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Introduction:

The Japanese bow is known as a "yumi". Mi means "beautiful" in Japanese , and Yu means "bow", so when combined together, the name comes out as "beautiful bow". A suitable name to describe the beautiful weapon of archery employed in Japan (used for hunting and warfare, as well as martial arts practice) for centuries (though the bow has changed form from different periods of time). 

The current form of yumi includes the longer "Daikyu" and the shorter "hankyu" used in the practice of "kyudo" (or Japanese archery). The yumi is quite tall (standing over two meters), surpassing the height of the average archer. They are traditionally made by laminating bamboo, wood, and leather, using techniques which have not changed for centuries, although some archers (particularly beginners) may use a synthetic yumi. Obviously, I prefer traditional materials though.

The yumi is asymmetric; the grip is positioned at about one-third the distance from the lower tip and upper and lower curves differ. Several hypotheses have been offered for this asymmetric shape. Some believe it was designed for use on a horse, where the yumi could be moved from one side of the horse to the other with ease. Others claim that asymmetry was needed to enable shooting from a kneeling position and yet another explanation is the characteristics of the wood from a time before laminating techniques. Whatever the case, the hand holding the yumi experiences less vibration at this point.

The "tsuru" (string) of a yumi is traditionally made out of hemp, although most modern archers will use strings made of synthetic material, such as Kevlar, which will last longer. Strings are usually not replaced until they break; this results in the yumi flexing in the direction opposite to the way it is drawn, and is considered beneficial to the health of the yumi. The nocking point on the string is built up through the application of hemp and glue to protect the string and to provide a thickness which helps hold the nock of the arrow in place while drawing the yumi.

Craftsmanship:

A standard yumi bow consists of 2 hardwood side strips and 3 bamboo strips sandwiched between bamboo faces.

This unique style of laminating has been done for hundreds of years in Japan. The immediate advantage results in a very light but very powerful bow.

Nearly any draw weight is possible. The length of a bow can vary depending on your draw length, but are no shorter than 66" and no longer than 74".

Translucent coats of "urushi" (Japanese lacquer) is the standard finish on all the bamboo yumi.

What is urushi?

Urushi comes from the sap that is collected from the lacquar tree which is native to China, Japan, Korea and some other Asian counties. The vicous milky sap is collected during the summer month by making cuts into the tree, much like we collect Maple sap, only the urushi season is longer. This sap provides the raw urushi which has been used for thousands of years, from simple coating of household objects to elaborated artwork, lacquerware and on weaponry such as bows and arrows.

Care:

A bamboo yumi requires careful attention. Left unattended, the yumi can become out-of-shape and may eventually become unusable. The shape of a yumi will change through normal use and can be re-formed when needed through manual application of pressure, through shaping blocks, or by leaving it strung or unstrung when not in use.

The shape of the curves of a yumi is greatly affected by whether it is left strung or unstrung when not in use. The decision to leave a yumi strung or unstrung depends upon the current shape of the yumi. A yumi that is relatively flat when unstrung will usually be left unstrung when not in use (a yumi in this state is sometimes referred toas being 'tired'). A yumi that has excessive curvature when unstrung is typically left strung for a period of time in order to 'tame' the yumi.

A well cared-for yumi can last many generations, while the usable life of a mistreated yumi can be very short.

Serious Kyudo practitioners treat the yumi with reverence, as pieces of great power, and as teachers with much to impart to the student (a yumi is said to hold within it part of the spirit of the person who made the yumi). A Kyudo student will never step over a yumi which lies on the ground (that would be considered disrespectful), and will typically treat a yumi like they themselves would wish to be treated (e.g. kept away from excessive heat or cold,  kept dry, kept away from excesses of humidity or dryness, carried upright). It is also considered disrespectful to so much as touch another person's yumi without his/her permission; "yumishi" (yumi-maker) Kajuro Shibato has said this is equilivant to touching someone else's spouse in a sexual manner.

Bow Lengths:

Height of archer                  Arrow length                   Suggested bow length

 < 150 cm                                 < 85 cm                             Sansun-zume (212 cm)

150–165 cm                             85–90 cm                             Namisun (221 cm)

165–180 cm                            90–100 cm                           Nisun-nobi (227 cm)

180–195 cm                           100–105 cm                        Yonsun-nobi (233 cm)

195–205 cm                           105–110 cm                        Rokusun-nobi (239 cm)

 > 205 cm                                 > 110 cm                             Hassun-nobi (245 cm)

References:

Yumi - Wikipedia, the free encyclopedia

YUMI BOWS - Where Art and Performance Meet