The koches were traditionally built shell-first, with overlapping planks, following the once-widespread Northern European clinker shipbuilding tradition. Iron rivets and brackets, as long as shrub branches or tree roots, were used to fasten the planks to each other. Ribs were inserted into the hull once the shell of planking was assembled. As these ships were in use as late as early 17th century, this may be by far the last use of the clinker technology on large sea-going vessels. They were flat-bottomed, but there is no reliable information whether the bottom was carvel built, as on the cogs, or clinker built, as on Viking ships (the latter is more likely, as the more recent Pomor boats are entirely clinker-built).