on shaft speed but combined they may be worth the effort. of course every action has a reaction, for example, you are not going to put a 1.3mm shooting line on a tuna gun but you get the point.

oh yah, the track itself will have an effect like harry said.

I have a mako 120cm railgun that fires a 7mm 160cm shaft.

I have a 120cm denton that fires a 140cm 7.5mm shaft.

They both use 16mm tight bands.

The shaft speed is way faster on the Denton and the penetration is much better. Interesting huh?

Steve mentioned mono thickness and he is so right.

I use 1.4mm mono. This makes a huge difference alone in long shots. If mono touches a wreck, it will bust no matter what thickness.

That being said, i have pulled big grouper, AJ, and permit as hard as i physically can away from wrecks and the mono never broke. Now, if it touches the wreck, its game over.

I also like to change my mono every trip even if its not scratched up. Its easy to do and the cost is super cheap.

yup, shorter, thicker shaft will have a more stable flight through the water because they flex less (wooble) as it travels and therefore will be quicker and more accurate.

surpirising how many people are resisting the idea of a short overhang and insist on aiming with the tip of the shaft.

Quote from metelin

yup, shorter, thicker shaft will have a more stable flight through the water because they flex less (wooble) as it travels and therefore will be quicker and more accurate.

surpirising how many people are resisting the idea of a short overhang and insist on aiming with the tip of the shaft.

It is harder to aim for sure especially far away or quick longer shots, i must admit. On quick shots, its harder to get the gun at eye level which is required for a short overhang gun. I am going to try 150cm 7.5mm rob allen shaft on my gun and see how it feels.

What is considering a short, medium, and long overhang on a speargun? How many inches?

This is a really fun thread to follow and it was making me use what's left of my gray matter. :crazy:

The original query was relating to max velocity of a rubber band and the relative limitations in reaching that speed? :confused1:

I figured if a test was made on a given rubber band.. where the rubber was stretched at 300% then released underwater with no payload (shaft).. that'd be the closest to max speed of the rubber by itself. O_o

Load the same rubber but with a spear shaft and measure it's velocity, then add as many rubber bands as needed to get as close to the max velocity of the initial test? <--- would throw practicality out the window. And yeah, this test is specific to the one rubber band size and shaft size..

But this is all assuming someone had the equipment to run this kind of test. (with SAFETY at the highest priority, of course)

So this test might answer how many bands it would take to shoot a shaft as close to max velocity of a band with no payload? What the shaft does after it leaves the gun is a whole nother issue... :confused1:

If I'm looking at this the wrong way.. just.. tell me to shut up. I'm not as smart..

~Frank

i don't aim, just point and shoot (hhhmmmm, maybe that's what's wrong) when i do try to aim i miss so..........

in the past on the guns i sold i shipped with about 8" of overhang including sliptip. on my personal guns i have gone as short as 5 which is just about enough for the flopper to stay open but i would have no problem with the flopper on the barrel. i think past 12'' is long, i personally don't see the point in it. long shafts have more mass so produce more recoil and i think it's one of the reasons riffes shoot low.

username- i think that makes lots of sense. i did come across one thread on an italian site where someone measured the time for a shaft to hit a target. if you knew that and the distance of the shoot you could figure all kinds of things out. the way he did it is so simple i had to shake my head. he simply shoot some video of the shots in a pool and he looked at audio track and measured the first loud spike (gun firing) and the next one (the shaft hitting the target).

Quote from metelin

i don't aim, just point and shoot (hhhmmmm, maybe that's what's wrong) when i do try to aim i miss so..........

in the past on the guns i sold i shipped with about 8" of overhang including sliptip. on my personal guns i have gone as short as 5 which is just about enough for the flopper to stay open but i would have no problem with the flopper on the barrel. i think past 12'' is long, i personally don't see the point in it. long shafts have more mass so produce more recoil and i think it's one of the reasons riffes shoot low.

When i see the fish coming from a long ways, i aim. When i don't have time to aim, i just point and shoot. In my opinion, i think that is the ideal way to shoot to have a high hit %.

If you always just point and shoot, you can get accurate but not as accurate as aiming.

Harry. Your comparison is a little off with your two guns cos the abellan has like five inches more band stretch doesn't it? That has to have something to do with it

To jeffs original question. The snap time of a particular band has to be a curve The issue of power transfer is the limiting factor I think. Add one band and it will move at c speed if pulled to y length. Add ten bands stretched to y length and the will still snap at x speed but would be imparting more energy. So they basically enable you to increase the mass of the shaft without losing the speed. To your initial example. More people pushing the wagon at the same speed will not speed up the wagon, it will make each persons load easier OR it will let you increase the weight of the wagon without losing speed

So working backwards, I think you get to pick the thickest shaft you feel will fly true and use enough bands to propel that at the speed you want. Then see how heavy the gun you just made needs to be and.... You know the adage, it is all compromise. A gun you can swim with, that is heavy enough to absorb recoil, that has the power to reach and penetrate fish, that is light enough to swim w .... Makes me understand why I have more than one gun

Quote from LunkerBuster

Harry. Your comparison is a little off with your two guns cos the abellan has like five inches more band stretch doesn't it? That has to have something to do with it

The Abellan is called a 120 because it has the same stretch as a 120cm gun. The gun is actually 112cm long.

I will take a picture of a 120cm mako and the 120 Denton from handle to muzzle to compare.

got it, i knew there was something like that cool about it..8 cm is still no 5 inches anyway

Here you go lunkerbuster. Measured from handle to handle

I am testing a larger overhang on the abellan. That is a 150cm shaft instead of a 140cm. I will see how it shoots with this shaft.

What do you think Steve? I dont think the overhang is that long.

Thanks Harry

the over hang looks to be just right actually.

that looks like 7-8'' which is what i like but i would be curious to hear what you find. is that a 7mm shaft?