To upset, to kill.

1

1848.  He keeled one of them [wolves] over with his air-gun.—C. W. Webber, ‘Old Hicks the Guide,’ p. 92 (N.Y.).

2

1856.  When we get keeled up, that will be the last of us.—H. B. Stowe, ‘Dred,’ ch. viii. (Bartlett).

3