Rudder - Rudder

Japanese: 舵 - かじ

A tool used to steer a ship. It can also be written as 'kaji', 'kaji', or 'kaji'.

history

In ancient times, this was a so-called steering oar operated on the side of the ship near the stern. Like oars, this was clearly depicted on drawings of Egyptian ships from about 5,000 years ago, and later became standard equipment on Greek, Roman and other European ships, and was used primarily until the 13th century. In China, similar steering oars were used until about 2,000 years ago, but in the 1st century Eastern Han Dynasty, a revolutionary method of placing the stern rudder at the stern on the centerline of the ship appeared. This is the origin of today's rudders, and in Europe, this method finally began to be used in the 13th century. In Japan, the use of rudders has not been confirmed in the Jomon period, but ships depicted on bronze bells and pottery from the Yayoi period are equipped with steering oars, and as can be seen from excavated ships and ship-shaped haniwa clay figures, steering oars were also used primarily in the Kofun period. China's adoption of the advanced stern rudders was quite late. The word "kaji" appears frequently in the "Manyoshu," but most of these refer to oars used for propulsion. There is also the word "kajitsuka," which suggests the presence of a rudder, but a rudder (kajitsuka) can also be used for steering, and the use of stern rudders cannot be confirmed. Therefore, it is thought that their introduction dates back to the 7th century or later, when Chinese junk technology was used to build ships for Japanese envoys to the Tang Dynasty. In the Heian period, there is a clause in the "Engishiki" that suggests the adoption of stern rudders, and by the Kamakura period they had become widely used, with all large ships depicted in picture scrolls and other works being equipped with stern rudders. The shape and installation method are similar to those of early modern Japanese ships, indicating that the prototype of the Japanese-style rudders was already established in the Middle Ages.

Early modern Japanese rudders were the same type for both merchant ships and military ships, and were designed to accommodate the shallow water conditions of many Japanese ports, with the rudders pulled up when entering port. However, this method of mounting the rudders was not sturdy, and they were often destroyed by rough waves in rough weather. The large rudder surface, which was out of proportion to the hull, ensured the necessary maneuverability for domestic ships that frequently entered and left ports, and was essential for improving sailing performance in crosswinds and headwinds, but this was also one of the reasons for their destruction in rough weather. In other words, its strengths were also weaknesses, and no effective measures were taken until the Meiji era, when today's rudders became the standard due to the predominance of steamships, while the distinctive Japanese-style rudders disappeared due to the decline of Japanese ships.

[Kenji Ishii]

kinds

Rudders can be classified according to their shape into three types: unbalanced, balanced, and semi-balanced. In an unbalanced rudders, the rudder blade that receives water pressure is located only behind the rudder's axis of rotation, while in a balanced rudders, the rudder surface is located in front of and behind the axis of rotation. Unbalanced rudders have been widely used for a long time since the days of sailing ships, but as ships have become larger and faster, balanced rudders, which require less rotational force than unbalanced rudders, have come to dominate. Semi-balanced rudders are intermediate between these two. In terms of structure, they can be classified into single-plate rudders, whose rudder blade is made of a single thick steel plate, and double-plate rudders, whose frame has steel plates on both sides. Double-plate rudders are used on most ships today because their cross-section is streamlined, which provides good steering effect and less water resistance. Single-plate rudders are simple in structure but have poor steering effect, so they are only used on small, slow-speed ships. The top of the rudder has a cast iron rudder stock that extends upwards and is connected to the ship's steering gear by a gear or a bracket-type device called a tiller, which transmits turning force to the rudder.

[Morita Tomoharu]

"Illustrated History of Japanese Ships" by Kenji Ishii (1983, Shiseido)

[Reference] | Paddle

Classification by rudder shape
©Shogakukan ">

Classification by rudder shape

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

船を操縦する要具。楫、梶、柁とも書く。

歴史

古くは船尾付近の舷側(げんそく)で操作するいわゆる操舵櫂(そうだかい)で、これは櫂と同様に約5000年前のエジプトの船の絵に明瞭(めいりょう)に描かれており、その後のギリシア、ローマをはじめとするヨーロッパの船の標準的装備となって13世紀まで主用された。中国では約2000年前までは同様の操舵櫂を使用していたが、1世紀の後漢(ごかん)の時代になると、船体中心線上の船尾に配置する画期的な船尾舵の方式が出現した。これが今日の舵の源流となるが、ヨーロッパでは13世紀になってようやくこの方式が使われるようになった。日本では、縄文時代は舵の使用は確認されていないが、弥生(やよい)時代の銅鐸(どうたく)や土器に描かれた船には操舵櫂が装備されており、発掘船や船型埴輪(はにわ)などでみる限り、古墳時代も操舵櫂が主用されている。中国の先進的な船尾舵の採用の時期はかなり遅れている。『万葉集』には「カヂ」が頻出するが、そのほとんどは推進用のオールである。また舵の存在を思わせることばに「カヂツカ」があるが、舵柄(かじつか)は操舵櫂でも使うことがあり、船尾舵の使用は確定づけられないので、その導入は7世紀以後の中国系ジャンク技術による遣唐使船建造のときまで下るとも考えられる。平安時代になると、『延喜式(えんぎしき)』に船尾舵採用を示唆する条項があり、鎌倉時代には十分普及して、絵巻などに描かれた大型船はすべて船尾舵を装備している。その形状や装備方式は近世の和船のそれに近く、すでに中世に日本式の舵の原型が確立していたことを示している。

　近世の日本式の舵は、商船、軍船とも同じ形式で、入港の際は舵をに引き上げるという、水深の浅い港の多い日本の港湾事情を考慮したものであった。しかしこの舵の装着法は堅固でなかったため、荒天時の激浪で破壊されることも多かった。また船体に比して不つり合いな大舵面は、頻繁に港へ出入りする内航船にとっては必要な操縦性を確保し、かつ横風や逆風の際の帆走性能向上に欠かせないものであったが、これもまた荒天時に破壊される一因となっていた。つまりその長所が短所でもあったわけで、効果的な対策が行われないまま明治時代に入り、蒸気船の主用によって今日のような舵が標準化される一方、和船の衰退もあって特徴的な日本式の舵は姿を消した。

［石井謙治］

種類

舵を形状によって分類すると、不釣合(ふつりあい)舵、釣合舵および半釣合舵の3種がある。不釣合舵は、水圧を受ける舵板が舵の回転軸の後方だけにあるが、釣合舵は、舵の面が回転軸の前後にある。帆船時代から長い間不釣合舵が広く用いられてきたが、船が大型・高速化するにつれて、不釣合舵より回転力が少なくてすむ釣合舵が大半を占めるようになった。半釣合舵はこれらの中間的なものである。また構造上から分類すると、舵板が1枚の厚い鋼板でできている単板舵と、骨組の両側に鋼板を張った複板舵とがある。複板舵は、断面が流線形で舵効きがよく、水の抵抗も少ないため、現在はほとんどの船で使用されている。単板舵は、構造が簡単であるが舵効きが悪いので、低速小型船で使用されるにすぎない。舵の上部には鋳物でできた舵頭材があって上方へ伸び、歯車またはチラーとよぶ腕木式の装置によって船内の操舵機へ連結されており、これらによって回転力が舵へ伝達される。

［森田知治］

『石井謙治著『図説和船史話』（1983・至誠堂）』

[参照項目] | 櫂

舵の形状による分類

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