清障船；挖泥船

Snag \Snag\, n. [Prov. E., n., a lump on a tree where a branch
has been cut off; v., to cut off the twigs and small branches
from a tree, of Celtic origin; cf. Gael. snaigh, snaidh, to
cut down, to prune, to sharpen, p. p. snaighte, snaidhte, cut
off, lopped, Ir. snaigh a hewing, cutting.]
1. A stump or base of a branch that has been lopped off; a
short branch, or a sharp or rough branch; a knot; a
protuberance.

The coat of arms
Now on a naked snag in triumph borne. --Dryden.

2. A tooth projecting beyond the rest; contemptuously, a
broken or decayed tooth. --Prior.

3. A tree, or a branch of a tree, fixed in the bottom of a
river or other navigable water, and rising nearly or quite
to the surface, by which boats are sometimes pierced and
sunk.

4. (Zo["o]l.) One of the secondary branches of an antler.

5. Any sharp protuberant part of an object, which may catch,
scratch, or tear other objects brought into contact with
it.

{Snag boat}, a steamboat fitted with apparatus for removing
snags and other obstructions in navigable streams. [U.S.]

{Snag tooth}. Same as {Snag}, 2.

How thy snag teeth stand orderly,
Like stakes which strut by the water side. --J.
Cotgrave.