Sentence:  At that time, the steam-traffic on the Thames was far below its present extent, and watermen's boats were far more numerous. ... Early as it was, there were plenty of <WSD>scullers</WSD> going here and there that morning, and plenty of barges dropping down with the tide ... 
Meaning of the word marked with <WSD> tags:  A boat rowed by one person with two sculls, or short oars.