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Why is the Katana Blade Curved?
At first, the Katana had straight blades, but as time passed, these received curves due to their efficiency in battle. Since the Katana are slicing weapons, its blades are made curved to execute a better cutting motion.
You might be wondering when did the Katana first appear in history? Generally, the Katana didn’t appear until about the 15th century. Its predecessor, the Tachi, was an efficient cavalry weapon and developed sometime between 900 & 1100 AD.
If you think about it, curved blades were more efficient and effective compared to straight swords. Cavalry often used these in battle since the blade’s curves add considerable downward force in the cutting motion.
So for a cavalry-dominated battlefield, it was sensible to wield a significantly curved blade. Do note that the Tachi sported a long handle for counterbalancing the blade during single-handed use.
The reason why curved blades cut efficiently well is due to its ability to create natural cutting motion. It’s most evident when the edge comes into contact with a specific target.
Instead of a draw cut, a curved blade links with targets differently. These blades can contact targets directly at an angle and continue in the line of force, where the sword’s geometry does all the work.
Also, the spot on the blade you come in contact with makes a huge difference. It’s because adequate cuts should only be made with the Monouchi. It is the top ¼ portion of the blade that’s close to the tip.
In the past, development of the Uchigatana symbolized the evolution in warfare tactics. During the Sengoku era in the 15th century, the Samurai began to require weapons for closed quarters and dismounted combat.
The deep curvature and long blade of the Tachi were difficult to use when dismounted. Because of that, the sword developed into the Katana that we know today.
Since the Katana became an efficient weapon, a lot of Tachi were shortened between the 15th and 17th centuries.
What are the Benefits of Having a Bohi on the Katana blade?
The Bohi – also referred to as the fuller, blood gutter, or blood groove – is a slanted or rounded slot on a blade’s flattened area.
It runs down the length of the sword’s blade and is beneficial by making the piece more lightweight. This feature also changes the blade’s balance point, making it quicker, swift, and easier to handle or wield.
You can quickly tell if the Katana sports a Bohi by merely inspecting the blade. To make it easier, the Bohi is an indention where steel drops down in the center. Do note that the Bohi, despite being called Blood Grooves or Blood Gutters, do not have anything to do with blood.
It appears like a simple feature of a Katana, but the Bohi does have its own set of benefits. First, it provides excellent Tachi Kaze, which is the sword wind sound.
When you swing the Katana, you’ll get outstanding feedback on its angle, as well as on the speed of your cut. This is what makes a Katana so special.
The form of a Bohi helps lessen any absence of durability. Plus, it acts like an I-beam when used in the construction business.
With proper heat treatment, distal tapers, and blade tempering, a blade with the Bohi can be 20 – 30 times lighter than a blade without Bohi.
Even with its reduced weight, it doesn’t sacrifice the strength or integrity of the blade. However, this specific effect lessens when the length of the blade decreases.
If a groove is on both sides of the blade, two Bohi can be used simultaneously. Doing so will press the workpiece at the center.
The Bohi also works as a tool for swordsmiths. It acts as a kind of swage since it features a distinct shape that is forged in its surface.
Swordsmiths utilize this to form that particular shape to the metal, since it’s impossible to achieve this by only using a hammer.