runghead

A runghead is the upper end of a floor timber, the curved wooden or metal structural member that runs athwartships (side to side) across the bottom of a ship's hull. The runghead is where this beam terminates at or connects to the ship's side frames, forming part of the internal cross-bracing system that gives the hull its strength against hogging and sagging stresses.

In wooden ship construction, floor timbers are shaped to follow the curve of the hull and secured to the keel or keelson centrally, with their ends rising toward the ship's sides. The runghead must be securely fastened, typically with wooden treenails (trunnels) or later with iron bolts, because it carries significant bending loads as the vessel pitches and the hull flexes under wave action. On larger ships, multiple floor timbers spaced at intervals along the keel create a lattice of athwartship members, each with its own runghead connection.

The term reflects practical shipbuilding language: a floor timber's upper end quite literally rests on or heads against the ship's frame structure, like a rung on a ladder pressing against the rails. In modern steel construction, the equivalent would be the upper end of a floor plate or web frame where it connects to the side shell.

Runghead placement and condition are critical inspection points, particularly in older wooden vessels. Rot, damage, or poor fastening at the runghead can allow excessive hull movement and lead to seam opening, caulking failure, and progressive structural degradation. Shipwrights and surveyors pay close attention to runghead integrity because failure there is often a sign of deeper structural problems below.