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http://en.wikipedia.org/wiki/Cog_(ship)

Cogs (German: Kogge, Hansekogge) or rather cog-built vessels came into existence around the 12th Century.They were characterized by flush-laid flat bottom at midships but gradually shifted to overlapped strakes near the posts. They had full lapstrake planking covering the sides, generally starting from the bilge strakes, and double-clenched iron nails for plank fastenings.The keel, or rather keelplank, was only slightly thicker than the adjacent garboards and had no rabbet. Both stem and stern posts, were straight and rather long, and connected to the keelplank through intermediate pieces called hooks.

The lower plank hoods terminated in rabbets in the hooks and posts, but upper hoods were nailed to the exterior faces of the posts.

コグ（cog）

　コグ（適切にいえばコグ造りの船）の存在は、だいたい１２世紀ぐらいに確認された。この船は、平らな船底と、端に向って徐々にそそり立つ船首・船尾に特徴づけられる。また、外板を船底がら重ね張りしたクリンカービルトである。また、二重に締めた鉄釘で板同士を繋ぎ合わせた。キール（竜骨）（と言うより、板状のキール）は、キールに隣接する板（ガーボード）よりわずかに厚く、また、板同士を繋ぎ合わせる溝はない。船首と船尾の両方がまっすぐで長く、フックと呼ばれる中間材を経由してキールにつながる。

Caulking was generally tarred mosses that was inserted into curved groves, covered with wooden laths, and secured by metal staples, called sintels. Finally, the cog-built structure could not be completed without a stern-mounted hanging central rudder, which was a unique northern development (Hocker, 1991; Crumlin-Pedersen, 2000).

Seal of Lübeck, with an undersized CogCogs were generally built of oak, which was an abundant Baltic timber. This vessel was fitted with a single mast and a square rigged single sail. Even though this type of rigging prohibited sailing into the wind, it could be handled by a smaller crew, which also reduced operational costs. These vessels were mostly associated with sea-going trade in medieval Europe, particularly in the Baltic Sea region.

The earliest development, according to the current archaeological evidence, directs us to the Frisian coast, Western Jutland, as the possible birthplace of this vessel. The transformation of the cog into a true seagoing trader came not only during the time of the intense merchant exchange between West and East, but also as a direct answer to the closure of the western entrance to the Limfjord. For centuries, Limfjord in northern Jutland offered fairly protected passage between the North Sea and the Baltic. Due to unusual geographical conditions and strong currents, the passage was constantly filling with sand and was completely blocked by the 12th century. This change produced new challenges. Bigger ships that could not be pulled across the sand bars had to sail around the Jutland peninsula and circumnavigate the dangerous Cape Skagen to get to the Baltic. This imposed major modifications to old ship structures, which can be observed by analyzing evolution of the earliest cog finds of Kollerup, Skagen, and Kolding. The new and improved cog was no longer a simple Frisian coaster but sturdy seagoing trader, which could cross even the most dangerous passages. Later on, fore and stern castles were added for defense against pirates, as well as to use these vessels as warships.

The need for spacious and relatively inexpensive ships led to the development of the first workhorse of the Hanseatic League, the cog. Eventually, around 14th century, cogs reached its structural limits, thus providing the desperate urge for a quick replacement. The replacement, however, was already in place and only waiting for the reconditioning. Even though there is no evidence that hulk ships descended from the cogs, it is clear that the 14th and 15th centuries witnessed an intense technological interchange of ideas between the two (Crumlin-Pedersen, 2000). In essence, the transition from cogs to hulks was never a linear function. According to some interpretations (Gardnier, 1994), both vessels coexisted for many centuries but followed diverse lines of evolution.

12〜13世紀あたりに発明されたと言われる。
　

なると、バルト海のハンザ同盟の諸都市でコグが発明された。コグは一本マストで、垂直にちかいそそり立った船首と船尾があり、しなやかな船体をもち、波の抵抗が少なくなっていた。さらに、喫水が深く積載量が増加し、バウスプリットという船首から突き出た棒が備わった。バウスプリットは風上に切り上がる際に、横帆がよじれないように引っ張るために生まれたという。外板はクリンカービルトであった。また、それまでの側舵が船尾舵になった。船舶史上重要な発明であった。