Clinker-built, also known as lapstrake-built, is a method of boat building in which the edges of longitudinal (lengthwise-running) hull planks overlap each other.

The technique originated in Northern Europe, with the first known examples using metal fastenings that join overlapped planks in c. 310-320 AD. It was employed by the Anglo-Saxons, Frisians, and Scandinavians in the early middle ages, and later in the Basque shipbuilding region where the Newport medieval ship was built. It was also used in cogs, the other major ship construction type found in Northern Europe in the latter part of the medieval period.

UNESCO named the Nordic clinker boat tradition to its List of Intangible Cultural Heritage on December 14, 2021, in the first approval of a joint Nordic application.

Clinker construction is a boat and ship-building method in which the hull planks overlap and are joined by nails that are driven through the overlap (often called the "lap"). These fastenings typically go through a metal rove over which the protruding end of the nail is deformed in a process comparable to riveting the planks together. This gives a distinctive appearance to the outside of the hull as the overlaps are obvious in the stepped nature of the hull surface.

Clinker construction is a shell-first technique (in contrast to the frame-based nature of carvel). The construction sequence begins with the joining of the keel, stem and sternpost (or transom) and setting these in place in the build area. Thereafter, the shape of the hull is determined by the shaping and fitting of the hull planking that forms the waterproof exterior of the hull. Any reinforcing frames, thwarts or beams are added after the joining of the hull planks. This may involve completely finishing the exterior planking first, or just some planking may be fitted with, for instance, floors being added whilst that part of the hull is accessible before planking is continued.

Medieval clinker construction used iron nails and roves – the latter often being a distinctive diamond shape. There are less common regional instances of planks being joined with treenails or by sewing, but iron fastening predominated. More modern boats generally use copper nails with an annular rove of the same material.

Historically, particularly in the traditional Nordic tradition, clinker construction most commonly used cleft, or radially split, oak planks. This gives a stronger piece of timber than with sawn material – not only is the grain continuous along the length of the piece, but the medullary rays are aligned in the same plane as the timber surface, so maximising the strength available. However, this timber conversion method does limit the maximum width of plank to slightly more than one third of the diameter of the tree from which it is split – the narrowest part (including any pith) and the sapwood are cut off. The slightly uneven surface found on cleft timber is the reason why caulking is laid in the overlap between the hull planks during construction, often using animal hair.

The term clinker derives from a common Germanic word for clinch or clench, a word meaning “to fasten together”.