What is a Needleboat?

I have come into possession of a rather wonderful book, The Joyce Book, published in a limited edition by Sylvan Press before the War. Sylvan Press was owned by my uncle Charles Rosner.
It is Joyce's Pomes Pennyeach, with settings by such composers as Arnold Bax, Arthur Bliss and Herbert Howells.
One of the pomes is
Watching the Needleboats at San Sabba:

I heard their young hearts crying
Loveward above the glancing oar
And heard the prairie grasses sighing:
No more, return no more!

O hearts, O sighing grasses,
Vainly your loveblown bannerets mourn!
No more will the wild wind that passes
Return, no more return.

San Sabba is a suburb of Trieste on the Adriatic. When Joyce lived there in 1912 with Nora, sullenly drinking while he tried to get The Dubliners published, it was part of the Austro-Hungarian Empire.
But what is a needleboat? I've wasted most of the evening googling and am none the wiser. Is it like the Venetian sandolo? Any ideas?