Sentence:  Every available spyglass was directed towards strange sail. It appeared, as we all watched it, to <WSD>lollop</WSD> up and down, as it were, with the jerk of the sea, according to no regular motion of a ship or boat. 
Meaning of the word marked with <WSD> tags:  To walk or move with a bouncing or undulating motion and at an unhurried pace.