You may have heard of this common fantasy trope, an archer firing multiple (usually 3) arrows in a single pull of the bow.
Now, I am not an expert at bows or tactics, but it seems to me that the loss of accuracy is not worth even attempting this and that's assuming it could work!
What problems appear with this 'Multi-arrow' bow and how can I overcome these? What are the actual realistic advantages and disadvantages of a multi-arrow bow if it could work?
Your main problem is that you're trying to fling multiple projectiles with a single bowstring. I'm no physics guru, but it seems that you're going to be dividing the pounds of pull across the total number of projectiles -- so you'll get correspondingly less range & target penetration than if you stuck with a single arrow (ignoring more obvious issues like aiming). Someone actually ran the numbers on how much kinetic energy from the bowstring is transferred to the arrow, if you're interested.
A crossbow is a much more workable solution, as the strings can be drawn in advance, and held in place. That leads to the possibility of firing more than one projectile, in quick succession. Such weapons are indeed a trope, usually because the increased firepower is desirable from an action standpoint, but the limitations of the time period will not allow firearms.
One solution to firing multiple arrows is a special crossbow, featured in a battle scene in the 2000 film The Gladiator. On first glance, it looks rather ridiculous, but I actually feel it is a workable design (albeit perhaps not terribly practical for anything other than a showy arena skirmish) for the simple reason that each crossbow bolt has its own string, rather than some sort of imaginary bolt "magazine" that ignores the necessity of re-cocking the string after each firing. Additionally, it dispenses with any sort of fanciful common trigger system, and appears to have the wielder just rotate the entire weapon on its axis.
A simpler version would be the double-sided crossbow, from the 2000 film Dracula:
Let me expand on "reduced accuracy". I base this on my own experience shooting target-weight bows and observing others.
Accuracy at any decent range depends on some fairly fine-grained factors. Aim a fraction of an inch high or low, or draw the string back not quite as far as usual (or just a bit farther), and you're probably going to miss your mark. You might still hit a large target somewhere, but it won't be what you were aiming for. It is not uncommon to mark the center-point of the string for this reason, so that you're nocking the arrow at the same position (and thus drawing at the same angle with respect to the bow) each time. The key to good aim is consistency.
If you add arrows to the string in a single draw, then by definition those arrows are not positioned to hit your target. Movies usually depict multiple arrows being spaced an inch or so apart on the string, maybe more. And if those arrows have fletching (feathers), you probably can't get them much closer than half a inch on the string. (For any decently-heavy bow, the arrow itself is about a quarter-inch in diameter.) That's a huge difference when shooting at even 30 yards, to say nothing of 50 or 100 yards. Those extra arrows may look pretty, but they aren't hitting your target. I suppose if you're shooting at a large charging army they might hit somebody else, if you're very lucky, but probably not (see "power").
Other answers have already addressed the reduced power so I won't repeat them. Your arrows aren't going to pack the punch you need to do damage. They're also not all going to get the same amount of power; the one in the middle will have more force than the others, which will likely fall short. (Thanks to XandarTheZenon for pointing this out in a comment.)
A competent archer can fire an aimed shot about once every five seconds; good ones are even faster. A lot of this speed comes from the ease of the load-draw-release cycle. It's a very smooth motion; you draw an arrow from the quiver by its nock and place it on the string. You don't even need to be looking at it; this is done by feel. (Instead you're looking at your target.)
Now, how long is it going to take you to load three arrows onto the bowstring? I don't think you can do them all at once, and if you do them one at a time then the ones already on the string are going to slow you down. I haven't tried the experiment, but I'm going to be bold and say that it will take you longer to load and fire your trio of arrows than it would take to fire them individually.
So you can shoot less-accurate under-powered arrows more slowly, or you can shoot them one at a time instead. I know which I'd choose.
I use a recurve and longbow. Getting good at this took practice, like a lot of practice.
First. There are some very expert opinions out there on why this is fake and or a bad idea but there are some problems with that. Most people aren't thinking of the bow as a weapon of war. They are thinking of it as a hunting/sport weapon. They are thinking of compound and recurve bows where it is pretty much a given that you are going to be using bow hand draw and not arrow hand draw.
Second, the physics around arrow flight are really REALLY complicated. So complicated that for a long time people thought bows were an impossible mechanism leading to the coining of the "archers paradox" now I'm not going to get into the specifics but suffice it to say that the loss of acceleration is correct but not as dramatic nor as important as you'd think in the context of a battle.
third thing is, Arrow hand draw is important which means owning a bow that allows you to do this is important, you can get a longbow, and if you are interested in them I highly reccommend it, or you can just get a recurve for the opposite of your dominant hand and sand the grip to shape it a bit. Professional olympic archers can fire an arrow maybe every once every 3-5 seconds an ancient archer could fire an arrow about once every second. The reason is arrow hand draw lets you rest, nock, and draw the arrow as a single motion rather than maneuvering the clumsy bow hand draw. This is going to help you keep the top arrow from going off course or worse, interfering with the flight of your other arrow.
fourth thing, in sports and hunting accuracy is important, in battle they are important but the MOST important thing is how many arrows you can put down range within a specific amount of time. It may not surprise you to learn that people really don't like getting shot with an arrow, so the less of a break in the screaming bodkin-pointed death missiles there was, the less of an opening you presented. Also the average range for an archer to be shooting at individual targets in battle is 170-200 feet at most otherwise they would just be firing into the mass of people hoping to hit. So you don't actually have to get it that far.
So to pull off the famed "multishot" you need to knock two arrows, I know theres a lot of ways to do that and some people use a mechanism to aid them in having a clean release. I've personally found this is the worst way to do this trick so I would avoid it. The method I've always used is one finger above the nock and two below but for this you are going to make an "arrow sandwich" with one below the first arrow one in the middle and one on top of the second. and you need to grip the bow so that your index (pointer) finger can extend and the tip can rest between the two.
