Building clinker boats is an ancient technique in the Nordic shipbuilding tradition. The old technology is still in use along parts of the Swedish coast, especially for smaller boats, such as the types called ekor, snipor, and jullar.
Clinker-built means that the edges of hull planks overlap each other and that they are held together along the overlapping edge, called the lands. The base of the boat consists of the keel or bottom platform with stems, to which the planks are attached. The frames are adapted to the shape of the boat and are held to the planks either with wooden pins (called treenails) or with nails of iron (later also copper). To prevent leakage, the boat is sealed with natural fiber (often flax) and tar. In earlier centuries, plant fibres such as moss or animal hair were used.
The method of fitting in the frames after the planking is finished is different from building boats in carvel technique, where the frames are set up on the backbone first, and the planks are attached to them edge to edge, to produce a smooth surface. Clinker boats and even ships were traditionally built without drawings, although in modern times building from drawings has become more common. Boatbuilders used sticks, string and levels or other simple tools to check the hull for symmetry, and could design some components using geometrical methods, such as arcs of circles.
Clinker construction is an historically dominant tradition in Scandinavian boatbuilding, and is usually thought to have originated in the region, although there are boatbuilding traditions using overlapping planks elsewhere in the world, including India and Vietnam.
The oldest clinker-built vessel found in Sweden is the Äskekärr ship. It was found in an area which proved to be an old shipyard in Ale municipality just outside Gothenburg. The ship, which is sixteen meters long, has been dated to c. 930 AD. It was built in oak, with caulking in wool and resin, and had been in use for many years, to judge by all the repairs. The Äskekärr ship, a so-called knarr, was a merchant ship propelled by sail. Since the ship was repaired with a piece of wood from much farther south, it is believed to have sailed to the continent. Measurements have been made and a full-scale copy, named Vidfamne, was built in the 1990s. Two more ships from the later Viking period have since been found just south of Varberg, of which one, a merchant ship, was about 15 meters long.
However, most clinker-built vessels were smaller working craft used in fishing, hunting and livestock farming. The boats are found everywhere in the Nordic countries, with different features in terms of length, width and depth. All of the earliest known examples are double-ended, with stems at both ends, and this tradition is still strong. A few later exceptions are the eka and julle, which have transom sterns, as do several types of flat-bottomed craft, such as dories, which can be built either double-ended or with a narrow transom. Clinker-built boats with transoms appeared first mainly on the Baltic coast, but gradually spread throughout Sweden.
Smaller clinker-built boats - generally referred to as allmogebåtar (vernacular boats) - are found in a range of variations depending on how and where in Sweden they were used. The choice of building materials is also different in different parts of the country. On the west coast, for example, oak is a much more common building material than on the east coast, where the boats are usually built in pine.
Many older boat types are still found in lakes and streams in central and northern Sweden. For example, Dalarna's church boat has striking similarities to Viking boats in its long and narrow form, the use of wide planks, and high stems. In Dalarna, boats have been built as a commercial enterprise for many years, so that this type has spread to other areas.
The julle built in the Swedish region of Bohuslän is traditionally made of pine planks on oak frames and primarily used for fishing. Smaller jullar four to five metres long could be sailed or rowed and were usually undecked. Larger jullar could have decks and even coamings. The form and size of the julle changed somewhat with the introduction of engines in the early 20th century.
Another common type in Bohuslän in the 19th century was a larger, decked boat called a drivgarnsbåt, originally used for fishing. These boats later became popular for sport and leisure, and came to be called koster. They were built all along the west coast, but mainly at Orust and Gothenburg. Several of these boats are still in use, some on Lake Mälaren.
Clinker boats were built mainly by local craftsmen, and the knowledge was passed on orally, often from father to son. The customer usually supplied both the timber and the building location. The boats were built with a simple kit of hand tools.
The old techniques are still used in parts of Sweden for the construction and maintenance of smaller boats. Although theoretical and practical woodworking education is of great importance for the preservation and transmission of knowledge, the core of the learning process lies in practice. Important skills include the choice of material, the knowledge of which part of the tree will work best as a stem or frame, and how to saw the timber to give planks the maximum strength. The skills to build and renovate a clinker-built boat are essential within the maritime historical arena for keeping vernacular craft and sailing cultural heritage alive.
There are a few high schools and vocational schools in Sweden which have education programmes in boatbuilding. These include instruction in tool and machine knowledge, how to read drawings, wood technology, and an introduction to shape and construction.
Preservation is today largely in the hands of non-profit organizations, not least the associations which maintain wooden vernacular craft and pass on the knowledge of how to maintain and sail them. However, major repairs, such as replacement of planking and caulking, usually have to be undertaken by people with professional experience, a skill set which is at risk of disappearing as the number of traditional boats decreases.
Construction and renovation of clinker-built boats takes place at Nyhamns Såg & Båtbyggeri in Nyhamnsläge. Comprehensive documentation is part of the process, and the shipyard also holds a collection of some of Skåne's oldest preserved working boats. A number of independent craftsmen in the region are also involved in operations.
On Holmön near Umeå there are several active boatbuilders. Activities are connected to the local boat museum, and in addition to a collection of older clinker working craft there is a teaching workshop. Boats are sometimes built in the Viking tradition, without drawings or moulds. Knowledge is passed on from older boatbuilders to younger. The boat museum’s teachers are promoting and carrying on the island’s traditional boatbuilding techniques.
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