sinkable--prophetes.ai

sinkable, a.
  (ˈsɪŋkəb(ə)l)
  [f. sink v. + -able.]
  Capable of being sunk.
  Cf. non-sinkable, of a life-boat, in recent use. (N.E.D.)

1865 Times 11 Mar. 8/5 The most seaworthy vessel is but too likely to be the most sinkable.

Oxford English Dictionary