If you did it right both the arrows should be perfectly straight.
Now here's the part that's going to take practice. There are two things i've found that generally make this trick work reliably. First, and most important, once you release the string your index finger needs to slide out from between the arrows, otherwise the hens (the two matching coloured flights) are going to sting it on the way past, your instinct is going to be to curl it back in but what usually happpens when you do that is it deflects the bottom arrow down. The best thing to do is to flick it straight out so it's out of the way, this may deflect the top arrow up a bit but over a longer distance it will drop back down and you should still get a pretty accurate shot. Second, draw the bow with only your middle finger, keep rour ring and index finger extended to stabilize the arrows but you should be pulling from the middle, the reason for this is, while the bow will deliver all of its force across the entire string it delivers the greatest acceleration from the point you drew it back, for maximum accuracy this should be directly between the two arrows.
As you mentioned, the accuracy of all of the arrows would be significantly degraded.
A bow transfers energy from the bent wood/materials of the bow into an arrow through its bowstring. The amount of momentum imparted depends upon a number of factors but by adding multiple arrows to the bow string, you are at the least dividing the momentum by the number of arrows added.
Decreased momentum means:
I suppose the best argument about whether you gain or lose more by adding arrows to the bow string is by looking through history. The trick is an obvious one so if the people who did it greatly benefited from it, you'd expect everyone to be doing it.
The limiting factors of arrow acceleration are:
Also there's a scaling factor, in that the firing of the bow causes the bowstring (and arrows) to pass through the entire draw length (perhaps 24-30 inches). Meanwhile the limbs of the bow (which are forcing the arrow through that distance) may only pass through a few inches. This distance might be 8-10 inches or so (see image below).
Bow drawn and at rest:
Because the ratio of motion between the arrow and bow limbs are not constant you actually get a relatively complex interaction between the two. Initially the force propelling arrow and limbs are high. As the string returns to rest, the amount for force decreases while the amount of motion increases.
Even if you set the arrow mass at zero (no arrow notched), the bow will take time to return to rest state (FYI, never draw and release a bow with no arrow notched, this can break your bow) because the bow limbs have finite mass.
Actually, it is quite possible to fire THREE arrows with a single draw. I first saw this technique in the Hindi movie, Bahubali (2), The Conclusion. Google for images and relevant yt clips.
Now, while I'm sure there was liberal application of Movie Magic, especially when the hero shot past the gal's head—two past her ears, one above her crown…I've not been able to figure out how to bump one of the arrows into a higher/wider flight—I've nonetheless been able to duplicate the draw if not the loading speed and fluency.
Note the draw hand's inverted grip with thumb-down, palm-away. Inverting is not necessary, but is definitely a conversation starter on ranges. When the arrows are parallel, their grouping is quite tight. I've yet to get a spread triple hit by putting angles between the shafts.
But instead of me telling y'all about it, I recently found this: https://youtu.be/l6HdEqOpgzE
Shooting multiple arrows is somewhat similar to throwing knives.
Certainly, it is possible and it isn't completely useless, but it's not something commonly done in a combat situation. Its unreliable and requires many hours of practice to perform with any modicum of skill.
With Knife Throwing, there are many other weapons that are far more effective at range. Instead of wasting your time trying to throw a knife, just pick up a bow or throw a javelin. The knife is just a backup weapon at close range and a tool.
Firing a second arrow will reduce the power of the bow, but if its being done at close range you can afford to sacrifice power against lightly armored targets. The real issue here is that you don't gain much. Let's say you fire two arrows at a single target. If one of them misses, the second one likely will as well. You've handicapped yourself for no benefit. One arrow in the chest is enough to fell most targets, so adding a second one isn't going to gain you much.
You'll be better served to simply draw and fire one arrow using the same technique you've trained and practiced hundreds or thousands of times rather than train a whole new one.
Now, just like with Throwing Knives, if a person was an expert that spent all of their time honing their skill then they would be quite fearsome. A normal person throwing their knife is just a somewhat sharp rock that needs to be dodged, while an expert can clip the wings off a fly at twenty yards. The same could be said of firing multiple arrows. Its certainly possible for a person to train so long and hard they could fire two arrows and strike two different targets(with reduced power), but who has that kind of time to devote ten or so years to constant training?
Just look at Lars Andersen. He's firing arrows faster than anyone thought was possible and can even fire them around obstacles. Of course, this is done with special arrow nocks and a weak bow, but he is a 50 year old man reinventing this stuff. Imagine young and extremely strong men with skills being passed down over many generations.
It's mainly an argument over the way that an army or large force would do things and the things that isolated experts can do. In your question you ask specifically about a multi-arrow bow. That would likely be the only way this sort of thing would work, creating special bows/equipment to help reduce the amount of training needed by the rank and file.
The bow might have large V-channels on it for the arrows to fall into. Quivers could have grids in them so the arrows are easy to grab in groups. They might even have special drawing devices that not only grip the string but keep the arrows spaced properly.
Of course, you'd want there to be a valid reason to do this. Why would you want to fire three weaker arrows rather than a single more accurate and powerful one? Is there some fantasy beast with three equally spaced eyes that are its only weakpoint? Do they have a special tri-part magic technique that needs three arrows flying in parallel to activate?
If there is a reason to do something, then people will go above and beyond to figure out a way to make it work.
This is a very interesting idea and one that I would like to look into. One factor that I would like to point out, is that all of the bows made today are for firing one arrow. so trying to fire multiple arrows will not work. If someone were to make a bow that was specifically designed for multiple arrows, the Idea might actually work. You could also work out a way for the arrows to shoot in such a way that they would fire at a wider angle and thus prove an actually useful point.
