In Japanese, the traditional boat is known as the wasen. Wa means "traditional Japanese thing" and sen is one suffix meaning boat or ship. The word for boat in Japanese is fune; when attached to a modifying noun it gains a hard sound and become ....bune. I point out this usage since I use Japanese boat names in the text which follows.
I began researching traditional Japanese boat building in 1990. As of 2007, I have been to Japan twelve times, focusing my research on the boat building techniques and design secrets of the craft: techniques which have traditionally been passed from master to apprentice with almost no written record. In 1996 I apprenticed with the last man still building the taraibune (tub boat) of Sado Island, Niigata Prefecture; in 2000 I built a bekabune (seaweed gathering boat) in Urayasu, Chiba Prefecture; and in 2002-2003 I built three traditional boats, two in Tokyo and one in Aomori, as part of a research grant funded by the Freeman Foundation.
My articles and photographs have been published in magazines in the United States, Great Britain and Japan. I have one book, The Tub Boats of Sado Island; A Japanese Craftsman's Methods.
Please see my Research and Publications page for a complete list of my
publications about Japan. You can also visit an online article I wrote
about my research at:
Designs of traditional Japanese boats have, in many cases, been passed down through generations, with small modifications. The craft has been an oral tradition, and where boat builders use drawings (known as itazu, always drawn on a wooden plank) these drawings are often incomplete. Drawings are sometimes a profile only, with perhaps the plank keel in plan view, or perhaps an expanded transom. But the boat builder preserves his secrets by memorizing key dimensions. The process of memorization is different for each individual. One of my teachers memorized two numbers: a single offset and a figure that he subtracted from that dimension. The result was another offset, which when subtracted by the same figure yielded the final offset. The frailty of this system is how easy it is to lose this knowledge as craftsmen disappear without apprentices.
Traditional Japanese boats are characterized by relatively thick planking and few, if any, frames. Where frames are not used, hulls are strengthened by athwartship beams which are connected to the hull with wedged mortise-and-tenons. Hulls are hard chine with a wide plank keel supporting two garboard planks, with two nearly vertical planks completing the hull. Planking is usually Japanese cedar with cypress often being used for beams, stem and transom.
Japanese boat nails are made of either soft iron or copper. They require a very precise hole: too tight and the nail bends, too loose and it does not hold. These nails are not round but flat, with the heads offset to one side. The iron nails are used to edge fasten planks to one another while the copper nails are driven through the hull and clenched over. These nails are all made by hand. The nails for my boats were made by a blacksmith in Yokohama. Sadly, this man passed away in 2005 and the firm will not be replacing him. To my knowledge this leaves one firm near Hiroshima as the only source of boat nails left in Japan.
Japanese boat builders do not use drills; instead special chisels called tsubanomi (sword hilt chisel) are used to cut holes for the nails. The hilt is used to hammer the chisel back out. A complete set of tsubanomi includes several sizes, curved chisels and special chisels for cleaning out the hole.
Where planks are edge fastened the seams are prepared using a method called suri awase (literally translated as "rub together," perhaps better translated as "reconcile"). Adjoining plank edges are planed and then placed edge-to-edge on blocks on the shop floor. Then the boat builder uses a special set of saws to cut through the seam. Woodworkers may be familiar with the technique of sawing through a joint to improve the fit, but here the sawing motion is critical. The saw must move parallel to the plank face at all times. In my apprenticeships (the tub boat, more coopering than boat building, does not utilize this method), this technique was by far the greatest focus of my instruction.
Just before assembly the planks are set upright and the edges are pounded in the center with a hammer to compress the fibers. This process too is more difficult than it appears. When I first used these methods I wondered why we were lavishing such attention on a seam that even if imperfect would swell tight in a matter of hours. When the planks were nailed together and the surfaces given their final dressing with a handplane I was stunned to see that, when done correctly, the seam is invisible. Also, the idea that a boat would leak at launch is an anathema to Japanese boat builders.