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Clinker (boat building)

From Wikipedia, the free encyclopedia

A Viking longship, displaying the overlapping planks that characterize clinker construction.

Clinker built (also known as lapstrake)[1][2] is a method of boat building where the edges of hull planks overlap each other. Where necessary in larger craft, shorter planks can be joined end to end into a longer strake or hull plank. The technique developed in northern Europe and was successfully used by the Anglo-Saxons, Frisians, Scandinavians, and typical for the Hanseatic cog. A contrasting method, where plank edges are butted smoothly seam to seam, is known as carvel construction.[3]

Examples of clinker-built boats directly descended from those of the early medieval period are seen in the traditional round-bottomed Thames skiffs, and the larger (originally) cargo-carrying Norfolk wherries of England.[4]


From clinch, or clench, a common Germanic word, meaning “to fasten together”.[5]


The technique of clinker developed in the Nordic shipbuilding tradition as distinct from the Mediterranean mortise and tenon planking technique which was introduced to the provinces of the north in the wake of Roman expansion. Overlapping seams already appear in the 4th century BC Hjortspring boat. The oldest evidence for a clinker-built vessel, dendrochronologically dated to 190 AD, are boat fragments which were found in recent excavations at the site of the famous Nydam Boat.[6] The Nydam Boat itself, built ca. 320 AD, is the oldest preserved clinker-built boat.[7] Clinker-built ships were a trademark of Nordic navigation throughout the Middle Ages, particularly of the longships of the Viking raiders and the trading cogs of the Hanseatic League.


A comparison of clinker and carvel building styles.
A comparison of clinker and carvel building styles.

In building a simple pulling boat, the keel, hog, stem, apron, deadwoods, sternpost and perhaps transom are assembled and securely set up. In normal practice, this will be the same way up as they will be in use. From the hog, the garboard, bottom, bilge, topside and sheer strakes are planked up, held together along their ‘lands’ – the areas of overlap between neighbouring strakes – by copper rivets. At the stem and, in a double-ended boat, the sternpost, geralds are formed. That is, in each case, the land of the lower strake is tapered to a feather edge at the end of the strake where it meets the stem or stern-post. This allows the end of the strake to be screwed to the apron with the outside of the planking mutually flush at that point and flush with the stem. This means that the boat's passage through the water will not tend to lift the ends of the planking away from the stem. Before the next plank is laid up, the face of the land on the lower strake is bevelled to suit the angle at which the next strake will lie in relation with it. This varies all along the land. Gripes are used to hold the new strake in position on the preceding one before the fastening is done.

Timbering or framing out

Once the shell of planking is assembled, transverse battens of oak, ash or elm, called timbers are steam-bent to fit the internal, concave side. Elm species are not durable where the boat is used frequently in fresh water. As the timbers are bent in, they are copper riveted to the shell, through the lands of the planking.

On many clinker built craft, e.g. in Scandinavia, in Thames skiffs, and larger working craft like the coble, sawn frames are used, assembled from floors and top timbers, joggled to fit the lands. Sometimes the timbers in larger craft were also joggled before being steamed in.









The planks may be fastened together in several ways:

  • With copper or iron rivets consisting of a square nail and a dish shaped washer called a rove. The land is pierced, the nail knocked through from the outside, the rove punched on while the head is held up by a dolly (a small portable anvil, usually of cylindrical shape). The nail is cut off just proud of the rove and the cut end clenched[Note 1] over the rove while the dolly is used to hold the nail in place. In planking up clinker work, one man can hold both dolly and clenching hammer. Although this is common where sawn frames are to be used, boats intended for steamed timbers are usually nailed but not clenched until the timbering out is complete. As timbering is a two handed job it is more efficient to leave the clenching until help is at hand then the helper dollies up, whilst the builder sits inside the hull and clenches up.
  • With iron nails with the pointed nail ends protruding on the inside of the boat, bent over and back into the wood in the form of a hook. This technique is somethings called clinching. It is the sort of thing which used to be found in Scandinavian-built boats but even with iron nails, on the lands, they were usually properly clenched over roves. Nails fastening timbers were sometimes turned over, particularly where removable bottom boards were to rest on the timbers. However, it was possible to tread the bottom boards onto the clenched nails and where marks were left, gouge out recesses to accommodate the clenched nails.

