The 4th floor of the Underwater Dungeon is, as the name suggests, an underwater environment where your HP constantly drains unless you have a water-breathing ability. In short, characters are fighting fish and hermit crabs while swinging swords, firing arrows, and casting spells underwater.

In reality, this presents more than a few problems. The first question that comes to mind is: 'Can you actually fire an arrow underwater?' How would an arrow attack that accurately intercepts an enemy from dozens of meters away hold up in the real world?

※ Lin-kle Science' is a fun, curiosity-driven series where I, a reporter with a science background (※Math grade 4) but a lack of actual scientific expertise, use AI to analyze the issues that arise at the boundary between reality and 'game logic.' Please take this with a grain of salt, as there may be a mountain of scientific errors. :)

= Using a standard bow underwater comes with massive limitations.

When a standard bow is used underwater, fluid resistance creates immense constraints. The speed at which the bent limbs snap back slows down, and the speed at which the drawn string moves forward is also reduced. It’s like trying to fan yourself in mud; the initial energy transferred to the arrow drops drastically.

Furthermore, a rapidly moving bowstring can cause 'cavitation.' When an object moves at high speed through a liquid, the pressure drops momentarily, causing the liquid to boil and vaporize, creating a temporary vacuum-like void. As this collapses, it pulls in surrounding objects, causing energy loss.

= Water is much denser than air, leading to significant energy loss

The rate at which an object's kinetic energy decreases over distance is governed by the drag equation, and so on... but there's no need to get that deep. The bottom line is that underwater resistance is over 800 times greater than in air. Consequently, the lethality of an arrow that flies 100m in the air is roughly equivalent to one that has traveled only 12cm underwater. Even if a real-world arrow could maintain lethality over hundreds of meters in the air, it would lose all killing power after just 2–3 meters underwater.

Moreover, the underwater dungeon is likely even denser and more viscous, filled with the waste of sharks, mermaids, crayfish, and hermit crabs, mixed with the sweat and blood of the humans and elves hunting them, which would only increase the resistance.

= Unlike standard bows, there is a weapon designed to be fired underwater: the speargun

Spearguns don't use a snapping string; instead, they use rubber bands to push the spear over a long distance, securing initial propulsion. Also, the projectile is much heavier and longer than a standard arrow and lacks fletching. While fletching is crucial in the air, it provides no benefit underwater and only creates massive resistance.

= So, what if we used a crossbow?

A real-world crossbow might look similar to a speargun, but its structure is completely different. It is designed to fire short, light arrows at high speeds, and underwater, this speed becomes a liability. Resistance increases in proportion to the square of the velocity, causing the arrow to bounce toward the surface the moment it's fired.

= The solution: a modified crossbow and specialized 'harpoon' arrows'

Ultimately, for arrows to pack a punch underwater in Lineage, you would need to modify a crossbow—shifting focus from string speed to a mechanism that produces a slower but more sustained, powerful force—and replace standard arrows with heavier, longer underwater-specific arrows or harpoons. However, because harpoons are heavy, you wouldn't be able to carry many.

If you used a bow with sufficient structural integrity and pushed the tension to the limit, you could achieve the same effect with a heavy, fletchless arrow, but you'd need to be an Elf with 30 Strength to draw such a bow.