keelson

Etymology

Late Middle English kelswayn, from Low German kielswîn, kielswīn, from kiel (“keel of a ship”) (from Old Norse kjǫlr) + swin (“swine”), used as the name of a timber (however, compare sill). Compare with Dutch kolzwijn, kolsem, Low German, kielswîn, German Kielschwein, Danish kølsvin, kölsvin, all with the same meaning.

noun

1. (nautical) A longitudinal beam fastened on top of the keel of a vessel for strength and stiffness.
   With regard to materials, all the frames should be of oak and so should the stem piece, stern post, upper portion of dead woods, knight heads, apron, beams, shelf clamp, bilge strakes, and keelson; the keel will generally be found to be either English or American elm. 1884, Dixon Kemp, A Manual of Yacht and Boat Sailing (Fourth Edition), page 13