Why are spears so long?

[Broseidon]

Something I've been wondering - why are spears so long?

This is not such a big deal for big guns but for small guns, it bugs me.

For example, my 70cm railgun has a 100cm spear which protrudes around 20cm from the head. Personally, to make it as manoeuvrable as possible, I'd prefer a much shorter spear, say 85 - 90cm.

Is there a particular reason that spears have to be so long or can I switch to a shorter spear without any worries?

 

[marginatus]

I've had this conversation with a very good spearo...
The main reason he pointed out was aiming. The way most people aim, a bigger spear helps. It's usually 40cm + barrel length in pipe guns.
I prefer to use a shorter but thicker spear. Assuming the mass is the same (more mass on diameter but less on length), it will be as fast, will vibrate less and will be less likely to bend or brake.

 

[scallywag]

In my view a longer spear is more accurate plus more length means it's closer to the fish to start with!
Going to start making my next gun over Christmas which is going to be short with a fat shaft and a beefy band for low viz/night spearing.

 

[marginatus]

In my view a longer spear is more accurate plus more length means it's closer to the fish to start with!
Going to start making my next gun over Christmas which is going to be short with a fat shaft and a beefy band for low viz/night spearing.

Why is it more accurate?

In a, say 3 meter shot, it's not those extra 10 cm that make the difference but the way the spear travels in those 3m

 

[sjurba]

I think there is something to the accuracy theory. I have a 90 with a 120cm spear,this spear got buggered from shooting into rocks,so I replaced it with a shorter spear from my 75 and my accuracy was way off ,especially on longer shots. I've changed back to a longer spear now. Had the same problem on my 75 when I had a very short spear on it.

 

[marginatus]

Two hipothesis:
1 - was the spear the same diameter? It most certainly had less mass so it was being overpowered. check this vid: [ame=http://www.youtube.com/watch?v=WzWrcpzuAp8]Archers Paradox - Short Version - YouTube[/ame]
It's with arrows but the principle is the same

2 - there's accuracy and then there's precision which is not the same.
If the shots were consistently off (to the same side, distance...) then they were accurate but not where you wanted
Couldn't it had to do with the way you aim the gun (using the tip of the spear as reference and not the gun barrel)?

 

[Yeti]

Stop them behaving like a 'ten bob swerver' would be my guess. Not claiming to know but my feeling is that a longer spear travels straighter over a longer distance. The protruding from the gun probably allows the spear to oscillate between the end of gun and where the bands load when fired. The rest of the spear oscillating or not may well just follow that bit that was poking out the end and going true. I've used a shorter spear in the same gun and it definately made a difference and my 'accuracy' is pretty consistent.....I think?

Probably just one of those things that have settled as they are over time like pushbike wheels. Just feels right? Like planes and boats. 'when lacking technical input, if they look right they often are'

edit: just watched the video after posting. coat!.....TAXI! aye that's what I was trying to say I guess. I used to shoot alongside traditional longbows when I lived in Warwick and their arrows were that big and heavy they almost travelled in slow motion and you could see the waggle dance in the air. Not supprising they were feared even with armour on. I've seen what they go through on a range.

 

[marginatus]

I didn't understand all of the above ...
For the same mass, a shorter, bigger section spear will oscillate less when the same force is applied. More Oscillation -> less kinetic energy -> less travel.
It's a personal thing and if it works for you, great!

 

[Simos]

I didn't understand all of the above ...
For the same mass, a shorter, bigger section spear will oscillate less when the same force is applied. More Oscillation -> less kinetic energy -> less travel.
It's a personal thing and if it works for you, great!

I am not a spearo but I doubt you can generalise like that, it will depend on many parameters. If anything a longer and thinner spear should have less drag I would have thought, no? (and hence longer range)

 

[marginatus]

the drag will be a function of the spear surface.
For the same mass (to be comparable in terms of gravity), a longer and thinner spear will have more surface area...

 

[Simos]

the drag will be a function of the spear surface.
For the same mass (to be comparable in terms of gravity), a longer and thinner spear will have more surface area...

Don't think you can base anything on that - if anything the thicker spear will have a bigger frontal area but again although that's an important factor, you can't base anything on that alone.

The shape really affects drag so you'd have to determine the drag experimentally - see some examples: Shape Effects on Drag

For the flat plate you'll see the drag is the highest even though the surface area is the smallest (as it's really short).

I am guessing the main reason for longer spears to exist would be longer range or more accuracy? (why would you want to carry something bigger otherwise, there has to be some advantage)

 

[Jonny250]

The drag is made from a number of components, but mainly from 'form' drag plus 'frictional' drag. At the speed a shaft leaves the gun it will be mainly form drag (creating pressure waves). The form drag inthe previous refernce will be based on the frontal surface area, not the total shaft area, whereas the frictional drag will be based on the shaft area.
Personally, having looked at the arrow analogy and tried to do the maths (and failed to get a good result) i dont think the analogy works very well. Mainly i dont think the natural frequency of the shaft is anything like the same as an arrow, due to mass and material. I wonder if the shaft oscillates even one full 'wobble' over the time it travel to the end of the line. Once it slows significantly then any wobble will be lost anyway and the range is usually only a few metres.
I know lots of people disagree with this because theres lots of talk about balancing power of the gun or band size with the correct thickness of shaft. My limited experience of overpowering spearguns (tried it on a 75, 90 and 110) is that the gun becomes uncontrollable 'at launch' rather than giving an impression of spear wobble. Just my 2p worth!
To go back to Bros's question, i think a shorter spear will be fine. But why not rig a hand-spear for night fishing? Much less hassle and no loaded gun when picking up flatties...

 

[foxfish]

I wont pretend to know the reasons or answers but I can definitely remember reading long & technical threads on the subject, especially during the early days of the Medfish forum where lots of our Mediterranean friends discussed the pros & cons of spear length.
These threads (that must still be available to read) were mainly based around target shooting disciplines with a speargun.
If i recall rightly the guns were nearly always single band 90-100 tube guns & fired in a swimming pool at various ranges.
Anyhow the spear overhand was crucial to maintain accuracy & as I remember it was difficult to better standard factory dimensions!
I realise that does not answer the question!!
Also - enclosed track guns - you could assume that their design would stop spear wobble & allow a wider choice of spears however I am pretty sure that single band open track gun remain the choice for target shooting competitions.

 

[marginatus]

All very good points here...
But let me clarify what I'm talking about... I'm considering a spear that it's a few cm shorter and has 0,5mm more in diameter. Let's say a 1300mm x 6,5mm (diameter) vs a 1120mm x 7.0mm (just so the mass is around the same).
Is the surface area difference is small so will be the form and thus the drag difference will also be small...
It all probably comes to personal preference and shape/mass of the gun
Here an example:
http://www.abellansub.com/media/productes/denton110/2010/hi/fusil05.jpg

But a thicker spear will be less prone to bend?

 

[foxfish]

My most used gun over the last 6 years has been a Omer 90 air gun, first fitted with a mamba kit & now a Tomba free spear kit. The gun fires a 100cm 6.5 spear, that is a very short spear for the guns performance & only overhangs 10cm from the muzzle.
However the spears driving force is delivered in a very different way to a band gun.

 

[omega3]

I always thought it was to increase mass/momentum and therefore increase the spears ability to puncture/penetrate its target.
Another balancing act, and completely calculable no doubt.

I would also guess this is the entire basis behind gun/spear sizing and an area where pneumatic guns could demonstrate a real advantage over band guns in repeating performance over time.