Keelson,
n. [Akin to Sw.
kölsvin, Dan.
kjölsviin, G.
kielschwein; apparently compounded of the words
keel and
swine; but cf. Norweg.
kjölsvill, where
svill is akin to E.
sill,
n. ].
A piece of timber in a ship laid on the middle of the floor timbers over the keel, and binding the floor timbers to the keel; in iron vessels, a structure of plates, situated like the keelson of a timber ship. [1913 Webster]
Cross keelson, a similar structure lying athwart the main keelson, to support the engines and boilers.