Fastening the centre-line structure

In the last few years of wooden boat construction, glue and screws took over, but until the 1950s, the keel, hog, stem, apron, deadwoods, sternpost, and perhaps transom would be fastened together by bolts set in white lead and grease. There are three kinds of bolt used, of which, nowadays, the screw bolt (i.e. threaded bolt), with its nut and washer, is by far the most common. The second type of bolt is the pin bolt or cotter bolt, which, instead of a thread, has a tapered hole forged through the end away from the head, into which a tapered pin or cotter is knocked. The taper is in effect a straight thread. In conjunction with a washer, this draws the bolt tight, as a nut does on a screw bolt. The third type of bolt is the clench bolt. It has some of the features of a rivet but was usually much longer than the normal rivet; in a wooden ship, perhaps a metre or more. For a shipwright's use, it is of copper. A head is formed by upsetting one end using a swage. It is then knocked through a hole bored through the work to be fastened, and through a washer. The head is held up with a dolly and the other end is upset over the washer in the same way as the head.[8] Until well into the nineteenth century, this is what held the great ships of the world together, though some may have used iron. Until the late 1950s, the centre-line assembly of British Admiralty twenty-five foot motor cutters were fastened this way.


Comparison between clinker and carvel

The clinker form of construction is linked in people's minds with the Vikings who used this method to build their famous longships from riven timber (split wood) planks. Clinker is the most common English term for this construction in both British and American English, though in American English the method is sometimes also known as lapstrake; lapboard was used especially before the 20th century to side buildings, where the right angles of the structure lend themselves to quick assembly.


Additionally, the clinker built method as used by the Vikings created a vessel which could twist and flex relative to the line extending length of the vessel, bow to stern. This gave it an advantage in North Atlantic rollers so long as the vessel was small in overall displacement. Increasing the beam, due to the light nature of the method, did not commensurately increase the vessel's survivability under the torsional forces of rolling waves, and greater beam widths may have made the resultant vessels more vulnerable.[citation needed]

There is an upper limit to the size of clinker built vessels, which could be and was exceeded by several orders of magnitude in later large sailing vessels incorporating carvel-built construction. Clinker requires relatively wide planking stock compared to carvel, as carvel can employ stealers to reduce plank widths amidships where the girth is greatest. The need for sufficient lap to accept the clench fastenings drives towards wider planks in proportion to thickness than can be employed in carvel. In all other areas of construction, including framing, deck, etc., clinker is as capable as carvel. Clinker construction remains to this day a valuable method of construction for small wooden vessels.

See also


  1. ^ Some people would pronounce this word as "clinched" but there always was room for regional variation in boatbuilding words.


  1. ^ Webb, Michael. "Clinker Boat History & Building". Wootton Bridge Industries. Archived from the original on 2008-12-02.
  2. ^ "Lapstrake". Danenberg Boatworks. Retrieved 2020-02-13.
  3. ^ "Clinker and Carvel – different types of planking". Traditional Maritime Skills project. Retrieved 2015-02-10.
  4. ^ "Clinker Boat Building". Australia.
  5. ^ Chisholm, Hugh, ed. (1911). "Clinker" . Encyclopædia Britannica. 6 (11th ed.). Cambridge University Press. p. 527.
  6. ^ Storgaard, Birger; Thomsen, Lone Gebauer (2003). Jørgensen, Lars (ed.). The Spoils of Victory – the north in the shadow of the Roman Empire. Nationalmuseet. p. 299.
  7. ^ The Nydam Boats
  8. ^ Zori, Davide (2007). "Nails, RIvers, and Clench Bolts: A Case for Typological Clarity". Archaeologia Islandica. 6: 32–47.

Other sources

  • Greenhill, Basil (1976). Archaeology of the Boat (London: Adam and Charles Black Publishers Ltd). ISBN 978-0-7136-1645-3.
  • Greenhill, Basil, and Morrison, John S. (1995). The Archaeology of Boats & Ships: An Introduction. (London: Conway Maritime Press) ISBN 978-1-55750-039-7.
  • McKee, Eric (1972). Clenched Lap or Clinker: An Appreciation of a Boatbuilding Technique (Greenwich: National Maritime Museum).
  • Leather, John (1990). Clinker Boatbuilding (Adlard Coles). ISBN 978-0-7136-3643-7.
This page was last edited on 18 February 2021, at 02:08