Posts by seaweed

Energy is conserved, if you put x amount of energy into loading a gun then x amount of energy will be expended shooting the gun. Doesn't matter what you shoot from a speargun it will have the same kinetic energy.

However if the same amount of Kinetic energy is put into 2 objects the heavier object will have more momentum.

There is a wall, it is when the force exerted by the bands equals the opposing forces such as drag, water resistance, and friction. This will cause the shaft not to accelerate. The opposing force is pretty small compared to the force of the bands, even near the end, so more bands will always equal higher speeds if the shaft can handle it.

Quote from LunkerBuster

I think the practical application for this kind of thought would be to design a device that used the bands from 350% stretch and released the spear at 50% as opposed to the current standard of 300% -0%.

Roller guns and pneumatics do something like this.

Quote from Tin Man

How fast can a rubber speargun band contract, and what (if any) limitations would that place on gun design?

My thinking goes like this. Suppose I am pushing my kid in a wagon. No matter how big or strong I am, (or how big or small my kid) that wagon will never go faster than I can run. I can get three friends to help me, and we might get the wagon up to to speed sooner, but it will still never go faster than we can run. All the extra strength of my three friends is wasted, because the limit is how fast we can run.

So I was wondering. There must be some maximum speed at which a speargun band can contract. So at some point, adding more bands to a gun might not increase the shaft speed at all. Or, moving in the opposite direction, using a lighter shaft might not result in any additional speed.

Anyone ever seen info on how fast a rubber band can contract?

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Short answer is speed of spear will never be faster or equal to band speed. The mass displaced of a band contracting alone is almost negligible compared to pushing a spear. F=ma, F is constant on a stretched band at a given distance. On a band alone m is very very small so a is almost infinte, compared to a with spear of mass m. Integrate over the distance of the band pull and velocity will be almost infinite with a band alone.

Now add some reality i.e. drag, friction, cavitation, etc and band speed will still be super fast.

On a rubber band F=kx, where k is a spring constant, x is the distance displaced, so a band exerts force as long as it is stretched, F>0 always until it reaches its unstretched length. On human running F=ma, you can't push your kid any faster because your top speed is constant hence a=0 then F=0.

The second your a=0 and velocity is max is like a band stopping at its length. Your analogy applies up to this point, you are like a band. Your velocity is limited by your strength and mass, a bands velocity is limited by how far it is stretched, mass, and its spring constant.

Distanced stretched and spring constant are "constant" on a spear gun. So again with a lighter mass you will get a higher velocity.

If shafts didn't whip I'm sure everybody would be using smaller diameter shafts.

Quote from phil herranen

just get a 22 rifle and use sub sonic or cb longs the cbs are quieter than most pellet guns
phil

Where he lives he would be in whole lot less trouble if he's found with a pellet gun.

Quote from Dan

I'd like to buy a good air rifle, and don't know anything about air rifles. What's a really good one?

How far you planning to shoot at?

Probably Alaska, I saw once on tv a guy flyfishing chad. He had about 60 huge ones in front of him but he would cast out to catch them because he said it was more sporting.

I'd say a railgun 100-120cm, preferably 120cm, will be good with a floatline for shooting dolphin. A wood gun is good also but more expensive. You don't need a reel for freediving but it is nice to have options available for different conditions. I'd imagine a reel on scuba is necessary unless a fish dragging you around is not a problem.

Keep us updated on your decision. You don't want to buy a gun and later find out it is junk.

Most reels have a hole that you pass the line through then make a figure 8 knot so it cant go back through.

I don't run the line through the guide at the front of the gun. I place the swivel right after the reel.

Reel it up with plenty of tension but not to the edge of the spool. You should be able to get at least 150ft of line on it.

Sweet fish, congrats.

Quote from Dan

I don't feel like a $300 camera setup gives me the right to ask for ownership of really good footage. But I can't put more into it financially, and I would want to be reimbursed for the money and time I put into editing and production.

I think it is more than fair. I'd be a really willing participant.

Good video, I guess bad weather is good for something.

That snook spot now has a bunch of lionfish, and the jewfish is missing. I think it ate a lionfish and croaked.

Also can try an O-ring or piece of bungie tubing also.

Are they double or single bevel?

Quote from Dan

Interesting effect in the pic of you in front of the pier.

Talk about glowing with pride. Nice fish. I've always seen cuda at the jacks but they were skittish as hell.

Only place tides matter is where they can cause an effect. Places like the intracoastal, bays, inlets, beach.

I've been diving close to the inlets to see if I have better chance to catch fish since everywhere else I try is lacking in fish. Reefs come alive when the tide is going out.

Monster permit Rolo, sounds like a great adventure to be remembered.

Quote from fishhound

Thank you captain obvious. No need to reply if you don't have any real info to share on this. ie you have done it or know other people who have or know hte science behind why it's good or bad. Thanks

As a matter of fact I've been researching what happens.

Hyperoxia= Oxygen excess

partial pressure of oxygen exceeds 360 mm Hg

At
23ft – the process of receiving O2 and releasing CO2 is hindered
50 ft – this process stops so that cells cannot accept oxygen despite of its abundance

Symptoms

at first – discomfort, nausea, spasms of lips and eyelids, disturbances in eyesight, sleepiness;
later – stiffness of muscles, convulsions (similar to the epileptic ones), blackout, death

So it won't matter how much oxygen is in your lungs your body won't be able to use it.

However I found very little info on how long exposure factors in and if the damage is cumulative or recedes after each dive.

Using a scuba tank can dramatically increase your bottom times as well.

I think there is more risk using pure O2.

I noticed a change here in Ft. Lauderdale. Definitely less fish than 5 years ago.

Giant swarms of grunts up and down the reefs. I guess they have little or no predators so they flourish.

Probably charged full speed after some ballyhoo hanging out around the pipe.